Suppressive substance produced by T cells from mice chronically infected with Trypanosoma cruzi. III. Genetic restriction and further characterization.

Earlier papers in this series reported that the culture supernatant of splenic L3T4+, Lyt-2- T cells from susceptible CBA mice chronically infected with Trypanosoma cruzi contain a SS3 that can inhibit the induction of delayed-type hypersensitivity to a wide range of Ag. The SS is a glycoprotein with an apparent molecular mass of 30 to 60 kDa and is distinct from T. cruzi Ag, IL-1, IL-2, IL-3 or IFN-gamma. It also has no effect on Th cells for antibody, cytotoxic T cells or immediate-type hypersensitivity. In this paper, we report that SS can suppress the induction of proliferating T cells but not the presentation of Ag to a cloned T cell line (D10). It also has no effect on the induction of delayed-type hypersensitivity in vitro. SS is produced by a number of inbred mouse strains irrespective of their susceptibility to infection with T. cruzi (BALB/c, highly susceptible; CBA, susceptible; C57BL/10, resistant) but only CBA mice are sensitive to the suppressive action of SS. This is so whether the SS is derived from CBA, BALB/c, or C57BL/10. The sensitivity to SS is not a feature of the H-2k haplotype inasmuch as B10.BR and BALB/k mice (also H-2k) do not respond to SS. Attempts to purify SS with a range of biochemical techniques substantially enriched the specific activity but failed to produce a substance visualizable by analytical gel electrophoresis. IEF chromatography revealed SS activity spanning a pH range from 6 to less than 4. This suggests that SS is likely to be a minor heterogeneous component of the suppressive supernatant. The genetically highly restricted nature of its action is intriguing and may explain some of the contradictory reports in the literature on this subject.