Schistosome-derived inhibitory factor: an immunosuppressive agent preferentially active on T lymphocytes.
We have previously shown that schistosome-derived inhibitory factors (SDIF) inhibited lymphocyte proliferation and induced immunosuppression. Crude SDIF was purified by successive gel filtration and reverse-phase high-performance liquid chromatography. Purified SDIF preparations strongly inhibited the proliferation of different T cell line cells, while other cell lines (B cells, macrophages and fibroblasts) were almost not affected by SDIF. The inhibition of T cell proliferation by SDIF was not mediated through an Interleukin-2-dependent mechanism since both Interleukin-2-dependent and -independent T cells were inhibited. SDIF-activity was absorbed by cells in a time- and cell-number-dependent fashion at 4 degrees C, suggesting the existence of a possible receptor for SDIF. However, the difference in sensitivity to SDIF proliferation inhibition could not be attributed to the presence or absence of this receptor since cells from SDIF-sensitive and SDIF-resistant cell lines absorbed SDIF activity in the same way.