Effect of capsule on interaction of Campylobacter jejuni cells with an analogue of a host cell receptor

Interaction of Campylobacter jejuni with host cells involves a variety of bacterial cell-surface structures. Whilst bacterial adhesins are required for specific binding to host cell receptors, such interaction may be impeded by production of a polysaccharide capsule. In order to elucidate a role of capsule in bacterial interaction with host cells we developed an assay based on bacterial binding to immobilised analogue of a host cell receptor, SBA lectin. The latter specifically interacts with GaNAc residues decorating N-linked glycoproteins located on the cell surface. One example of such glycoproteins, PEB3, was the main focus of this study. This model of attachment was verified in a series of experiments confirming specificity of interaction. Bacterial binding was found to be dose-dependent and affected by the presence of soluble fractions of lectin and GalNAc. Moreover, significant reduction of attachment was observed in several independent peb3 mutants. In contrast, attachment of non-capsulated kpsM was significantly increased. Expression of capsule at certain stages of infection may prevent bacterial recognition by innate host immune system, e.g. by macrophages carrying GalNAc-specific MGL receptors. On the other hand, de-protection of adhesins in non-capsulated cells may be beneficial for bacterial interaction with host tissues at the site of colonisation and attachment. A hypothesis of differential expression of adhesins and capsule was confirmed by qPCR. There was an increase of peb3 and decrease of kpsM gene expression over time. These findings suggest a role of capsule in fine tuning of C. jejuni interaction with host cells.