C-Type Lectin in Chlamys farreri (CfLec-1) Mediating Immune Recognition and Opsonization

TLDR

C‑type lectins are Ca²⁺‑dependent carbohydrate‑recognition proteins that mediate nonself recognition and clearance of pathogens, and CfLec‑1 is suspected to act as an attachment molecule to nonself agents, potentially serving as an immunoglobulin alternative. The study aimed to characterize CfLec‑1 expression, localization, and innate immune functions in the scallop Chlamys farreri. Recombinant CfLec‑1 binds LPS, PGN, and mannan, attaches to scallop hemocytes to recruit and enhance encapsulation and phagocytosis, and these activities are blocked by anti‑rCfLec‑1 antibody. CfLec‑1 mRNA was up‑regulated by LPS or β‑glucan and down‑regulated by PGN; immunofluorescence localized it to mantle and gill tissues, and functional assays showed it acts as a PRR and opsonin, boosting hemocyte encapsulation and phagocytosis of E.

Abstract

C-type lectins are a superfamily of Ca(2+) dependent carbohydrate-recognition proteins that play significant diverse roles in nonself-recognition and clearance of invaders. Though they are well characterized in vertebrates, the study of the potential function and mechanism of C-type lectins in invertebrate immunity is still in its infancy.A C-type lectin (CfLec-1) from scallop Chlamys farreri, a dominant cultured mollusk species in China, was selected to investigate its mRNA expression, localization and the possible functions in innate immunity in the present study. After scallop was stimulated by three typical PAMPs, the mRNA expression of CfLec-1 in hemocytes was poles apart. It was significantly up-regulated (p<0.01) after scallops were stimulated by LPS or β-glucan, but significantly down-regulated (p<0.01) after PGN stimulation. The binding ability of recombinant CfLec-1 (designated as rCfLec-1) towards eight PAMPs was investigated subsequently by PAMPs microarray, which revealed rCfLec-1 could bind LPS, PGN and mannan in vitro, indicating CfLec-1 served as a PRR involved in the pathogen recognition. Immunofluorescence assay with polyclonal antibody specific for CfLec-1 revealed that CfLec-1 was mainly located in the mantle and gill of the scallop. CfLec-1 could bind to the surface of scallop hemocytes and recruited hemocytes to enhance their encapsulation in vitro, and this process could be specifically blocked by anti-rCfLec-1 antibody. Meanwhile, rCfLec-1 could also enhance the phagocytic activity of scallop hemocytes against Escherichia coli.The results clearly suggested that CfLec-1 in C. farreri not only served as a PRR involved in the PAMPs recognition, but also functioned as an opsonin participating in the clearance of invaders. It is therefore suspected that CfLec-1 could be an attachment-molecule to nonself-agents acting as an alternative to immunoglobulin in vertebrates.