PERIPHERAL-BLOOD T-LYMPHOCYTE AND B-LYMPHOCYTE SUBPOPULATIONS IN INFANTS WITH ACUTE RESPIRATORY SYNCYTIAL VIRUS BROCHIOLITIS

Most data concerning immunopathogenetic mechanisms involved in respira tory 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 bloo d lymphocyte subpopulations in infants hospitalized for RSV bronchioli tis. Flow cytometric analysis with a large panel of monoclonals was pe rformed on peripheral blood lymphocytes in thirty-two infants (mean ag e: 4.9 months) admitted for RSV bronchiolitis. Data collected on admis sion were compared with age-matched control values and also with resul ts obtained at the end of the first week of hospitalization. Differenc es between age-groups (older or younger than 4 months) and between cli nical subgroups (clinical severity score more or less than 6) were loo ked for. In the group of infants as a whole, regardless of age and cli nical score the number of CD4+ cells on admission was significantly el evated 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 subpopulati on (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 sub population (CD8+/S6F1-) was seen. Absolute numbers and percentages of CD19+ B cells were significantly elevated (p < .0001) with a significa nt increase in the CD5+ subfraction (p < .0001) as well as in the CD10 + subfraction (p < .0001). In the older age group immunophenotypic cyt otoxicity was more pronounced with increased clinical score. During re recovery the CD45RA+:CD29+ ratio tended to normalize within the CD4T cells. Within the B lymphocyte subsets significant increase in the C D19+/CD5+ fraction (p < .05) was seen. We conclude that there are sign ificant changes in the number of peripheral blood lymphocyte subsets i n infants with RSV bronchiolitis as compared to age-related controls. We hope that present data could be useful in further exploration of RS V immunology in humans. A possible link between RSV bronchiolitis and the subsequent development of atopy is mentioned.