C-type lectins in immunity and homeostasis

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Abstract

The C-type lectins are a superfamily of proteins that recognize a broad repertoire of ligands and that regulate a diverse range of physiological functions. Most research attention has focused on the ability of C-type lectins to function in innate and adaptive antimicrobial immune responses, but these proteins are increasingly being recognized to have a major role in autoimmune diseases and to contribute to many other aspects of multicellular existence. Defects in these molecules lead to developmental and physiological abnormalities, as well as altered susceptibility to infectious and non-infectious diseases. In this Review, we present an overview of the roles of C-type lectins in immunity and homeostasis, with an emphasis on the most exciting recent discoveries.

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Interactions between commensal fungi and the C-type lectin receptor Dectin-1 influence colitis.

Iliyan Iliev, Vincent Funari, Kent D. Taylor … (2012)

The intestinal microflora, typically equated with bacteria, influences diseases such as obesity and inflammatory bowel disease. Here, we show that the mammalian gut contains a rich fungal community that interacts with the immune system through the innate immune receptor Dectin-1. Mice lacking Dectin-1 exhibited increased susceptibility to chemically induced colitis, which was the result of altered responses to indigenous fungi. In humans, we identified a polymorphism in the gene for Dectin-1 (CLEC7A) that is strongly linked to a severe form of ulcerative colitis. Together, our findings reveal a eukaryotic fungal community in the gut (the "mycobiome") that coexists with bacteria and substantially expands the repertoire of organisms interacting with the intestinal immune system to influence health and disease.

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CD69: from activation marker to metabolic gatekeeper.

Danay Cibrian, Francisco Sánchez-Madrid (2017)

CD69 is a membrane-bound, type II C-lectin receptor. It is a classical early marker of lymphocyte activation due to its rapid appearance on the surface of the plasma membrane after stimulation. CD69 is expressed by several subsets of tissue resident immune cells, including resident memory T (TRM) cells and gamma delta (γδ) T cells, and is therefore considered a marker of tissue retention. Recent evidence has revealed that CD69 regulates some specific functions of selected T-cell subsets, determining the migration-retention ratio as well as the acquisition of effector or regulatory phenotypes. Specifically, CD69 regulates the differentiation of regulatory T (Treg) cells as well as the secretion of IFN-γ, IL-17 and IL-22. The identification of putative CD69 ligands, such as Galectin-1 (Gal-1), suggests that CD69-induced signaling can be regulated not only during cognate contacts between T cells and antigen-presenting cells in lymphoid organs, but also in the periphery, where cytokines and other metabolites control the final outcome of the immune response. Here, we will discuss new aspects of the molecular signaling mediated by CD69, and its involvement in the metabolic reprogramming regulating TH-effector lineages and provide their ramifications and possible significance in homeostasis and pathological scenarios. This article is protected by copyright. All rights reserved.

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The C-type lectin-like domain superfamily.

Alex Zelensky, Jill Gready (2005)

The superfamily of proteins containing C-type lectin-like domains (CTLDs) is a large group of extracellular Metazoan proteins with diverse functions. The CTLD structure has a characteristic double-loop ('loop-in-a-loop') stabilized by two highly conserved disulfide bridges located at the bases of the loops, as well as a set of conserved hydrophobic and polar interactions. The second loop, called the long loop region, is structurally and evolutionarily flexible, and is involved in Ca2+-dependent carbohydrate binding and interaction with other ligands. This loop is completely absent in a subset of CTLDs, which we refer to as compact CTLDs; these include the Link/PTR domain and bacterial CTLDs. CTLD-containing proteins (CTLDcps) were originally classified into seven groups based on their overall domain structure. Analyses of the superfamily representation in several completely sequenced genomes have added 10 new groups to the classification, and shown that it is applicable only to vertebrate CTLDcps; despite the abundance of CTLDcps in the invertebrate genomes studied, the domain architectures of these proteins do not match those of the vertebrate groups. Ca2+-dependent carbohydrate binding is the most common CTLD function in vertebrates, and apparently the ancestral one, as suggested by the many humoral defense CTLDcps characterized in insects and other invertebrates. However, many CTLDs have evolved to specifically recognize protein, lipid and inorganic ligands, including the vertebrate clade-specific snake venoms, and fish antifreeze and bird egg-shell proteins. Recent studies highlight the functional versatility of this protein superfamily and the CTLD scaffold, and suggest further interesting discoveries have yet to be made.