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Harrison's Principles of Internal Medicine, 18e
| Part 15. Disorders of the Joints and Adjacent Tissues > Section 1. The Immune System in Health and Disease > |
Chapter 315. The Major Histocompatibility Complex
Sections: The HLA Complex and Its Products, MHC Structure and Function, Further Readings.
Topics Discussed: immune system evaluation; major histocompatibility complex.
Excerpt:"The human major histocompatibility complex (MHC), commonly called the human leukocyte antigen (HLA) complex, is a 4-megabase (Mb) region on chromosome 6 (6p21.3) that is densely packed with expressed genes. The best known of these genes are the HLA class I and class II genes, whose products are critical for immunologic specificity and transplantation histocompatibility, and they play a major role in susceptibility to a number of autoimmune diseases. Many other genes in the HLA region are also essential to the innate and antigen-specific functioning of the immune system. The HLA region shows extensive conservation with the MHC of other mammals in terms of genomic organization, gene sequence, and protein structure and function.In addition to the class I and class II genes themselves, there are numerous genes interspersed among the HLA loci that have interesting and important immunologic functions. Our current concept of the function of MHC genes now encompasses many of these additional genes, some of which are also highly polymorphic. Indeed, direct comparison of the complete DNA sequences for eight of the entire 4-Mb MHC regions from different haplotypes show >44,000 nucleotide variations, encoding an extremely high potential for biologic diversity, and at least..."
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