A comparison of cytokine responses in respiratory syncytial virus and influenza A infections in infants

Respiratory syncytial virus (RSV) infection is a major cause of bronchiolit is in infants while influenza A infection usually manifests as upper respir atory tract infection. We hypothesised that the immunological responses of infants to RSV infection and influenza A infection are different. This pros pective study was undertaken to compare the cytokine responses during RSV a nd influenza A infection. Sera and nasopharyngeal aspirates (NPA) were coll ected from infants with a coryzal illness with or without wheeze who were a dmitted to the paediatric wards during 1998. Cytokines, adhesion molecules, RANTES, IgE and eosinophil cationic protein (ECP) were measured by enzyme linked immunosorbent assay or fluorescence enzyme immunoassay. The diagnosi s of RSV and influenza infections was based on direct immunofluorescence an d viral culture. Of the 39 infants studied, RSV infection was confirmed in 11 patients and Influenza A in 10 patients. All RSV patients and one influe nza A patient had wheeze during the infection. The serum concentrations of interleukin (IL)-4 and IL-5, regulated upon activation normal T cell expres sed and secreted (RANTES) and soluble intercellular adhesion molecule 1 (sI CAM-1) in infants with RSV infection were significantly higher than those w ith influenza A infection tall P < 0.02). The concentration of tumour necro sis factor-<alpha> (TNF-alpha) in NPA was significantly lower in infants wi th RSV infection (P < 0.01). Conclusion A predominant T helper cell type 2 cytokine and related immunolo gical response was observed in infants with respiratory syncytial virus inf ection whereas a predominant pro-inflammatory cytokine response was observe d in infants with influenza A infection. This may explain the different cli nical manifestations of the two viral infections in infants.