Immune responses are produced by a complex, hierarchical organization of the immune system, tissues, organs, and components, but despite this fact, the unit of the cell has a specifically huge impact on the progression of the disease and the survival of the host.
Image Credit: https://science.sciencemag.org/content/340/6133/701
Called cell-autonomous immunity, these cell-level defense mechanisms are one of the most significant determinants of the survival of humans and are millions to billions of years old. They are inherited from the humans’ single-celled and prokaryotic ancestors.
The study’s authors argued that interpreting the evolution of cell-autonomous immunity in primates is important to understand the evolution of humans, because infectious agents believed to have affected the evolution of human genomes are exceptional manipulators of cell-autonomous immunity, and also because these defenses are present in all cells in all body systems.
The latest study was reported in the September 2020 issue of The Quarterly Review of Biology.
In an article titled “Cell-Autonomous Immunity and the Pathogen-Mediated Evolution of Humans: Or How Our Prokaryotic and Single-Celled Origins Affect the Human Evolutionary Story,” Jessica F. Brinkworth and Alexander S. Alvarado discussed the ubiquity of cell-autonomous immunity and how it underlines a biological reality that is seldom addressed in human evolutionary research works—pathogens can control the evolution of every body cell, and thus, all human body systems.
The article analyzed these old strategies in light of the evolutionarily significant human pathogens and showed inter-primate variations in their function. The authors also theorized that the immune system, which is frequently regarded as a separate physiological system in human evolutionary biology, is omnipresent and incorporated into every other facet of human physiology.
We argue, therefore, that immunity and pathogen-mediated natural selection is a consideration in the examination of the evolution and function of any human physiological system or trait.”
The authors demonstrated how human pathogens, believed to be significant in human genomic evolution, exploit cell-autonomous immunity and have molded the evolution of primates, including phagosomes such as Yersinia pestis (the causative bacteria of plague) and also antimicrobial peptides such as Toxoplasma gondii—the 1 to 2 million-year-old obligate intracellular feline-borne parasite.
The ancient nature of these defenses is an important consideration in human evolutionary studies because their antiquity is both why cell-autonomous immunity exists in every cell, and the pathogens commonly considered the most pernicious and to have exerted the most stringent selective pressure on the human lineage tend to be organisms that bear microbiological innovations that manipulate these tactics.”
The article also showed that such defenses are deviating in primate immune cells and current evidence shows that they are also modifying in “nonimmune” tissues.
“For decades, it has been understood that microorganisms and cell-autonomous immune responses to them alter human behavior and vice versa,” added the team.
Incorporation of the same biological relationships between pathogens, cell-autonomous defenses, and body system X extended to other physiological systems or traits at the center of the classic questions of human evolutionary biology (e.g., why does skin color vary in humans, why do primate placentae vary in shape and size, how did human bipedal locomotion evolve, how does primate bone and dental microstructure vary) can enrich and improve our understanding of why such features evolved.”
However, scientists from this field should increase the incorporation of morphological and molecular findings or techniques in human evolutionary analyses because only then this kind of information would contribute to a better interpretation of the gross traits of human evolution, stated the authors.
“Any examination of human evolutionary biology, regardless of physiological system and when possible, should consider autonomous immunity of the cells in that system and how microorganisms have shaped them,” the researchers concluded.
Brinkworth, J F & Alvarado, A S (2020) Cell-Autonomous Immunity and The Pathogen-Mediated Evolution of Humans: Or How Our Prokaryotic and Single-Celled Origins Affect The Human Evolutionary Story. The Quarterly Review of Biology. doi.org/10.1086/710389.