Immunochemical comparison between worm extracts of Onchocerca volvulus from savanna and rain forest

Abstract

Summary Crude phospate-buffered extracts of adult Onchocerca volvulus from savanna (Mali) and rain forest (Cameroon) areas were comparatively analysed using biochemical and immunological methods. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and isoelectric focusing revealed only minor differences between the two extracts. Out of 42 bands detectable by SDS-PAGE at least 21 were identified as glycoproteins by their affinity to concanavalin A. High resolution analysis using two dimensional gel electrophoresis (2D-G) showed marked differences in the polypeptide patterns of the two extracts. Some of the over 100 polypeptides demonstrable by Coomassie blue staining (especially at pIs between 4·3 and 5·6 and mol. wts over 64kD) were clearly different when the two extracts were compared. Antigenic differences between the two extracts could be detected by crossed immunoelectrophoresis using a rabbit anti-O. volvulus hyperimmune serum. The comparison by tandem crossed immunoelectrophoresis demonstrated clearly the existence of at least three antigenic differences, four partial identities and 13 antigenic identities between the extracts. For the identification of O. volvulus antigens serologically recognized by infected patients, we combined the 2D-G with an immunoblotting technique using a pool of highly reactive onchocerciasis sera from Mali. IgG binding antigens were then identified by incubating the blot membrane with this serum pool and with ¹²⁵I-labelled protein A followed by autoradiography. IgE binding antigens were detected using a ¹²⁵I-labelled anti-human IgE antiserum. Whilst the overall antigenic patterns were similar, there were, however, clear differences between the antigen preparations which gives further evidence for antigenic diversity of O. volvulus from savanna and rain forest areas.