Characterization of T-cell receptor γδ T cells appearing at the early phase of murine Listeria monocytogenes infection

It has been shown that T-cell receptor (TcR) γδ⁺ CD4^- CD8^- T cells increase in number and have an important role in early protection in murine Listeria monocytogenes infection. In this report, to characterize further the phenotype of the γδ T cells in listeriosis, we analysed V region gene usage and in vitro antigen recognition of the TcR γδ T cells in the peritoneal cavity of mice at the early phase after i.p. infection with a sublethal dose of L. monocytogenes. The γδ T cells predominantly expressed Vδ6 which has been reported to be expressed by TcR γδ-bearing foetal thymocyte hybridomas specific to mycobacterial and self heat-shock protein (hsp) 60. These early appearing CD3⁺ CD4^- CD8^- T cells in Listeria-infected mice, which were reported to be TcR γδ T cells, increased in proportion and in size by in vitro stimulation with recombinant hsp 60 from Mycobacterium bovis and purified protein derivative from M. tuberculosis but not by stimulation with heat-killed L. monocytogenes. A 65,000 MW molecule was detected in the lysate of viable L. monocytogenes but not in the lysate of heat-killed L. monocytogenes by a monoclonal antibody (mAb) raised against mycobacterial hsp 60. These results suggest that the Vδ6-bearing peripheral γδ T cells are activated by recognizing listerial hsp 60 expressed by viable L. monocytogenes. The hsp 60-reactive Vδ6-bearing T cells may have an important role in protection against L. monocytogenes and other parasites that express hsp 60 at high level.