Expression of Toxoplasma gondii-specific heat shock protein 70 during In vivo conversion of bradyzoites to tachyzoites

Abstract

Stage conversion between bradyzoites and tachyzoites was investigated in C57BL/6 mice chronically infected with the ME-49 strain of Toxoplasma gondii. In order to promote bradyzoite-tachyzoite conversion, mice were treated in vivo with neutralizing doses of anti-gamma interferon (IFN-gamma) or anti-tumor necrosis factor alpha (TNF-alpha) antibodies. Expression of parasite-specific antigens SAG-1, SAG-2, and heat shock protein 70 (Hsp-70) was visualized in the central nervous system by immunocytochemistry and measured by photometric assay. The immunosuppressive effect of anti-IFN-gamma or anti-TNF-alpha treatment was immediate, leading to parasite stage conversion as indicated by the increased expression of tachyzoite-specific antigens (SAG-1 and SAG-2) and by rapid parasite replication. We also observed expression of high levels of Hsp-70 during a short period of conversion of bradyzoites to tachyzoites. Our data suggest that Hsp-70 may have an important role in the process of bradyzoite-tachyzoite conversion during the reactivation of chronic toxoplasmosis.

FIG. 1

Detection of SAG-1 (A), SAG-2 (B), and Hsp-70 (C) antigens by photometric assay in brain cysts from mice chronically infected with T. gondii. The data were obtained from several cysts analyzed from groups of three mice. Intensities of expression under the indicated treatment conditions are shown in absorbance units. Asterisks indicate values significantly different from those obtained with controls (P < 0.05).

FIG. 2

Illustration of SAG-1 (top panels) and Hsp-70 (bottom panels) immunoperoxidase staining in parasites inside cysts (A, B, D, and E) and free tachyzoites (C and F) of T. gondii present in the CNSs of animals treated with either control MAb (A and D) or anti-IFN-γ (B, C, E, and F) and shown at a magnification of ×244. Background staining with an unrelated control polyclonal antibody is shown in the inset (G) at a magnification of ×101. For the methodological details, see the text.