Molecular cloning and characterization of a novel neutrophil chemotactic factor from a filarial parasite.

To compare the molecular structure of a parasite-derived neutrophil chemotactic factor (NCF) with host-derived NCFs or other NCFs, molecular cloning of cDNA encoding NCF derived from Dirofilaria immitis adult worm (DiNCF) was performed. A D. immitis cDNA library was screened with an antibody to DiNCF, and one DiNCF cDNA clone (pD-4) was isolated. A fusion protein of pD-4 and gene 10 protein showed significant neutrophil chemotactic activity whereas gene 10 protein itself showed marginal neutrophil chemotactic activity. The total nucleotide sequence analysis revealed that pD-4 was 994 bp long with a 432 bp open leading frame encoding a 143 residue protein. The NH2-terminal amino acid sequence of the natural DiNCF and the deduced amino acid sequence from the cDNA showed that the mature functional protein was comprised of 112 amino acids. Although the deduced amino acid sequence of this protein did not show overall homology to host-derived NCFs or other known proteins, it contained a similar sequence (Met-Phe-Lys) to the known chemotactic peptides. The possibility of the functional epitope of DiNCF is discussed.