The modulation of specific and non-specific cell-mediated immunity in baboons (Papio anubis) infected with Schistosoma mansoni.

Peripheral blood lymphocytes from baboon donors, with infections, were tested for activity at various times post-infection. Non-specific mitogenic responses following concanavalin A (Con A), and phytohaemagglutinin (PHA) stimulation were notably depressed between 4 and 15 weeks after a primary exposure to the parasite. Thereafter PHA and Con A reactivity returned to normal control levels. Specific cell-mediated immunity was evaluated by stimulating lymphocytes with an adult worm homogenate (SWA). Significant responses to the specific Ag were present only from 4 to 16 weeks post-infection. Thus, in the early `acute' phase of infection in the baboon, approximately from 4 to 16 weeks post-infection, there occurs a notable modulation of the host's specific and non-specific cell-mediated immunity (CMI). Cells from immunosuppressed animals, with a 9-week infection, were briefly treated with trypsin and then stimulated with Con A. Such trypsinization restored the lymphocyte response back to control level indicating the possibility that a surface protein molecule on the lymphocyte was causing the reduced mitogenesis to Con A. Accordingly, sera taken from baboons over the first 30 weeks of infection were tested for circulating immune complexes (CIC) using 3.5% polyethylene glycol precipitation. High levels of CIC were evident from approximately 4 to 6 weeks after infection, reached maximum amounts by week 9, and thereafter declined to control levels from approximately 13 weeks onwards. Thus the appearance of CIC is largely confined to the early acute phase. Serum from 9 week infected donors caused notable suppression of the Con A response of normal cells, as did purified CIC from the same serum. From this it is proposed that CIC may play a significant role in the regulation of host cell-mediated immunity in schistosomiasis.