What is the significance of antigens and Antibodies in the blood?

Answer 1

Antigens are foreign substance that are recognized by a body as being harmful. Generally, they cause the release of histamines, which cause dilation of blood vessels, contraction of smooth muscle tissue and other affects associated with the body's attempt to repair itself. (The body, recognizing non-harmful antigens as dangerous, produce histamines which produce the symptoms of allergy.) This reaction is an early step in the body's immunological response to attack. Antigens can be large or small: generally the larger irritants and infection-causing bacteria are dealt with by one or more variety of "macrophage" (gk. for "large eater"): white blood cells. There are many varieties of white blood cells, some of which serve the macrophage function by engulfing the invader and immobilizing or digesting it.

Antibodies are produced by one variety of white blood cells (mast cells) and distributed into the blood. The antibodies are keyed to be able to combine with the antigen and neutralize their affect. Once antibodies have been produced, the body can create more of them to ward off any further attacks. Because the body never actually stops generating antibodies, they can eliminate the keyed antagonist before infection can even start, giving that person an immunity. (In medicine, this is invoked with a vaccine made of dead antagonist components, which a body is exposed to by injection or other means. Once the body has become immune (by learning the antigen and producing antibodies) it is prepared to ward off further attacks by the live antigen.

The presence of antibodies is also used as a test, to see if an antigen has been or is in the body. Some of the tests used for detecting HIV rely on antibody presence, despite the logical conundrum that antibodies are produced by a healthy immunoresponse to an antigen, and HIV is purported to be The virus that causes AIDs, a syndrome where immunoresponse is so depressed that the patient dies of opportunistic infection. One possible explanation for this is that the test is detecting component presence of more than one antibodies which are keyed to other antigens (in which case HIV may not be present at all) or that HIV is not the actual cause of AIDs (a position being voiced by more and more virologists.)

Be as that may be, antigens cause an immune response, and antibodies are the response of the body to certain antigens.