Analysis of in situ NK cell responses during viral infection

NK cells are required for early control of murine CMV (MCMV) infection, but the distribution of murine NK cells in situ has not been clearly defined. We tested the reactivity of all available NK cell receptor-specific mAbs by immunohistochemistry. Only one mAb, 4D11 (anti-Ly-49G2), was reactive with C57BL/6 tissue sections. mAb 4D1-reactive cells expressed the nuclear morphology and flow cytometric profile of NK cells. In lymphoid organs, NK cells were distributed primarily in the splenic red pulp, between adjacent lobes in lymph node and randomly in the cortex and medulla of the thymus. No NK cells were detected in normal liver sections. Two days following MCMV infection, most splenic NK cells were associated with the lymphoid follicles and marginal zone. By day 3 following infection, the number of liver NK cells had increased significantly and the cells were detected within inflammatory foci. These changes were independent of IL-12, IFN-γ, and TNF-α, as assessed in mice with targeted mutations. Concurrent immunostaining for NK cells and viral Ags revealed close association of NK cells and MCMV-infected cells in the spleen and liver. Similar results were obtained in CD1^-/- and recombination activation gene-1^-/- mice lacking NK T or T and B cells, respectively, indicating specificity of staining for NK cells. Thus, following MCMV infection, NK cells accumulate at sites of viral replication in an IL-12-, IFN-γ-, and TNF-α-independent manner.