Structural analysis and antibody response to the extracellular glutathioneS-transferases from Onchocerca volvulus

Onchocerca volvulus is a human pathogenic filarial parasite which, like oth er parasitic nematodes, is capable of surviving in an immunologically compe tent host by employing a variety of immune evasion strategies and defense m echanisms including the detoxification and repair mechanisms of the glutath ione S-transferases (GSTs). In this study we analyzed the glycosylation pat tern and the immunological properties of extracellular O. volvulus GST1a an d -1b (OvGST1a and -1b). The enzymes differ in only 10 amino acids, and bot h are glycoproteins that have cleavable signal peptides and unusual N-termi nal extensions. These characteristics have not been described for other GST s so far. Mass spectrometry analyses indicate that both enzymes carry high- mannose type oligosaccharides on at least four glycosylation sites. Glycosy lation sites 1 to 3 of OvGST1a (OvGST1b sites 2 to 4) are occupied by trunc ated N-glycans (Man(2)GlcNAc2 to Man(5)GlcNAc(2)), and N glycosylation site 4 of OvGST1a (OvGST1b site 5) carries Man(5)GlcNAc2 to Man(9)GlcNAc(2). To analyze the capacity of these secretory GSTs to stimulate host immune resp onses, we studied the antibody responses of onchocerciasis patients against the native affinity-purified OvGST1a and -1b. By enzyme-linked immunosorbe nt assay we showed that OvGST1a and -1b are immunodominant antigens, with l ess than 7% nonresponder patients. A direct comparison of the antibody resp onses to the glycosylated and deglycosylated forms demonstrates the high im munogenicity of the N-glycans. Analyses of the antibody responses to the un usual N-terminal extension show an enhanced recognition of this portion by patients as opposed to recognition of the recombinant protein without exten sion.