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OCTOBER 1985 7^ 2 0 2 . 3 Immunology & Allergy Practice 405/13 Effect of Chemical Sensitivity on the Immune System Loren D. Koller, D. V M ., Pk.D. Abstract Immunotoxicology is a science which deals with the effects of physical and chemical agents and other toxic substances on the immune system. The discipline in cludes detection, occurrence, adverse effects, and mechanisms of chemical-induced immune dysfunc::-jn. Many chemicals are known to compromise the immune response of a host. The immune system is ex tremely vulnerable and sensitive to perturbation by drugs and 'chemicals. Immunocytes are exposed to chemicals and their metabolites in the circulation, tis sues, and organs, as well as in .extracellular fluids. Therefore, exposure can be continuous rather than brief, regardless of distribution. The consequences of immune dysfunction may result in increased suscepti bility to infectious and neoplastic diseases, or provoke hypersensitivity and autoimmunity. The immunomodulating characteristics of a chemical may be diverse, ilTecting several components of the immune system, or selectively compromise one particular compartment of the immune response. Many chemicals result in im mune dysfunction in animals, but very little informa tion is available to indicate the effects a chemical may have on systemic immunity in humans. A major con cern is to identify chemicals that may compromise im mune responses at dosages lower than those that pro duce other signs or symptoms of toxicosis. Several chemicals, following prolonged exposure, alter im mune function in animals at low dosages, but the re sponse is transient and recovery is rapid upon removal Or. Roller ii Dean, College of Veterinary Medicine, Ore gon State University, Corvallis, Oregon. He presented this paper at the 19th Annual Congress of the American Association for Clinical Immunology and Allergy, San Francisco, California, July 13-16, 1985. of the toxicant. In contrast, xenobiotics (excluding drugs) generally will not markedly compromise im mune function following a single dose that does not at least incite some other sign or symptom of toxicosis. Therefore, permanent immune dysfunction resulting from chemical exposure would be extremely rare and not expected to occur following a single exposure. A definitive diagnosis for chemical-induced immunomodulation must include several etiologies and body organ systems, since a triad of reciprocal interactions exists between the immune, endocrine, and central nervous systems. Numerous abnormalities of these systems could express immune dysfunction which is completely unrelated to the putative incitive chemical. Finally, although it is dogma that chemicals often mod ulate immunity in animals, the paucity of information substantiating sim ilar effects in man precludes diagnosing chemical rinduced immune dysrgulation unless epidemiologic and/or experimental data com piled for humans unequivocally supports and confirms the diagnosis. Immune System T he immune system is composed of a deli cate network of organs, tissues, cells and cell products that act in unison to protect the liv ing organism against invasion by foreign agents. This complex system, which is dis persed throughout the body of living or ganisms, regulates body defense mechanisms by monitoring and responding to altered antigenic composition of the body. The regu latory events of the immune system arc to: 1) 14/406 Immunology & Allergy Practice VOL. VII, NO' distinguish, but not react with, normal anti gens of the body; 2) identify foreign antigens such as microorganisms and neoplastic cells and successfully destroy and eliminate them from the body; and 3) maintain a delicate balance for optimum performance. The immune system is regulated by multi ple chemical signals operating at different levels. Antigens trigger local chemical signals, which in turn trigger a network of responding cells operating throughout the body. The overall responsiveness of the sys tem is controlled by modification of cellular components and their secretory products, and signals from endocrine glands and the central nervous system. Thymic hormones and corticosteroids in particular have immunoregulatory activities. Disruption of any one of these events may result in immune dysrgulation, either suppression or en hancement. Four major classes of immunocytes are T and B lymphocytes, macrophages, and nat ural killer cells (NKC). The B cells are pri marily the effector cells of humoral immunity (i.e., antibody production),' but require the " help** of T cells and macrophages for opti mal response to most antigens. The T cells are composed of both effector and regulator subpopulations. The effector T cells can be divided into at least two subsets based on function and phenotype. These are the cyto toxic T cells and T cells that mediate delayed hypersensitivity reactions. Effector T cells act mainly via cell-cell contact, as opposed to . production of humoral factors like anti bodies, and therefore are responsible for what is termed cell-mediated immunity. The regulatory T cells can be roughly divided into helper (H T) and suppressor (ST) subsets, based on phenotype and regulatory activity. The phenotypic surface molecules for the lymphocytes responsible for HT, mixed lym phocyte reactions, and cutaneous hypersen sitivity in mice are Lyt 1* (T 4 in humans), while Lyt 23 * (Ts in humans) are the surface molecules expressed on ST and cytotoxic;1 lymphocytes. Macrophages are also composed of effe1 and regulator subsets. Macrophages are p*V gocytic cells which can act directly to ing kill, or inactivate foreign agents, or " j r ess" the antigen so it is recognizable to ot_ types of immunocytes as foreign. Natural killer cells (NKC) are a popul of large granular immunocytes which hi some characteristics of both lymphocytes;*' macrophages. The NKC are considered an important " first line defense mechanis~ (i.e. innate immunity) since, unlike T ce they react immediately with foreign agen without prior sensitization. The NKC areb; lieved to be especially important in immujji surveillance to viruses and neoplastic cellsV In addition to direct effector actions of di ferent types of immunocytes, these cells a' ` produce a variety of immunoregulatory kines. Prominent among these cytokines ^ the lymphokines, interleukin 2 (IL2) and terferons (IFN), and the monokines, inf leukin 1 (IL1) and prostaglandins (PGE These cytokines act on activated effector v munocytes in an interrelated m anner to ulate the magnitude of ongoing immune^' sponses. The interleukins are required, clonal proliferation of antigen-activated " fector T cells, but also act on B cells r. NKC to augment their effector functions. I terferons can act synergistically or antago tically with interleukins to regulate B cell,? cell, macrophage or NKC response. In t:. ferons are probably best known for their an' viral activity. Prostaglandins are arachido acid metabolites produced by activated m rophages (and other cells), and are gener , considered to be immunosuppressive. P' duction of prostaglandins may.be one mech nism by which suppressor macrophag' operate to down-regulate responsiveness other immunocytes. The complexity of the immune system n' gates the use of any single, currently av OCTOBER 1985 Immunology & Allergy Practice 7/15 able assay to adequately assess overall immune competence. Substantial documen tation amply demonstrates that one major arm of the immune system may be impaired or enhanced while other major components remain relatively normal in function. There fore, a battery of immunoassays is required which are designed to monitor different as pects of the immune system in order to com prehensively assess the immune status of an individual. Immunotoxicology Immunotoxicology as a discipline was spawned in the early 1970s and is currently recognized by toxicologists, the medical pro fession, and governmental agencies who are concerned that chemicals which pollute the environment may dramatically alter immune mechanisms, thereby increasing' susceptibil ity of an individual to infectious and neoplas tic agents. Such effects could occur at low levels of exposure in absence of overt toxicity (subclinical) and, thus, remain unrecognized as a contributor in the process of.infectious disease and neoplasia. Therefore, it is of con siderable public health concern not only to be able to identify accurately those substances that alter immunity, but also to determine ex posure levels and mechanisms by which those reactions occur. Immunotoxicology, as a science, deals with the effects of physical and chemical agents and other toxic substances on the immune system. The discipline includes detection of occurrence, adverse effects, and mechanisms of chemical-induced immune dysfunction. Immunopharmacology parallels and admixes with this discipline, but deals predominantly with the effects of drugs and biological re sponse modifiers on -the immune system of living organisms. Both fields are rapidly ex panding because of the ubiquitous spread of chemicals in the environment and the wide spread use of drugs that can potentially im pact the immune responsiveness of human beings. Chemicals can have a marked effect on the immune system. These effects may be advan tageous when chemicals are used therapeuti cally, or may be detrimental if exposure re sults from toxic substances that contaminate the environment. Occasionally, a therapeutic agent that may be effective for treatment of selected nonimmune-related disorders or dis eases may inadvertently compromise im mune function. When this occurs, the side effects may preclude use of the chemical for the intended purpose because an immunosuppressed host may be highly susceptible to infectious agents, carcinogens, or sponta neous neoplasia. M any chemicals alter the immune re sponse of a host.1'3 For some chemicals, these effects are insidious, whereas for others they are more tangible and must be considered in the overall action of the compound. Because certain chemicals alter immune function and these effects are frequently subtle or occur at dosages well below desired (drugs) or toxic amounts (toxicants), development of sensi tive assays is vital for detection of those al terations. The immune system is extremely vulner able and sensitive to perturbation by drugs and chemicals. It is a rapidly proliferating and differentiating target organ system, com posed of many cell types regulated by a network of cellular components and soluble factors representing several organ systems. Thus, there is an inordinate amount of in teraction with other body systems. In addi tion, immune cells are exposed to chemicals and their metabolites in the circulation, tis sues, and organs, as well as extracellular fluids. Therefore, exposure can be continu ous rather than brief, regardless of distribu tion. Chemicals can react with- cell mem branes, receptors, or internal structures and interfere at numerous points in the ensuing cascade of immune events. For example," 16/408 Immunology & Allergy Practice VOL. VII, NO.': these reactions could occur at any level, in cluding the macrophage, which process the antigens and secretes IL1, which in turn stimulates activated T cells to produce IL2 necessary for proliferation of H T cells, which augment B cells to differentiate into anti body-secreting plasma cells. What are the consequences of immune dysfunction? Immunosuppression results in increased susceptibility to infectious and neo plastic diseases, while immunoenhancement can provoke hypersensitivity and auto im m unity. The extent and degree of immunomodulation must be ascertained to predict the impact .on the host. Generally, immunomodulation occurs during exposure to the chemical, and once the source is re moved, recovery is relatively rapid. How ever, once sensitized to an immunotoxic dose of a chemical, permanent damage may be ex pressed by autoimmunity, contact hypersen sitivity, or neoplasia. Nevertheless, a single or acute exposure, unless at toxic dosages, is less apt to alter immune function, while pro longed exposure (chronic) is most apt to pro duce immunotoxicity. However, the re sponses frequently do not follow a typical dose response pattern, but may be selective for a specific component(s) of the immune network. Thus, immune responsiveness to a given chemical may affect different compo nents of immune function, precluding a typi cal linear dose response effect. These effects generally revert to normal within days after removal of the test agent. In te rp re ta tio n <an d e x tra p o la tio n of chemical-induced im m une modulation, in laboratory animals is frequently questioned. The immune procedures are generally repro ducible, quantitative, and highly sensitive to detect immune mediated events. In fact, many chemicals impair immune function at dosages lower than other toxic responses nor mally delineated by a battery of standard tox icological indices utilized in drug and chemi cal efficacy testing programs. However, many of these concerns can be dispelled on the premise that the immune systems of mais and man are comparable, that aninf models are available for conditions of i mune dysfunction, that positive immunosu pressants such as cyclophosphamide and co ticosteroids can be used to validate assays ( well as for extrapolation purposes), finally, that animal data has been verified' man. These criteria emulate the similaritj of immunocomptence for both animals man. Granted, variations of immune respo siveness do occur between various species but the principles and phenomena are b asi cally similar and comparable. Priority candidates for drug and chemica immune assessment should be those tha present the greatest exposure to humans fori prolonged periods of time. These include products used for long-term therapy; thos' that persist in the environment, particularlythose which accumulate in the food chain; and those used during pregnancy, since th developing fetus is extremely vulnerable to exogenous stimuli. An awareness of im munotoxic properties of chemicals could be assessed both during the development of a drug and during experimental trials in man.' Immunopharmacotoxicology has made considerable advances in the past decade. In terest has been generated not only from haz ards to human health, but also from the as pect of developm ent of satisfactory chemo-preventive and -therapeutic drugs to treat infectious diseases and cancer. The ad vent of biotechnology and discovery of bio logical response modifiers has provided the momentum necessary to perpetuate and pro pel this discipline into a formidable science. Im m une Sensitivity to Chemicals Local H ypersensitivity Allergic responses are a rather common reaction in man following sequential expo sures to specific drugs and chemicals. Typical clinical manifestations may involve any or gan in the body, but the most prevalent re- NO. 10 OCTOBER 1985 Immunology & Allergy Practice 409/17 s of anianimal of imunosupmd corsays (as s), and rifled in lilarities lals and responspecies, re basi- hemical *se that ans for include /; those icularly : chain; nee the rable to i of im- ' ould be j i rnt of a : .n man. ^i 3 made . j adc.In- : )m haz- | the asfactory i irugs to The adof bioded the nd pro.cience. cals iramon 1 expoTypical any or ient re- sponscs are either pulmonary or topical. It has been estimated that 15% of all adverse drug reactions are due to allergic responses.4 Hypersensitivity responses can be classi fied into four major types. Type I reactions are initiated by interactions of an allergen or antigen with performed antibodies (IgE) and are immediate hypersensitivities (anaphy laxis and atopy) that generally occur within 30 minutes after exposure to the antigen. This reaction is mediated by the immune complex (Ag/Ab) binding to mast cells or ba sophils which release pharmacologically ac tive substances (histamine, serotonin, etc.) that are responsible for the inflammatory process. Type II reactions occur when antibodies (IgG) combine directly with an antigenic component of a tissue cell or with an antigen which has become fixed to tissue cells. These complexes in turn fix complement, which is followed by a cascade of activation, which may lead to increased cell permeability and even cell lysis. Certain complement proteins evoke activation of anaphylatoxins, which re sults in the release of histamine from mast cells arid chemotactic attraction of poly morphonuclear leukocytes (PMNs). This reaction occurs within 2 to 6 hours after ex posure to the sensitizing agent. The cytotoxic reactions are frequently directed against ele ments of the blood vascular system and are emulated by autoimmunity. Type III hypersensitivity reactions result from deposition of antigen-antibody (IgM/ IgG) complexes combined with complement in tissue spaces and walls of small blood ves sels. These complexes attract PM Ns to the reaction site, which release lysosomal en zymes that are responsible for the cell injury and tissue damage. This reaction (Arthus) generally occurs 2 to 6 hours following expo sure to the sensitizing antigen and is typified by serum sickness and chronic membranous glomerulonephritis. 'Type IV allergic reactions, or delayed-type hypersensitivity (DTH), are differentially separated from the other three types of hy persensitivities by a delayed onset (12 to 48 hours) of the reaction. This reaction is characteristic of cell-mediated immunity and is elicited by lymphocytes in the absence of antibody. Antibody-mediated reactions are a manifestation of Types I, II, and III. The D TH reaction is characterized by erythema, edema, and histologically by a predominance of a mononuclear cell infiltrate (lymphocytes and monocytes). Delayed-type hypersensitiv ity is typical of graft vs. host reaction and contact hypersensitivity. This portion of the review will be concerned primarily with Type IV hypersensitivity as a local response to drug and chemical insult. All contact sensitivity-inducing substances have at least two common features. They have a low molecular weight which permits diffusion through intact skin and, upon per cutaneous absorption, they combine with amino acid side chains of proteins to form conjugates that are generally non-antigenic themselves. Contact hypersensitivity results when the sensitizing hapten-carrier conju gates form locally in the skin. Contact hypersensitivity is regarded as a localized skin reactivity which is not lifethreatening. Numerous chemicals are known to be highly allergenic for contact sensitivity and result in various degrees of discomfort. Nevertheless, susceptibility to contact irri tants is not indicative of systemic immune re sponsiveness, and thus the main emphasis of this report will be directed at chemical sen sitivity of the systemic immune response, which includes D T H responses. Recent data, derived from rodent studies, implies that D TH reactions are biphasic, in volving both classical immediate and delayed hypersensitivity, and that both are mast celldependent.57 A cascade of immune events occurs upon introduction of antigen. Sen sitized T cells (Ly-1 *) secrete a soluble factor that activates mast cells to release serotonin, which augments local vascular permeability. Consequent to this early event, a second T 18/410 Immunology & Allergy Practice VOL. VII, N 02 cell (Ly-1 *) population enters the reaction site and interacts with the antigen, which elicits a late response responsible for the immunocytes and- PM N infiltrate. In con trast, others6dispute the hypothesis that mast cell products are required for leukocyte emi gration or swelling associated with D TH . Their'Contradictory results reveal that mast cell-deficient mice expressed D T H reactions of equal .intensity or in excess of that of heterozygous litter-mate controls. Additional investigations will be necessary to d e finitively ascertain the mechanistic events which precipitate and perpetuate D T H reac tions. DTH responses are controlled by acces sory (macrophages) cells and a complex ST cell circuit.9,10 Macrophages secrete num er ous monokines such as IL1, IFN and PGEs, which can affect proliferation and differentia tion of all T cell subsets. Therefore, classical D TH reactions encompass an intricate network of cells and their secretory products which regulate the intensity of the D T H ef fector T lymphocytes. Drugs and chemicals may alter the magnitude of response at several points in this pathway. Systemic Sensitivity The intact immune system provides pro tection of the host against invasion by foreign organisms and neoplastic agents. Dysrgula tion of the system may suppress or enhance immune responses which may be beneficial (destroy microorganisms, neoplastic cells, etc.) or detrimental (autoimmunity, hyper sensitivity) to the host. In the past decade, it has been well documented that certain en vironmental chemicals, at relatively low dos ages, do adversely affect normal function of the mammalian immune system1*3 Until re cently, the impact and implications of these reactions in man have not been fully realized or appreciated. However, attention has been directed at attaining information concerning the health hazards of many xenobiotics are ubiquitous in the environment. In ad' tion, a particular concern is that a small centage of the human population may be'tij nately hypersensitive to chemicals. TH^ article will review chem ical-induce immunomodulation and discuss some of th' ramifications associated with this phenomi non. A myriad of assays are available by whic to assess the integrity of the immune systenji both in vivo and in vitro. A consensus of mosi immunotoxicologists is that a panel of immu: noassays should include, as a minimum* assessment of hum oral immunity, cell^ m ediated im m unity (C M I), macrophage?! function, pathotoxicologic examination o$ lymphoid tissues, and host resistance to ari^ infectious or oncogenic agent. These assays have more recently been expanded to included natural killer cell (NKC) and production/^ activity of numerous regulatory cytokinesi| Most of these procedures are quantitative^ and inclusive, in order to formulate a com-3 plete immunotoxic profile for a specified^ drug or chemical. Therefore, a battery of im munoassays is available in order to compre-; hensively assess the immune status of an ani-.j mal. I Humoral immunity is characterized by lymphocytes, which differentiate into plasma^ cells that synthesize and secrete antibody into ; the circulation. Antibody can be easily enu-^ merated by several acceptable techniques, particularly by two commonly used proce- % dures, radioim m unoassay (RIA) and i enzym e-linked im m unosorbent assay I (ELISA), that are quantitative and possess d an extremely high degree of sensitivity. Table 1 I lists several chemicals that are known to sig- \ nificantly (p 0.05) alter antibody synthesis ' in an im als.1'311'17 These agents represent several classes of chemicals and compromise im m unity in several species of animals, j M any of the effects occurred at dosages lower I than those that notably alter other standard >ifi S T B E R 1985 Immunology & Allergy Practice 411/19 Table 1 Chemicals Known to Alter Antibody Synthesis In Animais Chemical Species Effect1 Lead I Cadmium Mercury Selenium Nickel Tetrachlorodibenzodioxin Tetrachlorodibenzofuran Pentachlorophenol Polychlorinated biphenyl Polybrominated biphenyl Benzo-a-pyrene Dimethylbenz(a)anthracene Methylcholanthrene Dimethyl vinyl chloride Urethane T phorbol acetate Lindane Toxaphene Monochloramine ` Chlorine dioxide Ethyl nitrosourea 2.4 difihlorophenol Tetrachlorobiphenyl Diethylnitrosamine Zinc Mouse, rat. rabbit Mouse, rat, rabbit Mouse, rabbit Mouse, rat Rat Mouse, guinea pig Mouse Mouse, rat Mouse, rat, monkey, rabbit. guinea pig Mouse Mouse Mouse Mouse Mouse Mouse Mouse Rat Mouse, rat : Rat Rat Rat Rat Mouse Mouse Mouse M = increase, D = decrease. D D D l,D D D D D D D D D D D D D D D D D 1 D D D toxicological indices such as weight loss, al tered serum chemistries, or impaired mixed notion oxidase activity. The ease of assess ing humoral immunity has contributed to the numerous chemicals tested (positive) for al tered antibody synthesis, more so. than for other immune parameters. It is noteworthy that most chemicals suppress humoral im mune responses. The humoral immune re sponse could be particularly sensitive to per turbation by chemicals, since this system is 'Vgulated by other components (T lympho' ytes and macrophages) of the immune network. Drugs and chemicals tend to inhibit the Table 11 Chemicals Known to Alter Delayed-type Hypersensitivity In Animals Chemical Species Effect' Lead Selenium Tetrachlorodibenzodioxin Tetrachlorodibenzofuran Polychlorinated biphenyl Methylcholanthrene Carbofuran 2.4 Dichlorophenol Sodium hypochloride Diethylnitrosamine Triphenyltin Dialkyltin Mouse, rat Rat Mouse, guinea pig, rat Guinea pig Rabbit Mouse Rabbit Rat Rat Mouse Rat Mouse U = increase, = decrease. D D D D D D D D D 1 D D primary immune response more so than the secondary response. The anamnestic re sponse is more resilient to respond to re peated chemical insult. The stages of the im mune response also differ markedly in their susceptibility to immunomodulators. Sup*pressive agents are most effective 'when used before antigenic challenge or during the induction phase of the immune response.18 Further, many drugs and chemicals express a differential toxicity for B and T lymphocytes, i.e., cyclophosphamide produces a propor tionately greater reduction in B than T cells. Subsequent to discontinuance of exposure, the modulating properties of these agents are generally of brief duration and transient. These factors must be considered to fully ap preciate the immune dysregulatory activity of drugs and chemicals. Cell-m ediated immunity (C M I) is ex pressed by T cells composed both of effector and regulator subpopulations. The effector T cells are derived from two distinct lineages and are divided into subsets based on func tion and phenotype. These include cytotoxic T lymphocytes (CTL), cells that mediate delayed-type hypersensitivity (DTH), and 20/412 Immunology & Allergy Practice VOL. VII, NO,- Table 111 Chemicals Known to Alter Macrophage Phagocytic Activity in Animals Chemical Species Effect' Lead Cadmium Mercury Nickel Pentachlorophenol T phorbol acetate Toxaphene Mouse, rat Mouse Mouse Mouse, rat, rabbit Mouse, rat Mouse Mouse 'I * increase, 0 decrease. l,D l,D N D. 1 1 D Table IV Chemicals Known to Alter Natural Killer Cell Activity In Animals Chemical Species Polychlorinated biphenyl Chlorine dioxide Selenium Ethylnitrosourea Diethyl nitrosamine Methylchotanthrene Manganese Nickel Rat Rat Rat Rat Mouse Mouse Mouse Mouse M - increase, D - decrease. Effect': &K those active in mixed lymphocyte reactions (M LR). The regulatory T cells consist of helper (HT) and suppressor (ST) subsets. These cells synthesize and secrete soluble products (lymphokines) which mediate their activity. The test accepted by immunotoxicologists as most representative of C M I is various modifications of D TH . These techniques have been modified and adapted to a particu lar species and have proven to be quite sensi tive as well as quantitative to assess chemicalmediated dysfunction of CM I. Table II lists several chemicals known to significantly (p <, 0.05) alter D T H in animals.1'5*' 17 The majority of the agents de press C M I, which would suggest that the host would be more receptive to invasion by mycobacteria, fungi, viruses and other or ganisms that replicate intracellularity, as well as carcinogens that are immunoresponsive. Macrophages are phagocytic cells which process antigens..The phagocytic index has not proven to be a satisfactory method to assess immunotoxicity of xenobiotics. This procedure appears to be relatively insensi tive, since macrophages can compensate for considerable insult before marked effects in phagocytosis can be detected. It is notewor thy that some chemicals can either stimulate or depress phagocytic activity, depending on the amount and time or dose of the chemical (Table III).1'51''17 Monokines appear to be a much more sensitive indicator of macro' phage function. Natural killer cells (NKC) do not require prior antigen sensitization to be activate and thus are considered as an important firstj line defense mechanism (innate immunity)*' These cells are of particular importance in1 initial immune surveillance to virus-infected and neoplastic cells. The NKC procedure has recently been in corporated in immunotoxicity assessment and has proven to be an extremely sensitive' procedure to detect chem ical-induced,, im m unom odulation. Table IV lists some chemicals known to significantly (p < 0.05) alter NKC activity in anim als.17Carcinogens{ or promoters of neoplasia tend to decrease, NKC, while other chemicals, such as sele-? nium, an inhibitor of promotion, amplify the NKC response. This quantitative procedure? appears to have great prom ise for immunopharmacology/toxicology efficacy, testing programs. T lymphocytes and macrophages produce* a variety of immunoregulatory cytokines such as interleukin 1 (IL1), interleukin 2. (IL2), interferons (IFN), and prostaglandins* (PGE). These cytokines act in concert to reg-v ulate the magnitude of ongoing immune re-, sponses. The interleukins and interferons' stimulate immune response, while prosta-t glandins, which are produced primarily byj activated macrophages, generally " down-". i O C T O B E R 1985 Immunology & Allergy Practice 413/21 Table V Chemicals Known to Alter Cytokine Productlon/Actlvity In Animals Chemical Species Cytokine Effect' Lead Selenium Manganese Polychlorinated biphenyl Diethyinitrosamine Chlorine dioxide * Chlorine dioxide Sodium hypochlorite Monochloramine 1I increase, D decrease. Rat Rat Mouse Rat Rat Rat Rat Rat Rat Interleukin 2 Prostaglandin E2 Interferon Interleukin 2 Prostaglandin E2 Interleukin 2 Prostaglandin E2 Prostaglandin E2 Prostaglandin E2 D D 1 D l l 1 l ens a- , Table VI Immune Components of Animals Affected by Selected Chemicals Lymphocyte Chemical B T Macrophage Natural Killer Cell Polychlorinated biphenyls D' D Pentachlorophenol DD Toxaphene D . NE t Selenium I/O D 2,4 Dichlorophenol 1D Dialykyltin NE D '! = increase, D = decrease, NE = no effect, -- = not done. D ! D l/D NE NE D -- -- 1 -- regulate" immune response. An extremely small quantity (picogram) of cytokines will provoke a reaction which makes these " immunohormones" particularly sensitive and desirable for assessment of immunotoxicants. These indices have been utilized in our labo ratory and have provided a better under standing of the mechanisms by which chemi cals compromise immunity. A few chemicals known to significantly (p > 0.05) alter cytokine production/activity in animals are listed in Table V.1719-22-23 Gener ally, the cytokine data directly correlates with effector cell activity. Further investigations will delineate and confirm the application of cytokines for im m unopharm acological/ toxicological testing purposes. These data support the philosophy that non-toxic dosages of chemicals result in im mune dysfunction. Frequently, these effects are selective for specific components of the immune network. Table VI depicts the selec tivity certain chemicals express. For in stance, polychlorinated biphenyls (aroclor 1254) suppress virtually all aspects of the im mune system, but are relatively weak inhibi tors of C M I.1'3,17 Pentachlorophenol will de press humoral immunity (H I) and CM I, while actually augmenting macrophage ac tivity.15 Toxaphene spares C M I, but impairs both HI and the m acrophage.13 Selenium may actually stimulate H I and the macro phage with moderate excess dosages,2 but larger dosages w,ill suppress H I, C M I, and the macrophage but enhance NKC activity.23 2,4 dichlorophenol will potentiate HI but re duce CM I responses while sparing the mac rophage.2* Dialkyltin is selective in depress ing CM I in the absence of affecting the other major arms of immunity.23 These examples illustrate that the immunotoxic profiles of chemicals differ even within a given class, thereby prohibiting the prediction of the im munotoxic characteristics for similar agents. 22/414 Immunology & Allergy Practice VOL. VII, N dl Table VII Chemicals Known to Modulate Immunity in Humans Chemical Parameter Polychlorinated biphenyl Polybrominated biphenyl Lead Nickel Cobalt Zinc (deficiency) Selenium (deficiency) *1 - increase, 0 = decrease. IgA. IgM Membrane receptors DTH Active T and HT cells Mitogens T lymphocytes Resistance to infectious agents IgA IgA, IgM, IgG IgA Response T-dependent antigens Cylocidal capacity PMN Effect* D D D D D D D D 1 1 D D '0a. /MsT M :.V* Chemical Sensitivity in Humans (System ic) A paucity of information, scattered in the literature, indicates that chemicals elicit im mune dysfunction in humans. The accidental exposure of humans to PCBs in Yusho, J a pan, and western Taiwan have permitted scientists to assess the immunotoxic proper ties of this compound over an extended pe riod. Patients exposed to PCB had significant decreases in serum IgA and IgM, a defi ciency of membrane receptors on monocytes and PMNs, depressed D TH responsiveness, and reduced percentages of total T, active T, and H T cells26 (Table VII). Suppressor T cells were unaffected. The effects of lead on bacterial and viral infections in humans have never been ade quately studied, but there is evidence to sug gest that human host resistance may be low ered by lead. Children with persistently high blood lead levels who were infected with Shi gella enteris had prolonged diarrhea.27 In addi tion, lead workers with blood lead levels of 22-89 /ig/dl have been reported to manifest more colds and influenza than non-lead ex posed individuals.28This study also indicated that secretory IgA levels, were suppressed sig nificantly in lead workers with a medium blood lead level of 55 /g/dl. Secretory IgA is a major factor in immune defense against-; respiratory as well as gastrointestinal infect tions. Epidemiological investigations couldascertain if lead alters the immune system oL man and consequently increases susceptibily ity to infectious agents and neoplasia. In 1973, a commercial preparation ofpolyrbrominated biphenyl (PBB) was inadver^ tently substituted as a supplement of dairyt. cattle feed and was distributed throughout"; Michigan. Contam inated dairy products were consumed for the ensuing 5 years', which resulted in exposure of a substantial^ percent of the Michigan population, particu-, larly to the dairy producers' families. Im-, mune dysfunction in humans has been asso ciated with PBB exposure.29,30 The immune'1 dysregulation certainly is not definitive but;, rather suggestive, since a small percentage of the dairy farm residents exhibited a decrease, in the percent of absolute num ber of T lym phocytes, had a concomitant increase of lym-;J phocytes without detectable membrane sur face markers, and showed reduced response' to antigen stimulation. Serum immunoglobulin concentrations have been assessed in individuals exposed to nickel or cobalt. A significant increase in IgM, IgG and IgA levels was present in workers exposed to nickel, while those ex posed to cobalt had elevated serum IgA.31 In I, NO. ll OCTOBER 1985 Immunology & Allergy Practice 415/23 against infeccould tem of 'ptibil- f polyadverdairy ghout 'ducts rears, antial rticu- Im`assonune - but ge of rease Iymlymsuronse ions d to - in t in ex1 In addition, both nickel sulfate and mercuric chloride possess mitogenic properties and stimulate blastogenesis of lymphocytes.32 A deficiency of some essential elements will contribute to immune dysfunction. For in stance, zinc deficiency results in atrophy of the thymus and decreased capacity to re spond to many T-dependent antigens.33 Granulocytes from selenium-deficient indi viduals had a lower cytocidal capacity than those from selenium -supplem ented recipients.34 A considerable am ount of epidemiological and experimental data must be obtained for humans to actually confirm or refute the data compiled from animals as to the relevance of chemical-induced immune dysrgulation in man. It is obvious that chemicals can compro mise immune function. In retrospect, can al tered immunity provoke other syndromes that may be somewhat dissociated with im mune function, as has been envisioned in the past half-century? For example, the immune system was considered to be somewhat autonomous in regulation and action until the recent discoveries that there.is, indeed, a regulatory interaction between the nervous, endocrine, and immune systems. Convinc ing evidence has been presented which sug gests that a significant reciprocal interaction occurs between these three systems.35'38 For instance, some classical neuroendocrine hor mones and neurotransm itters possess immunomodulating activity, while immunocytokine hormones have been discovered to affect the central nervous system and func tion as endocrine glands.37,38 These interregulatory patterns confirm the existence of a nervous-endocrine-im m une axis, which further illustrates the complexity and sophis tication of immunity. The regulatory role of the central nervous system on immunity is best exemplified by the ability of stressful situations, including emotional stress, to compromise immune re sponses. For instance, death of a spouse can impair immune responsiveness for up to 6 weeks.39 In animals, a loud noise, electric shock, infant-mother separation, and over crowding can result in marked suppression of the immune response.40 Individuals who are separated, divorced, or widowed are suscep tible to immunological dysfunction which is thought to predispose these subjects to can cer.41 Since severe emotional and mental dys function can be accompanied by immunolog ical abnormalities, these factors must be carefully considered in a definitive diagnosis of chemical-induced immune dysregulation. The putative causes of immune modulation, particularly in hum ans, are quite diverse and, therefore, must at least include emo tional distress as a contributing factor. In summary, the fact that certain drugs and chemicals alter immunity is dogma. M any drugs are purposely developed and manufactured for their immunomodulatory characteristics and value for chemoprevention and -therapy. A major concern, however, is the immunomodulating proper ties of drugs used for non-immunological purposes, as well as chemicals that are ubiq uitous in the environment and enter the food chain, or may present potential hazards to human health by other routes of exposure. Since the immune system is extremely com plex and sophisticated, many drugs and chemicals frequently compromise immune function at dosages much lower than those which produce other signs or symptoms of toxicosis. These features, whether suppres sive or stimulatory, may be detrimental to the host and expressed by several types of immunologically related syndromes. Several chemicals, generally during prolonged expo sure, alter immune function at low dosages, but the response is transient and the subject rapidly recovers upon discontinuance of ex posure to the chemical. Contrary to multiple exposure, a single exposure to an immunotoxicant (non-drug) rarely results in immune dysfunction at dosages that do not incite 24/416 Immunology & Allergy Practice VOL. VII, N ucto; * other toxicologic signs or symptoms. There is no known chemical where exposure occurs in this capacity that produces permanent im mune dysrgulation. Finally, the interregulatory network and circuit consisting of the im mune, endocrine, and central nervous systems suggests that, particularly in man, abnormalities of these two systems also could contribute to immune dysfunction. There fore, a definitive diagnosis of chemicalinduced immune dysrgulation is inclusive of several etiologies and body systems which must be adequately assessed before a diagno sis incriminating a chemical can be con firmed. Additional information must be compiled for man to implicate and equivo cate chemical perturbation of immune reac tivity in humans. References 1. 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