30 kDa protein antigen, a major secreted protein antigen of Mycobacterium tuberculosis, exhibits strong T cell stimulatory activity. In order to better understand the immunologic activities of 30 kDa antigen, lymphocyte proliferation by
3H-thymidine
incorporation, cytokine mRNA expression pattern using reverse transcription-polymerase chain reaction (RT-PCR), and cytotoxicity in response to in vitro stimulation of human peripheral blood mononuclear cells (PBMCs) with 30 kDa antigen were
evaluated.
Lymphoproliferative responses to 30 kDa and crude protein antigens in PBMCs of normal PPD-negative and positive donors were compared. As expected, PPD negative donors demonstrated no thymidine incorporation in response to 30 kDa and crude protein
antigens, while PPD positive donors showed extensive proliferation to both antigens. Freshly isolated PBMCs were stimulated with 30 kDa antigen for 0, 6, 12, 24, 48 hr, 1 wk, and 2 wk and examined for the induction of IFN-γand IL-4 mRNA using
RT-PCR.
The expression of IFN-γmRNA was greatly augmented after 1 wk, and there was also early inductions at 6 and 24 hr, whereas IL-4 mRNA is consistently expressed through 0 to 48 hr and markedly decreased after 1 wk. In contrast, freshly isolated
human
tonsillar cells failed to express detectable level of IFN-γmRNA but showed enhanced IL-4 mRNA expression after in vitro stimulation with 30 kDa antigen for 1 wk.
Both natural killer (NK) and T cell cytotoxic antivities induced by 30 kDa and crude antigens were also evaluated. PBMCs from PPD positive donors stimulated with 30 kDa antigen showed significantly higher NK and T cell cytotoxic activities than
those in
PPD negative donors. Crude antigen also induced similar level of cytotoxicity with that of 30 kDa antigen.
These results suggest that 30 kDa antigen of M. tuberculosis may selectively activate Th1 cells and be a strong inducer of IFN-γexpression. In conclusion, 30 kDa antigen can be used as a standard T cell immunogen.
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