Little is known about the interactions of chicken host defense peptides (HDPs) with Campylobacter jejuni in young chicks. To examine the role of the chicken HDP, cathelicidin-2 (CATH-2) in host-pathogen interactions we challenged 4-day-old Ross 308 broilers with a chicken-derived C jejuni isolate (WS356) and used the chicken pathogen Salmonella enterica Enteritidis phage type 4 (FGT1) as a reference. Immunohistochemical staining was used to localize CATH-2, C jejuni and Salmonella enteritidis. Intestinal CATH-2 mRNA expression levels were determined by quantitative PCR. Antibacterial activities of CATH-2 peptide against C. jejuni and S. enteritidis isolates were assessed in colony count assays. In contrast to S. enteritidis, C jejuni was not seen to attach to intestinal epithelium and C jejuni challenge did not result in recruitment of CATH-2 containing heterophils to the small intestinal lamina propria. Minimal inhibitory concentrations found for CATH-2 peptide against human- and chicken-derived C. jejuni isolates were similar (0.6-2.5 mu M) and much lower than for S. enteritidis (20 mu M). Compared to wild-type C. jejuni 81116, the lipooligosaccharide (LOS)-deficient 81116 Delta waaF mutant was much more susceptible to CATH-2. Interestingly, CATH-2 mRNA expression levels in the small intestine were significantly lower 48 h p.i. in C jejuni-challenged chicks. These findings indicate that human clinical and chicken-derived C jejuni are equally highly susceptible to chicken CATH-2 peptide and that C jejuni uses LOS to protect itself to some extent against HDPs. Moreover, suppression of intestinal CATH-2 expression levels may be part of the C. jejuni immune evasion strategy.
- enteric infections