Mucosal T cells recovered from mice after infection with respiratory syncytial virus display a memory/activation phenotype

Involvement of toll-like receptor 4 in innate immunity to respiratory syncytial virus

The mammalian Toll-like receptor 4, TLR4, is an important component in the innate immune response to gram-negative bacterial infection. The role of TLR4 in antiviral immunity has been largely unexplored. In this study, the in vivo immune responses to respiratory syncytial virus (RSV) and influenza virus infection were examined in TLR4-deficient (C57BL/10ScNCr) and TLR4-expressing (C57BL/10Sn) mice. TLR4-deficient mice challenged with RSV, but not influenza virus, exhibited impaired natural killer (NK) cell and CD14(+) cell pulmonary trafficking, deficient NK cell function, impaired interleukin-12 expression, and impaired virus clearance compared to mice expressing TLR4. These findings suggest that Toll signaling pathways have an important role in innate immunity to RSV.

T cell subset analysis in peripheral blood of children with RSV bronchiolitis

Respiratory syncytial virus (RSV) bronchiolitis is partially an immune-mediated disease in which RSV-specific T cells play a predominant role. The peripheral blood T cell response was studied in patients with RSV bronchiolitis in order to detect evidence for T cell redistribution during natural RSV infection and if so, which subsets are involved. 18 patients with RSV bronchiolitis and 13 control patients were studied. The white blood cell count, the number of T cells and T cell subsets in blood on admission and after 1 week were measured. The absolute count of natural killer cells and gamma delta + T cells on admission were significantly lower in RSV patients in comparison with the control group. During the course of RSV bronchiolitis CD8+ T cells and IL-2 receptor-positive T cells increased significantly. In the ventilated patients the total lymphocytes and the number of T cells and several T cell subsets with surface molecules compatible with an activation state of the cell were decreased in comparison with the non-ventilated RSV patients on admission. During RSV bronchiolitis, consistent shifts in T cell subsets can be demonstrated in the peripheral blood compatible with redistribution from the circulation probably towards the lungs. These findings are more pronounced in patients with severe disease.

Peripheral blood T and B lymphocyte subpopulations in infants with acute respiratory syncytial virus brochiolitis

Most data concerning immunopathogenetic mechanisms involved in respiratory syncytial virus (RSV) infection are derived from animal studies. In infants with RSV bronchiolitis the target organ i.e. the airway is hard to explore. We looked for specific alterations in peripheral blood lymphocyte subpopulations in infants hospitalized for RSV bronchiolitis. Flow cytometric analysis with a large panel of monoclonals was performed on peripheral blood lymphocytes in thirty-two infants (mean age: 4.9 months) admitted for RSV bronchiolitis. Data collected on admission were compared with age-matched control values and also with results obtained at the end of the first week of hospitalization. Differences between age-groups (older or younger than 4 months) and between clinical subgroups (clinical severity score more or less than 6) were looked for. In the group of infants as a whole, regardless of age and clinical score the number of CD4+ cells on admission was significantly elevated compared to normal values for age (p<.0001) including a high fraction of the naive suppressor-inducer subpopulation (CD4+/CD45RA+) and a low fraction of the reciprocal memory helper-inducer subpopulation (CD4+/CD29+). Within the CD8+ cell population the number of T cells with cytotoxic activity (CD8+/S6F1+) was significantly elevated (p<.0001) as were other types of cytotoxic cells. A significant decrease (p<.0001) in the proportion of the precursor/suppressor-effector subpopulation (CD8+/S6F1-) was seen. Absolute numbers and percentages of CD19+ B cells were significantly elevated (p<.0001) with a significant increase in the CD5+ subfraction (p<.0001) as well as in the CD10+ subfraction (p<.0001). In the older age group immunophenotypic cytotoxicity was more pronounced with increased clinical score. During recovery the CD45RA+:CD29+ ratio tended to normalize within the CD4+ T cells. Within the B lymphocyte subsets significant increase in the CD19+/CD5+ fraction (p<.05) was seen. We conclude that there are significant changes in the number of peripheral blood lymphocyte subsets in infants with RSV bronchiolitis as compared to age-related controls. We hope that present data could be useful in further exploration of RSV immunology in humans. A possible link between RSV bronchiolitis and the subsequent development of atopy is mentioned.