Classification of C‐Type Lectins and Recognition of Pathogens

ABSTRACT C‐type lectins are calcium‐dependent glycan‐binding proteins that play key roles in the innate immune response by recognizing pathogens. Soluble C‐type lectins agglutinate and neutralize pathogens, activate the complement system, and promote pathogen clearance via opsonization. Membrane‐bound C‐type lectins, also known as C‐type lectin receptors (CLRs), internalize pathogens and induce their degradation in lysosomes, presenting pathogen‐derived antigens to MHC‐II molecules to activate adaptive immunity. CLRs also have signaling capabilities. Some contain the immunoreceptor tyrosine‐based activation motif (ITAM), which induces inflammatory responses by activating transcription factors, such as NF‐κB and NFAT. Others contain the immunoreceptor tyrosine‐based inhibitory motif (ITIM), which suppresses activating signals by activating phosphatases, such as SHP‐1. This creates a balance between activation and inhibition. C‐type lectins are classified into 17 groups based on their structural domains, with Groups II and V members being particularly important for pathogen recognition. In this review, we present the accumulated and recent information on pathogen recognition by C‐type lectins, along with their classification and basic functions.