Control of Trypanosoma cruzi Infection in Mice Deprived of T‐Cell Help

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Abstract
The role of CD4+ T lymphocytes in the resistance of BALB/c mice to Trypanosoma cruzi was examined by in vivo depletion using monoclonal anti-CD4 antibodies (MoAbs)<. When the administration of MoAbs was initiated 2 days before, or 5 to 12 days after the infeetion (dpi) with 50 bloodstream-from trypomastigotes of the Tulahun strain, mice showed an enhanced susceptibility to the parasite. Speeific IgM. but not IgM responses, were inhibited in anti-CD4-treated and infected mice However, when anti-CD4 treatment of mice was delayed until the 8th week of infection. neither a reactivation of the infection as determined by mortality or parasitaemia. nor a modulation of the titre of anti- T. cruzi IgG antibodies was detected. Furthermore, mice chronically infeeted with T. cruzi and deprived of CD4 or T cells resisted the challenge with 50,000 trypomastigotes (approximately 1000 LD50) Secondary antibody responses against parasite antigens were inhibited after in vitro depletion of CD4+ cells in chronically infected mice before boosting with T. cruzi antigens. However, recipients of CD4 or T-cell-depleled spleen cells from mice chronieally infected with T. cruzi were protected when challenged with the parasite The possibility that the parasite control is maintained by long-lived B cells capable of rapid differentiation into IgG-secreting plasma cells in the absence of T helper cells is discussed considering the present data