| hepatitis B surface antigen | <virology> A serologic marker on the surface of the hepatitis B virus. The body will normally produce antibodies to hepatitis B surface antigen as part of the normal immune response to infection. It is the presence of antibodies to the hepatitis B surface antigen that are detected in a positive hepatitis B blood test. (27 Sep 1997) |
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| prostate-specific antigen | <tumour marker> A simple blood test used to detect prostate cancer in men. The test measures a specific antigen normally secreted by the prostate. If cancer is developing, the prostate secretes greater amounts of prostate-specific antigen. This test is recommended for men with an enlarged prostate and an increased risk of prostate cancer. It is an enzyme that is produced by epithelial cells of both benign and malignant prostate tissue. It is an important marker for the diagnosis of prostate cancer. It is a single chain 31 kilodalton glycoprotein with 240 amino acid residues and 4 carbohydrate side chains that is a kallikrein protease. It is found in normal seminal fluid and produced by the prostatic epithelial cells. Elevated levels in blood serum are associated with prostatic enlargement and prostatic adenocarcinoma, and this allows early detection of cancer in many cases. In about 70% of cases, the rise is due to a cancerous condition. No large scale clinical studies have been completed to assess the impact of testing on survival from prostate cancer, and the medical and economic value of testing remain uncertain. Acronym: PSA Registry number: EC 3.4.21.77 (22 Sep 2002) |
| heterogeneic antigen | An antigen or antigenic determinant which is found in different tissues in more than one species. (05 Mar 2000) |
| heterogenetic antigen | An antigen which is possessed by a variety of different phylogenetically unrelated species; e.g., the various organ-or tissue-specific antigen's, the alpha-and beta-crystalline protein of the lens of the eye, and Forssman antigen. Synonym: heterophil antigen. (05 Mar 2000) |
| heterogenic enterobacterial antigen | Cross reacting antigen (epitope), a common antigen that occurs in 2 or more different molecules/organisms. Synonym: heterogenic enterobacterial antigen. (05 Mar 2000) |
| heterophil antigen | An antigen which is possessed by a variety of different phylogenetically unrelated species; e.g., the various organ-or tissue-specific antigen's, the alpha-and beta-crystalline protein of the lens of the eye, and Forssman antigen. Synonym: heterophil antigen. (05 Mar 2000) |
| heterophile antigen | An antigen or antigenic determinant which is found in different tissues in more than one species. (05 Mar 2000) |
| 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) |