POTENTIAL SIGNIFICANCE OF THE CELLULAR IMMUNE-RESPONSE AGAINST THE MACAQUE STRAIN OF SIMIAN IMMUNODEFICIENCY VIRUS (SIVMAC) IN IMMUNIZED AND INFECTED RHESUS MACAQUES

The cellular immune response of seven rhesus macaques immunized with Tween-ether-treated macaque strain of simian immunodeficiency virus (SIV(MAC)) and three non-vaccinated control animals was investigated. Immunization elicited antigen-specific proliferating CD4+ cells in five of seven monkeys. Proliferating T cells were found in all animals protected from a first virus challenge. Cytotoxic T lymphocytes (CTLs) were not induced by the immunization. After the second challenge, the four formerly protected animals became infected, despite a strong proliferative CD4+ cell activity in three of them. All animals lost their proliferative activity 2 weeks after infection. After the first challenge four of the six infected animals exhibited a CTL response and after the second challenge, one of four newly infected macaques acquired a CTL response. The five animals with a CTL activity against SIV(MAC) proteins were protected from severe thrombocytopenia, which appeared in the five CTL-negative animals after infection. Our data show the induction of proliferative T cells by immunization with soluble SIV(MAC) antigen. This T cell reactivity was found in all animals protected from the first virus challenge, but did not confer protection from the second challenge. Interestingly, the proliferative T cell reactivity disappeared 2 weeks after virus infection. Furthermore a CTL response against viral proteins seems to protect infected animals from severe thrombocytopenia which is an early sign of AIDS in monkeys.