Prominence of IgG4 antibodies in the human responses to Strongyloides stercoralis infection.

The participation of the four subclasses of IgG in the humoral response to Strongyloides stercoralis was assessed by analyzing total and parasite-specific responses of each IgG subclass in 20 patients with uncomplicated strongyloidiasis and 21 immunocompromised patients with extraintestinal disease. The total component of each subclass was normal in most patients. IgG4 antibodies (measured by ELISA) were the most prominent parasite-specific response in both groups. Specific IgG2 and IgG4 responses were significantly more elevated in immunocompetent than in immunosuppressed patients. When the reactivity of each IgG subclass was analyzed by immunoblotting on SDS-PAGE-separated larval antigens, IgG4 recognized more antigens than did any other subclass. No parasite antigens were selectively recognized by either clinical group. Thus the continuous antigenic stimulation of chronic strongyloidiasis may result in an enhanced IgG4 subclass response. However, no presence or absence of humoral responses specific for filariform larval antigens was associated with the extraintestinal dissemination of the parasite.