The immune system is a combination of many biological structures and processes that aim to protect the body primarily by detecting and eliminating pathogens and disease. To enhance the functions of the immune system, a host organism can evolve innate abilities to protect itself from the negative impacts of disease by increasing its fitness via avoidance, resistance, and tolerance mechanisms.
Avoidance, Resistance, and Tolerance as Immune Defense Strategies
499 Progress Report after 1 Semester
This report follows the format of Science: American Assn. for the Advancement of Science
Avoidance, Resistance, and Tolerance as Immune Defense Strategies
The immune system has long been understood as the primary source of defense against pathogenic burdens and infection. By detecting and eradicating the invading pathogens and potentially harmful foreign threats, the immune system aims to return the host’s body to homeostasis. The defense mechanisms which are employed during the time of infection or disease are traditionally thought to be a response by immune system to the invading pathogens (2, 5). However, over many species of organisms, the susceptibility to disease and pathogens is genetically variable and may ultimately impact the organism’s ability to handle pathogenic burden (5). This variation has lead to the fact that distinct organisms have differential abilities to tolerate the presence of infection and disease, thus making the concept of tolerance a separate mechanism of host defense (3). Ultimately, the three mechanistic strategies a host can use in protect itself from pathogenic burden and diseases are avoidance, resistance, and tolerance (5).
Avoidance
In order to employ the avoidance strategy, a host must first be capable of early on detection of the pathogen and avoid the possible risk of exposure to disease. In a majority of organisms, this detection of a potential threat is done primarily by the olfactory and gustatory systems (5). The detection of the presence of pathogenic organisms in the environment involves various molecular mechanisms to function at a high capacity. To begin, the host must be able to recognize a high pathogen density. For many organisms, including pathogens, it is a natural tendency to produce volatile metabolites and byproducts (4). For example, methane thiol is a product produced by the breakdown of L-methionine and leads to a distinct odor associated with the presence of high density bacteria on a human host’s skin (3). At high concentrations, these bacteria can produce a very foul odor distinct to the human olfactory system which can thus report the possibility of disease or infection. After the detection of the possible risk, the host will then alter its behavior to avoid any potential damage and reduce the risk for infection by the pathogen. The vomeronasal region of the human body is an example of how the avoidance strategy functions. In most mammals, the vomeronasal organ contains a series of formyl-pept...
