Immune responses during human schistosomiasis mansoni. V. Suppression of schistosome antigen-specific lymphocyte blastogenesis by adherent/phagocytic cells

Peripheral blood mononuclear cells (PBMN) from chronically infected schistosomiasis mansoni patients responded poorly in vitro to a soluble schistosomal egg antigen preparation (SEA) and moderately well to either soluble worm (SWAP) or soluble cercarial (CAP) antigenic preparations. The responses induced by SWAP or CAP were dramatically increased, in 84 and 92%, respectively, of the 24 chronically infected patients tested, upon removal of adherent/phagocytic (A/P) cells from the original cell populations. In contrast, removal of A/P cells from the PBMN of treated patients, transiently infected patients, and uninfected control subjects did not result in enhanced reactivity to these antigens. Overall, SEA-induced responsiveness of chronically infected patients' cells remained low in spite of A/P cell removal. Lymphocyte transformation induced by phytohemagglutinin-P and Candida albicans extract was not significantly altered by removal of A/P cells in any of the groups tested. The expression of another regulatory system concerned with a nonspecific suppressive influence exerted by SEA was also unaffected by the presence or absence of A/P cells. The previously reported, in vitro, schistosome antigen-specific, serosuppression mediated by sera from most chronically infected patients was effective in the presence or absence of A/P cells. However, serosuppression and A/P cells combined to exert maximum suppression of both the SWAP- and CAP-induced responses of chronically infected patients' cells. The enhanced responses observed after A/P cell depletion represented actual increases in blastogenesis, as determined morphologically, as well as increased incorporation of tritiated thymidine. These studies have demonstrated the presence of immunoregulatory A/P cells in the PBMN cells of chronically schistosomiasis mansoni patients which have the capability to suppress lymphocyte blastogenesis induced by the antigenic preparations derived from adult worms and the infectious, cercarial, larval stage of the parasite Schistosoma mansoni.