In vivo expression of perforin by natural killer cells during a viral infection: Studies on uveitis produced by herpes simplex virus type I

A potent cytolytic pore-forming protein (PFP, perforin, or cytolysin) is associated with the cytoplasmic granules of cytotoxic Tlymphocytes (CTL) and natural killer (NK) cells. The role of PFP/perforin in cytolytic reactions carried out in vivo is still unclear. Here, the authors performed immunohistochemical analysis using antibodies monospeciflc for perform and made use of a murine uveitis model produced by intracameral inoculation of herpes simplex virus I (HSV-I). The main cell infiltrate found in the anterior segment of virus-inocutated eyes consisted of Thy-1⁺/asialo GM₁⁺/CD8^-/ CD4^- cells, presumably representing NK cells. Perforin staining was detected mainly in cells bearing this phenotype. Perform was only detected in cells displaying the large granular lymphocyte morphology. A small number of perforin-positive cells (<5%) colabeled as CD8⁺, indicating that these cells could have belonged to the CTL lineage. These observations show for the first time the presence of perform-containing NK cells in tissues of animals undergoing acute viral infections.