Serum immunoglobulin A as a biomarker for respiratory syncytial virus infection in children aged <2 years.

AIMS: Past research suggested respiratory syncytial virus (RSV) specific serum immunoglobulin A (IgA) antibodies as a biomarker of previous RSV infections in young infants accounting for maternal immunity. This study aimed to confirm this association and to establish a serological threshold for discriminating RSV-naïve infants from those who have experienced RSV.

MATERIAL AND

METHODS

This study involves 135 infants from the LoewenKIDS study with nasal swabs collected at each acute respiratory infection, and serum samples collected at ages 1 and 2 years. RSV presence in swabs was ascertained by reverse transcriptase PCR; RSV-specific IgG and IgA antibody levels against five different structural proteins and RSV neutralising antibodies were measured in sera. Robust Mixture Discriminant Analysis was used to determine the cut-off values and account for false negatives.

RESULTS

Of 135 included infants, 131 had available data at year 1 (Y1) and 95 at year 2 (Y2). Pre-F IgA concentrations were higher in infants with PCR-confirmed RSV infections. There was a further increase in IgA, IgG and neutralising antibody titre concentrations from Y1 to Y2 consistent with re-infections. Based on robust mixture discriminant analysis, the cut-off values of pre-F IgA level indicative of past RSV infection were 0.23 AU·mL-1 at Y1 and 0.22 AU·mL-1 at Y2.

CONCLUSION

This study shows that in children aged <2 years, a previous RSV infection is accompanied by serum pre-F IgA antibody levels above 0.22 AU·mL-1, a value close to a previously proposed cut-off (0.19 AU·mL-1) based on seroresponse data only. The confirmed threshold can be of use in studies assessing vaccination strategies.