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Mycobacterium Tuberculosis Resitance Archives of Immunology and Allergy ISSN: 2639-1848 Volume 1, Issue 2, 2018, PP: 31-39 Mycobacterium Tuberculosis Resitance Mechanisms to Bactericidal Activity of Phagocytes: A Review Diso SU1, Nasir AS2, Ali M3* 1Department of Pharmaceutical Technology, School of Technology, Kano State Polytechnics. 2Department of Medical Laboratory Science, Bayero University Kano. 3*Department of Biological Sciences, Federal University Gusau. [email protected] *Corresponding Author: Muhammad Ali, Department of Biological Sciences, Federal University Gusau. Abstract The human immune is extremely complex. It has evolved over hundreds of millions of years to respond to invasion by the pathogenic microbes that regularly attempt to infect our bodies, and invasion by the microbes that tried to infect our genetic ancestors. Phagocytes are the soldiers of the immune system, and provide innate immunity. They are responsible for swallowing, killing and digesting invading microbes by phagocytosis. Despite the presence of antimicrobial host factors (from immune system), many pathogens such as Mycobacterium tuberculosis can survive inside the host cell due to evolvement of multitude of strategies to counteract host defense mechanisms. The paper review the strategies adopted by Mycobacterium tuberculosis to evade bactericidal activity of innate immune phagocytes. Keywords: Bactericidal activity, innate immunity, Mycobacterium tuberculosis, phagocytes Introduction Despite the presence of antimicrobial host factors (from immune system), many pathogens can survive The human immune is extremely complex. It has inside the host cell. Such pathogens, which include evolved over hundreds of millions of years to respond bacteria, fungi and viruses, have evolved a multitude of to invasion by the pathogenic microbes that regularly strategies to counteract host defences. Some bacterial attempt to infect our bodies, and invasion by the species interfere with the ability of phagocytes to microbes that tried to infect our genetic ancestors engulf them [5,6], either by scavenging, inhibiting or [1]. There are similarities between the immune even degrading opsonic antibodies or complement system of humans and those of the most primitive [7,8,9], or by directly impairing the phagocytic on the evolutionary ladder [2]. The immune system machinery of macrophages and neutrophils [5,6,10]. doesof vertebrates, not rely goingon one back single five hundredmechanism million to yearsdeter Other bacteria have become resistant to one or invaders, but instead uses many strategies. The main more of the antimicrobial factors of phagocytes. division between the strategies is that between innate Some species have developed metabolic pathways immunity, which does not require previous exposure to counteract acid accumulation inside phagosomes to the invading microbe, and Acquired immunity, or have acquired uniquely resistant proteins to whereby the immune system “remembers” how to withstand the low pH [11,12]. Yet other bacteria deal with a microbe that it has dealt with before [3]. protect themselves by actively degrading [13] or Phagocytes are the soldiers of the immune system, shielding themselves [14,15] from the antimicrobial and provide innate immunity. They are responsible for peptides and proteins produced by phagocytes, or swallowing, killing and digesting invading microbes. by expressing detoxifying enzymes, such as catalase, The process of swallowing microbes is known that neutralize ROS and/or RnS [16,17]. Alternatively, as phagocytosis [4]. some bacterial species prevent RnS and ROS formation Archives of Immunology and Allergy V1 . I2 . 2018 31 Mycobacterium Tuberculosis Resitance Mechanisms to Bactericidal Activity of Phagocytes: A Review by impairing recruitment of the proteins that mediate system, which is unique to vertebrates, and is their their synthesis [18,19]. second immune system. It adapts to pathogens that the individual organism is exposed to during life [26]. Other species have devised means of overcoming the scarcity of iron by secreting specialized iron- The adaptive immune system takes longer to respond scavenging molecules called siderophores, which to threats than the innate immune system, in part sequester and target the cation for bacterial use [20], or by expressing iron storage [21] or transport threats. The adaptive immune system is the one that because it is much more specific in its response to proteins [22]. Lastly, many bacteria improve their humans rely on when receiving vaccinations in order intraphagosomal survival by mounting a vigorous stress response to dispose of and replace damaged smallpox or numerous other infectious diseases [27]. to avoid becoming ill in the future with influenza, proteins [23]. Although most bacteria use one or The adaptive immune system is also responsible more of these resistance mechanisms, only a select again become infected with chicken pox, for example, group of bacteria are ‘professional’ intracellular becausefor the confidence they were asick person with has it whenthat they they will were never six pathogens. These species survive and replicate years old. In this second kind of immune system, antimicrobial factors. To accomplish this feat, such inside phagocytes, effectively avoiding attack by their an antigen, either through illness or vaccination. That pathogens have evolved multiple strategies towards there is a first exposure to an infectious agent, called one common goal: to perturb phagosomal maturation recognize the antigen. If the antigen invades another timefirst exposurein the future, teaches receptors the adaptive on theimmune surface system of the to the mechanisms used by Mycobacterium tuberculosis. antigen will trigger a series of immune responses Mycobacteria[24]. These different are most strategies usually found are exemplifiedas Bacilli, orby rod-shaped bacteria. Their cell walls are surrounded Phagocytes, however, are primarily involved in the by thick waxy coat, which protects them in harsh innatetailor-made immune for system that [28].specific strain of infection. environments. Sometimes, they shed their cell wall. In this case they are known as the Spheroplast form of The First Line of Defense the bacteria [25]. Mycobacteria are extremely hardy. They are highly resistant to germicides, because against pathogens as part of the innate immune of their thick protective cell wall. They are highly system,Before the the phagocytesbody uses a becomeless costly involved line of defensein the fight that resistant to drying, and can exist outside the body consists of physical barriers and chemical barriers. without moisture for long periods [24]. This organism The environment is full of toxins and infectious parasitize host cells by arresting or reprogramming agents in the air, water and food. There are a number phagosomal maturation, by escaping maturing of physical barriers in the human body that block or phagosomes or by withstanding the microbicidal expel invaders. For example, both mucus membranes properties of the phagolysosome [25]. and hairs in the nostrils prevent debris, pathogens and pollutants from entering the airways [29]. The The Human Immune Systems Like other vertebrates, humans have two types of urine, through the urethra. The skin is coated with a body flushes toxins and microbes out of the body in immune systems for protection against pathogens. One thick layer of dead cells that block pathogens from of the immune systems is called the innate immune entering through pores. This layer sheds frequently, system. The innate immune system is also present other pathogens clinging to the dead skin cells [30]. in most other life forms. In vertebrates, this system which effectively removes any potential microbes and employs phagocytes as one of its lines of defense. The innate immune system is called that because of defense in the innate immune system; the other the instructions for its operations are written into armThe physicalconsists barriersof chemical make barriers. up one These arm of chemicals the first line are substances in the body that break down microbes and the beginning of an individual’s life, and it reacts to other pathogens before they can cause harm. Acidity pathogensspecies’ genetic that have codes. been This around system for is millennia. effective Thisfrom on the skin from oils and sweat prevent bacteria from is in contrast to the adaptive, or acquired, immune growing and causing infections. The highly acidic 32 Archives of Immunology and Allergy V1 . I2 . 2018 Mycobacterium Tuberculosis Resitance Mechanisms to Bactericidal Activity of Phagocytes: A Review gastric juice of the stomach kills most bacteria and or the respiratory burst and anaerobically, i.e. without other toxins that might be ingested – and vomiting using oxygen. One way to kill the microbe without acts as a physical barrier to remove pathogenic agents oxygen is by using a chemical that deprives the such as “food poisoning,” as well. Working together, the microbe of iron, thus preventing it from metabolizing. ever-vigilant chemical and physical barriers do a great Another way is to increase the acidity of the internal deal to keep out many of the microscopic dangers of environment of the phagocyte [28]. the environment that attempt to enter the body and cause harm [28]. When these tasks are complete, the Macrophages have one further task to complete. They return to the lymph The Phagocytes nodes, displaying the remnants of the destroyed Phagocytes are the soldiers of the immune system, and provide
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