Specific and sensitive IgG4 immunodiagnosis of onchocerciasis with a recombinant 33 kD Onchocerca volvulus protein (Ov33).

The full length cDNA of the immunodominant Ov33 protein of Onchocerca volvulus was expressed in E. coli using various vector constructs. Expression was best with the vectors pGEX2T and pCG808fx, yielding fusion protein Ov33-GST and Ov33-MBP, respectively. Purified fusion protein Ov33-GST and O. volvulus antigen extracts (OvAg) were used to compare antibody responses (IgM and IgG-subclasses) of patients infected with O. volvulus, Brugia malayi, Wuchereria bancrofti, Mansonella perstans/Loa loa and of Sudanese control sera. Sera of all groups contained IgM reacting with Ov33-GST and with OvAg. There was no IgG1 response to Ov33-GST. IgG1 responses to OvAg were only detected in filariasis sera. IgG2 and IgG3 responses were not detectable or marginal in all groups. The IgG4 reaction of onchocerciasis patients to Ov33-GST and to OvAg was high, whereas few other filariasis sera contained IgG4 antibodies to Ov33-GST and to OvAg. A serodiagnostic test for onchocerciasis based on detection of IgG4 to Ov33-GST had a sensitivity of 93.3% and a specificity of 96%. An epitope common to Ov33 and to the homologous proteins of other filarial species was demonstrated with a monoclonal antibody. Purified Ov33-MBP fusion protein was used to follow the development of the antibody response of four chimpanzees experimentally infected with O. volvulus. The data indicates that antibodies to Ov33 are induced by developing worms and later parasite stages.