Abstract

Group II C-type lectin domain (CTLD) containing receptors belong to a large family of pattern recognition receptors which mainly act on the innate immunity. They are structurally related and consist of a cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM) and a single extracellular CTLD. Although they have been described in teleost fish, their involvement in immune responses is not well understood. In this study, four immune-related lectin-like receptors (termed Ci ILLR1 and Ci ILLR5-7), belonging to the group II CTLD receptors, were identified in grass carp ( Ctenopharyngodon idella ). They contain a short cytoplasmic tail and a single CTLD in the extracellular region. The Ci ILLR1 has a WxHxxxxxY motif similar to the WxHxxxxY motif which is required for the recognition of β-glucans by some of the group II CTLD containing lectins in mammals. Further, a modified QPD motif (EPD) known to be involved in binding to carbohydrate ligands is present in the Ci ILLR1, 5 and 6. However, Ci ILLR7 lacks these motifs. Expression analysis revealed that they were constitutively expressed in the head kidney and spleen. Moreover, Ci ILLR1, 5 and 6 could be up-regulated in the head kidney and spleen of fish after infection with Flavobacterium columnare and in the primary head kidney leukocytes by LPS and PHA. Expression of Ci ILLR1, Ci ILLR5 and Ci ILLR6 were mainly detected in the enriched lymphocytes whilst Ci ILLR7 was expressed in the enriched monocytes/macrophages. The results expand existing knowledge on the immune responses of the C-type lectin receptors in teleost fish.