CD1b in Review: High TCR Specificity Limits Auto-Reactivity

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CD1b in Review: High TCR Specificity Limits Auto-Reactivity

Journal Title: Biomedical Journal of Scientific & Technical Research (BJSTR) - Year 2019, Vol 12, Issue 5

Abstract

The immune system is commonly divided into two broad sections: innate immunity and adaptive immunity. Innate immunity is described as non-specific and hereditary whereas adaptive immunity is characterized by high specificity encoded somatically [1-5]. The adaptive immune system has two functional cell types: T cells and B cells [6-10]. While B cells participate in humoral immunity by releasing antibodies into the body to opsonize or incapacitate foreign bodies, cytotoxic T cells attack individual cells that may be compromised. This system of developing immunity against a specific antigen is dependent on antigen presentation to T cells [11].The primary molecule of antigen presentation is the major histocompatibility complex (MHC) which are loaded with short peptides [14]. While MHCII presents peptides from extracellular pathogens to CD4+ helper T cells, MHCI is presents peptides from intracellular pathogens to CD8+ cytotoxic T cells [15]. T cells bind to MHC and antigen via T cell receptors (TCRs), highly specific receptors refined somatically by VJ recombination, very similar to antibodies [1] (p. 115). The structure of TCR is similar to the Fab fragment of an antibody, consisting of two chains, α and β [1] (p.114). MHC contains a short, shallow grooved on which it presents a peptide [16]. All antigens go through antigen processing before presentation on MHC, a process in which foreign proteins are processed into smaller peptides [17]. Proteins can be degraded, cut, and trimmed to size before being presented on MHC. MHCI, specifically, usually presents nanomers. As a result, MHC is capable of presenting any protein. Contributing to the diversity of antigens recognized by MHC are the array of subclasses therein and polymorphism said sublclasses, many of which are highly polymorphic [18].While MHC efficiently presets protein antigens, other forms of antigens exist. With regards to microbial pathogens, specifically, the presentation of lipid antigens can be crucial in generating an effective immune response [1] (p. 314-5). Presentation of lipids to T cells is accomplished via MHCI related proteins CD1 [19] and MR1 [20], which contain an α chain and non-covalently associated β2-microglobulin. The understanding of alternate presentation systems has developed slowly. The first paper describing CD1-restricted T cells was published in 1989, but the nature of the antigen presented was not precisely identified. The emergence of lipids as T cell antigens presented by CD1 molecules was only established five years later by the discovery of the antigenic properties of mycolic acid. Currently, a variety of lipids, from both self- or non-self-origin, are known to bind CD1 molecules and to participate in lipid-specific T cell development and activation” [5].

Authors and Affiliations

Nathaniel Elkaim, Radhashree Maitra

Keywords

Radhashree Maitra Innate Immunity Cytotoxic T Cells Major Histocompatibility Complex CD4+ Helper T Cells Polymorphic β2-Microglobulin Chaperones Endoplasmic Reticulum Cytoplasmic Tails Mycolyl Lipids

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EP ID EP587507
DOI 10.26717/BJSTR.2019.12.002328
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