The human major histocompatibility complex (MHC) on chromosome 6 encodes three classical class-I genes: human leukocyte antigens (HLA) A, B, and C. These polymorphic genes encode a 43-to 45-kDa cell surface glycoprotein that, in association with the 12-kDa β 2 -microglobulin molecule, functions in the presentation of nine amino acid peptides to the T-cell receptor of CD8-bearing T lymphocytes and killer inhibitory receptors on natural killer cells. In addition to these ubiquitously expressed, polymorphic proteins, the human genome also encodes several nonclassical MHC class-I-like, or class Ib, genes that, in general, encode nonpolymorphic molecules involved in various specific immunological functions. Many of these genes, including CD1, the neonatal Fc receptor for IgG, HLA-G, HLA-E, the MHC class-I chain-related gene A, and Hfe, are prominently displayed on epithelial cells, suggesting an important role in epithelial cell biology. KeywordsEpithelium; intestine; major histocompatibility complex It is increasingly recognized that epithelial cells, especially intestinal epithelial cells (IEC), play an important role in innate and adaptive immune functions in addition to their important barrier, absorption, and transport functions (1). A structural form that is particularly useful to the epithelial cells in fulfilling these immunological functions is that provided by the major histocompatibility complex (MHC) class-I-related molecules. By understanding the composition of these molecules, insight can be provided into possible functions of these molecules in epithelial cells. Classical MHC class I moleculesThe basic structure of the MHC class-I-related molecules reflects that encoded by the classical MHC class-I or class Ia genes (2,3). These genes are encoded within the MHC class-I locus on human chromosome 6 and consist of the human leukocyte antigens (HLA) A, B, and C.Publisher's Disclaimer: Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. The open reading frame of these genes consists of structural domains encoded by discrete exons that translate into an approximately 43-to 45-kDa glycoprotein containing three membrane distal domains (α1, α2, and α3), a transmembrane domain, and a cytoplasmic tail. The most membrane-proximal ec...