Abstract

Objective: To look for specific alterations in peripheral blood lymphocyte subpopulations in infants hospitalized for respiratory syncytial virus (RSV) bronchiolitis in order to learn more about RSV immunology.

Study design: Flow cytometric analysis with a large panel of monoclonals was performed on peripheral blood lymphocytes in thirty-two infants (mean age: 4.9 months) hospitalised for RSV bronchiolitis. Data on admission were compared with age-matched control values and also with results at the end of the first week of hospitalisation. Differences between age-groups (more or less than 4 months) and between clinical subgroups(clinical severity score more or less than 6) were looked for.

Results: In the whole group of infants regardless of age and clinical score, CD4+ cells on admission were significantly elevated compared for normal values for age (p<.0001) with 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, T cells with cytotoxic activity (CD8+S6FI+) were significantly elevated ((p<.0001). as well as 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 CD5+ subfraction (p<.0001) as well as in CD10+ subfraction (p<.0001).

In the older age group immunophenotypic cytotoxicity was more pronounced with increased clinical score.

During recovery CD45+/CD29+ ratio tended to normalize in the whole group. Within the B lymphocyte subsets a significant increase in the CD19+CD5+ fraction (p<.05) was seen.

Conclusion: Flow cytometric analysis on peripheral blood lymphocytes in infants hospitalised with acute RSV bronchiolitis shows a significant increase in CD4+ T-cells in contrast to the CD8+ predominance seen in other viral infections in humans. Within the CD4+ cells an imbalance is seen between the naive CD45RA+ and the memory CD29+ subpopulations. There is a significant increase in peripheral cytotoxicity, more pronounced in the most severe infected infants of the older age group. The CD8+ precursor/suppressor-effector subpopulation (CD8+SFI-) is significantly decreased.

Our results suggest that by studying lymphocyte cell surface antigen expression in peripheral blood it may be possible to further unravel immunological mechanisms involved in RSV bronchiolitis. Our data can be useful for the discussion about a possible link between RSV bronchiolitis and subsequent development of atopy.