Document aBNq4jzdOXq41D91OQ3aLknyb

NATUiU VOL. 232 AUGUST 27 1971 * lions, which me stimulated lo synthesize DNA by con(;tct with antigen, enter a resting phase until stimulated to re-enter division by secondary exposure to the same' antigen. Hy definition these would be memory cells. They apparently correspond to Mitchell and Miller's "educated 1 lympho cytes"1, for they were only observed at a time when the mitotic response of thymus-derived lymphoevtcs is maximal1. We arc curt cully seeking direct expet internal proof of their identity. Previous attempts to establish this point" hate failed, perhaps because of the use of Salmonella antigens, which arc poor stimulators of thymus-derived cells11. Our finding implies that cell replication may serve as a means of enlarging and/or altering the pool of thymus-derived cells capable of reacting with certain antigens. Replication may not, however, be essential to the helper function of these cells13. A! the peak of Ihc secondary response to SRC 30 -40% of the cells in mitosis in the spleen are thymus-derived1. Thus we were initially stnpiised to lind only 8-9% of the spleen cells responding mitotic,illy to a second injection of anligcn which showed evidence of having responded in the earlier ptitnaty response. It is important to remember that the work delineating the time and magnitude of ihc response of thymusderived cells to antigen was carried out in irradiated, thymusgrafted mice. Thus it is possible that there may he some differences in normal mice. If there should he any significant differences, however, there would probably he an increase of thymus-derived cells responding in normal mice. Davies et al. have shown that increasing the number of reconstituting thymus grafts up to a point increases (lie number of peripheral thymus-dcriscd cells5. * This Incteasc does not. however, alter the |>creent<igc of thymus-derived cells responding to antigen in lymph nodes nor does it change the liming of (heir response. It is possible that some thymus-dcriscd memory cells losl their lalxT through division after the period of labelling. We are investigating the possibility of recruitment of thymus-derived cells by olher thymus-demed cells responding specifically. The small number (0- I %l of labelled cells found in conltol animals may he due, at least in part, to the emergence and subsequent response of a few thymus-derived cells which were undergoing division in the thymus at the time of thymidine administration. The chief conclusion we should like to draw from (his experiment is that one result of the DNA synthesis which follows primary antigenic stimulation is the generation of memory celts. 'I lie ability to identify these cells should be of value in characterizing them further. R. K. (>. is h recipient of a US Public Health Service Career Development Award. The work was supported by US Public Health Set Gee grants fioin (be National Cancer Institute, the National Institute of Allergy and Infectious Diseases and an American Cancel Society sub-grant. We thank Kazunari Kendo and Anne Shapiro for technical assistance. Note added in proof: Since we submitted this manuscript, another report in which memory cells were identified by autoradiography, has appeared. Hosm.inn, C.. and Feldman, 3. D., Clin. Exp. Immunol., 7, 565; 1970. R. K. Gershon J. KrOcur J. D. Naysmith B. IT. WxKSMAN Depaatnents of Pathology and Microbiology, Yale Vnirersiiy School of Medicine. S'ew Haven, Conncrtiriti 06510 Kc,circd Noveinl>s'i 23, I VO; revved March 10. 1071. 1 Gcnv.uis, }. I ., and l.'lir, J \V , J li.xp. Med., 124. 1017 (1966). 1 Millet. J I . A. IV, and MiUhell, G I'., 'Etanxplunt. Rev., 1, 3 (iyr,9) 1 D.ntcv A, T. S , i'uiro/Unn Roy . t. a7 (1969) - 1 it.,a', m ( .. \..n.re.::o :: v >i"'m ' IA. J. S., Inn!i;-.i\ I-.. Wallis, V,, and Holler, P. l\, littnrpliinltition, a, 4 >3 (I'((,6/ 641 f' Miller, }. J. IH.7. Immunol., 92. 673 (1964). 7 Miller, J. J. III. ami foie. L. J.. J /-.T/> Mr,!.. 126, 109 flv/.Tt " Millet. J. 5 III, and Cole, !.. J., J Immunol. 98. 9X2 (|9i,', ' Busman, C., and I eldinjn, J. I)., J. Exp. Mr,!.. 12H. 2'i t (p/r.M 10 I'oid, G. I-'., in 7>.iv//r Hruftiny anti Rnilinlmn (edit by Muklem. II. S., and l.outit, J. I-'.), 197 (Academic ("revs. New YuiL 1966). 11 M iller. J. J. Mi. and Cole. U. J.. J. 1/wtwnoi, I III. 11.1 (! 96S). 15 Carier, K. L., Davies, A. J. S,, l.cuchars, p... Wallis, V. J , and Ciershon, R. K., in Lxmphuiic Tissue and Cietoxuuil Cmtetj in Immune Response, 143 (Plenum Press, New York, |9(,9j. 15 Katz, D. If., Paul, W. F.. Goidl, li. A., and Bcnaceiiaf' 0 Science. 170,462 (1970). "" Polychlorinated Biphenyls: Photolysis of 2,4,6,2',4',6'- Hcxachlorobiphenyl Many aromatic orgaiiochloripc compounds arc readily utilized or otherwise decomposed by a number of specific micro organisms. In the environment, however, these compounds arc relatively stable and resistant lo general microbial break down. For many of these compounds photochemical degra dation, induced hy the ultraviolet content of (lie Sun s light, may be a major pathway of decomposition. Because a large number of pesticides contain a chloroarnmalic moiety as a primary structural feature, consider.)! !. attention has been paid to the photolysis of these com pounds' '7. Photochemical decomposition ol chlorohiphcm h may he a significant process in the environment because the. absorb in that region of (he ultraviolet (ref. 8 and our unpub lished demonstrations) which is uvailablc in natural conditions (compare ref. 1) from sunlight. Commetcially available polychlorinated biphenyls (I'Ll)) for example `AiosloT, consist of a complex mixtutc of cldoi inated biphenyls which can be resolved into more than fife, peaks by gas chromatography on 'Scot columns' (private communication from D. J. Sissons and G. M. Telling! As it is difficult to correlate data from such a complex mixture we have synthesized a series of isomeric di. tri, tclra, penta. hexa. otta and decachlorobiphcnyls lo facililate fundamvi;:.!l studies on analytical, biological and chemical aspect' M i'CH (manuscript in preparation). We have also show n dial .n! these compounds give strong molecular ions on clcciron Table 1 GLC and M.iss Special Data for Hcjxachlo/oiuohf f'hotolysis Pioducts TLC band I I'cak 1 Peak 2 Peak 3 Peak 4 Peak 5 Peak 6 Peak 7 Peak 8 Retention lime * (win) 5.6 8.2 9.9 1.1.5 14 1 19.0 29.7 56.9 TLC band 11 Peak 1 Peak 2 Peak 3 19.6 26.8 35 25 ffi/r of M * __* i 222 256 290 (256) 324 (290) 358 304 290 324 358 Chlorine f content 0 0 2 3 4, (3"l 5, (4") 6 2 4 5 6 * (.'pntlilinns; mMrunu'nl, licwlctl Par.!,.ml 5750; column, (- . Oi l 4",, SI.10 on 'C'bronutxnrb' (AM) (21 XO mesh V, 1 a outside diameter, glass, injection poll tern,'culture, 230 ,o!nu n li-mpt'r u me, 17S' i'; jl.nr.e iv-iiizat/on dznsior temperature n collecti-.'i' pon temperature, 240 ('. hclnan llow rale, 40 nit nun 7 la u'u t H'-pc ;x'.n. dva: itwition . Ir. trace. . ! 1 !> .in-carbon peaks, xl rail uicniincrl. tj Con e-pramling lo starling material. DSW 0 2 6 4 7 6 STLCOPCB4010437 C42 ' NATURE VOL 232 AUGUST ?7 ip7t UN KU - Fig. I 70 cV mass spectrum (DuPont/CFC 21-11 OB instrument). 7 he tcrnpcraime of the sample, controlled independently (rom the source temperature10, was 40 C. 7 lie intensity of ions corresponding to the com ponents (Cl,.- Ci >H,C U, C!> - C, j} I,(. I,, and so on) in the mixture varies with sample temperature. F,ach isomer shows an M*-70 ion as the most important fragment. 7 licse ions me indicated as CI6-70, Clj-70, and so on. >T ICi,) rntttjt HOUt,-ro: ----1---- j~Lt -r - -t 1 J00 l*W I8U MKi,.li >>i to, !.,i jjl >04 - - ...fci <----r r-- ' v 260 MX) 340 )K0 ni/c Impact, followed by less intense ions resulting from successive loss of Cl and/or MCI (manuscript in preparation). As the general formula for PCI) is C,,li,o-iCI, the molecular ions of individual isomers are rims readily recognized in a mass speed urn or a mixture of these compounds (compare ref, V). We now wish to report the photochemical behaviour of 2,4,(i,7.',`r,6'-liexachlorobiphci)yl. A sample of 25 mg of this compound in 2.0 ml. of hexane was irradiated at VTM,, 3 100 A for 100 min. Hun-layer chromatography, using "Merck Silica (tel I-2.S4' and hexane, revealed the presence of two major bands; band I (A'f 0.40) and band II [Kr 0,65, corresponding to starling material).- lire mass spectrum of band I (Fig. I) indicated molecular ions corresponding to di, tri, tetra, penta and licxachlorobiphcnyls. Gas liquid chromatogiaphy (GLC) of bands I and II revealed eight and three major peaks rcspcctivcly. Detention times and mass siKctra data for all peak components arc reported in I able I. When irradiation was carried out in methanol, similar results were obtained, but in addition a third and more polar band appeared, containing oxygenated polychlorinated compounds with slrueluies which have not Irccn investigated further. Two conclusions can be drawn from the results of this slimy: (i) miring photolysis, chlorine is removed rather readily from hcxachlorobiphcnyl yielding compounds of lower chlorine content; (ii) photochemical production of new compounds formed by loss of chlorine, reariangcment or condensation may lead to further complications in residue analysis with the possible appearance of ehlorobiphenyls ("peaks") in environmental samples that are not present in commercial PCB mixtures. , S. Safe O. flinZINGHK Atlantic Regional laboratory, . National Research Council of Canada, Halifax, Nova Scotia Received March 22, 1971. i r'.r'-r'... ts n ...a i ; m _v ;n nrP.-v-,.>n ,,r '"'(edit." by Kearney, p! C.,' and Kaufman, I). lYi.HI (DekkeV! New York, 1969). Ciosby. IV G , Ann. AT Aeod. Sci. 160, 82 (!**69. 5 Crosby, I). G., and Lcitis, IJ. Agric. load Chan., 17, 1033 10)1. (1909). * Cioshy, IV (i., and Tang, C S , J. Agric. load Chan . 17. 10-11 (1969). ' Mosirr, A. R., Guenzi. W. P., and Miller, L. L., Science, 164, I OK3 (1969). ' * glimmer, J., Klingcbicl, It. I., and Hummer, I). ., .Science, J67, 67 (1970). 1 Millci, l.. I-., and N'arang, R. S., Science. 169, 308 (1970). Friedel, R., and Orchin, M., U V Spectra of Aromatic Compounds (Wiley, New York. 1951). ' Hulzingcr, U , Jamieson, W. to., and Zitko, V., Nature 2Z0 (>64 (1970). 10 Jamieson, W. D., and Mason, F. G., Rev. Sci. Instrum.. 41, 778 (1970). Selection for Resistance to Carbamate and Organophosphorus Insecticides in Anopheles albimanus The development of resistance in anephehne mosquitoes to DDT, IICI1, and cydodicncs, and the consequent set back in malaria eradication programmes has lent urgency to the st arch for alternative insecticides to replace the chlorinated h> Jrocarbons. During the past few years, more than 1,300 new insecticides, chiefly organophosphates and carbamates, have been tested under an international collaborative progtumme of the World Health Organization'. Testing consists of seven sequential stages and only insecticides that satisfy the criteria in all stages are recommended for use on a hirer scale One of the insecticides that satisfied the cnteru of stage VI (operational evaluation) and has been found suitable for stage V'l (epidemiological evaluation) is the carbamate, pmpoxur'. It is intrinsically more toxic to adults of many mosquito species than dicldiin, nialatluon, fenthion and fcnilroihion, and as a residual spray has been found to be effective for 2 to J months against Anopheles gnmhiac and A. funestus in Africa, A. Stephensi and A. dlhali in Iran, and A. albimanus in LI Saha dor'. No case of resistance to caibamatc or organophosphorus insecticides has yet been reported although tolerance to malathion has been suspected in A. albimanus in Guatemala and Nicaragua5,4 and subsequently demonstrated in LI Salvador'". In this communication we report the development of high degrees of Carbamate and organophosphorus resistance in A. albimanus resulting from intensive selection pressure in the field, and subsequently in the laboratory. Earlier attempts to induce carbamate resistance in A. albimanus by laboratory selection have been unsuccessful, although in Cities pipiens fatigans a 30 x level of ic-isl-mrc to propoxtir developed in larvae within twenty-live generations of selection piessurc5,1'. A strain of A. albimanus fto-n Pan,mu selected with ni-isopropylphcnyl mcthylcaib.imate L-: I t1:-' generations developed only a 2.8 x increase in the LC'ji- lesel . Another strain from Haiti, containing dicldrm-rr aslant ii.urnduals. when subjected to larval selection pressure !v. mcrov-ir for nineteen generations and to aonit pressure duui-.g "ae DSW 026477 STLCOPCB4010438