The immune response in primary asymptomatic and symptomatic rotavirus infection in newborn infants.

Systemic and mucosal immune responses were determined using an enzyme-linked immunosorbent assay in 18 infants (7-86 days old) experiencing primary rotavirus infections over two winters. Fifteen infected infants were asymptomatic; 3 had diarrhea. Neutralization antibody (NA) was assayed in two asymptomatic infants who had a serotype 1 isolate identified. Seven asymptomatic infants had sera available for analysis; none had IgG, 1 had IgM, but 4 had IgA antibody responses. Neither tested infant had a serotype 1 NA rise. In the 3 symptomatic infants, 1 had IgG, 2 had IgM, and all had IgA serum antibody responses detected. Eleven (73%) of 15 asymptomatic and all symptomatic infants had a rotavirus-specific fecal antibody response. These findings identify IgA as an important antibody in primary rotavirus infection in very young infants. The predominance of this antibody in asymptomatic infants suggests that their responses (and protection on subsequent reexposure) may be primarily mucosal.