A plasmid DNA encoding chicken interleukin-6 and Escherichia coli K88 fimbrial protein FaeG stimulates the production of anti-K88 fimbrial antibodies in chickens.

Immunization using a plasmid to deliver an encoded protein for expression in situ as the antigen is a promising technology. A plasmid encoding the enterotoxigenic Escherichia coli K88 fimbrial protein FaeG when injected into chickens stimulates the production of antibodies against the fimbrial protein, similar to what has been observed in mice. The efficacy of a genetic adjuvant on fimbrial antibody production was tested by introducing the gene for chicken interleukin-6 in tandem with the faeG gene. Expression of both the fimbrial FaeG protein and chicken interleukin-6 protein was confirmed in COS-M6 cells. Slightly higher antiFaeG antibody titer in chickens was obtained compared with immunization with the plasmid encoding FaeG alone, especially at 10 (19%, P < 0.05) and 12 (27%, P < 0.05) wk, respectively, after the secondary immunization. Elevated antiFaeG antibody titer induced by chicken interleukin-6 and FaeG proteins expressed jointly persisted longer than when induced by FaeG protein alone. This is the first report of an avian cytokine enhancing an immune response, and confirms that coexpression of the antigen and adjuvant from a plasmid delivered by DNA immunization is an effective protocol.