Expression of the DX5 antigen on CD8(+) T cells is associated with activation and subsequent cell death or memory during influenza virus infection

The antigen recognized by the DX5 antibody (DX5 antigen) is expressed on al l murine NK cells. In the present study we found that a proportion of CD8() T cells (similar to5%) also express the DX5 antigen in uninfected mice, a nd that numbers of CD8(+) T cells expressing DX5 are significantly higher i n the lungs of influenza virus-infected mice representing up to 50% of all CD8(+) T cells on day 10 post infection. The expression of the DX5 antigen on CD8(+) T cells was associated with a memory phenotype in uninfected C57B L/6 mice and with an activation phenotype during influenza virus infection. Interestingly, when lymphocytes were isolated from lungs of influenza viru s-infected mice on day 10 post infection and adoptively transferred into re combination activating gene-1 (RAG1)-deficient mice, CD8(+)DX5(+) cells cou ld not be recovered from the recipient mice 2 days later. Moreover, CD8(+)D X5(+) cells were not detected when lung cells were removed from day 10 infl uenza virus-infected mice and cultured in vitro for 2 days. However, CD8(+) DX5(+) cells could be detected when apoptosis inhibitors were added to thes e cultures, suggesting that the CD8(+)DX5(+) cells underwent apoptosis duri ng cell culture. Furthermore, almost all DX5 expressing CD8(+) cells from l ungs of mice on day 10 post influenza virus infection stained positively wi th Annexin-V. Taken together, the data suggest that CD8(+) T cells expressi ng DX5 are associated with an activation/memory phenotype and are biased to wards apoptosis.