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The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, distinguishing them from the organism's own healthy tissue. Many species have two major subsystems of the immune system. The innate immune system provides a preconfigured response to broad groups of situations and stimuli. The adaptive immune system provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use molecules and cells to perform their functions.
An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, parasites, and fungi which could cause serious problems to the health of the host organism if not cleared from the body. There are two distinct aspects of the immune response, the innate and the adaptive, which work together to protect against pathogens. The innate branch—the body's first reaction to an invader—is known to be a non-specific and quick response to any sort of pathogen. Components of the innate immune response include physical barriers like the skin and mucous membranes, immune cells such as neutrophils, macrophages, and monocytes, and soluble factors including cytokines and complement. On the other hand, the adaptive branch is the body's immune response which is catered against specific antigens and thus, it takes longer to activate the components involved. The adaptive branch include cells such as dendritic cells, T cell, and B cells as well as antibodies—also known as immunoglobulins—which directly interact with antigen and are a very important component for a strong response against an invader.
A cytotoxic T cell (also known as TC, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8+ T-cell or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected by intracellular pathogens (such as viruses or bacteria), or cells that are damaged in other ways.
The T helper cells (Th cells), also known as CD4+ cells or CD4-positive cells, are a type of T cell that play an important role in the adaptive immune system. They aid the activity of other immune cells by releasing cytokines. They are considered essential in B cell antibody class switching, breaking cross-tolerance in dendritic cells, in the activation and growth of cytotoxic T cells, and in maximizing bactericidal activity of phagocytes such as macrophages and neutrophils. CD4+ cells are mature Th cells that express the surface protein CD4. Genetic variation in regulatory elements expressed by CD4+ cells determines susceptibility to a broad class of autoimmune diseases.
CD32, also known as FcγRII or FCGR2, is a surface receptor glycoprotein belonging to the Ig gene superfamily. CD32 can be found on the surface of a variety of immune cells. CD32 has a low-affinity for the Fc region of IgG antibodies in monomeric form, but high affinity for IgG immune complexes. CD32 has two major functions: cellular response regulation, and the uptake of immune complexes. Cellular responses regulated by CD32 include phagocytosis, cytokine stimulation, and endocytic transport. Dysregulated CD32 is associated with different forms of autoimmunity, including systemic lupus erythematosus. In humans, there are three major CD32 subtypes: CD32A, CD32B, and CD32C. While CD32A and CD32C are involved in activating cellular responses, CD32B is inhibitory.
A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells, T cells, and B cells. They are the main type of cell found in lymph, which prompted the name "lymphocyte". Lymphocytes make up between 18% and 42% of circulating white blood cells.
Phagocytes are cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. Their name comes from the Greek phagein, "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell", from the Greek kutos, "hollow vessel". They are essential for fighting infections and for subsequent immunity. Phagocytes are important throughout the animal kingdom and are highly developed within vertebrates. One litre of human blood contains about six billion phagocytes. They were discovered in 1882 by Ilya Ilyich Mechnikov while he was studying starfish larvae. Mechnikov was awarded the 1908 Nobel Prize in Physiology or Medicine for his discovery. Phagocytes occur in many species; some amoebae behave like macrophage phagocytes, which suggests that phagocytes appeared early in the evolution of life.
Cell-mediated immunity or cellular immunity is an immune response that does not involve antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
The adaptive immune system, also known as the acquired immune system, is a subsystem of the immune system that is composed of specialized, systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system is one of the two main immunity strategies found in vertebrates.
An antigen-presenting cell (APC) or accessory cell is a cell that displays antigen bound by major histocompatibility complex (MHC) proteins on its surface; this process is known as antigen presentation. T cells may recognize these complexes using their T cell receptors (TCRs). APCs process antigens and present them to T-cells.
Interleukin 12 (IL-12) is an interleukin that is naturally produced by dendritic cells, macrophages, neutrophils, and human B-lymphoblastoid cells (NC-37) in response to antigenic stimulation. IL-12 belongs to the family of interleukin-12. IL-12 family is unique in comprising the only heterodimeric cytokines, which includes IL-12, IL-23, IL-27 and IL-35. Despite sharing many structural features and molecular partners, they mediate surprisingly diverse functional effects.
Interferon gamma (IFN-γ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. The existence of this interferon, which early in its history was known as immune interferon, was described by E. F. Wheelock as a product of human leukocytes stimulated with phytohemagglutinin, and by others as a product of antigen-stimulated lymphocytes. It was also shown to be produced in human lymphocytes. or tuberculin-sensitized mouse peritoneal lymphocytes challenged with Mantoux test (PPD); the resulting supernatants were shown to inhibit growth of vesicular stomatitis virus. Those reports also contained the basic observation underlying the now widely employed IFN-γ release assay used to test for tuberculosis. In humans, the IFN-γ protein is encoded by the IFNG gene.
Gut-associated lymphoid tissue (GALT) is a component of the mucosa-associated lymphoid tissue (MALT) which works in the immune system to protect the body from invasion in the gut.
The innate, or nonspecific, immune system is one of the two main immunity strategies in vertebrates. The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants, fungi, insects, and primitive multicellular organisms.
Lymphopoiesis (lĭm'fō-poi-ē'sĭs) is the generation of lymphocytes, one of the five types of white blood cells (WBCs). It is more formally known as lymphoid hematopoiesis.
Ralph Marvin Steinman was a Canadian physician and medical researcher at Rockefeller University, who in 1973 discovered and named dendritic cells while working as a postdoctoral fellow in the laboratory of Zanvil A. Cohn, also at Rockefeller University. Steinman was one of the recipients of the 2011 Nobel Prize in Physiology or Medicine.
Interferon regulatory factor 4 (IRF4) also known as MUM1 is a protein that in humans is encoded by the IRF4 gene, located at 6p25-p23. IRF4 functions as a key regulatory transcription factor in the development of human immune cells. The expression of IRF4 is essential for the differentiation of T lymphocytes and B lymphocytes as well as certain myeloid cells.
PR domain zinc finger protein 1, or B lymphocyte-induced maturation protein-1 (BLIMP-1), is a protein in humans encoded by the gene PRDM1 located on chromosome 6q21. BLIMP-1 is considered a 'master regulator' of hematopoietic stem cells, and plays a critical role in the development of plasma B cells, T cells, dendritic cells (DCs), macrophages, and osteoclasts. Pattern Recognition Receptors (PRRs) can activate BLIMP-1, both as a direct target and through downstream activation. BLIMP-1 is a transcription factor that triggers expression of many downstream signaling cascades. As a fine-tuned and contextual rheostat of the immune system, BLIMP-1 up- or down-regulates immune responses depending on the precise scenarios. BLIMP-1 is highly expressed in exhausted T-cells – clones of dysfunctional T-cells with diminished functions due to chronic immune response against cancer, viral infections, or organ transplant.
Phagoptosis is a type of cell death caused by the cell being phagocytosed by another cell, and therefore this form of cell death is prevented by blocking phagocytosis.
T independent antigen elicits antibody production by B lymphocytes without T lymphocyte involvement. There are 2 distinct subgroups of TI antigens, different in mechanism of activating B lymphocytes. TI-1 antigen, which has an activity that can directly activate B cells and TI-2 antigen, which has highly repetitive structure and causes simultaneous cross-linking of specific B cell receptors (BCR) on B lymphocyte. The most commonly released isotype of antibodies in this type of immune reaction is low affinity IgM.
References
- ↑ "Pluripotent". Merriam-Webster Dictionary Online. Retrieved 14 March 2015.
- 1 2 Willey, J., Sherwood, L., & Woolverton, C. (2014). Prescott's microbiology. Innate Host Resistance and Adaptive Immunity: McGraw Hill. pp. 723–788. ISBN 978-0073402406.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ↑ Ikeda, H., Old, L., & Schreiber, R. (2002). "The roles of IFN in protection against tumor development and cancer immunoediting". Cytokine & Growth Factor Reviews. 13 (2): 95–109. doi:10.1016/S1359-6101(01)00038-7. PMID 11900986.
{{cite journal}}: CS1 maint: multiple names: authors list (link)