| Xg antigen | xg blood group |
|---|---|
| histocompatibility antigen | <immunology> A set of plasmalemmal glycoproteins on the surface of all nucleated cells that are crucial for T-cell recognition of antigens. Particularly the HLA system in humans and the H2 system in mice. They are the major antigens responsible for tissue recognition. For this reason, they are of prime importance in determining compatible organ donors for a specific transplantation procedure. Each person has unique HLA antigens. Some HLA antigens have been identified to be correlated with the presence of certain autoimmune diseases. One of these is the HLA-B27 site. Approximately 85% of patients with ankylosing spondylitis and Reiter's syndrome will have the HLA-B27 antigen present on the leukocytes. There are two classes of histocompatibility antigens: 1. Class I, histocompatibility antigens composed of two glycosylated subunits, a heavy chain of 44 kD and beta2 microglobulin (12 kD). The heavy chain may be coded by K, D or L genes of mouse H2 and A, B or C genes of human HLA complex. Class I antigens are important in T-cell killing and are recognised in conjunction with the foreign cell surface antigens MHC restriction). 2. Class II antigens, heterodimeric histocompatibility antigens composed of alpha (32 kD) and beta (28 kD) chains. Found mostly on B lymphocytes, macrophages and accessory cells. The response of T helper cells requires that the foreign antigen is presented in conjunction with the appropriate Class II antigens. (Murine H2 Ia antigens and human HLA DR antigens are Class II). (14 Oct 1997) |
| HLA-a1 antigen | <immunology> Human histocompatibility (HLA) surface antigen encoded by the a locus on chromosome 6. Individuals bearing this allele are more susceptible to hodgkin's disease. HLA-a1 is in linkage disequilibrium with HLA-b8 and HLA-dr3. (12 Dec 1998) |
| HLA-a2 antigen | <immunology> Human histocompatibility (HLA) surface antigen encoded by the a locus on chromosome 6. The HLA-a2 antigen is associated with recognition of the influenza a virus. (12 Dec 1998) |
| HLA-a3 antigen | <immunology> Human histocompatibility (HLA) surface antigen encoded by the a locus on chromosome 6. The allele occurs with increased frequency in individuals with idiopathic haemochromatosis. HLA-a3 is in linkage disequilibrium with HLA-b7 and HLA-dr2. (12 Dec 1998) |
| HLA-b27 antigen | <immunology> Human histocompatibility (HLA) surface antigen encoded by the b locus on chromosome 6. It is strongly associated with acute anterior uveitis, ankylosing spondylitis, and reiter's disease. Increased frequency of antigen in: ankylosing spondylitis (90%), Reiter syndrome (90%), enteropathic arthritis (75%), psoriatic arthritis (60%) normal frequency: white: 8%, black: 4% (12 Dec 1998) |
| HLA-b35 antigen | <immunology> Human histocompatibility (HLA) surface antigen encoded by the b locus on chromosome 6. It is weakly associated with a number of diseases. (12 Dec 1998) |
| HLA-b7 antigen | <immunology> Human histocompatibility (HLA) surface antigen encoded by the b locus on chromosome 6. There is a weak association between the presence of the HLA-b7 antigen and the diseases of narcolepsy and idiopathic haemochromatosis. HLA-b7 is in linkage disequilibrium with HLA-a3 and HLA-dr2. (12 Dec 1998) |
| HLA-b8 antigen | <immunology> Human histocompatibility (HLA) surface antigen encoded by the b locus on chromosome 6. It is in linkage disequilibrium with HLA-a1 and HLA-dr3. This explains the fact that though HLA-b8 was originally associated with several diseases, including coeliac disease, dermatitis herpetiformis, and myasthenia gravis, their association with HLA-dr3 is now considered more significant. (12 Dec 1998) |
| HLA-dr1 antigen | <immunology> Human immune-response, d-related antigen encoded by the d locus on chromosome 6 and found on lymphoid cells. (12 Dec 1998) |
| HLA-dr2 antigen | <immunology> Human immune-response, d-related antigen encoded by the d locus on chromosome 6 and found on lymphoid cells. It is in linkage disequilibrium with HLA-a3 and HLA-b7 and is strongly associated with goodpasture syndrome, multiple sclerosis, and narcolepsy. (12 Dec 1998) |
| HLA-dr3 antigen | <immunology> Human immune-response, d-related antigen encoded by the d locus on chromosome 6 and found on lymphoid cells. It is in linkage disequilibrium with HLA-a1 and HLA-b8. The HLA-dr3 antigen is strongly associated with coeliac disease, grave's disease, dermatitis herpetiformis, early-age onset myasthenia gravis, systemic lupus erythematosus, juvenile diabetes, and opportunistic infections in aids. (12 Dec 1998) |
| HLA-dr4 antigen | <immunology> Human immune-response, d-related antigen encoded by the d locus on chromosome 6 and found on lymphoid cells. It is strongly associated with rheumatoid arthritis and juvenile diabetes. (12 Dec 1998) |
| HLA-dr5 antigen | <immunology> Human immune-response, d-related antigen encoded by the d-locus on chromosome 6 and found on lymphoid cells. It is associated with kaposi sarcoma in aids and juvenile rheumatoid arthritis. (12 Dec 1998) |
| HLA-dr6 antigen | <immunology> Human immune-response, d-related antigen encoded by the d locus on chromosome 6 and found on lymphoid cells. (12 Dec 1998) |