Induction of immune responses by schistosome granuloma macrophages

In mice, granuloma formation after Schistosomiasis mansoni infection is known to be a T cell-dependent response to schistosome eggs that peaks at 6 to 8 wk after infection (early) then regresses to a minimum by 20 to 32 wk (late). This decline in host responsiveness, termed modulation, has been attributed to T cell-mediated suppression. We now have investigated the macrophages from either Early or Late schistosome granulomas phenotypically and found no difference in expression of I-A subregion encoded antigens. We also tested granuloma macrophage (Gm) populations in their capacity to induce positive and negative antigen-specific immune responses to the hapten 4-hydroxy-3-nitrophenyl acetyl (NP). As few as 10(3) to 10(4) NP-coupled Early or Late Gm given s.c. were equally capable of inducing MHC-restricted NP-specific delayed-type hypersensitivity (DTH) responses and this DTH-inducing capability was equivalent to that of splenic adherent cell (SAC) controls. Further, both Early and Late Gm were able to generate NP-specific induction-phase suppressor cells (Ts1) when as few as 10(2) NP-coupled Gm were given i.v., the same as NP-SAC controls. Finally, NP-specific effector-phase suppressor cells (Ts3) were equally induced by Early Gm, Late Gm, or SAC controls. Therefore, macrophages derived from Early or Late schistosome granulomas or normal spleens are apparently phenotypically indistinguishable and equally capable, in extremely small quantities, of inducing NP-specific DTH, Ts1, and Ts3 immune responses.