Inhibitory effects of the Trypanosoma cruzi membrane glycoprotein AGC10 on the expression of IL-2 receptor chains and secretion of cytokines by subpopulations of activated human T lymphocytes.

The Trypanosoma cruzi membrane glycoprotein AGC10 has been shown to alter some human macrophage functions (De Diego, J. L. et al., J. Immunol. 1997. 159: 4983 – 4989). We show here that, in the presence of AGC10, [3 H] thymidine incorporation by normal human lymphocytes stimulated with anti-CD3 or phytohemagglutinin (PHA) is severely curtailed. This effect was found to involve down-regulation of the expression of both CD25 (IL-2Rα) and CD122 (IL-2Rβ) on the lymphocyte membrane and a marked decrease in the level of up-regulation of the expression of surface CD132 (IL-2Rγ or γc ). These alterations occurred in fairly large proportions of CD4+ and CD8+ lymphocytes. AGC10 also inhibited proliferation and expression of IL-2 receptor chains by activated T lymphocytes virtually depleted of monocytes/macrophages, indicating that these effects do not necessarily require prior modification of monocyte/macrophage function by AGC10. Human lymphocytes stimulated with anti-CD3 or PHA also displayed a markedly decreased capacity to secrete IL-2 and IFN-γ, suggesting that AGC10 affected at least Th1 cell functions. Cell viability in cultures containing or lacking AGC10 was comparable over a 72-h period, and neither CD25 expression by, nor the viability of, PHA-stimulated Jurkat cells was altered by AGC10, ruling out that the effects of AGC10 are due to cell killing. These results highlight down-regulatory effects on activated T lymphocytes exerted by a membrane molecule from a parasite causing a disease whose acute phase is accompanied by immunosuppression.