Natural killer (NK) cells prevent virus production in cell culture

Natural killer (NK) cells (CD3-/CD16+/CD56+ lymphocytes) play an important role in early immune defense against viral infection, a fact which is of prime significance for heavily immunosuppressed patients after bone marrow transplantation. In this study we demonstrate that NK cells preferentially lyse human colon adenocarcinoma (Colo-205) tumor cells infected with herpes simplex virus type 1 (HSV-1) and vaccinia virus (VV) and autologous T cells infected with VV. This phenomenon was assessed by the viral infectious center (IC) method and compared with the results obtained by means of the standard 51Cr-release assay. Using the IC assay, we found that NK cells lyse virus infected cells at an early stage of infection, thereby preventing viral dissemination to neighboring cells. 51Cr-release assay verified by propidium iodide (PI) penetration showed that the early effects of NK mediated anti-viral activity are not the result of membrane damage. The effect of NK cells on HSV-1 infected Colo-205 cells appears to be independent of the level of expression of major histocompatibility complex (MHC) class I molecules while the killing of autologous VV-infected T cells correlates with a reduction in MHC class I expression. Our results suggest that additional factors besides MHC play a role in the regulation of NK cell-mediated lysis of virus infected cells. This may be of clinical importance in patients who are heavily immunosuppressed after bone marrow transplantation.