MAIT cells

Group of evolutionarily conserved T cells (MAIT stands for: mucosa-associated invariant T cells) that can directly fight bacteria and at the same time perform control functions in the immune system (Nel I et al. 2021). MAIT cells were first described as a subset of T cells in 2003. MAIT cells are mainly found in the liver and blood, but also colonize mucosal surfaces such as the skin, mouth, intestine, respiratory tract and genitourinary tract, surfaces of the human organism that are in contact with the environment and the microbiota of their host (Magalhaes I et al. 2020).

MAIT cells express a semi-invariant T cell receptor controlled by the MHC class I molecule (MR1). They are activated in an MR1-dependent manner in response to microbial riboflavin metabolites, resulting in rapid effector functions. However, MAIT cells can also be activated MR1-independently by cytokines and viruses (Magalhaes I et al. 2020).

MAIT cells are essential for the hygiene of the microbiome on skin and mucous membranes, which in healthy organisms consists of fungi and bacteria (Nel I et al. 2021). MAIT cells, whether isolated from liver or blood, are derived from only a few cells of origin. MAIT cells have a limited repertoire of T cell antigen receptors (TCRs) with specific antigenic specificities that are conserved across species. They can be activated by TCR-dependent and TCR-independent mechanisms and exhibit rapid innate effector responses.

A subpopulation of MAIT cells recognizes vitamin B2 metabolites from bacteria and induces the release of cytokines that play an important role in regulating the antimicrobial immune response. It is likely that MAIT cells can also activate other immune cells, thereby enhancing local inflammation at the site of infection. These observations suggest important protective and regulatory functions of MAIT cells within the immune system and help to better understand immune control in human organs.

1. Godfrey DI et al (2019) The biology and functional importance of MAIT cells. Nat Immunol 20:1110-1128.
2. Lepore M et al (2014) Parallel T-cell cloning and deep sequencing of human MAIT cells reveal stable oligoclonal TCRβ repertoire. Nature Communications doi: 10.1038/ncomms4866.
3. Magalhaes I et al (2020) MAIT Cells in Health and Disease. Methods Mol Biol 2098:3-21.
4. Nel I et al. (2021) MAIT cells, guardians of skin and mucosa? Mucosal Immunol 14:803-814.