Molecular cloning of caprine IL-6 cDNA and its expression in insect cells

To analyze the interactions among immunoneuroendocrinological systems in a miniature Shiba goat, we attempted to clone and express caprine cDNA-encoding interleukin-6 (IL-6) which is well-known to exert a variety of effects on neuroendocrinological functions in small experimental animals. The cDNA-encoding caprine IL-6 was molecularly cloned from a lipopolysaccharide-stimulated adherent splenocyte library by the reverse transcription-polymerase chain reaction. The sequence analysis shows that the cloned caprine IL-6 cDNA encodes a precursor protein of 208 amino acids that is processed to mature protein of 180 amino acids with a predicted molecular weight of 20,524. The amino acid sequence of caprine IL-6 displays 97.8 and 51.1% degree of homology with ovine and human equivalents, respectively. A recombinant baculovirus containing the caprine IL-6 cDNA was shown to induce insect cells to efficiently secrete caprine IL-6 into culture supernatant up to 10(5) U/ml, as confirmed by Western blot analysis and bioassay with an IL-6-dependent cell line.