Development of cell-mediated cytotoxic activity in the respiratory tract after experimental infection with respiratory syncytial virus.

The development of natural killer cell and other antibody-independent cellular cytotoxic response to RSV were studied in splenic and pulmonary mononuclear effector cells obtained from groups of 6-week-old cotton rats after subcutaneous (SC) or intranasal (IN) immunization with live virulent or ultra-violet (UV) inactivated respiratory syncytial virus (RSV). No virus-induced cytotoxic activity was observed after SC immunization with live virus or IN inoculation of inactivated non-infectious virus. On the other hand significant cytotoxic activity was observed after IN infection with live RSV. The peak responses appeared on day 4 in the pulmonary cells and on day 7 in the splenic mononuclear cells. These cytotoxic activities declined to baseline levels 10 and 15 days after immunization in pulmonary and splenic cells respectively. In addition, the amount of 51Cr released was significantly reduced when unlabelled 'cold' HEp-2 cells were added to 51Cr-labelled RSV-infected CRF target cells and vice versa in the cytotoxic assay. It is suggested that viral replication at the mucosal site is essential for the induction of local as well as systemic cytotoxic activity following RSV infection. The development of such cellular reactivity may be important in the elimination of RSV following human infection.