Characterization of a recombinant T cell and B cell reactive polypeptide of Onchocerca volvulus.

To identify potentially protective Ag of the filarial nematode Onchocerca volvulus on the molecular level we screened a cDNA library of O. volvulus with a human serum raised against radiation-attenuated infective larvae of O. volvulus. A cDNA clone of 218 bp (OvL3-1) was selected for further studies. It was expressed in Escherichia coli and affinity purified recombinant polypeptide was tested for its ability to stimulate in vitro PBMC from African onchocerciasis patients and PBMC from chimpanzees experimentally infected with O. volvulus. An enhanced cell proliferation by PBMC was observed in many patients after stimulation with the recombinant OvL3-1 polypeptide. In addition, some patients' PBMC responded to OvL3-1 stimulation with enhanced IL-2 production. Infected chimpanzees also showed an increase in T cell proliferation. Onchocerciasis patients had variable levels of specific antibodies directed to the recombinant polypeptide when sera were tested by ELISA. A mAb directed against the recombinant protein located the native target Ag in the muscles of the adult worm. The molecular mass of native OvL3-1 was found to be 50 kDa on immunoblots. Polymerase chain reaction analysis of RNA from different life stages of the parasite showed that OvL3-1 is transcribed in all parasite stages within the mammalian host. A homologous gene is also present in other filarial parasites. The protein corresponding to OvL3-1, therefore, represents an immunogen present during the whole life-span of the parasite, and because of its B and T cell stimulatory properties, it may be a candidate for a protective Ag in human filariasis.