IFN-GAMMA AND DELAYED-TYPE HYPERSENSITIVITY ARE ASSOCIATED WITH CUTANEOUS LEISHMANIASIS IN VERVET MONKEYS FOLLOWING SECONDARY RECHALLENGE WITH LEISHMANIA-MAJOR

IFN-gamma levels and delayed-type hypersensitivity (DTH) responses were evaluated in vervet monkeys, following secondary infection with Leishmania major (L. major). The animals had previously been vaccinated with leishmanial antigen, exposed to a primary infection and allowed to self-cure. Supernatants of peripheral blood mononuclear cell (PBMC) cultures, stimulated with either L. major antigen or Concanavalin A (Con A), were examined for the presence of IFN-gamma in a double sandwich enzyme-linked immunosorbent assay (ELISA). Significant levels of IFN-gamma were detected during active disease and following self-cure in both antigen and Con A supernatants. Higher levels of IFN-gamma were, however, present during active disease as compared with after self-cure. Positive and strong DTH responses were elicited in all experimental animals, following intradermal injection of fixed promastigotes (5 x 10(7)/animal) before rechallenge, during active infection and following self-cure. Again, strongest DTH responses were obtained during active infection as compared with the other sampling points. There was a correlation between IFN-gamma levels and DTH responses. It was concluded that IFN-gamma secretion and positive DTH responses are associated with secondary L. major infection and represent specific immunological correlates of protection in this disease model.