A putative protein related to human chemokines encoded antisense to the cDNA of an Onchocerca volvulus antigen.

Chronic hyperactive dermatitis (sowda) in humans infected with the filarial parasite Onchocerca volvulus appears to reflect a hyperresponsiveness to parasite antigens. To identify antigens which play a role in this hyperresponsiveness an expression cDNA library of adult O. volvulus was screened with sera from patients with sowda. One further characterized cDNA clone, S1, consisting of 723 bp, surprisingly shows open reading frames (ORF) in both orientations. While a single ORF of 171 amino acids is present in sense orientation, a putative ORF of 95 AA is found in antisense orientation (aS1). Whereas no homologies to known proteins are found in S1, the sequence of aS1 shows a striking structural homology to human CC chemokines. The genomic organization of the coding region of aS1 shows the conserved three exon/two intron structure of the CC chemokine family. In adult worms transcription of mRNA corresponding to S1 but not to aS1 was detected. Expression of S1 as a non fusion protein and Western blot analysis revealed antibody recognition by all sera from patients with sowda, by 60% of sera from patients with the generalized form of onchocerciasis, but not by sera of exposed individuals with no evidence of onchocerciasis. IgG subclass analysis showed that IgG3 reactivity was restricted to sowda sera. In adult worms the S1 protein was localized to the hypodermis. Here we present the cloning and characterization of an O. volvulus antigen, which may be useful in the diagnosis of onchocerciasis. Furthermore, the results suggest the presence of a gene structurally related to human inflammatory cytokines in antisense orientation, raising the question of bidirectional transcription in O. volvulus.