Isolation and Characterization of Expression cDNA Clones Encoding Antigens

The isolation of recombinant cDNA clones expressing antigens found in Onchocerca volvulus infective larvae is described. To isolate such clones, an expression cDNA library constructed from adult 0. volvulus RNA was screened with antiserum raised against infective larvae. One clone, designated XRAL-1 was characterized further. The recombinant antigen produced by XRAL-1 stimulates proliferation of peripheral blood mononuclear cells from 0. volvulus infected humans. XRAL-1 is derived from a 1450 bases message that encodes a protein with an apparent molecular weight of 42,000 in adult 0. volvulus. The inserted DNA of XRAL-1 contains an open reading frame of 1008 bp. The amino acid sequence predicted by this open reading frame contains three repeats of the sequence KKPEDWD. The identification of clones such as XRAL-1 will provide quantities of purified antigens sufficient to begin to study the immune response to and explore the development of immunity against the infectious form of the parasite.