In Defense of You: Your Immune System

Our immune system is designed to react to anything foreign. When a pathogen enters our body, a system of special cells mobilizes in a coordinated defense response. This can involve the secretion of specific molecules to bind to and neutralize the pathogen or it can involve special cells that engulf or otherwise eliminate the germ.

The immune system is comprised of two main systems working together, the innate immune system and the adaptive immune system (a third type, “passive” immunity is the “borrowed” protection a baby receives from breast milk). Each system uses different specialized cells to carry out its defense.

Innate immunity is the line of defense that responds to infection, wounds or pathogens in a non-specific, or generic, manner, meaning that all foreign cells are treated the same. This type of immune response is more primitive, in evolutionary terms, and relies on a range of white blood cells, or leukocytes, that seek out and destroy foreign cells, or strive to isolate and protect damaged tissue through defensive measures such as inflammation. Innate immunity is a blank slate and remains unchanged no matter how often it encounters a particular foreign cell.

Adaptive immunity, on the other hand, is a line of defense that “learns” and forms cellular “memories” about the exact identity of each invader. This enables the system to prepare for future encounters with a specific invader and mount even more effective counter-measures. Adaptive immunity relies on antibodies that circulate in the body and serve as the immunological memory that offers long-lasting protection against specific pathogens. Vaccines are possible because of the adaptive immune system. LESS

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Antibodies represent a 24/7 continuing-education course with life-or-death stakes. They are the spearhead of a high-tech recognition system. Each antibody is designed by the body to recognize a specific distinctive structure on an invading foreign cell or particle. Once an antibody is created to match a distinctive little piece of the foreign object, it attaches to that structure (called an antigen) and signals the rest of the immune system to destroy the foreigner. (Imagine a cellular cop jumping on the getaway car so that the police helicopters know who and where the bad guys are.)

The first time the body is exposed to a particular foreign substance, like a virus or bacterium, it can take the immune system some time to create antibodies to match up with that particular threat. But once created, this antibody remains at the ready to leap into action the next time the antigen appears in the system. If and when that happens, the body’s immune system is able to respond as swiftly and strongly as an expert swat team.

This is the basis for vaccines. A vaccine uses a weakened or partial version of a pathogen (too weak or fragmented to actually cause the disease) to “train” the body to produce appropriate antibodies. And then, should the person vaccinated ever encounter the “real” pathogen, his or her body is primed to respond decisively to the threat. Some pathogens, such as the ever-changing flu virus, can pose daunting challenges to vaccine makers. The ubiquitous rhinovirus, responsible for the common cold, may remain outside vaccination for the foreseeable future. LESS

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Our immune systems make mistakes. One category of such mistakes are the autoimmune diseases that can affect a single organ or be systemic, affecting many tissues or organs. Type I diabetes is an example, in which the immune system destroys the pancreatic cells that produce insulin; rheumatoid arthritis is an example of a system wide attack by the immune system on joint tissue.

Another category include allergic reactions, including asthma, where an aggressive response is mounted to foreign substances, such as foods (peanuts, for example), pollens, molds, animal dander or mild toxins (a bee sting), that represent no significant threat. And yet the response by the immune system can indeed pose a serious threat.

And a third category that is more understandable, from a biological perspective, is the violent reaction to a transfusion or transplanted organ, even though donor blood or organ is matched as closely as possible to recipient. LESS

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