Enhanced Diagnostic Specificity in Human Filariasis by IgG4 Antibody Assessment

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Abstract
Phosphocholine (PC), an immunodominant molecule present on a wide range of organisms, including filariae, evokes antibody responses that lead to false-positive reactions in routine serological assays. Humans essentially do not respond to PC in the IgG4 subclass; therefore, by configuring an enzyme immunoassay to assess antibodies of the IgG4 subclass only, we were able to eliminate serological false-positive results in 32 of 34 crossreactive sera from patients with non-filarial parasitic infections. Specificity was thus greatly enhanced with minimal loss of sensitivity. Because preadsorption of these cross-reactive sera to remove antibodies to PC eliminated only ∼50% of the original cross-reactivity, other shared epitopes (perhaps similar to PC) are also likely to be restricted by IgO subclass.