Class I and II Structure and Function Summary

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The page below is a sample from the LabCE course The Human Leukocyte Antigen (HLA) System. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Class I and II Structure and Function Summary

  • All HLA genes come from chromosome 6 (p arm and band 21).
  • HLA Class I and II are transmembranous proteins, which means that one end is inside the cell, goes through the cell's membrane, and the other end is outside the cell and can interact with other cells.
  • Class I quick facts:
    • Class I genes (A, B, and C) are composed of three alpha chains and one B2-microglobulin.
    • Class I glycoproteins are found on all nucleated cells and function to express intracellular (endogenous) molecules from within the cell for detection. Class I is best useful for the detection of human cells that are infected with viruses or cancer cells.
    • Class I glycoproteins interact with CD8+ cytotoxic T cells and Natural Killer cells.
  • Class II quick facts:
    • Class II genes (DRB1, DPB1, DQB1) are composed of two alpha chains and two beta chains to form a heterodimer complex.
    • Class II glycoproteins are found on antigen-presenting cells like B cells, macrophages, and dendritic cells. Class II HLA express external molecules after they are internalized by APCs (exogenous presentation) for delivery to CD4+ T cells. Examples are bacterial infections.
8. Atropos235. "Schematic representation of MHC class I molecule, consisting of three α-domains and one β2-microglobulin molecule. The peptide-binding groove is situated between domains α1 and α2." Wikimedia Commons, 18 Mar 2007, https://commons.wikimedia.org/wiki/File:MHC_Class_1.svg
10. Atropos235. "Schematic representation of MHC class II molecule, consisting of two α-domains and two β-domains. The peptide-binding groove is situated between domains α1and β1." Wikimedia Commons, 18 Mar 2007, https://commons.wikimedia.org/wiki/File:MHC_Class_2.svg

Schematic representation of MHC class I molecule, consisting of three a-domains and one ß2-microglobulin molecule. The peptide-binding groove is situated between domains a1 and a2 (8).
Schematic representation of MHC class II molecule, consisting of two a-domains and two ß-domains. The peptide-binding groove is situated between domains a1and ß1 (10).