Galectins in innate immunity: dual functions of host soluble beta-galactoside-binding lectins as damage-associated molecular patterns (DAMPs) and as receptors for pathogen-associated molecular patterns (PAMPs).
The glycocalyx is a glycan layer found on the surfaces of host cells as well as microorganisms and enveloped virus. Its thickness may easily exceed 50 nm. The glycocalyx does not only serve as a physical protective barrier but also contains various structurally different glycans, which provide cell- or microorganism-specific 'glycoinformation'. This information is decoded by host glycan-binding proteins, lectins. The roles of lectins in innate immunity are well established, as exemplified by collectins, dectin-1, and dendritic cell (DC)-specific intracellular adhesion molecule-3-grabbing non-integrin (DC-SIGN). These mammalian lectins are synthesized in the secretory pathway and presented on the cell surface to bind to specific glycan 'epitopes'. As they recognize non-self glycans presented by microorganisms, they can be considered as receptors for pathogen-associated molecular patterns (PAMPs), i.e. pattern recognition receptors (PRRs). One notable exception is the galectin family. Galectins are synthesized and stored in the cytoplasm, but upon infection-initiated tissue damage and/or following prolonged infection, cytosolic galectins are either passively released by dying cells or actively secreted by inflammatory activated cells through a non-classical pathway, the 'leaderless' secretory pathway. Once exported, galectins act as PRR, as well as immunomodulators (or cytokine-like modulators) in the innate response to some infectious diseases. As galectins are dominantly found in the lesions where pathogen-initiated tissue damage signals appear, this lectin family is also considered as potential damage-associated molecular pattern (DAMP) candidates that orchestrate innate immune responses alongside the PAMP system.
Sato
Sachiko
S
Glycobiology Laboratory, Research Centre for Infectious Diseases, Faculty of Medicine, Laval University, QC, Canada. Sachiko.Sato@crchul.ulaval.ca
St-Pierre
Christian
C
Bhaumik
Pampa
P
Nieminen
Julie
J
D000818:Animals; D003713:Dendritic Cells / Q000276:immunology / Q000378:metabolism; D004804:Eosinophils / Q000276:immunology / Q000378:metabolism; D037161:Galectins / Q000276:immunology* / Q000378:metabolism; D019276:Glycocalyx / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007113:Immunity, Innate; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D009504:Neutrophils / Q000276:immunology / Q000378:metabolism; D011134:Polysaccharides / Q000276:immunology* / Q000378:metabolism; D051192:Receptors, Pattern Recognition / Q000276:immunology* / Q000378:metabolism
D037161:Galectins; D011134:Polysaccharides; D051192:Receptors, Pattern Recognition