Abstract
Natural killer T cells (NKT) are a subset of T lymphocytes bridging innate and adaptive immunity. These cells recognize self and microbial glycolipids bound to non-polymorphic and highly conserved CD1d molecules. Three NKT cell subsets, type I, II, and NKT-like expressing different antigen receptors (TCR) were described and TCR activation promotes intracellular events leading to specific functional activities. NKT can exhibit different functions depending on the secretion of soluble molecules and the interaction with other cell types. NKT cells act as regulatory cells in the defense against infections but, on the other hand, their effector functions can be involved in the pathogenesis of several inflammatory disorders due to their exposure to different microbial or self-antigens, respectively. A deep understanding of the biology and functions of type I, II, and NKT-like cells as well as their interplay with cell types acting in innate (neuthrophils, innate lymphoid cells, machrophages, and dendritic cells) and adaptive immunity (CD4+,CD8+, and double negative T cells) should be important to design potential immunotherapies for infectious and autoimmune diseases.
Highlights
In humans, CD1a–c isoforms are able to bound mycobacterial as well as self-antigens [2,3,4,5,6,7,8,9]
Natural killer T cells (NKT) cells act as regulatory cells in the defense against infections but, on the other hand, their effector functions can be involved in the pathogenesis of several inflammatory disorders due to their exposure to different microbial or self-antigens, respectively
CD1d isoforms activate the majority of NKT cells expressing an invariant T-cell receptor (TCR)-α chain rearrangement and are called type I NKT or invariant NKT
Summary
CD1 molecule is a family of glycoproteins expressed on the surface of several antigen-presenting cells (APC) involved in the presentation of glycolipid antigens to T cells [1]. TCRs involved in recognition of CD1-glycolipids or MR1-vitamin B metabolites complexes have a common distinctive characteristic: they display an invariant α chain and few β chains In contrast to their reduced antigen receptor repertoire, these cells show a marked plasticity in their functions as demonstrated by the production of different cytokines after in vivo stimulation of naïve mice with α-galactosylceramide (α-GalCer) [10]. Type I NKT cells recognize a glycolipid obtained by a marine sponge, α-GalCer, in humans and mice Another subset of NKT cells, called type II NKT cells, does not react with α-GalCer, but binds a self-lipid, sulfatide, highly expressed central nervous system (CNS), kidney, pancreas, and liver [13]. Type I and II NKT can be involved in autoimmune and infectious diseases
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