DETECTION OF A NOVEL 40,000 MW EXCRETORY TOXOPLASMA-GONDII ANTIGEN BYMURINE TH1 CLONE WHICH INDUCES TOXOPLASMACIDAL ACTIVITY WHEN EXPOSED TO INFECTED MACROPHAGES

To analyse target molecules of the CD4(+) T-cell response to toxoplasm a infection, a panel of Toxoplasma gondii-specific murine CD4(+) T-cel l clones has been established. Clone 3Tx15, belonging to the T helper 1 (Th1) subtype, abolished intracellular parasite growth when co-cultu red with macrophages and live toxoplasma at a ratio of 2:2:1. This eff ect results from macrophage toxoplasmicidal activity induced upon para site-dependent cellular interaction, an irrelevant Th1 clone failed in this three-party system. Clone 3Tx15 detects its corresponding antige n in the supernatant of infected cells and also reacts with a host cel l-free preparation of T. gondii-excreted/secreted antigens. T-cell blo t analysis of two-dimensionally separated toxoplasma Lysate revealed a molecular weight of about 40000 for the fractions stimulating clone 3 Tx15, As checked in parallel enzyme-linked immunosorbent assay, the 40 000 MW T-cell antigen co-migrates with the excretory protein GRA4, the sole 40000 MW T. gondii antigen hitherto known to be recognized by T lymphocytes. Nevertheless, neither recombinant GRA4 nor immunoaffinity -purified natural GRA4 was stimulatory for clone 3Tx15. Our findings t hus demonstrate that Th1 clone 3Tx15 which induces toxoplasmicidal act ivity during antigenic interaction with infected macrophages defines a new 40000 MW excretory T. gondii antigen.