MURINE TH1 CLONE DEFINES A 60 KD TACHYZOITE ANTIGEN OF TOXOPLASMA-GONDII

Toxoplasma gondii-specific murine CD4(+) T cell clone 3Tx9 belongs to the Th1 subtype by virtue of secreting high levels of interleukin(IL)- 2, interferon-gamma and tumor necrosis factor without producing IL4 an d IL10. To characterize the clonal antigen, Toxoplasma lysate was sepa rated by SDS-PAGE and probed in T cell blot analysis with 3Tx9 T cells , revealing a fraction of about 60 kD molecular weight. This fraction proved highly stimulatory also for CD4(+) splenocytes isolated from in fected mice. The expression pattern of the relevant 60 kD antigen was determined by challenge of clone 3Tx9 with T. gondii strains from all three intraspecies subgroups and tachyzoites versus bradyzoites isolat ed from two strains as a source of antigen. While the T cell clone rea cted with tachyzoites of all strains tested, bradyzoites lacked antige nic activity. Parallel T cell blot and ELISA confirmed co-migration of the T-cell stimulatory antigen p60 and rhoptry proteins ROP1, ROP2,3, 4, and ROP5 among which ROP1 is a molecule of similar size and has onl y been shown on tachyzoites. However, a ROP1 knock-out Toxoplasma muta nt still had antigen activity for 3Tx9 T cells. Since the two known ta chyzoite-specific proteins, surface antigens SAG1/p30 and SAG2/p22, ha ve a much lower molecular weight, we suggest that p60 represents a new T. gondii tachyzoite marker which is defined by clone 3Tx9.