L3 antigen-specific antibody isotype responses in human strongyloidiasis: correlations with larval output.

Autoinfective strongyloidiasis is potentially fatal, yet the majority of infected individuals harbour asymptomatic and chronic infections. The role of humoral responses in modulating autoinfection was assessed by examining antibody isotype responses to filariform larval antigens amongst chronically infected ex-Far East Prisoners of War (exFEPOWs) with longstanding (> 30 years) infection. Serum immunoglobulin (Ig)G1, IgG4, IgE and IgA responses to whole Strongyloides stercoralis L3 extracts and their constituent antigenic components were characterized by ELISA and quantitative immunoblotting. Comparison of two groups of S. stercoralis infected exFEPOWs with and without detectable larvae in stool demonstrated novel trends. Significantly enhanced recognition of six immunodominant antigenic components by IgA was associated with undetectable larval output, as was enhanced IgE recognition of several components. Additionally, IgE and IgG4 exhibited parallel antigen recognition patterns. These findings are consistent with roles for IgA in modulating larval output, for IgE in regulating autoinfection, and for IgG4 in blocking IgE-mediated responses in human strongyloidiasis.