Cellular immune response to infection with respiratory syncytial virus and influence of breast-feeding on the response.

Virus-specific lymphocyte transformation (LTF) activity in vitro was examined in 78 infants with various forms of illness due to respiratory syncytial virus (RSV) infection. In 73 subjects with lower respiratory tract disease, significant LTF activity was often detected within one week after onset of initial symptoms, and responses characteristic for each clinical form were observed in the subsequent rise. Thus, mean activity in subjects with tracheobronchitis increased gradually, with the maximum response being detected at the fourth week after the onset of illness. In subjects with pneumonia the response was rather low during the first week of illness, and then a sharp increase of activity was observed at the second week. Although patients with bronchiolitis elicited similar levels of the activity until the first week, the response was significantly suppressed during the subsequent two weeks. The response at the second week in this group was significantly lower than those of corresponding specimens obtained from patients with pneumonia (p less than 0.01) or tracheobronchitis (p less than 0.05), suggesting a close association of the responsiveness with underlying mechanisms of bronchiolitis induced by RSV. The present study further indicated a possibility that breast-feeding of RSV-infected infants may alter levels of the LTF activity in these subjects.