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 k Da antigenic polypeptide product was demonstrated by immunoprecipitation. cDNA was synthesized from mRNA and a λ 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 consider 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.
