Abstract
The detection of pathogen-derived molecules as foreign particles by adaptive immune cells triggers T and B lymphocytes to mount protective cellular and humoral responses, respectively. Recent immunological advances elucidated that proteins and some lipids are the principle biological molecules that induce protective T cell responses during microbial infections. Polysaccharides are important components of microbial pathogens and many vaccines. However, research concerning the activation of the adaptive immune system by polysaccharides gained interest only recently. Traditionally, polysaccharides were considered to be T cell-independent antigens that did not directly activate T cells or induce protective immune responses. Here, we review several recent advances in “carbohydrate immunobiology”. A group of bacterial polysaccharides that are known as “zwitterionic polysaccharides (ZPSs)” were recently identified as potent immune modulators. The immunomodulatory effect of ZPSs required antigen processing and presentation by antigen presenting cells, the activation of CD4 T cells and subpopulations of CD8 T cells and the modulation of host cytokine responses. In this review, we also discuss the potential use of these unique immunomodulatory ZPSs in new vaccination strategies against chronic inflammatory conditions, autoimmunity, infectious diseases, allergies and asthmatic conditions.
Highlights
The primary role of the immune system is to protect the host from microbial invasions and infections
As abscess formation was inhibited by the transfer of T cells from animals that were immunized with ZPS [34], these results suggest that abscess inductions and protection in the presence of ZPS are likely mediated by T-cell components of the adaptive immune system
The thymic selection mechanisms underlying the in vivo generation of this ZPS-specific T cell clones are currently unknown
Summary
The primary role of the immune system is to protect the host from microbial invasions and infections. Innate immune mechanisms mediate the first stage of transient protection against the invading pathogens, more advanced adaptive immune mechanisms prevent microbial invasions and infections by activating antigen-specific T and B cells. Even though microbial pathogens are composed of proteins, carbohydrates, lipids, and nucleic acids, only protein antigens are currently believed to be processed and presented on MHC molecules by APCs for T-cell recognition and activation [5, 8,9,10]. Several studies that used TCR transgenic mouse models show that T cells are positively selected by peptideMHC complexes in the thymic cortex, and the availability of the crystal structures for TCR-peptide-MHC-complexes [11] reinforces the theory that T cells only recognize peptide antigens The results of these studies further confirmed the notion that only proteinaceous antigens induce adaptive T cell responses. Recent advances in research of antigen processing and presentation and carbohydrate immunobiology are challenging this traditional concept
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