Strategies used by our bodies to fight infection.

Analogies of Anti-Infection Strategies Used by Our Bodies

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These are given in approximate order of time of use: front line defenses come into play first, and so on, until specific immunity involving antibodies takes up the final defensive stance.

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Name Counter-Strategy Comments

Probiotic microbes Use other microbes as guard-dogs that kill intruders These are listed first because they are on the outside of the body, and thus form the first line of defense. This is a field that is again becoming better recognized with a great deal of attention being directed at the "dairy" bacteria - those lactic acid bacteria associate with dairy products. These bacteria are known to inject bactericins into invaders. Three evolutionarily important facets of these are (1) that they are found also in doing their protective jobs in plants, (2) that they are the only known countermeasure that is not governed by the host's own genes, and (3) that they are the only countermeasure that can mutate as fast as can the invaders and so keep up with the rise of resistant mutant pathogens.

Complement Serum complement punches holes in targetted cells, which then explode due to their extremely high osmotic pressure. Complement is one of the body's first lines of defense. It consists of a number of proteins that assemble on the surfaces of targetted cells and form the lining of a hole - or transmembrane complex. Complement is often repelled by the bacterial underwear layer called LPS. However, once the body has produced antibodies to the invader, the attached antibodies form a nexus upon which the transmembrane complex can aggregate.

Enzymes Kills the invader by dissolving its exterior walls, or by being activated to produce highly toxic substances such as chlorine The two most common examples of this strategy are lysozyme in tears and eggwhite, and the digestive enzymes released by lysosomes into food vacuoles.

White Blood Cells Just plain ordinary catch 'em and eat 'em strategy. There are many types of phagocytes found in people (and taxonomically, all the way down to jellyfish). Probably the best known are the macrophages, which send out tendriles that lassoo invaders, which are then drawn in, engulfed and digested. Less known are the polymorphonuclear lymphocytes (PMN's or "polys"), which are far more gluttonous than their larger cousins, the macrophages.

Sound the Alarm! Man the battle-stations! This is the only countermeasure that actually does not directly affect the invader. Normally, the body is somewhat lax in its defenses - particularly with regard to viruses. However, when a cell gets "sick" from a viral attack, its sounds its alarm and sends out chemical signals that alert other cells that there is a pathogen among us, and the other cells put into motion added protective devices, which may slow their own growth, but prevent the viruses from replicating. These alarm signals are called cytokines, of which the best known are the interferons, which alert cells to viral invaders. Other cytokines call white blood cells to points of infection, sometimes resulting in abscesses, which are good in that they prevent the invaders from spreading throughout the body. New types of cytokines are being discovered continuously.

Sticky Albumin This is a hypothetical strategy that the body might be using. Various goos might clog up the pores of invaders preventing them from growing as fast as they would like to. The function of albumin is not well understood, although it can be easily shown that actively growing bacterial cultures suddenly slow their growth if albumin is added.

Fever Damages to the invader Fever has a number of deleterious effects on pathogens. It prevents the formation of the Gram-negative bacterial LPS layer so that complement can puncture and explode the invader. In Gram-positive cells, it seems to cause the bacteria to make thinner, and weaker cell walls that are much more sensitive to lysozyme and to the effects of penicillin. It has long been known that fever interfers with the production of many viruses.

Net Man Traps the invader and locks it away secluding it from the remainder of the body like putting it in jail. Examples of these are tubercles as in TB, or, more commonly, as abscesses.

Antibodies These proteins are extremely specific as to what they will latch onto, and are used by the body to tag (opsinize) intruders for subsequent attack by complement and phagocytosis There are potentially millions of different kinds of antibodies, which are divided into three main (IgG, IgM, IgA) and two minor (IgK, IgL) classes. While the production of the needed type of antibody takes several days (during which time the body depends on the other defenses to keep the invader from winning), once the body had "learned" how to make a type of antibody and the disease is cured, the next time that type of invader comes into the body, the system remembers, and within hours overwhelms the invader and subdues it. This is the basis of immunizations - to "teach" the body how to do it before the invader comes around.
physical barriers like castle walls, fences and palisades. Skin and other membranes and tissues are not only physical barriers but also might be the hunting grounds of probiotic organisms.

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