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Introduction
Basic Immunology and Immunotherapy essentially tackles the most basic concepts of Immunology, specifically the two lines of defense in Immunology, referred to as innate immunity and adaptive immunity. Both mechanisms are complementary in the immune system, carrying out functions in which the other system lacks. Innate immunity is the first, non-specific mechanism in which it functions as the first line of defense to a pathogen entering the body. The innate immune mechanism is antigen-independent, responding to infections based on pattern recognition receptors (PRR). Innate immunity as its immune response covers several cells and processes to perform the elimination of pathogens in the body at a rapid pace. Numerous functions such as degranulation, phagocytosis and antigen presentation are processed by these cells, including phagocytes, mast cells, basophils and eosinophils. Adaptive Immunity is antigen-specific and responds based on the mechanism’s capacity for immunologic memory should the body be exposed to the same pathogen. Critical processes of adaptive immunity depend on the regulated reciprocation of T cells, B cells and APCs. These cells perform functions that develop the immunologic memory of the adaptive immune system, leading to effective immune responses upon recurring pathogens. As the relationship between adaptive and innate immune systems are not mutually exclusive, there is a required synergy for the mechanisms to correlate to one another. This means that defects or malfunction in either system could lead to disorders regarding immunopathology. Some immunopathological disorders such as immunodeficiency, autoimmune diseases, and hypersensitivity reactions are results of such malfunction.
Innate Immunity & Acquired Immunity
Innate immunity
Innate immunity relies on pattern recognition receptors in order to detect antigens and rapidly respond to pathogens with similar characteristics and structures, therefore unique pathogens that don’t fit the criteria of pattern recognition are not detected by innate immunity. Examples of pathogen associated molecular patterns (PAMPs) could be double stranded RNA or bacterial cell wall components (such as liposaccharides). Innate immunity functions by recruiting immune cells to sites of inflammation using cytokine and chemokine production. Another function of innate immunity includes the complement system, which works like a biochemical cascade and enhances phagocytosis (immune cells engulfing cell debris and microbes which can kill pathogens and infected cells through lysis). Immune cells that are involved with innate immunity play a large role in phagocytosis, in which these cells engulf and kill infected microbes . Cells such as phagocytes (neutrophils & macrophages), dendritic cells, mast cells, eosinophils, basophils, natural killer cells (NK), and innate lymphoid cells are all part of innate immunity.
Adaptive Immunity
Adaptive immunity is antigen-dependent and relies on “memory” to detect specific antigens should the body be exposed to the same antigen again. Living organisms are not innately born with adaptive immunity and this mechanism is only acquired through certain experiences that allow the body to be exposed to pathogens, such as infections or vaccination. Unlike innate immunity, adaptive immunity takes far longer to develop when encountering a new pathogen, however as the mechanism responds, the adaptive immune system will “adapt” and enable a faster response if the pathogen is encountered again.
Figure 1; Table of listed cells involved in the immune system
Marshall, Jean S., et al. “An Introduction to Immunology and Immunopathology.” Allergy, Asthma & Clinical Immunology, vol. 14, no. S2, Sept. 2018, www.aacijournal.biomedcentral.com/articles/10.1186/s13223-018-0278-1, 10.1186/s13223-018-0278-1.
T cells and APC’s
T-cells express function with antigen-binding receptors on their membrane, known as the T-cell receptor (TCR)
T-cells require signals or action from dendritic cells, antigen presenting cells or other cells functioning from innate immunity to be able to recognize specific antigens
On APCs (antigen presenting cells), MHC (Major Histocompatibility complex: Surface of APCs which express proteins) showcases fragments of antigens on APCs surface when there is an infected cell from a pathogen
When the MHC-antigen complex activates the TCR, the T-cell secretes cytokines to regulate the immune response, stimulating T-cells to differentiate into cytotoxic T-cells and T-helper cells
Cytotoxic T-cells: involved in destruction of foreign substances and agents, directly killing infected cells
T-helper cells: releases cytokines to activate and recruit different cell types
B cells
B cells can detect antigens directly without the need for APCs and dendritic cells
B cells function by producing antibodies for the body to fight against antigens, allowing them to differentiate into plasma cells or memory B cells.
Memory B cells are long-lived cells that “memorize” past antigens that have infiltrated the body before
Memory B cells respond to infection through producing certain antibodies to eliminate an antigen if re-exposed.
Plasma cells are short lived in comparison, however they produce great amounts of antibodies to protect against pathogens
Antibody-Mediated Immunity vs Cell-Mediated Immunity
Figure 2; Immunoglobulin function table, Marshall, Jean S., et al. “An Introduction to Immunology and Immunopathology.” Allergy, Asthma & Clinical Immunology, vol. 14, no. S2, Sept. 2018, www.aacijournal.biomedcentral.com/articles/10.1186/s13223-018-0278-1, 10.1186/s13223-018-0278-1.
Antibody-mediated immunity
The antibody-mediated immunity is a section of the acquired immune system that the B-cell antibody production mediates. The antibody-mediated immunity begins with the secretion of cytokines, leading to proliferation of B cells and the direction of the antibody needed to be produced for a certain antigen. Once B-cells mature into antibody-secreting plasma cells with the help of IL-6, the plasma cells would secrete antibodies that bind to antigens and flag them for destruction through the complement system (opsonization to phagocytosis to elimination of pathogen). The five major antibodies that mediate this process are:
IgAn (immunoglobulin A)
IgG (immunoglobulin G)
IgD (immunoglobulin D)
IgE (immunoglobulin E)
IgM (immunoglobulin M)
Cell-mediated immunity
Cell-mediated immunity does not include the production of secretion of antibodies against pathogens but rather fight off the pathogen with cells themselves. This type of immunity largely targets phagocytes that have not fully eliminated microbes from themselves, or non-phagocytes that can also be affected. This includes:
Activation of cytotoxic T cells, inducing apoptosis in abnormal cells to avoid proliferation (abnormal cells would have specific antigens bound to its surface based on the type of pathogen)
Activation of NK (natural killer) cells and macrophages, which destroys or engulfs pathogens
Production of cytokines, activating the cells that induce elimination of pathogens
Passive Immunization vs Active Immunization
Passive Immunization
Acquired Immunity can be obtained through Passive immunization, which is applied in the transfer of active humoral immunity. This can be transferred through the placenta in maternal antibodies, or artificially through injection.
Active Immunization
Acquired Immunity can also be obtained through Active immunization. This refers to the production of antibodies when fighting against a particular pathogen or antigen after re-exposure. This can be processed through natural infection or it could be injected through vaccination.
Source
Marshall, Jean S., et al. “An Introduction to Immunology and Immunopathology.” Allergy, Asthma & Clinical Immunology, vol. 14, no. S2, Sept. 2018, www.aacijournal.biomedcentral.com/articles/10.1186/s13223-018-0278-1, 10.1186/s13223-018-0278-1.
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