13. Explain the roles of antigens and antibodies in the body’s immune response including the involvement of plasma cells, macrophages and antigen-presenting cells.
The specific immune response relies on the lymphocytes, of which there are two main kinds, each with a number of sub-types. Both types respond to foreign (non-self) antigens, such as proteins on the surface of bacteria and viruses. Macrophages are also involved, engulfing bacteria and displaying the non-self antigens. They alert the immune system to the presence of the foreign antigens. When any cell in the immune system displays antigens in this way, it is called an antigen-presenting cell.
An antigen is a substance that stimulates the production of an antibody when it gets into the body. Antigens are often chemicals on the surface of a cell such as proteins, glycoproteins or carbohydrates. They can also be toxins made by bacteria, or sometime are whole microorganisms such as bacteria or viruses.
Macrophages function in both non-specific defence as well as help initiate specific defence mechanisms. Their role is to engulf and digest cellular debris and pathogens, either as stationary or mobile cells. They also stimulate lymphocytes and other immune cells to respond to pathogens. They are specialised phagocytic cells that attack foreign substances, infectious microbes and cancer cells through destruction and ingestion.