Campylobacter jejuni is highly susceptible to killing by chicken host defense peptide cathelicidin-2 and suppresses intestinal cathelicidin-2 expression in young broilers

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 μM) and much lower than for S. enteritidis (20 μM). Compared to wild-type C. jejuni 81116, the lipooligosaccharide (LOS)-deficient 81116ΔwaaF 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.