Protective immunity in human filariasis: a role for parasite-specific IgA responses.

BACKGROUND Filaria-specific antibodies of immunoglobulin (Ig) G, IgE, and IgM isotypes have been correlated with acquired immunity in the literature, but the status of filaria-specific IgA and its role in human filariasis has not been addressed. The present study attempts to fill this lacuna. METHODS Both total and filaria-specific IgA to different developmental stages of filarial parasites were quantified by solid-phase immunoassays in 412 clinically and parasitologically defined cases occurring in an area endemic for human bancroftian filariasis in Orissa, India. RESULTS Compared with other clinical categories, microfilariae carriers were deficient in total as well as filaria-specific IgA. More crucially, significantly high levels were observed in putatively immune control subjects from areas of endemicity. These associations were also related to sex; female subjects in each category displayed higher levels of filaria-specific IgA than did male subjects. CONCLUSION The study demonstrates, for the first time, a positive correlation between protective immunity and increased levels of filaria-specific IgA in human bancroftian filariasis. Furthermore, filaria-specific IgA appears to be an immunological window for the sex-related differences in susceptibility to infection observed in human filariasis.