Mucosal-associated invariant T (MAIT) cells: an evolutionarily conserved T cell subset.

Area of Science:

• Immunology
• Microbiology

Background:

• TCRalphabeta T cells exhibit diverse repertoires, but invariant subsets suggest specialized roles.
• CD1d-restricted NK-T cells are known invariant T cells involved in immunity and autoimmunity.
• Another invariant T cell subset, MAIT cells, is conserved across species.

Purpose of the Study:

• To review the characteristics and functions of mucosal-associated invariant T (MAIT) cells.
• To highlight the unique TCR structure and species conservation of MAIT cells.
• To discuss the dependence of MAIT cell expansion on B cells, MR1, and commensal flora.

Main Methods:

• Review of existing literature on invariant T cell subsets.
• Analysis of TCR Valpha and Vbeta chain usage in MAIT cells.
• Discussion of MR1-dependent selection and microbial-driven expansion.

Main Results:

• MAIT cells possess a canonical hValpha7.2/mValpha19-Jalpha33 TCRalpha chain paired with restricted Vbeta segments.
• These cells are found in mice, humans, and cattle, primarily in the gut lamina propria.
• MAIT cell population requires B cells expressing MR1 and is absent in germ-free mice, indicating dependence on commensal microbiota.

Conclusions:

• MAIT cells represent a distinct, evolutionarily conserved T cell population with a specialized immune function.
• Their development and expansion are tightly regulated by host factors (MR1) and environmental cues (microbiota).
• Further research is needed to elucidate the specific ligands and functions of MAIT cells in host defense and disease.