1. Types of adaptive immunity
1.1. Humoral immunity
1.1.1. Humoral immunity is defence against extracellular microbes and includes the B lymphocytes and antibodies. The purpose of B cells that are activated is to secrete antibodies which are proteins known as immunoglobulins.
1.2. Cell-mediated immunity
1.2.1. Cell-mediated immunity is defence against intracellular microbes and involves the T lymphocytes and cytotoxins. T cells are activated to react directly towards foreign antigens that are on the surface of the host cells.
2. Development of B lymphocytes and T lymphocytes
2.1. Development of B lymphocytes
2.1.1. The production site of B lymphocytes occurs at the bone marrow and is also the place where it matures. Plasma cells is known as effector cells and produce antibodies which are derived from B cells. The process starts off with B cells which then forms plasma cells and eventually as antibodies. The B cells circulate using the bloodstream, lymph nodes and the lymphoid tissues. The B cell contains a molecule known as antibody (Ab); naive B cells interact with an antigen (Ag) that will proliferate and differentiate into plasma and memory cells. Plasma cells does not contain Ab but they secrete Ab however memory cells have Ab on their membranes and remain in resting phase until they have a next encounter with the same Ag.
2.2. Development of T lymphocytes
2.2.1. The T lymphocytes are produced to T proginetor cells in the bone marrow which is then transferred to the thymus where they become mature T cells. The T cells in the thymus develop to become receptors such as T cell receptors (TCRs), CD4 and CD8 receptors. T cells are either T cell receptors, CD4, CD8 never both. T cell receptors identify antigens that are bounded with certain receptor molecules that is known as Major Histocompatibility Complex class 1 (MHCI) and class 2 (MHCII). MHC molecules are membrane-bound surface receptors and is found on antigen-presenting cells such as dendritic cells and macrophages. The purpose of CD4 and CD8 is for cell recognition of the T cells and activation by binding process to either MHCI or MHCII.
3. Keywords
3.1. Proliferation: expand in number of antigen-specific cells.
3.2. Differentiation: conversion of lymphocytes into effective defenders.
3.3. Naive lymphocytes: Mature lymphocytes that are immunologically inexperienced by means that it is not previously recognised or responded to antigens.
4. Activation of Naive T cells
4.1. There are 3 types of activated T cells which includes Helper T cells, Cytotoxic T cells and T regulatory cells. Naive T cells which has antigen receptor CD4+ and will be activated to Helper T cell. The purpose is to recognize and bind the antigens, secrete chemical substance (cytokines) that will stimulate B cells to produce Ab (IgA, IgG and IgE). Naive T cells which has CD8+ will be activated to Cytotoxic T cell and this is done so that it is able to distinguish between foreign and host cells which contains antigens to destroy them. T regulatory cells has CD4 and another receptor CD25. The purpose of these T regulatory cells is to regulate the immune response is deactivated once the pathogen is detected.
5. Antigen and Immunogen
5.1. Antigen is basically substance or molecules that are recognised by the immune system and is usually protein on the surface of the microbe and their by-product such as toxins or chemicals.
6. Introduction to adaptive immunity
6.1. Adaptive immunity is a type of specific immunity which is immunity that is present when it is activated by antigens after exposure to antigens derived from either pathogens or vaccination.
6.2. There are 3 levels to the defense against infections which includes barriers (level 1), non-specific internal defenses (level 2) and specific immune responses (level 3). Level 1 in compromised of the skin and the mucous membranes whereas level 2 has phagocytosis, natural killer cells and body reactions such as fevers and inflammations. Level 3 has 2 types of immunity which is cell-mediated immunity and humoral immunity.
6.3. Adaptive immunity can occur in 2 ways; through specific immunity which is when lymphocytes use receptors that specifically recognise certain antigens and through adaptive immunity/acquired immunity when microbes or their antigens are triggered to pass through the epithelial barrier which occurs when infection happens.
6.4. Adaptive immunity is the 3rd line defense and happens after the 2nd line defense and also has different reactions according to the infections. Adaptive immunity has different cells like lymphocytes and macrophages as well as different organs like thymus and lymph nodes. This type of immunity is slower than non-specific immunity as it takes at least a few days for the response to occur. The reason it is slower is because it recognizes the antigen and then uses stimulation to trigger the lymphocytes to proliferate and differentiate into effector and memory cells.
7. Characteristics of adaptive immunity
7.1. 1-Self nonself recognition occurs when cells or organs has the ability to recognize itself from non-self and responds to the foreign non-self molecules. The body’s self has a self marker which separates it from the non-self molecules which contains antigens. This will ensure which molecules the immune system will get rid off and which the immune system will tolerate.
7.2. 2-Antigen specificity is the ability of the immune system to differentiate between the subtle difference in the antigens and targets certain molecules which is needed rather at random. Innate immune components of the 2nd line defence recognise the markers found on the foreign non-self molecules whereas specific adaptive components are able to identify the specific markers. These antibodies have the ability to distinguish between 2 protein molecules that differ in a single amino acid or have 2 isomers that have the same molecules.
7.3. 3-Immunological memory is the ability of the immunity to recall previous infection regarding the same type of foreign molecules which will result in a response that is more systematic and efficient.
8. Pathways of antigens processing
8.1. Class I MHC pathways converts the cytoplasm in the proteins to peptides which binds the class I MHC molecules for recognition of T and CD8 cells. Class II MHC pathways converts protein antigens that were endocytosed into APC vesicles into peptides that binds class II MHC molecules for CD4 and T cells recognition.
9. Comparison of adaptive immunity
9.1. Humoral immunity
9.2. Cell-mediated immunity
9.2.1. Humoral immunity is provided by B lymphocytes which recognizes protein, polysaccharides, phospholipid and nucleic acid antigens.It acts against soluble or free antigens and provides immunity to extracellular viruses, bacteria and toxins which causes type I,II and III sensitivity.
9.2.2. Cell-mediated immunity is provided by T lymphocytes which can only recognise protein antigens and antigens presented by APCs with class I and II MHC molecules. This immunity does not need Helper T cells to induce antibody production which is able to cause type IV hypersensitivity.