BM-20

Ov20 is a structurally novel 20-kDa retinol binding protein secreted byOnchocerca volvulus. Immunological and biological investigation of this protein has been hampered by the inability to maintainO. volvulusin a laboratory setting. In an effort to find a system more amenable to laboratory investigation, we have cloned, sequenced, and expressed cDNA encoding homologues of Ov20 from two closely related filarial species,Brugia malayi(Bm20) andAcanthocheilonema viteae(Av20). Sequence comparisons have highlighted differences in glycosylation of the homologues. We present here an analysis of mouse immune responses to Ov20, Bm20, and Av20. The results suggest a strong genetic restriction in response to native Bm20 that is overcome when recombinant, nonnative material is used. Reactivity of human filarial sera to the three recombinant proteins confirmed previous specificity studies with Ov20 but highlighted important differences in the reactivity patterns of theO. volvulusandB. malayihomologues that may be due to differences in glycosylation patterns. Ov20 is a dominant antigen in infected individuals, while Bm20 is not. The availability of theB. malayihomologue enabled us to use defined murine reagents and inbred strains for genetic analysis of responsiveness in a way that is not possible for Ov20. However, the close sequence similarity between Ov20 and Av20 suggests that theA. viteaemodel may be more suited to the investigation of the biological functions of Ov20.