A lirniting dilution assa y was developed to quantitate urushiol (the antigen of poiso n ivy; Toxicodetldroll radicalls) specifi c T cells from peripheral blood of a patient with a history of rhus (poison ivy) dermatitis. It was found that maximal sensitivity with minimal nonspecific proliferation could be produced with the use of 5 U / ml of recombinant IL2 added to the assay on day 6. This donor was found to have a fre-9"ency of urushiol specific peripheral blood T cel ls of (1/2935). Five

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... erleukin 2 (IL2) dependent urushiol specific T-cell clones were generated from the peripheral blood of this patient. These T-cell clones had a CD8+ (T8+) phenotype and proliferated speciJically to both extracts of Toxicod. lldroll radieallS (poison ivy) leaves and pure urushiol. Penwdccylcatcchol was an inferior antigen. only stimulating proliferation of one clone. The ability of all clones to proliferate to pure urushiol. despite theif having been induced with R hUS dermaticis caused by ToxilOJewiro" radicalJs (poison ivy) has the characteristics of a delayed type hypersensitivity (DTH) and is known co be the result of sensitization to the hapten urushio l [t ,21. Animal models have shown that cutaneous delayed hypersensitivity may be mediated by either CD4+ (L3T4+) clones 13J or CD8+ (Lyt2+) clones 14J. although th e majority ofDTH inducing ManUSCript Portions of thiS work .1ippe:l r in abstract form in Clin Res 35:693A. This work was supported by AM33713. RSK was the recipient of NOItional InStitutes of Health Individ ual N:lItional Research Service Award AM07804. Repri nt requcsts to: Richard S. Kalish: Department of Dermatology, Box 98, Room 4-240. 5 16 Delaware Street SE. Minneapolis. Minnesota 55455-0392. Abbreviations: ConA: concanavalin A DMSO: dimethysulfoxide DTH: delayed type hypersensitivi ty E+: sheep erythrocyte receptor positive cells E-: sheep eryth rocyte receptor negative cells FCS: fetal calf serum IFN : mterferon Il2: intcrleukin 2 l OA: limiting dilution analysis lDCC: leCtIn depcndrllt cellular cytotoxicity NK : natural killer PBM: penpheral blood mononuclear cdl (lymphocytes & monocytes) PDe: pentadecylcatechol PWM: pokeweed mitogen rll2: recomblllant Il2 leaf ex tract, suggests that urushiol. or closely related catechols, represent the onl y allerge nic cons tituents of Toxicodendron radicans. Lyrnphokine production in response to ant igen varied between (0.6-5.0) units/ 1ll1 ofinterleukin 2 (IL2) and (1.0-120) units/ ml of ga mma interferon. Although