Molecular cloning of the cDNA encoding an immunodominant antigen of Dirofilaria immitis.

An immunodominant antigen of Dirofilaria immitis was studied using recombinant DNA techniques. The mRNA from D. immitis adult female worms was translated in vitro and a major 34 kDa antigenic polypeptide product was demonstrated by immunoprecipitation. cDNA was synthesized from mRNA and a lambda gt11 expression library was constructed and immunoscreened with dirofilariasis positive serum. A positive clone containing a nearly full length cDNA was isolated. The cDNA was 2415 bp in length and consisted of a single open reading frame followed by a long 3' non-coding region of 1446 bp. The open reading frame of 969 bp encoded a polypeptide of 322 amino acids with a molecular weight of 34,400. A cDNA fusion protein synthesized by bacteria (Escherichia coli JM109) using the expression vector pGEMEX-1 was identified as an immunodominant antigen by absorption experiments and had no cross-reactivity with sera from patients with other filarial species.