Production and immunological characterization of a recombinant subunit of a Loa loa polyprotein antigen.

Diagnosis of loiasis and analysis of the specific immune response are limited by a paucity of parasite material. To circumvent this problem, a Loa loa antigen has been expressed in a prokaryote vector (pTrcHis). Immunization of Balb/c mice with this soluble recombinant protein produced a strong antibody response, with antibodies recognizing 2 major bands of 38 and 20 kDa in a native crude extract of Loa loa adult worms and microfilariae on Western blots. The target molecule was located mainly in the hypodermis and cuticle of the adult worm. Analysis of human IgG subclasses against this antigen by enzyme-linked immunosorbent assay (ELISA) showed IgG1, IgG2 and IgG3 but not IgG4 reactivity. IgG2 against this recombinant antigen was 100% specific for loiasis when tested against samples from European donor individuals. The same IgG2 antibodies showed 91% specificity for loiasis by comparison with Wuchereria bancrofti, Onchocerca volvulus, Mansonnella perstans and other helminth infections. Furthermore, the IgG2 antibody level correlated with the density of Loa loa microfilariae (r=0.400; P=0.02). This recombinant 15r3 molecule and specific IgG2 assay may be useful for monitoring control programmes.