Opposing effects of filariasis and chronic malaria on immunoregulatory T lymphocytes.

The effect of parasitic infections on immunoregulatory T lymphocytes was evaluated by means of quantitative determinations of total T cell and T-cell subset populations present in peripheral blood of patients with lymphatic filariasis, with the malaria-induced tropical splenomegaly syndrome (TSS), and with both infections. Total T-cell numbers were similar to control values in patients without TSS, and reduced in donors with TSS. OKT4+/OKT8+ T-cell ratios were decreased in microfilaremic donors without TSS (0.76 +/- 0.08) and elevated in patients with TSS without microfilaremia (1.97 +/- 0.16). Patients with dual infections tended to yield results similar to uninfected control donors. Thus, filariasis and chronic malaria (TSS) have opposing effects on the normal balance of immunoregulatory T lymphocytes. In patients with TSS, the imbalance appears to result from a decrease in the absolute number of circulating T cells with suppressor/cytotoxic phenotype.