Binds peptides derived from antigens that access the endocytic route of antigen presenting cells (APC) and presents them on the cell surface for recognition by the CD4 T-cells. The peptide binding cleft accommodates peptides of 10-30 residues. The peptides presented by MHC class II molecules are generated mostly by degradation of proteins that access the endocytic route; where they are processed by lysosomal proteases and other hydrolases. Exogenous antigens that have been endocytosed by the APC are thus readily available for presentation via MHC II molecules; and for this reason this antigen presentation pathway is usually referred to as exogenous. As membrane proteins on their way to degradation in lysosomes as part of their normal turn-over are also contained in the endosomal/lysosomal compartments; exogenous antigens must compete with those derived from endogenous components. Autophagy is also a source of endogenous peptides; autophagosomes constitutively fuse with MHC class II loading compartments. In addition to APCs; other cells of the gastrointestinal tract; such as epithelial cells; express MHC class II molecules and CD74 and act as APCs; which is an unusual trait of the GI tract. To produce a MHC class II molecule that presents an antigen; three MHC class II molecules (heterodimers of an alpha and a beta chain) associate with a CD74 trimer in the ER to form a heterononamer. Soon after the entry of this complex into the endosomal/lysosomal system where antigen processing occurs; CD74 undergoes a sequential degradation by various proteases; including CTSS and CTSL; leaving a small fragment termed CLIP (class-II-associated invariant chain peptide). The removal of CLIP is facilitated by HLA-DM via direct binding to the alpha-beta-CLIP complex so that CLIP is released. HLA-DM stabilizes MHC class II molecules until primary high affinity antigenic peptides are bound. The MHC II molecule bound to a peptide is then transported to the cell membrane surface. In B-cells; the interaction between HLA-DM and MHC class II molecules is regulated by HLA-DO. Primary dendritic cells (DCs) also to express HLA-DO. Lysosomal miroenvironment has been implicated in the regulation of antigen loading into MHC II molecules; increased acidification produces increased proteolysis and efficient peptide loading.
BACKGROUND/AIMS: Type 2 autoimmune hepatitis (AIH) is characterized by the presence of anti-liver kidney microsome (anti-LKM-1) and/or anti-liver cytosol type 1 (anti-LC1) autoantibodies. However, the correlation between these autoantibodies and the genetic background has not been studied. METHODS: Frequencies of HLA class II alleles were compared between the 60 Caucasian children with type 2 AIH and 313 control subjects. The anti-LKM1 antibody reactivity directed against antigenic sites of CYP2D6 was analysed by ELISA. RESULTS: HLA-DQB1 *0201 allele was found to be the primary genetic determinant of susceptibility to type 2 AIH by conferring the highest odd-ratio (OR = 6.4). HLA-DRB1 *03 allele was significantly increased (P < 0.0001) among patients with both anti-LKM1 and anti-LC1 autoantibodies as well as in those with only anti-LC1(+) compared to those with anti-LKM1(+) alone. In contrast, HLA-DRB1 *07 allele was significantly associated (P < 0.0001) with anti-LKM1(+) alone compared to groups with both anti-LKM and anti-LC1 or with LC1+ alone. Children with the DRB1 *07 allele develop anti-LKM1 autoantibodies having a more restricted specificity (2 epitopes) than to those having HLA-DRB1 *03 allele (5 epitopes). CONCLUSIONS: The HLA-DR locus is involved in autoantibody expression, while the DQ locus appears to be a critical determinant for the development of type 2 AIH.
Immunoglobulin production involved in immunoglobulin mediated immune responsedefinition[GO:0002381]
The appearance of immunoglobulin due to biosynthesis or secretion following a cellular stimulus during an immune response, resulting in an increase in its intracellular or extracellular levels.
BACKGROUND/AIMS: Type 2 autoimmune hepatitis (AIH) is characterized by the presence of anti-liver kidney microsome (anti-LKM-1) and/or anti-liver cytosol type 1 (anti-LC1) autoantibodies. However, the correlation between these autoantibodies and the genetic background has not been studied. METHODS: Frequencies of HLA class II alleles were compared between the 60 Caucasian children with type 2 AIH and 313 control subjects. The anti-LKM1 antibody reactivity directed against antigenic sites of CYP2D6 was analysed by ELISA. RESULTS: HLA-DQB1 *0201 allele was found to be the primary genetic determinant of susceptibility to type 2 AIH by conferring the highest odd-ratio (OR = 6.4). HLA-DRB1 *03 allele was significantly increased (P < 0.0001) among patients with both anti-LKM1 and anti-LC1 autoantibodies as well as in those with only anti-LC1(+) compared to those with anti-LKM1(+) alone. In contrast, HLA-DRB1 *07 allele was significantly associated (P < 0.0001) with anti-LKM1(+) alone compared to groups with both anti-LKM and anti-LC1 or with LC1+ alone. Children with the DRB1 *07 allele develop anti-LKM1 autoantibodies having a more restricted specificity (2 epitopes) than to those having HLA-DRB1 *03 allele (5 epitopes). CONCLUSIONS: The HLA-DR locus is involved in autoantibody expression, while the DQ locus appears to be a critical determinant for the development of type 2 AIH.
Protein involved in immunity, any immune system process that functions in the response of an organism to a potential internal or invasive threat. The vertebrate immune system is formed by the innate immune system (composed of phagocytes, complement, antimicrobial peptides, etc) and by the adaptive immune system which consists of T- and B- lymphocytes.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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