Molecular cloning, expression, and localization of E1, an Onchocerca volvulus antigen with similarity to brain...

Protective immunity against human onchocerciasis may best be reflected by the existence of individuals who in spite of exposure to the filarial nematode Onchocerca volvulus do not develop disease (putatively immune). We observed preferential recognition of an O. volvulus antigen of approximately 90 kDa by sera from putatively immune individuals compared with sera from diseased individuals. Screening of an adult worm cDNA library with one serum recognizing this antigen almost exclusively led to the identification of a full length clone of 2043 base pairs designated E1. The open reading frame of 462 amino acid residues shows similarity to human brain ankyrin. E1 appears to represent a small transcript of the O. volvulus ankyrin gene. The nonfusion protein obtained by expression of the complete E1 cDNA exhibits an apparent molecular mass of 90 kDa on SDS-polyacrylamide gel electrophoresis. An antiserum against the recombinant protein reacts with the 90-kDa antigen in O. volvulus extract. In O. volvulus, E1 was localized in the neuronal cell bodies, the nerve ring, and the extracellular clefts of the basal labyrinth. These results identify an ankyrin-related O. volvulus protein as an immunogen to putatively immune individuals, suggesting that neuronal proteins may be important targets for immunity against O. volvulus in vivo.