Major histocompatibility complex (MHC) molecules help immune cells distinguish normal cells from cells displaying foreign antigens. They also provide the molecular platform needed to present antigens to T cells, linking recognition of infection with adaptive immunity.
The major histocompatibility complex (MHC) is a group of genes that encode molecules displayed on cell surfaces. In humans, these genes are called human leukocyte antigen (HLA) genes.
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What does MHC stand for, and what are human MHC genes called?
MHC stands for major histocompatibility complex. In humans, the MHC genes are called human leukocyte antigen (HLA) genes.
Which cells express MHC I?
Nearly all nucleated cells express MHC I. Mature red blood cells are the exception because they lack a nucleus and do not express MHC molecules.
What are the components of MHC I?
MHC I has a large α chain associated with a smaller β₂-microglobulin protein. Only the α chain spans the plasma membrane.
How is MHC II structured?
MHC II has an α chain and a β chain of roughly similar length. Both chains have membrane-spanning portions, and each chain has two domains.
Which domains form the peptide-binding clefts?
The MHC I cleft is formed by its α₁ and α₂ domains. The MHC II cleft is formed by its α₁ and β₁ domains.
Quiz questions
Where are peptides for MHC II presentation generally processed?Answer: In phagosomal and phagolysosomal compartments.
Which structures commonly break down intracellular proteins into peptides for MHC I presentation?Answer: Proteasomes in the cytoplasm.
What is cross-presentation?Answer: Displaying peptides from externally acquired material on MHC I.
Why is cross-presentation useful when a pathogen does not infect an antigen-presenting cell?Answer: It can enable activation of CD8 T cells against that pathogen.
How does MHC I contribute to natural killer cell recognition of healthy cells?Answer: Its presence helps mark cells as healthy self-cells.
Based on Microbiology by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.