Universal life defense concept: global biology.

Abstract

Life can be considered as a perpetual struggle against the inexorable increase in entropy of the universe, in other words, the increase in disorder. Living organisms need materials (e.g., glucides, lipids, proteins, minerals) energy, work, and organization in order to thrive. In the environment such organisms are to subject to aggression by ionizing radiations, natural and synthetic chemicals, viruses, bacteria, and parasites; to protect themselves they have developed various defense mechanisms. The aim of this short contribution is to propose the existence of a universal life defense system and thus provide a good example of global biology. From an analytical point of view three systems have been described: the innate immune system (IIS), the adaptive immune system (AIS), and the chemical defense system (CDS). The IIS is a kind of chemical barrier that organisms from insects to humans use to stop dangerous microbes at their first point of contact—skin, mucous membranes, etc.—and its characteristics have already been reviewed (Gura 2001). The IIS depends on peptides and small proteins to counteract any dangerous microbes. The mechanisms of action of these substances are not yet completely understood but are known to exist in all living organisms: insects, plants, animals, and humans. The AIS is very well known, and the antibodies and killer cells have been extensively described. It is a very important complex system. A decrease in its activity, as observed in elderly persons and in those with diseases such as AIDS, enables many normally nonpathogenic microbes to develop and subsequently to kill their carrier. The CDS, as recently proposed (Rico 2001), consists of various defense mechanisms against toxic compounds, for example, lipophilic compounds subjected to biotransformation involving mixed-function oxidase, where cytochrome P450 mono-oxigenase plays a pivotal role, multidrug transporters, oxidants and oxidative species, mutagens, and metals. The CDS presents many analogies with the adaptive immune system: partial immaturity of young subjects, inducibility, lack of specificity, specificity, and saturability. It is the dose that makes the poison, as in bacteriology where it is the bacterial quantum which determines the disease. The tools involved in these different systems are biochemical in nature, and most often enzyme reactions. The characteristics of these enzyme reactions are similar to those of the above systems: specificity, sometimes reversibility, induction, inhibition, deficiencies, saturation. It is interesting to note that the tools are identical or very similar in all three systems, as illustrated by the following examples. Many enzymes in the lysosomes of macrophages are able to degrade or digest bacteria and various phagocyted bodies. All these enzymes are also present in the CDS and act in the same way. The superoxide dismutases which degrade active oxygen species are also a good example.