Antibodies: Definition, Structure & Function | Immune System Explained

Antibodies, or immunoglobulins, are a vital element in the body's immune system, and are secreted by the white blood cells. Their sole purpose is to fight antigens, or foreign substances, that may be found in foods, red blood cells, cancer cells and pollen.

Structure

• Antibodies are made of protein, which is divided into four units. Each unit is composed of amino acids, the building blocks of protein.

Indirect Attack

• The most effective way for antibodies to destroy antigens is by activating complement proteins that help attack the antigens. These proteins can rupture the invading cells, promote clumping of the cells or weaken the foreign antigens.

Direct Attack

• Antibodies also attack antigens by binding to an antigen. This antigen-antibody reaction causes the cells to clump together, or agglutinate.

Primary Response

• The primary response of the body to an antigen is a slow process in which few antibodies are produced. This is why it takes days to fight off a disease.

Secondary Response

• The second time the body notices an antigen, it reacts by producing large numbers of antigens quickly. This is the mechanism that allows you to become immune to certain diseases.