Early appearing γ/δ-bearing T cells during infection with Calmette Guerin Bacillus

To search for a potential role of TCR γ/δ T cells in host-defense against mycobacterial infection, we analyzed the kinetics, repertoire, specificity, and cytokine production of γ/δ T cells in the peritoneal exudate cells (PEC), lymph node (LN) cells and spleen cells during an i.p. infection with a sublethal dose (5 x 10⁵) of viable Bacillus Calmette-Guerin (BCG) in mice. In the PEC on day 7 after infection, approximately 26% of the CD3⁺ cells were CD4^-CD8^-, most of which expressed TCR γ/δ on their surface. However, the PEC on day 28 contained an increased number of α/β T cells that were CD4⁺8^- or CD4^-8⁺ and the proportion of γ/δ T cells in the PEC reciprocally decreased to 18% of the CD3⁺ cells. The kinetics of γ/δ and α/β T cells in the LN during BCG infection showed in much the same pattern as that seen in the PEC. When purified CD4^-CD8^- cells in the LN on day 7 after BCG infection were cultured with sonicated BCG lysate, PPD derived from Mycobacterium tuberculosis or recombinant 65 kDa heat shock protein derived from Mycobacterium bovis, the γ/δ T cells on this stage significantly proliferated and secreted IL-2 in response to sonicated BCG lysate and PPD but not to 65 kDa heat shock protein. V gene segment usage analysis with PCR method revealed that purified protein derivative-reactive γ/δ T cells preferentially used Vγ( 1/2 )/Vδ₆, whereas γ/δ T cells polyclonally expanded in response to the BCG lysate. These results suggest that γ/δ T cells specific for mycobacterial antigens preceding α/β T cells in appearance during infection may serve as a first line of defense against mycobacterial infection.