The evolution of immune mechanisms

Abstract

From early on in evolution, organisms have had to protect themselves from pathogens. Mechanisms for discriminating ''self'' from ''non-self'' evolved to accomplish this task, launching a long history of host-pathogen co-evolution. Evolution of mechanisms of immune defense has resulted in a variety of strategies. Even unicellular organisms have rich arsenals of mechanisms for protection, such as restriction endonucleases, antimicrobial peptides, and RNA interference.In multicellular organisms, specialized immune cells have evolved, capable of recognition, phagocytosis, and killing of foreign cells as well as removing their own cells changed by damage, senescence, infection, or cancer. Additional humoral factors, such as the complement cascade, have developed that co-operate with cellular immunity in fighting infection and maintaining homeostasis. Defensive mechanisms based on germline-encoded receptors constitute a system known as innate immunity. In jaw vertebrates, this system is supplemented with a second system, adaptive immunity, which in contrast to innate immunity is based on diversification of immune receptors and on immunological memory in each individual.Usually, each newly evolved defense mechanism did not replace the previous one, but supplemented it, resulting in a layered structure of the immune system. The immune system is not one system but rather a sophisticated network of various defensive mechanisms operating on different levels, ranging from mechanisms common for every cell in the body to specialized immune cells and responses at the level of the whole organism. Adaptive changes in pathogens have shaped the evolution of the immune system at all levels.

Tenebrionid secretions and a fungal benzoquinone oxidoreductase form competing components of an arms race between a host and pathogen

“…serves as a concise metaphor for the selection pressures on hosts to constantly change defense mechanisms against pathogens and the counterselection on the pathogens for continuously developing means for overcoming such evolving defenses, resulting in the appearance of both organisms "running in place" (1). Variations of the Red Queen as well as alternative theories, most unified around the centrality of biotic interactions as a driving force, have been proposed as explanations for (i) taxon extinction [Van Valen's original Red Queen's hypothesis (2)]; (ii) the evolution and maintenance of sex, genetic recombination, and immune systems (3)(4)(5); (iii) as a framework for understanding invasions of exotic species (6); and (iv) as mechanism(s) selecting for hostpathogen coevolution [i.e., broad versus specific host ranges and/or host tolerance (7)(8)(9)]. …”

Mechanisms of Maternal Immune Tolerance During Pregnancy

“…Over 30 proteins are involved in its activation and they act in concert to protect the host against invading organisms (Girardi, 2008;Girardi et al, 2006). Activation of the complement cascade promotes chemotaxis of inflammatory cells and osmotic lysis of mammalian and bacterial cells through the formation of membrane attack complexes and is commonly used by the immune system to kill foreign or cancerous cells (Danilova, 2006). The complement cascade is regulated by complement regulatory proteins (CRP) that are expressed on cells and are critical for protecting tissues from inflammation that occurs in response to complement activation.…”

Polysaccharides from Red Algae: Genesis of a Renaissance

“…Individual resistance to pathogens depends on the combination of receptors on cells from the immune system although non-immune genes also influence resistance [67]. Signs of natural selection in a human population are especially illustrative, when a mutation in a certain gene is dangerous in normal conditions but confers resistance to infections widespread in the region.…”