Sera of patients with high titers of immunoglobulin G against Toxoplasma gondii induce secretion of tumor necrosis factor alpha by human monocytes

Abstract

Toxoplasma gondii alone does not induce tumor necrosis factor alpha (TNF- α) secretion by human monocytes and macrophages. Nevertheless, sera from infected patients with high titers of specific immunoglobulin G antibodies against T. gondii induce TNF-α secretion, which is significantly higher than the corresponding induction by negative sera (P < 0.05). After incubation with the positive serum, parasites also induce secretion of this cytokine, but TNF-α levels are lower (11.4 to 71.8%) than those obtained with positive serum alone. Therefore, this secretion seems to be elicited in part by antibody-T. gondii complexes and/or another unidentified factor(s), probably different from lipopolysaccharide, interleukin-1, TNF-α, and gamma interferon. In this study, monocytes secreted more TNF-α into the culture fluid than macrophages did (P < 0.05), and no correlation was observed between secretion of this cytokine by the monocytes and the intracellular multiplication of the parasites, evaluated by [3H]uracil incorporation. Sera from patients with other infectious diseases did not induce secretion of TNF- α; however, serum free of antibodies to T. gondii, obtained from patients with leishmaniosis, also stimulated secretion of the cytokine.