Immune system inner-workings: the very basics

The primary function of your immune system is to equip your body with the capacity to recognize materials that are foreign to you and to neutralize, eliminate, engulf, or kill them, hopefully without any injury to you. Foreign particles can be bacteria, viruses, parasites, fungi, and even food that is absorbed without being properly digested (the genesis of food allergies). The ability to differentiate “self” from “foreign” is the crux of its job.

Your skin and the mucous membranes in your mouth, nose, and GI tract are the first lines of natural defense, and natural substances secreted in your sweat and saliva are detrimental to the growth of foreign microorganisms. Three examples: your skin and stomach have a naturally acidic level that inhibits bacterial growth; enzymatic lysosomes in your tears and saliva break down bacterial cell walls; and your sweat contains glycoproteins that adhere to microbes to trap and “wash” them away.

If foreign particles make it through these natural ports of entry into the blood or lymph, then they can initiate an immune response depending on your immune tolerance. Your innate immune system reacts first and provides a fixed response to these substances it encounters. This can include developing a fever or secreting a variety of enzymes and proteins intended to kill pathogenic microorganisms. The pathways that complement these processes trigger a natural inflammatory response that facilitates the movement of necessary immune system components to the site of infection or damage. In addition to the various types of white blood cells – monocytes, lymphocytes, macrophages, eosinophils, basophils, and neutrophils – dozens of proteins, cytokines, and other substances in this complex response are activated in different locations, all with the same goal – to kill invaders.

Although it’s different, but not entirely separate from your innate immune system, you also have an adaptive immune response that provides a complex set of genetically controlled, interdependent, and interactive responses to foreign substances. Your adaptive immune system is comprised of a relatively small number of cells that have the capacity to recognize certain foreign substances. The different types of cells of the adaptive immune system – B-cells and T-cells – work synergistically with the innate immune system to recognize foreign substances (usually bacteria and viruses) and produce antibodies against these foreign substances that eventually kill them. And although this might sound relatively simple, this intricate process also requires the assistance of many other essential and complex steps for it to function properly.

One unique aspect about the adaptive immune response is that it can produce large quantities of long-lived cells (i.e., memory cells) that live dormant but can be quickly re-expressed during subsequent encounters with the same foreign substance. For example, your adaptive immune response is what triggers an allergic reaction or rejects transplanted tissue.

GI tract and the immune system

Although much immune activity goes on in your blood, the important role that your gut plays in your immune system can’t be overlooked. Although you encounter bacteria in the air, on objects you touch, and naturally on your skin, the most bacteria you are exposed to reside in your gut. The mix of these bacteria, both good and bad, plays a huge role not only in your digestive system but also in your immune system. In fact, it is estimated that 80 percent of your immune system might be located in your gut.

The protective lining in your gut, which includes epithelial cells and its mucosal lining, acts as a physical barrier to foreign invaders to your bloodstream, assisted by the principal immune-protective antibody, secretory immunoglobulin A (sIgA). Compromises in gut integrity, which can occur from nutrient deficiencies, free radical damage, antibiotic use, and inflammation, can allow more “bad” bacteria into your bloodstream. Acting in concert, the beneficial gut bacteria also play a major role in preventing pathogens from being absorbed.