Incorporating mucosal-associated invariant T cells into the pathogenesis of chronic liver disease

Table 1 Mucosal-associated invariant T cell characteristics and clinical implications

Feature	Characteristics	Clinical implications
Semi-invariant TCR	Semi-invariant α-chain in the TCR[3,7,72]; Canonical Vα7.2-Jα33 α-chain[3,7]; TRAV1-2/TRAJ33 encodes Vα7.2-Jα33[3]; Vβ6 and Vβ20 most common β-chains[61]; TRBV6, TRBV20-1 encode Vβ6, Vβ20[8,74]; Restricted length of CDRs[8,75]; CDR3β key to antigen recognition[10]	Limited number of antigens recognized[8,10]; Antigen diversity still possible[10]
MR1-restricted antigens	Class 1b antigen-presenting molecule[2,7]; Expressed on surface of APC[3]	MR1 limits antigens presented by APCs[10,114]
CD161	High surface expression[77-79]	Shared phenotypic marker with other T cells[78]
Cytokine receptors	IL-7, IL-12, IL-18, IL-23 receptors[80]	Multiple cytokines can activate MAIT cells[80,81]
Chemokine receptors	CCR5, CCR6, CCR9, CXCR6[59,62,77,82]	Chemokine-directed tissue migration[77]
Nuclear transcription factors	PLZF (also known as ZBTB16)[61,84,85]; RORγt[86]; T-bet[87,88,90,91]; ABCB1[11,62,83]	Control phenotype and functionality[84-88]; Direct development of memory phenotype[91]; Activate caspases and induce apoptosis[99]; Increase resistance to drugs, xenobiotics[11]
Cytokine production	IFN-γ, TNF-α, IL-17A, IL-22[11,17,81,102]; IL-13, IL-4, IL-5 (anti-inflammatory)[64,66]; IL-10 (mainly in adipose tissue)[106]	Pro-inflammatory and antiviral effects[17,81,102]; Anti-inflammatory effects[66,106]; Cross regulation of immune responses[64,65]
Effector phenotype	Granzyme B[4,107,108]; Perforin[4,74,108]	Antimicrobial and pro-apoptotic actions[4]; Eliminates infected or altered cells[4,107,108]
Subsets	Mostly CD8αα cells in liver and blood[101]	More IFN-γ and TNF-α than CD8αβ subset[101]

ABCB1: Multidrug resistance protein 1; APCs: Antigen presenting cells; CDRs: Complementarity-determining regions; IL: Interleukin; IFN-γ: Interferon-gamma; MAIT: Mucosal-associated invariant T cell; MR1: Major histocompatibility complex I-related molecule; PLZF: Promyelocytic leukemia zinc finger; T-bet: T-box transcription factor; TCR: T cells antigen receptor; t RORγt: Retinoic acid-related orphan receptor gamma t; TNF-α: Tumor necrosis factor-alpha.