Algonquin College
16.6 - Specific Defenses Overview
The specific or adaptive body defenses respond to individual pathogens. The response of the specific defenses (also called the immune system) is systemic (body-wide). It also has "immunological memory", meaning the immune system "remembers" specific invaders and can respond more quickly if the body becomes re-infected with the same invader.

The specific defenses has two main components: humoral and cellular immunity.

Antigens and antibodies

An antigen is a substance capable of activating the immune system. Antigens are usually molecules on the surface of a pathogen or infected cell. An antigen is also said to be a nonself marker, since self-antigens are found on every body cell and are recognized by immune cells as part of the host body.

Self-antigens can trigger immune responses in other people, such as when an organ or tissue is transplanted. Anti-rejection drugs must be used to make sure the transplant recipient's immune system does not destroy the transplanted tissue.

Haptens are a type of antigen that can link up with body proteins to trigger allergic responses.

Antibodies are proteins manufactured by B-lymphocytes that have been activated (plasma cells). They are also known as immunoglobulins (Igs) and are involved in the humoral immune response. Antibodies attach onto antigens at their antigen-binding sites, which are found on the variable regions (light chains) of the antibodies. Each antigen-binding site is unique to a specific antigen, which means there is a different antibody manufactured for every antigen the body encounters. The constant regions (heavy chain) of the antibody is the same in every antibody of a given type.

Antibody


Figure 16.6.1 - An antibody and several antigens. Note that only one antigen has the proper shape to fit the antigen-binding site of the antibody.

Source: "Antibody" - By Fvasconcellos 19:03, 6 May 2007 (UTC) [Public domain], via Wikimedia Commons

There are several types of antibodies, all which are combinations of a basic "Y" shaped antibody with two light chains (at the tips of the "Y") and two heavy chains (makes up the rest of the "Y". The most common antibody is the IgG antibody, which is of the basic "Y" shape.

Antibody functions

Antibodies serve several functions in destroying or helping to destroy foreign invaders in the body. Antibodies most often serve to clump up with antigens or mark them for destruction by macrophages.