Carcino-embryonic Antigen: From 1 Different Sources
(CEA) a protein produced in the fetus but not in normal adult life. It may be produced by carcinomas, particularly of the colon, and is a rather insensitive marker of malignancy. It is an example of an *oncofetal antigen that is used as a *tumour marker, particularly in the follow-up of colorectal cancer.
A substance, usually a protein, that induces the formation of defending antibodies. Example: bacterial toxins, Juniper pollen (in allergies). Auto-immune disorders can occur when antibodies are formed against normal proteins created within the body.... antigen
See HLA SYSTEM.... human leucocyte antigen (hla)
An ENZYME produced by glandular tissue in the PROSTATE GLAND. When the gland enlarges (see PROSTATE, DISEASES OF), greater amounts of PSA are secreted, raising the concentration of the enzyme in the blood. This is especially so in cancer of the prostate, and testing the level of PSA is an indicator that the disease may be present. There is much controversy about the use of PSA as a screening test. Its proponents claim that its use reduces deaths from prostate cancer; its opponents suggest that it does this only by bringing to light many cases that needed no treatment and would not have caused death in any case. Further, if the level of PSA is very high, the disease is already advanced; where the result is equivocal it is uncertain whether the bene?ts of treatment outweigh the risks.... prostate specific antigen (psa)
Substances, usually harmful, that when entering the body stimulate the immune system to produce antibodies. Invaders may be polio virus, typhoid bacillus, or chain-like streptococcal bacteria – the usual pus-forming type found in infected wounds, or toxins they release into the blood stream. ... antigens
(HLA) A type of protein belonging to the group known as histocompatibility antigens, which play a role in the immune system.... human leukocyte antigen
(APC) a cell, such as a *dendritic cell or a *macrophage, that processes antigen for presentation to a T lymphocytes (see helper T cell).... antigen-presenting cell
another name for the *hepatitis B antigen, which was first discovered in the blood of an Australian aborigine. This disease is caused by a virus of which the Australia antigen forms part.... australia antigen
the early embryo before the formation of *somites. It is a flat disc of tissue bounded dorsally by the amniotic cavity and ventrally by the yolk sac. The formation of the *primitive streak and *archenteron in the embryonic disc determines the orientation of the embryo, which then becomes progressively elongated.... embryonic disc
see HLA system.... human leucocyte antigen system
a group of antigens that may or may not be present on the surface of red blood cells, forming the basis of a *blood group. This group is important in blood transfusion reactions. [Mrs Kell (20th century), patient in whom they were first demonstrated]... kell antigens
a protein normally produced only by fetal tissue but often produced by certain tumours. An example is *carcino-embryonic antigen (CEA), which has been used as a *tumour marker, especially in colorectal carcinomas.... oncofetal antigen
a protein produced by cancer cells. Its presence in the blood can be revealed by means of a simple blood test, aiding the diagnosis of malignant melanoma and other cancers at their earliest – and most treatable – stages of development.... tumour-associated antigen
(PSA) a protease enzyme produced by the glandular epithelium of the prostate. Its effect is to liquefy the semen within the ejaculate. Overall PSA has a half-life of 2–3 days. Increased quantities are secreted when the gland becomes enlarged or inflamed, and levels of PSA in the blood are significantly elevated in cancer of the prostate. Although there is no clear ‘cut-off’ level for normality, over 4 ng/ml in the blood is associated with a 20% risk of prostate cancer, even in patients with normal-feeling prostates on rectal examination. Age-specific PSA reference ranges are often used. Newer PSA assays can measure free PSA and compare it to the total PSA in the blood. Low free:total PSA ratios indicate a greater risk of prostate cancer and improve the discrimination between cancer and benign disease in men with a PSA in the range 4–10 ng/ml. PSA levels tend to be much higher in advanced prostate cancer and the rate of fall on treatment (e.g. after radical prostatectomy or radiotherapy) is a good prognostic indicator of response.... prostate specific antigen
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