STUDY OF PERSISTENCE AND LOSS OF PATCH TEST REACTIONS TO DICHROMATE AND COBALT

Hyposensitization is a poorly understood phenomenon that refers to the conversion from a positive to a negative (or less positive) patch tes t. We studied 180 cement workers with contact dermatitis, who original ly had a total of 163 positive patch test reactions to potassium dichr omate and 98 positive reactions to cobalt chloride. They were patch te sted a 2nd time after 2-6 years. On the 2nd patch test to dichromate, 103 (63%) remained positive, while reactivity decreased in 33 (20%) an d 27 (17%) had become non-reactive. Cobalt sensitivity persisted in 47 %, diminished in 13%, and 40% of the patch tests became non-reactive. In 10 patients with persistent patch test reactions and 10 matched pat ients with diminished reactions or loss of reactivity, circulating T-c ell responses to dichromate and cobalt were studied in vivo. Circulati ng T cells that proliferated only to specific contact allergens were i solated and in all patients they were primarily CD4+. However, in pati ents with persistent reactions, they were CD4+ CD45RO+ (memory cells), while in the group that lost sensitivity, they were CD4+ CD45RA+ (sup pressor - inducer cells). These differences support an immunologic bas is for hyposensitization.