Naturally occurring human IgA autoantibodies against IgE-DES myeloma protein. Prevalence and specificity.

The prevalence and specificity of naturally occurring human IgA anti-IgE autoantibodies (a-E Ab) were studied by ELISA with anti-IgA monoclonal antibodies (mAb) and a purified myeloma IgE as solid-phase protein, i.e., IgE-DES(kappa). Such detected IgA a-E Ab were common among adults, and significantly increased geometric means (GM) were found in patients with atopy (P = 0.006; n = 41; GM = 79.3 arbitrary units (AU)/ml) and filariasis (P = 0.02; n = 41; GM = 75.9 AU/ml), as compared with nonatopic controls (n = 42; GM = 48.8 AU/ml). No such difference was observed between age-matched nonatopic (n = 22; GM = 36.7 AU/ml) and atopic (n = 22; GM = 38.6 AU/ml) children. Children had significantly (P<0.001) lower IgA a-E Ab concentrations than adults, probably as a result of age, because IgA a-E Ab concentrations and age of children were significantly correlated (n = 44; P<0.05; r(s) = 0.30). IgA a-E Ab concentrations were very low in cord serum (n = 32; median <0.1 AU/ml). Sex did not influence IgA a-E Ab concentrations in any study group. The specificity of IgA a-E Ab in nine sera was studied by ELISA inhibition assay using IgE-DES myeloma as solid-phase protein and inhibitory proteins of the IgG, IgM, IgD, and IgE classes, including five different IgE myeloma proteins, as well as three enzymatic fragments of IgE-DES. The inhibitions indicated that all IgA a-E Ab tested reacted in a low-affinity reaction with determinants restricted to IgE-DES, i.e., the solid-phase protein. These epitopes were heat-resistant (2 h; 56 degrees C) and located in the Fab(epsilon)-DES fragment. No isotype-specific IgA a-E Ab were found because none of the four other IgE proteins were inhibitory. Subclass typing indicated that most IgA a-E Ab belonged to the IgA1 subclass. It is unlikely, for reasons of restricted specificity, low affinity, and common prevalence, that such IgA1 a-E Ab are connected with IgE-mediated disorders. The study also raises questions on the definition of anti-IgE antibodies.