Binding and neutralising antibodies to respiratory syncytial virus and influenza A virus in serum and bronchoalveolar lavage fluid of healthy adults in the United States: A cross-sectional study.

Using serum and bronchoalveolar lavage (BAL) fluid collected from 20 healthy adults (23-37 years, 55 % female) in the United States, we measured immunoglobulin (Ig) A, IgG, and neutralising activity against respiratory syncytial virus (RSV) and influenza A (H1N1) virus. RSV-binding IgA and IgG measurements in serum were positively correlated with those in BAL. For influenza A (H1N1) virus, serum and BAL IgA antibodies were positively correlated, whereas IgG antibodies did not show a significant correlation. RSV-specific and influenza A (H1N1)-specific neutralising activity did not correlate between serum and BAL samples. These results demonstrate virus-specific correlations between antibodies in the serum and BAL that may not necessarily reflect correlations in functional activity. Further work is needed to confirm our preliminary observations, and define the immune correlates of neutralising activity to these and other respiratory viruses in the lower respiratory tract.