III-3. Participation of γ/δ-T cells in the protection against mycobacterial infection

To search for a potential role of T cell receptor (TcR) γ/δ T cells in host-defense against mycobacterial infection, we analyzed the kinetics, repertoire, specificity and function of γ/δ T cells in the peritoneal cavity, lymph node (LN) and spleen during an intraperitoneal infection with a sublethal dose (5 x 10⁵) of viable BCG in mice. The number of bacteria in the organs increased to a maximal level by 28 days after infection, and thereafter decreased gradually. Of the CD3⁺ cells in PEC on day 7 after infection, approximately 25% were CD4^-CD8^-, most of which express TcR γ/δ on their surface. On the other hand, the PEC on day 28 contained an increased number of α/β T cells which were CD⁺CD8^- or CD4^-CD8⁺ and the proportion of γ/δ T cells was reciprocally decreased. The kinetics of γ/δ and α/β T cels in the LN and spleen during BCG infection are much the same as that seen in the PEC. The early appearing γ/δ T cells preferentially used Vγ1/Vδ6 although the repertoire of these T cells are diversified. The γ/δ T cells in PEC on day 7 remarkably proliferated and produced γIFN and IL-2 in response to sonicated BCG or PPD derived from Mycobacterium tuberculosis but not to 65 kd heat shock protein (HSP) derived from M. bovis. These results suggests that γ/δ T cells precede α/β T cells in appearance during mycobacterial infection and the early appearing γ/δ T cells may participated in the protection at the early stage against the mycobacterial infection.