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Modulation of the host response in human schistosomiasis. I. Adherent suppressor cells that inhibit lymphocyte proliferative responses to parasite antigens.

Previous studies have demonstrated that peripheral blood mononuclear cells (PBMC) from patients with chronic schistosomiasis are unable to generate strong in vitro proliferative responses to parasite antigens but that responses to mitogens and nonschistosome antigens are normal. In the present study PBMC from eight patients with schistosomiasis mansoni and five normal individuals were fractionated with nylon wool columns to remove adherent cells. Whereas the removal of such cells regularly diminished the proliferative responses of normals to both antigens and mitogens, in patients with chronic schistosomiasis, removal of adherent cells significantly enhanced the responsiveness to parasite antigens (p < 0.05). The enhancement was specific for schistosome antigens (derived from the cercarial, adult, and egg states of the parasite) and did not extend to nonparasite antigens or mitogens. The suppression found originally in the unfractionated PBMC could be consistently reinduced in vitro by the addition of adherent to nonadherent cells of these patients.

Studies on a single patient evaluated during both acute and chronic stages of S. mansoni infection showed the absence of adherent suppressor cells early in infection, but they showed development of such cells by 20 months. Thus, our observations demonstrate clearly that adherent suppressor cells are a regular constituent of the PBMC of patients with chronic schistosomiasis and that the development of such cells may be partially responsible for the progressive modulation of specific lymphocyte responsiveness to parasite antigens seen in these patients as their acute infections advance to more chronic stages.