Paper on The Immune System

The Immune System Introduction The immune system refers to the complex system composed of cells, tissues, and collection of molecules that functions together in fighting infections and other foreign microorganisms invading the human body. Ideally, the human immune system is responsible for defending the body against harmful agents. An antigen is any foreign substance that enters the body and is perceived as a threat to the immune system (Immune System, 2017). When antigens enter the body, the immune system initiates a defense mechanism to destroy the disease-causing agents. The immune system comprises two subsystems including the innate and the adaptive immune systems, and they function collaboratively to guarantee the whole-body immunity that is imperative for survival. Composition The immune system has various components that circulate within the body’s blood system. The entire components can be classified into cells as well as soluble proteins. Cells occur in three categories comprising of lymphocytes, granulocytes, and lastly, macrophages also called monocytes (Immune System, 2017). On the other side, proteins are primarily composed of antibodies also known as immunoglobulin, protein cytokines, and interleukins. For a robust immune response, the immunoglobulin works alongside complimentary proteins (Immune System, 2017). The complement proteins bind to a complex compound formed by the antibody-antigen reactions, and improved processes such as phagocytosis that is initiated by the cells within the immune system. Cells of the Immune System Lymphocytes. They are regarded as the most crucial cells of the immune system. Lymphocytes are broadly classified into three populations or types including the B lymphocytes, T lymphocytes, and the natural killer cells. These various types of cells function differently for the effectiveness in the process of destroying antigens (Immune System, 2017). The formation of lymphocytes occurs in the bone marrow where some develop into B-cells while others move to thymus gland and morph into T lymphocytes (Bledsoe, 2007). In addition, they are composed in different percentages within the blood system. In particular, lymphocytes are responsible for storing memory of previous antigens or substances that attack the body, and they recall and identify invaders in case of another attack. B lymphocytes. They are responsible for generating antibodies and notifying T-cells in case of an attack. B lymphocytes play a role in the humoral immune response in the sense that they work together with plasma cells (their direct descendants) in producing the immunoglobulin proteins (blood-serum antibodies) (Immune System, 2017). Therefore, any time the body is attacked by foreign materials or antigens, the B lymphocytes generate antibodies that counter the antigen. It is worth noting, every single B-cell creates a specific antibody against a specific disease-causing microorganism. For example, an antibody against pneumonia is produced by a unique B-cell. T lymphocytes. They usually destroy cells that get compromised within the body, and at the same time alerts leukocytes. Simply, T-cells are accountable for cellular immunity. They directly attack and destroy antigens. Noticeably, the T lymphocytes regulate other components within the immune system either by increasing or suppressing the entire immune response (Bledsoe, 2007). Additionally, they are also associated with secretion of cytokines, a defensive blood protein. Statistically, they comprise 70% of the lymphocytes while the B and Natural killer cells make up the remaining 30% (Immune System, 2017). T cells occur in various types such as helper T cells that coordinate the immune response, and the killer T cells that raids viruses and other unnecessary cells (Immune System, 2017). Biochemically, B and T lymphocytes can remember previous exposures or attacks by specific antigens. This involves lymphocytes recognizing antigens that had formerly attacked the body leading to rapid destruction after a repeated invasion. Natural killer cells. They are also known as the killer cells, K-cells, or NK cells. Natural killer cells create the innate or inborn immune system. Principally, the NK cells are cytotoxic lymphocytes that directly destroy infected cells (Totsch & Sorge, 2017). In addition, they identify worn out cells that should be exterminated and initiate non-specific responses using chemicals. Eventually, the unwanted cells die as the Killer cells’ chemicals trigger the formation of pores in the infected cells plasma membrane. Mononuclear Phagocytes. They exist as either monocytes-macrophages. The mononuclear phagocytes make up the mononuclear phagocytic system (MPS) in the immune system (Immune System, 2017). The monocytes, as well as the macrophages, have their derivation from the bone marrow and most precisely precursor cells. After they are released into the blood circulatory system, they occupy the lymph nodes and the spleen. Monocytes. They are single-nucleated white blood cells (WBC) that differentiate into tissue macrophages when outside the blood system. They mainly work to boost the innate immune response. Even though they form the largest percentage of leukocytes, WBC, they occupy just a small percentage of total blood cells (Immune System, 2017). Monocytes are also associated with the effectiveness of the immune response in the sense that they help in modifying antigens making them easily digestible. Normally, they physically and morphologically mutate into macrophages when localized in the tissues outside of the blood circulation system. Macrophages. They form the other part of the MPS, mononuclear phagocytic system. Manifestly, macrophages function similarly to granulocytes by ingesting through phagocytosis. Phagocytosis is the process where a cell engulfs and digest infected or unwanted cells that are known as tissue debris (Immune System, 2017). Some of the tissue debris includes cancer cells, antigens, microbes, and other non-specific proteins that do not aid the body defense unit. The mode of operation for macrophages involves attaching to antibodies and protein complements thereby ingesting foreign materials(debris). Additionally, macrophages tend to transport potent enzymes to their respective areas of operation such as cytoplasm. Granulocytes. They are nucleus-containing blood cells. Predominantly, granulocytes are known for their phagocytizing tendency that aids in the digestion of antigens. They are made up of enzymes that destroy engulfed foreign materials (Immune System, 2017). There are three primary categories of granulocytes including basophils, neutrophils, and eosinophils. Together, they also form the innate immune response. Neutrophils. They for the greatest population of granulocytes. As indicated before, their work is to engulf and ingest foreign substances. They can destroy 5 to 20 bacteria in their entire lifetime. Eosinophils. They mainly participate in allergic inflammations. Similarly, they help in fighting multinuclear parasites. Basophils. Similar to eosinophils, they engage in allergic reactions. They react by producing histamine that elicits inflammation. Basophils also produce heparin, a protein responsible for inhibiting the formation of blood clots. Soluble Factors The immune system is comprised of three protein types that are soluble. The immune-related proteins dissolve in serum, usually the liquid part of blood. Earlier, it became manifest that the three kind of soluble proteins that boosts the immune response encompasses antibodies, cytokines, and lastly, complement proteins (Totsch & Sorge, 2017). Phenomenal scientists believe that thousands of protein strains exist in the form of antibodies. Various immunoglobulin proteins bind to specific complementary antigens pursuing to eliminate the foreign objects from the body (Immune System, 2017). Typically, the cytokines, immunoglobulin proteins, and complement proteins work collaboratively with other types of white blood cells to reinforce the body’s defense mechanism that exemplifies the whole immune system. Cytokines. Refer to a huge population of proteins or glycoproteins derived from specific WBCs in the immune system. Thus, cytokines are considered as hematopoietic cells, meaning they are precursor cells for other blood cells. Some cytokines include interleukins, monokines, interferons, lymphokines, and chemokines among others. Cytokines can either function by inducing inflammation or alleviating it. Both the inflammatory and anti-inflammatory cytokines play a critical role in improving the interaction between other immune cells. As such, they are soluble and have different roles based on their interaction with other defense cells to create immune-response factors. Complement proteins. As the name suggests, they coordinate with antibodies or immunoglobulin proteins for a strong immune response. They enhance the complex substance formed between immunoglobulin and antigens. By binding to the antibody-antigen compound, complement proteins facilitate ingestion of foreign materials through phagocytosis. Antigens. An antigen refers to a foreign molecule that triggers secretion of complimentary antibodies when introduced in the body. Antigens tend to stimulate immune response as they are detected as threats to the body (Newman & Murrell, 2018). Chemically, an antigen consists of conjugated glycoproteins, lipoproteins, and even nucleoproteins. Figure 1: Antigen-Antibody Binding Sites Structure. The structure of an antigen consists of epitopes commonly called antigenic determinants and antigen components that occur on the cell wall. Epitopes refer to discrete sites on a foreign substance’s macromolecule. Characteristically, the epitope sites are understood to be immunologically active. Hence, they easily bind membranes that are antigen-specific. Every antigen has numerous epitopes that act as the binding elements that form a link with antibodies. Immunoglobulin has a Y shape with two arms that attach to two different cells (Jain, 2018). When an antigen connects to an antibody they form a key and lock analogy structure. Fig 2 & 3: Images of Epitopes and Antigen-antibody Binding Sites (Jain, 2018). Types of antigens. Antigen can be categorized based on their capacity to function as expected, and these include complete as well as incomplete antigens. A complete antigen can inherently trigger production of a unique antibody for countering the antigen-effect through antigen-antibody reaction. Contrariwise, an incomplete (hapten) lacks the capacity to independently stimulate the formation of a countering antibody (Newman & Murrell, 2018). However, haptens can potentially elicit antibody production when joined with carriers or large protein molecules. Furthermore, some antigens occur on body cells and are known as auto-antigens or even self-antigens. On the contrary, foreign antigens come from outside the body and are referred to as non-self cells. Another notable typology is H antigen that occurs on the red blood corpuscles (Newman & Murrell, 2018). The H antigen is associated with the production of A and B antigens that correspond to the ABO blood groups. The other known type of antigen is named on the grounds of its stimulation and biding cells. For example, the T dependent antigen (Td-Ag) that relies on helper T-cell and activation of B-cell. Td-Ag oversees activation of B-cell that consequently proliferates forming many plasma cells as well as memory cells that detect similar antigen in future. Likewise, there exists a T independent antigen (Ti-Ag) that refers to an antigen that directly excites B-cells without needing the T-cells’ co-stimulation (Jain, 2018). The Ti-Ag forms a crosslink with antigen receptors found on the B-cell membranes; hence, activating them. Lastly, another common category antigen is the super antigen (SAg) (Jain, 2018). In this category, an enormous immune response occurs resulting from polyclonal activation of T-cells. Fig 3 & 4: Showing Normal and Super-antigen’s activation of T Lymphocytes (Jain, 2018). Antibodies. An antibody or immunoglobulins refer to proteins generated by the body to fight infection-causing microorganisms and antigens. Apparently, antibodies are manufactured in response to an attack by foreign bodies or internal harmful elements. The functionality of immunoglobulin proteins depends on how they attach to the antigen igniting the defense process. Structure. Naturally, an antibody molecule is Y-shaped (Jain, 2018). The binding sites of an antibody are the two arms of the Y structure. As previously seen, every antibody is unique and binds to only its complementary antigen. The uniqueness of the antibody’s arms ensures it matches to only a specific antigen that can fit into the shapes effortlessly. Types of Antibodies. Antibodies are classified into distinct subgroups with unique tasks. The five major classes comprise the IgG, IgA, IgD, IgM, and IgE. Immunoglobulin is customarily symbolized by letters “Ig” which also implies to an antibody (Jain, 2018). The most prevalent and vital immunoglobulin is the IgG that prevents bacterial invasion. IgG binds to virus and bacteria facilitating digestion by relevant immune cells after having been engulfed. Most body fluids such as tears, mucus, saliva, as well as, secretion made from the gut, reproductive, urinary, and respiratory tracts, contain the IgA (Jain, 2018). IgM is also specialized in killing bacteria (Jain, 2018). IgE is accountable for allergies along with protection from parasitic attacks. IgD initiates the immune response as it is linked to B lymphocytes. Immune Response A robust immune response depends on the coordination between the key components of the immune system. Ideally, the response occurs chronologically from the time a foreign element is detected in the body. The first phase of identification of disease-causing antigen starts from granulocytes and monocytes. At this stage, the antigen becomes neutralized through the effects of antibodies and the related complement proteins. Then, lymphocytes and macrophages enter the invasion site to strengthen the immune reaction. Again, highly-specialized antibodies get created and establish memory of the attacking pathogen or antibody. The response goes hand in hand with other potential reactions that occur near lymph nodes heightening the intensity of the defense. Eventually, the invading virus, disease, bacteria, and other pathogens become smothered and completely suppressed. Immunity As previously indicated, the innate and the adaptive immune systems form the primary components of the human immune system. The innate immune system refers to the in-born defense mechanism that helps to identify antigens or harmful foreign materials attacking the body. On the other side, the adaptive immune structure is customarily acquired after exposure to infection. Adaptive, acquired, or the specific immune system plays several fundamental roles encompassing reaction to pathogens and, at the same time, it prepares the body for future attacks. The core reason behind future responses to attacks are because it keeps memory in case of pathogenic invasions. Typically, innate together with the adaptive immune systems work to ensure the body is safe from a disease-causing microorganism. Immunity can be described as the state of protection against disease-causing microorganisms. In other words, immunity is the ability of the body to fight or resist infections. Immunity could be classified into innate immunity and adaptive immunity. For a robust immunity, the innate system is made up of cell-mediated response comprising the T cells, phagocytes, along with cytokines. Besides, the innate resistant structure has a humoral response mechanism made of extracellular fluid molecules. On the other hand, the adaptive immune system has T cells in its cell-mediated immunity. The humoral immunity of the adaptive system consists of antibodies formed by B cells in the extracellular fluid. Types of Immunity Innate Immunity Innate immunity refers to the type of immunity that a person is born with through immunologic memory. Chiefly, the innate resistance describes the anatomical or physical barriers in first-line defense against antigens. Examples of physical barriers include the skin and mucous membranes (Totsch & Sorge, 2017). This response cannot be modified, and thus, do not defend the body from internal attacks. The physiological barriers entail the cellular conditions including temperature, low pH, soluble proteins, and chemicals such as lysozymes, peroxidases, interferons, defensins, and collectins (Totsch & Sorge, 2017). They act as complementary elements in the binding process while facilitating pathogens digestion. The phagocytic or the endocytic blockages comprise the phagosomes, monocytes, neutrophils, macrophages, and pinocytosis (Totsch & Sorge, 2017). All these cells complement each other in ensuring complete ingestion of foreign materials. Lastly, the inflammatory barricades refer to the inflammation-mediated reaction that occurs through vasodilation, capillary permeability increase, and influx phagocytes. Customarily, inflammation response occurs during necrotic tissue death. Apoptosis or programmed cell death occurs and leaves cells like phosphatidyl serine exposed (Totsch & Sorge, 2017). Thus, they are detected as infectious material for phagocytosis. Adaptive Immunity The adaptive immunity occurs from stimulation by microbes or foreign substances that attack the body in life. The response arises from the lymph nodes, spleen, as well as, the tissues of mucosa-related lymphoids. These antigens eventually lead to an immune reaction. The idea behind adaptive resistance is that the body develops a memory after first exposure either through vaccination or disease attack (Totsch & Sorge, 2017). Again, a library of immunoglobulin proteins is created that reminds the defense system upon another attack. Adaptive immunity is characterized by the antigen specificity, diversity, immunologic memory, self, and non-self-recognition (Totsch & Sorge, 2017). Through this mechanism, the immune system can readily react whenever antigens get attached to receptors found in innate or even acquired resistance. As a result, the body stays ready and alert in case any harmful or suspicious substances provokes the immune system. Types of adaptive immunity. Can be divided broadly into humoral immunity and cell-mediated or cellular responses. Usually, the adaptive immunity entails dormant components that get stimulated leading to subsequent reaction (Totsch & Sorge, 2017). The duration of an innate mechanism ranges between days and weeks. Humoral immunity. Antibody-mediated kind of immunity that is made up of mainly B-cells. B-cells aid in recognizing antigens. First, T-cell initiates activation of B-cells that differentiate or morph forming plasma cells (Totsch & Sorge, 2017). Ultimately, the plasma cell produces massive numbers of immunoglobulins that keep memory after exposure. Cellular immunity. Often, known as cell-mediated immunity that involves the reaction between T-cells in coordination with their respective effector products. The helper T-cells, as well as cytotoxic T-cells, are commonly involved. The role of helper T-cells is to facilitate the innate response (Totsch & Sorge, 2017). The above process happens through the production of chemicals that enhance other structures, for example, B-cells. On the other hand, Cytotoxic T-Cells eliminate antigens directly. In particular, T-cells are regarded as immunosuppressive (Totsch & Sorge, 2017). They also manufacture CD4+ that represents a cluster of differentiation availability or presence on the surface of a cell. The core reason is that helper T cells, Th-1, Th-2, and Th-17 are responsible for expressing CD (cluster of differentiation) (Totsch & Sorge, 2017). Briefly, they boost the innate response whereby B-cells detect antigens that are intact, and T-cells section the antigens. Antigen-Antibody Interactions The antigen-antibody reaction occurs between antibodies and antigens that are detected as foreign material. The process secures the body from infection-causing microorganisms and even pathogenic attacks. Affinity refers to the degree of antigen-antibody attraction. Avidity refers to the strength of having multiple affinities. Cross-reactivity occurs when different species react with each other. Agglutination may occur after cross-link between antibodies and clumping cell particles. The Ig's produced by B cells in blood can react with high-affinity molecules forming a stable compound (Schuurman, van Loveren, Kuper, Kimber & Vos, 2003). The Ag-Ig complex is then removed from the blood and transported to cellular regions for deactivation. It is worth noting that the high-affinity complex can block blood vessels leading to suffocation or even death under severe cases. Antibody-Mediated Effector Functions Antibodies perform a range of activities such as response- effector-functions for effectively, recognizing, killing, and removing or clearing of death materials. Some strain of antibodies such as neutralizing antibodies (NAb) perform neutralization of antigens to minimize the severity of infections by binding to the cell before an antigen binds (Ochoa, Minute, Rodriguez, Garasa, Perez?Ruiz, Inogés & Berraondo, 2017). Also, agglutination reaction is the clumping of cells emanating from reaction of the antibody with particulate antigens. Opsonization is the process where phagocytes target to kill bacteria or other particles within the immune system (Jiravanichpaisal, Lee & Söderhäll, 2006). Activation of the complement is a specific immune response requiring formation of antigen-antibody complexes for stimulation. Antibody-dependent cell-mediated cytotoxicity, ADCC refers to the situation where immune system cells vigorously lyse cells that have specific antibodies binding to their membrane-surface antigens (Teillaud, 2012). Neonatal immunity explains the state in which newborns gets exposed to a harsh environment and starts developing an independent immunity based on exposure. The Major Histocompatibility Molecules Class, I MHC molecules is among the primary categories of major histocompatibility complex molecules that exist on nucleated cells’ cell surface (Pandey, 2007). MHC class one is useful in studying the function of antigen presentation pathway in providing a signal for virus attack to the immune system. Class II MHC molecules occur only on cells that present antigens or rather antigen-presenting cells (Pandey, 2007). For example, monocytes, macrophages, dendritic, and B cells among others. Class III MHC molecules have a high density of genes that have a role in the component’s levels of complement proteins within the immune system. Antigen Processing and Presentation Antigen processing entails and immunological procedure for preparing antigens that are then presented to T lymphocytes, immune system’s special cells. On the other hand, antigen presentation entails presenting antigen to lymphocytes as short peptide fragments (Cresswell, 2005). Thus, antigen processing and presentation refers to the process whereby proteins are digested by antigen-presenting cells either endogenously or exogenously; then, the resultant peptide fragments are displayed in MHC cell surface for recognition by the T cells. Antibody-Dependent Effector Mechanism against Infectious Agents and Parasitic Infestations Ideally, microbes exploit the envelope on cell walls and penetrate into the cell. Neutralization of microbes occurs when antibodies attach to microbes and microbial toxins to prevent them from obtaining entry into host cells. In contrast, microbial toxins that bind on host cells are blocked by antibodies that fight toxins. A good example is Emil von Behring that counters diphtheria toxin. Opsonization is the phenomenon where phagocytes target bacteria and kill them before they invade the host (Jiravanichpaisal, Lee & Söderhäll, 2006). Phagocytosis is the process of phagocytes and tissue macrophages engulfing microorganism such as bacteria and digest them using a lysosomal enzyme. Antibody-dependent cell cytotoxicity refers to a series of strategies aimed at preying IgG coated cells particularly of the proper subcategories using the cell-to-cell cytolysis. The process is frequently performed by immune cells exhibiting FcRIIIA (CD16A) Microbial Mechanism for Escaping Host Defenses Some microbial organisms evading the complement system through their inherent abilities to repel bactericidal mechanism in the host. For instance, Bacillus anthracis have poly-D-glutamate capsule for defending itself against cell breakdown that is normally caused by cationic proteins occurring in phagocytes (Todar, 2018). Others can resist phagocytosis using evading techniques such as blocking and interrupting phagocyte’s activities at different stages. Hence, the phagocyte becomes unable to complete the engulfing and ingesting processes. Several bacteria including Bacillus anthracis and Mycobacterium tuberculosis survive inside phagocytic cells due to resistance against obstruction or killing by host’s lysosomal contents (Todar, 2018). Furthermore, some microbial organisms evade the specific immune responses completely so that they are not caught up by the immune response. In fact, some pathogens have clever timing such that they escape phagosome vacuole before digestive enzymes are released. References Bledsoe, K. (2007). The Immune System. Logan, Iowa: Perfection Learning. Cresswell, P. (2005). Antigen processing and presentation. Immunological reviews, 207(1), 5-7. Immune System. (2017). Funk & Wagnalls New World Encyclopedia, 1p. 1. Jain, K. (2018). Antigens in the body: Definition, types, and structure. Retrieved from http://www.biologydiscussion.com/antigens/antigens-in-body-definition-types-and-structure/1437 Jiravanichpaisal, P., Lee, B. L., & Söderhäll, K. (2006). Cell-mediated immunity in arthropods: hematopoiesis, coagulation, melanization, and opsonization. Immunobiology, 211(4), 213-236. Newman, T., & Murrell, D. (2018). The immune system: Cells, tissues, function, and disease. 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