Expression of a diversified mannose receptor family in chickens

The Mannose Receptor plays important roles in capture and internalisation of endogenous and pathogen-derived ligands and consequent regulation of physiological and immunological processes. Whereas mammals have a single Mannose Receptor gene, birds have five paralogous genes that have diversified their intracellular and extracellular domains. Using synthesised, codon-optimised genes transfected into Cos-7 and CHO cells we produced fusion proteins that were used in a novel DNA, DNA, Protein prime-boost immunisation strategy to produce monoclonal antibodies with specificities to each of the proteins MRC1L A-E. Cross-reactivity of the macrophage-specific KUL01 monoclonal antibody with only the MRC1L-B protein definitively confirms the identity of the KUL01 gene as MRC1L-B. Immunohistochemistry with the MRC1L-B monoclonal antibody locates a population of cells consistent with the understood locations of chicken macrophages. Expression of MRC1L-A was largely restricted to vascular endothelial cells, alongside MHC II. In this regard expression of the two avian proteins mirrors the single mammalian orthologue, MRC1. MRC1L-C and D were found on occasional cells in specific tissues, while MRC1L-E was identified more widely, though with a more restricted distribution than with MRC1L-B. The diversified functions of this gene family remain to be elucidated. Particularly, it is of note that while the cytoplasmic domains of MRC1L-A, B and D possess recognisable endocytosis motifs, only the MRC1L-A gene encodes a di-aromatic sorting motif, with potential consequences for immune function, including cross-presentation of exogenous antigens.