The role of MHC class Ib-restricted T cells during infection

Abstract

Even though major histocompatibility complex (MHC) class Ia and many Ib molecules have similarities in structure, MHC class Ib molecules tend to have more specialized functions, which include the presentation of non-peptidic antigens to non-classical T cells. Likewise, non-classical T cells also have unique characteristics, including an innate-like phenotype in naïve animals and rapid effector functions. In this review, we discuss the role of MAIT and NKT cells during infection but also the contribution of less studied MHC class Ib-restricted T cells such as Qa-1-, Qa-2-, and M3-restricted T cells. We focus on describing the types of antigens presented to non-classical T cells, their response and cytokine profile following infection, as well as the overall impact of these T cells to the immune system.

Keywords: Infectious diseases; MHC class Ib; NKT and MAIT cells; Non-classical T cells.

Figure 1. The family of CD1-restricted αβ T cells

Group 1 CD1-specific T cells are depicted with examples of Mtb glycolipid antigens.

Figure 2. Examples of non-classical αβ T cell populations during microbial infection.

Figure 3. Proposed roles of non-classical CD8⁺ αβ T cell populations in humans and mice, compared to conventional CD8⁺ T cells

A) MHC class Ib-restricted CD8⁺ T cells, e.g. iNKT cells and MAIT cells, have a faster effector response following infection, compared to MHC class Ia-restricted T cells. B) During chronic infection, microorganisms can employ immunoevasion mechanisms to dampen the classical T cell response and/or NK cell response. MHC class Ib-specific responses could represent a backup system that responds following MHC class Ib upregulation, for example HLA-E.