Characterization of CD4^- CD8^- CD3⁺ T-cell receptor-αβ⁺ T cells in murine cytomegalovirus infection

In this study, we have investigated that after the intraperitoneal infection with murine cytomegalovirus (MCMV), the CD3⁺ CD4^-CD8^-(double negative; DN) T-cell receptor (TCR)αβ⁺ T cells increased in peritoneal cavity, liver and spleen in both resistant C57BL/6 and susceptible BALB/c mice. The total cellular population of these cells showed peak levels around day 5 after infection in all the three investigated organs and the following phenotypical and functional characteristics emerged. The peritoneal DN TCRαβ⁺ T cells expressed highly skewed TCRVβ8 on day 5 after infection compared with the uninfected mice, but those in spleen and liver showed moderate and low skewed TCRVβ8, respectively. The percentages of NK1.1⁺ DN TCRαβ⁺ T cells gradually decreased as did modulation of some of their activation markers consistent with an activated cell phenotype. The peritoneal DN TCRαβ⁺ T cells on day 5 after infection expressed the genes of interferon-γ (IFN-γ), tumour necrosis factor-α, Eta-1 (early T-cell activation-1) and MCP-1 (monocyte chemoattractant protein 1) but lacked expression of interleukin-4 (IL-4). After in vitro stimulation with phorbol 12-myristate 13-acetate and calcium ionophore in the presence of Brefeldin A, higher frequencies of intracellular IFN-γ⁺ DN TCRαβ⁺ T cells were detected in all three investigated organs of infected mice compared with those of uninfected mice. Stimulation of peritoneal DN TCRαβ⁺ T cells with plate-bound anti-TCRβ monoclonal antibodies showed proliferation and also produced IFN-γ but not IL-4. These results suggest that DN TCRαβ⁺ T cells were activated and may have an antiviral effect through producing IFN-γ and some macrophage-activating factors during an early phase of MCMV infection.