TOXOPLASMA GONDII SOLUBLE ANTIGEN INDUCES A SUBSET OF LPS INDUCIBLE GENES AND TYROSINE PHOSPHOPROTEINS IN PERITONEAL MACROPHAGES

Abstract

Previous studies have shown that activated macrophages play an important role in the immune response to infection by Taxoplasma gondii, a protozoan parasite. The purpose of this investigation was to characterize the responses of macrophages to a soluble extract of T. gondii (STAg). In particular, (i) to compare the responses induced by STAg to those induced by the protypic macrophage activator, lipopolysaccharide (LPS), as measured by TNF secretion, the induction of six LPSinducible genes, and protein tyrosine phosphorylation; (ii) to determine whether signaling induced by STAg requires a functional Lps gene by examining macrophages from C3H/OuJ (Lpsn, LPS responsive) and C3H/HeJ both (Lpsd, hyporesponsive to LPS) mice; and (iii) to compare the sensitivity of human and mouse macrophages to STAg in terms of TNF secretion. In this report, it is demonstrated that STAg stimulates murine macrophages to secrete bioactive TNF-a and to express a subset of the LPS-inducible genes tested (TNF-α, TNFR-2, IL-1β). However, STAg did not stimulate Lpsn macrophages to express other LPS-inducible genes, e.g., IP-10, D3, or D8. Like LPS, STAg also induces the tyrosine phosphorylation of MAP kinases (47-kD and 43-kD isoforms), and a 41-kD protein of undetermined identity. The responses to STAg exhibited by C3H/OuJ (Lpsn) and C3H/HeJ (Lpsd) macrophages are very similar. This implies that macrophage responses toSTAg are not modulated by the Lps gene. In addition, a human monocytic cell line (THP-1) was also found to secrete TNF-α activity in response to STAg. The THP-1 cell response to STAg does not require serum, differentiation of THP-1 cells. but does require prior The ability of STAg to induce TNF-α, a subset of LPS inducible genes, and tyrosine hosphoproteins could not be attributed to LPS contamination, because the response of macrophages to STAg are not blocked by inhibitors of LPS; polymyxin B, rBPI₂₃. We propose that STAg may share with LPS two signaling pathways which are intact in C3H/HeJ macrophages.