The human body is surrounded by dangerous microbes from the environment that pose health risks. These microbes could be infectious viruses, bacteria, fungi, protozoa, and helminths. However, an intact human immune system fights and eliminates all these disease-causing organisms to keep human beings healthy and disease-free. While some immune responses are triggered quickly and contain the disease-causing organisms, some responses are slow, and the invading organisms can multiply fast and cause disease before they are eliminated. The immune system has two arms, the innate immune system, which is also referred to as the non-specific immune system, and the adaptive immune system ( Fox, 2015). A fully functional immune system is essential for survival, and any serious impairment of an arm could predispose a person to be severe and potentially life-threatening infections.
The immune system is activated by anything that the body fails to recognize as its own. These substances are called antigens. They include proteins that are found on the surface of fungi, viruses, and bacteria. Once these microbes invade the body, immune cells recognize them, and a cascade of immune responses begins. Fox (2015) notes that if it is the first time a specific organism has invaded the body, memory B cells are produced, and subsequent encounters with the same antigens trigger even faster responses ( Fox, 2015) .
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The body's own cells contain protein substances which can be antigenic as well. Sometimes, the immune system recognizes these proteins as foreign and then attacks the otherwise healthy cells in an autoimmune response, resulting in autoimmune diseases such as Systemic Lupus Erythematosus (SLE). Development of central tolerance enables the body to prevent the development of autoimmune T cells as they undergo anergy, clonal deletion, and receptor editing in the thymus ( Abbas et al., 2019) . Therefore, the body fights against autoimmune diseases by clearing any T cells that display high-affinity T cell receptor interactions with the self-peptide-MHC complexes.
According to Murray et al. (2020), the body relies on natural barriers to prevent organisms from invading the system. These barriers, unless broken, are effective in keeping off microorganisms. Intact skin, including mucous membranes that line the mouth, eyes, and the reproductive canal, are potential barriers. Typically, the mucous membranes are coated with secretions that have substances that help fight off infections. For instance, tears contain lysozymes that lyse bacterial membranes. Airways are lined with cilia and mucus, which traps these microorganisms. The mucociliary escalator motion helps sweep mucus up, thus preventing the germs from getting to the lungs and causing diseases ( Murray et al., 2020) .
The digestive tract has elaborate defense mechanisms as well. First, there is the hydrochloric acid, which kills bacteria in ingested food among other microbes. There are pancreatic juices with enzymes, bile, and other intestinal secretions that kill and digest harmful microbes. The urinary tract also forms an effective barrier alongside actions such as frequent voiding, which clears any organism's system that could multiply and cause disease along the tract ( Murray et al., 2020 ). For males, the urethra is long, making it impossible for bacteria to reach the bladder, while for females, the vagina has an acidic PH that prevents the growth of harmful bacteria while encouraging the growth of commensal bacteria.
As Sompayrac writes out, w henever infections develop, the body’s immune system is activated with mechanisms that lead to the production of substances and agents that attack specific organisms. The Natural Killer T cells are in constant circulation, and they can recognize and kill invading organisms via cytotoxicity. Activated T cells also proliferate and differentiate to plasma cells, which produce antibodies. The antibodies bind to the organisms and neutralize them or enable a process such as opsonization that enables other immune cells such as neutrophils and eosinophils to recognize and produce substances that kill the organisms. Substances released could be perforins or granules that contain the major basic protein and eosinophilic cationic protein that kills organisms. Blood also contains white blood cells, such as neutrophils that form the first line of defense and monocytes. These cells engulf disease-causing organisms and kill them through the respiratory burst, where reactive oxygen species kills the bacteria ( Sompayrac, 2019).
In conclusion, it is worth noting that the body relies on multiple mechanisms from the defense. All these systems have to work effectively to prevent microorganisms from causing diseases. The natural arm of immunity works with the adaptive arm as the first line of defense mechanisms such as dendritic cells present antigenic materials to T cells, which are of the adaptive arm of immunity. At the same time, an intact immune system recognizes and eliminates autoimmunity by preventing autoimmune T cells from reaching circulation. The various proteins, such as antibodies, secretions, and the physical barriers are important in preventing diseases' entry, causing organisms, the first step to fighting diseases. Memory B cells specialized from other B cells and facilitate a robust, rapid response to prevent subsequent infections by accelerated antibody-mediated responses.
References
Abbas, A. K., Lichtman, A. H., & Pillai, S. (2019). Basic Immunology E-Book: Functions and Disorders of the Immune System . Elsevier Health Sciences.
Fox, S. (2015). Human physiology . McGraw-Hill Education.
Murray, P. R., Rosenthal, K. S., & Pfaller, M. A. (2020). Medical Microbiology E-Book . Elsevier Health Sciences.
Sompayrac, L. M. (2019). How the immune system works . John Wiley & Sons.
