Immune responses during human schistosomiasis mansoni. X. Production and standardization of an antigen-induced mitogenic activity by peripheral blood mononuclear cells from treated, but not active cases of schistosomiasis.

Peripheral blood mononuclear cells (PBMN) from patients with active schistosomiasis mansoni are generally induced to proliferate upon exposure to a soluble worm antigenic preparation (SWAP). In contrast, only 25% of such patients responded to SWAP exposure by the production of detectable levels of a mitogenic factor (MF) activity capable of stimulating proliferation of resting cultures of allogeneic PBMN. When former schistosomal patients (chemotherapeutically cured 10 to 40 yr previously) were tested for these two responses to SWAP, all manifested blastogenesis; 80% also responded by the production of MF activity. Only 9% of control subjects with no history of schistosomiasis produced MF activity when exposed to SWAP. The production and assay of MF activity by former schistosomiasis patients was standardized. Reliable, optimal production was achieved by using 6 X 10(6) PBMN in 2-ml cultures upon exposure to 15 micrograms protein SWAP/ml. The cells were incubated for 20 hr in the presence or absence of SWAP, at which time they were washed and recultured in fresh medium for at least 28 more hours. Subject to subject variability occurred in the optimal time of detection of MF activity in culture supernatant fluids, but detection was assured between 24 and 48 hr after the wash. The assay system for MF detection required a 5 to 7-day culture. The consistent production of MF activity by former schistosomal patients emphasized the longevity of immunologic memory to SWAP, and may indicate a post-treatment decline of immunoregulatory mechanisms that are operative in patients with active schistosome infections.