Immune regulatory networks coordinated by glycans and glycan-binding proteins in autoimmunity and infection

The immune system is coordinated by an intricate network of stimulatory and inhibitory circuits that regulate host responses against endogenous and exogenous insults.Disruption of these safeguard and homeostatic mechanisms can lead to unpredictable inflammatory and autoimmune responses,whereas deficiency of immune stimulatory pathways may orchestrate immunosuppressive programs that contribute to perpetuate chronic infections,but also influence cancer development and progression.Glycans have emerged as essential components of homeostatic circuits,acting as fine-tuners of immunological responses and potential molecular targets for manipulation of immune tolerance and activation in a wide range of pathologic settings.Cell surface glycans,present in cells,tissues and the extracellular matrix,have been proposed to serve as“self-associated molecular patterns”that store structurally relevant biological data.The responsibility of deciphering this information relies on different families of glycan-binding proteins(including galectins,siglecs and C-type lectins)which,upon recognition of specific carbohydrate structures,can recalibrate the magnitude,nature and fate of immune responses.This process is tightly regulated by the diversity of glycan structures and the establishment of multivalent interactions on cell surface receptors and the extracellular matrix.Here we review the spatiotemporal regulation of selected glycan-modifying processes including mannosylation,complex N-glycan branching,core 2 O-glycan elongation,LacNAc extension,as well as terminal sialylation and fucosylation.Moreover,we illustrate examples that highlight the contribution of these processes to the control of immune responses and their integration with canonical tolerogenic pathways.Finally,we discuss the power of glycans and glycan-binding proteins as a source of immunomodulatory signals that could be leveraged for the treatment of autoimmune inflammation and chronic infection.

Mannosylated glycans impair normal T-cell development by reprogramming commitment and repertoire diversity

T-cell development ensures the formation of diverse repertoires of T-cell receptors(TCRs)that recognize a variety of antigens.Glycosylation is a major posttranslational modification present in virtually all cells,including T-lymphocytes,that regulates activity/functions.Although these structures are known to be involved in TCR-selection in DP thymocytes,it is unclear how glycans regulate other thymic development processes and how they influence susceptibility to disease.Here,we discovered stage-specific glycome compositions during T-cell development in human and murine thymocytes,as well as dynamic alterations.After restricting the N-glycosylation profile of thymocytes to high-mannose structures,using specific glycoengineered mice(Rag1CreMgat1fl/fl),we showed remarkable defects in key developmental checkpoints,includingß-selection,regulatory T-cell generation andγδT-cell development,associated with increased susceptibility to colon and kidney inflammation and infection.We further demonstrated that a single N-glycan antenna(modeled in Rag1CreMgat2fl/fl mice)is the sine-qua-non condition to ensure normal development.In conclusion,we revealed that mannosylated thymocytes lead to a dysregulation in T-cell development that is associated with inflammation susceptibility.