If the role of our immune system is to fight off germs, then the obvious question is - why do we carry germs in the first place? Why doesn't our immune system fight off all germs so that we remain germ free? If our immune system is designed to protect us from polio, tetanus, diphtheria and other supposedly disease causing germs, then why is it that for most people who carry these germs, their immune systems take no defensive action (meaning that no antibodies are produced) and yet they remain perfectly well?
There is only one logical answer to these questions - our immune system is not designed to fight off germs, for in reality, germs are not our enemies but our friends. Their real purpose is to feed on the waste matter within our bodies and thus assist in the important task of keeping our system clean. The true relationship between man and germ is not one of open warfare but one of peaceful co-existence, a relationship that Biology refers to as symbiosis.
"..when germs are found within a sick body, it is not that they entered from outside and caused the disease. It is because they developed from the decaying cells within the body and have an important part to play in helping to handle the waste and destruction bought about by serums, drugs and other poisons forced upon the body from without."
Eleanor McBean "The Poisoned Needle"
So what is the true role of our immune system?
Our immune system is made up of millions of white blood cells and antibodies which are designed to bind, engulf and ultimately destroy foreign proteins, bacterial excretions and other harmful substances. In other words, the true role of our immune system is not to fight off germs, but to rid the body of foreign harmful material and thus assist in the important task of preserving physiological health.
Humoral and Cell-Mediated Immune Responses
The immune system distinguishes two groups of foreign substances. One group consists of antigens that are freely circulating in the body. These include molecules, viruses, and foreign cells. A second group consists of self cells that display aberrant MHC proteins. Aberrant MHC proteins can originate from antigens that have been engulfed and broken down (exogenous antigens) or from virus‐infected and tumor cells that are actively synthesizing foreign proteins (endogenous antigens). Depending on the kind of foreign invasion, two different immune responses occur:
- The humoral response (or antibody‐mediated response) involves B cells that recognize antigens or pathogens that are circulating in the lymph or blood (“humor” is a medieval term for body fluid). The response follows this chain of events:
- Antigens bind to B cells.
- Interleukins or helper T cells costimulate B cells. In most cases, both an antigen and a costimulator are required to activate a B cell and initiate B cell proliferation.
- B cells proliferate and produce plasma cells. The plasma cells bear antibodies with the identical antigen specificity as the antigen receptors of the activated B cells. The antibodies are released and circulate through the body, binding to antigens.
- B cells produce memory cells. Memory cells provide future immunity.
- The cell‐mediated response involves mostly T cells and responds to any cell that displays aberrant MHC markers, including cells invaded by pathogens, tumor cells, or transplanted cells. The following chain of events describes this immune response:
- Self cells or APCs displaying foreign antigens bind to T cells.
- Interleukins (secreted by APCs or helper T cells) costimulate activation of T cells.
- If MHC‐I and endogenous antigens are displayed on the plasma membrane, T cells proliferate, producing cytotoxic T cells. Cytotoxic T cells destroy cells displaying the antigens.
- If MHC‐II and exogenous antigens are displayed on the plasma membrane, T cells proliferate, producing helper T cells. Helper T cells release interleukins (and other cytokines), which stimulate B cells to produce antibodies that bind to the antigens and stimulate nonspecific agents (NK and macrophages) to destroy the antigens.