Preexisting poliovirus-specific IgA in the circulation correlates with protection against virus excretion in the elderly

BACKGROUND: Epidemiological studies have indicated that at least 10% of the Dutch elderly do not have poliovirus serotype-specific neutralizing antibody titers and might be at risk for poliovirus infection. Previously we established that memory immunity does not protect the elderly against poliovirus replication. In this study, we investigated whether preexisting immunoglobulin (Ig) A protects against poliovirus infection. METHODS: Elderly individuals (n = 383), divided into seronegative and seropositive groups, were challenged with monovalent oral poliovirus vaccine (mOPV), either serotype 1 or serotype 3. After challenge, poliovirus serotype-specific circulating and salivary IgA responses were measured by enzyme-linked immunosorbent assays, and poliovirus excretion in stool was measured. RESULTS: The majority of elderly persons without preexisting IgA excreted poliovirus in the stool. In contrast, most elderly persons seropositive for IgA did not excrete poliovirus. Significant inverse correlations were found between preexisting titers of poliovirus serotype-specific circulating IgA and virus excretion. Challenge with mOPV (re)induced IgA responses; low salivary IgA responses correlated with that in the circulation but not with virus excretion. CONCLUSIONS: These results indicate that preexisting IgA values in the circulation correlate with protection against poliovirus infection in the elderly. This further implies that persons without preexisting IgA might contribute to the circulation of poliovirus and therefore may threaten its eradication.