How does Campylobacter evade and/or avoid chicken’s immune response?

Abstract

Campylobacter jejuni causes gastroenteritis in humans and is mainly acquired via consumption of contaminated poultry. C. jejuni is a frequent coloniser of chickens, often in the absence of overt pathology, yet produces a time- and magnitude- limited inflammatory response. One hypothesis is that glycosylation of surface moieties may mask the bacteria from recognition by the avian immune system, resulting in limited host responses. An O-linked flagellin glycosylation island (Δcj1321-cj1325/6) has been previously shown to play a role in the colonisation of chickens.

Previously described methods for generation of avian antigen-presenting cells (APCs) were applied and tested. The objective of this project was to investigate the interactions between chicken APCs and C. jejuni strains that vary in legioniminic acid substitution of the flagellum (Δcj1321-cj1325/6 and Δcj1324); Δcj1321-25/6 being a whole locus knock out, and Δcj1324 being a single gene knockout.

Primary bone-marrow derived APCs, macrophages (BMMs) and dendritic cells (BMDCs) were cultured for 6 days under standard conditions, then stimulated with either lipopolysaccharide (LPS, 100ng/ml), wild-type C. jejuni (11168H), mutant strains lacking genes responsible for flagellin O-glycosylation (Δcj1321-cj1325/6 and Δcj1324) (108 CFU/ml) for 4 hours. Stimulated cells were then harvested and RNA was extracted.

Changes in mRNA expression of pro-inflammatory cytokine chIL--1β were quantified Taqman RT-qPCR assay.

The mRNA expression levels of chIL-1β in BMMs, stimulated with mutant Δcj1321-cj1325/6 were significantly decreased p=0.042; no significant effect in chIL-1β mRNA expression (p=0.989) in BMMs stimulated with mutant Δcj1324 when compared to those stimulated with the wild-type.

The mRNA expression of chIL-1β in BMDCs, stimulated with the mutant Δcj1321-cj1325/6 was decreased (p=0.052). BMDCs stimulated with the mutant Δcj1324 have displayed a significant decrease (p=0.013) in chIL-1β, when compared to wild-type stimulated control (11168H).

Although the results presented are not conclusive of overall biological relevance, data appears to be indicative that C. jejuni flagellin O-glycosylation island may play a role in an immune response of chickens against C. jejuni, as there was notable decrease in expression levels of chIL-1β in both BMMs and BMDCs in response to the whole locus knock out mutant strain cj1321-25/6. This suggests that this locus might be important for host-bacteria interaction and, which in turn will allow C. jejuni colonisation to persist.