Activation of unusual Mac-1⁺CD4^-CD8^- T cells bearing αβ antigen receptor in murine lungs during infection with Mycobacterium bovis BCG: Regulation by interferon-γ

We have recently (Kawakami et al, Immunol. Lett. 1995;46: 143) demonstrated that unusual Mac1⁺CD4^-CD8^- T cells bearing αβ antigen receptor (Mac-1⁺ αβ T cells) reside in a considerable proportion in murine lungs. The present study was performed to examine the dynamics of accumulation of these cells in the lungs following intravenous administration of Mycobacterium bovis BCG (BCG). Mac-1⁺ αβ T cells accumulated rapidly 24 hr after infection, followed by a gradual increase over the observation period of 15 days. Furthermore, the expression of Ia, ICAM-1 and FcγR II/III on their surface intensified dramatically after BCG infection. The kinetics of enhancement of Ia expression was slower than that of ICAM-1, with the maximum level attained in one day in the latter molecule but in two weeks in the former. Neutralization of endogenous IFN-γ by specific mAb completely blocked the augmented expression of Ia on Mac-1⁺ αβ T cells after BCG infection, but did not have any significant effect on that of ICAM-1. In contrast, in vivo administration of IFN-γ enhanced the expression of ICAM-1 as well as that of Ia. Our results indicate that accumulation of Mac-1⁺ αβ T cells within the lung is associated with a differential change in the expression of surface antigens, and suggest that these cells may play a role in the host defense against mycobacterial infection.