CD94/NKG2 expression does not inhibit cytotoxic function of lymphocytic choriomeningitis virus-specific CD8+ T cells

Murine Ag-specific CD8(+) T cells express various NK markers and NK inhibitory receptors that have been proposed to modulate immune responses. Following acute infection of C57BL/6 and BALB/cJ mice with lymphocytic choriomeningitis virus (LCMV), we observed that Ag-specific CD8(+), T cells expressed CD94/NKG2. Only slight expression of Ly49A and Ly49C receptors was observed on NP396-specific T cells, while all NP396-specific T cells expressed the NKT cell marker U5A2-13 Ag. Expression of CD94/NKG2 was maintained for at least 1 year following LCMV infection, as was the NKT cell marker. By means of cell sorting and quantitative PCR, we found that NP118-specific CD8(+) T cells primarily express transcripts for inhibitory NKG2 receptor isoforms. CD94/NKG2 expression was also observed on Ag-specific CD8(+) T cells following infection with polyoma virus, influenza virus, and Listeria monocytogenes, suggesting that it may be a common characteristic of Ag-specific CD8(+) T cells following infection with viral or bacterial pathogens. Expression of CD94/NKG2 on memory-specific CD8(+) T cells did not change following secondary challenge with LCMV clone 13 and did not inhibit viral clearance. Furthermore, we found no evidence that CD94/NKG2 inhibits either the lytic function of LCMV-specific T cells or their capacity to produce effector cytokines upon peptide stimulation. Finally, down-regulation of CD94/NKG2 was found to occur only during chronic LCMV infection. Altogether, this study suggests that CD94/NKG2 expression is not necessarily correlated with inhibition of T cell function.