Association of Hla-B27 and D3 Vitamin Level in Iraqi Ankylosing Spondylitis Patients

Abstract

Major histocompatibility complex (MHC), that plays pivotal role in self/non-self-discrimination in order to survive, is called 'Human Leukocyte Antigens (HLA)' in humans; is encoded on the short arm of chromosome 6 by MHC locus and is divided into 4 classes: Class I HLA molecules are composed of a 3-domained α chain together with a β2-microglobulin chain while Class II HLA molecules are heterodimers involving 2 α and 2 β domains.β2-microglobulin is encoded on chromosome 15. Class III HLA molecules are encoded by the region located between Class I and II genes and are not involved in antigen presentation. Class III and IV HLA molecules are primarily important in inflammation and autoimmune diseases.

The main duty of HLA molecule is to present antigen to T cells. Class I HLA molecules present antigens to CD8+ cytotoxic T cells whilst Class II Molecules present to CD4+ hepler T cells. Besides Classical Class I and II HLA molecules, there are non-classical HLA Class I and II molecules with various functions.