γδ T, NKT, and MAIT Cells During Evolution: Redundancy or Specialized Functions?

Area of Science:

• Immunology
• Evolutionary Biology
• Cell Biology

Background:

• Innate-like T cells share traits with innate lymphoid cells (ILCs) and mainstream αβ T cells.
• These cells are found in vertebrates, with better-characterized functions in amphibians and mammals.
• Innate-like T cells include both γδ and αβ T cell types.

Purpose of the Study:

• To review the characteristics and evolutionary conservation of innate-like T cells.
• To explore the antigen recognition systems and functional roles of different innate-like T cell subsets.
• To highlight the non-redundant functions of these cells based on their specificities.

Main Methods:

• Review of existing literature on innate-like T cells.
• Comparative analysis of T cell receptor (TCR) evolution and antigen-presenting molecules.
• Discussion of functional data across different vertebrate species.

Main Results:

• Innate-like T cells are present in all vertebrates, with extensive knowledge in mammals and amphibians.
• Mammalian γδ TCRs likely coevolved with butyrophilin molecules.
• Semi-invariant TCRs of iNKT and mucosal-associated invariant T cells are locked with CD1d and MR1, respectively.

Conclusions:

• The conserved antigen recognition systems of innate-like T cell subsets indicate specialized, non-overlapping roles.
• Each subset fulfills distinct functions dictated by their specific antigen recognition capabilities.
• Understanding these conserved systems is key to deciphering innate-like T cell biology.