Galectins as self/non-self recognition receptors in innate and adaptive immunity: an unresolved paradox
- 1 Department of Microbiology and Immunology, Institute of Marine and Environmental Technology, University of Maryland School of Medicine, Baltimore, MD, USA
- 2 Department of Biochemistry and Molecular Biology, Institute of Marine and Environmental Technology, University of Maryland School of Medicine, Baltimore, MD, USA
- 3 The Community College of Baltimore County, Catonsville, MD, USA
Galectins are characterized by their binding affinity for β-galactosides, a unique binding site sequence motif, and wide taxonomic distribution and structural conservation in vertebrates, invertebrates, protista, and fungi. Since their initial description, galectins were considered to bind endogenous (“self”) glycans and mediate developmental processes and cancer. In the past few years, however, numerous studies have described the diverse effects of galectins on cells involved in both innate and adaptive immune responses, and the mechanistic aspects of their regulatory roles in immune homeostasis. More recently, however, evidence has accumulated to suggest that galectins also bind exogenous (“non-self”) glycans on the surface of potentially pathogenic microbes, parasites, and fungi, suggesting that galectins can function as pattern recognition receptors (PRRs) in innate immunity. Thus, a perplexing paradox arises by the fact that galectins also recognize lactosamine-containing glycans on the host cell surface during developmental processes and regulation of immune responses. According to the currently accepted model for non-self recognition, PRRs recognize pathogens via highly conserved microbial surface molecules of wide distribution such as LPS or peptidoglycan (pathogen-associated molecular patterns; PAMPs), which are absent in the host. Hence, this would not apply to galectins, which apparently bind similar self/non-self molecular patterns on host and microbial cells. This paradox underscores first, an oversimplification in the use of the PRR/PAMP terminology. Second, and most importantly, it reveals significant gaps in our knowledge about the diversity of the host galectin repertoire, and the subcellular targeting, localization, and secretion. Furthermore, our knowledge about the structural and biophysical aspects of their interactions with the host and microbial carbohydrate moieties is fragmentary, and warrants further investigation.
Keywords: galectin, C-type lectin, microbial recognition, glycan ligands
Citation: Vasta GR, Ahmed H, Nita-Lazar M, Banerjee A, Pasek M, Shridhar S, Guha P and Fernández-Robledo JA (2012) Galectins as self/non-self recognition receptors in innate and adaptive immunity: an unresolved paradox. Front. Immun. 3:199. doi: 10.3389/fimmu.2012.00199
Received: 26 April 2012; Accepted: 26 June 2012;
Published online: 13 July 2012.
Edited by:Larry J. Dishaw, University of South Florida, USA
Reviewed by:Carlo Pucillo, University of Udine, Italy
George Hajishengallis, University of Pennsylvania, USA
Copyright: © 2012 Vasta, Ahmed, Nita-Lazar, Banerjee, Pasek, Shridhar, Guha and Fernández-Robledo. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution, and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Gerardo R. Vasta, Department of Microbiology and Immunology, Institute of Marine and Environmental Technology, University of Maryland School of Medicine, Columbus Center, 701 East Pratt Street, Baltimore, MD 21202-3101, USA. e-mail: firstname.lastname@example.org