An immune receptor (or immunologic receptor) is a receptor, usually on a cell membrane, which binds to a ligand (usually another protein, such as cytokine) and causes a response in the immune system.
An immune receptor (or immunologic receptor) is a receptor, usually on a cell membrane, which binds to a ligand (usually another protein, such as cytokine) and causes a response in the immune system.
The main receptors in the immune system are pattern recognition receptors (PRRs), Toll-like receptors (TLRs), killer activated and killer inhibitor receptors (KARs and KIRs), complement receptors, Fc receptors, B cell receptors and T cell receptors. [1]
| Receptor | Bind to [1] | Function [1] |
|---|---|---|
| Pattern recognition receptors (PRRs) (e.g. TLRs, NLRs) | Pathogen-associated molecular patterns (PAMP) | Mediate cytokine production → inflammation → destroying pathogen |
| Killer activated and killer inhibitor receptors (KARs and KIRs) | Avails NK cells to identify abnormal host cells (KAR) or inhibit inappropriate host cell destruction (KIR) | |
| Complement receptors | Complement proteins on e.g. microbes | Allow phagocytic and B cells to recognize microbes and immune complexes |
| Fc receptors | Epitope-antibody complexes | Stimulate phagocytosis |
| B cell receptors | Epitopes | B cell differentiation into plasma cells and proliferation |
| T cell receptors | Linear epitopes bound to MHC | Activate T cells |
| Cytokine receptors | Cytokines | Regulation and co-ordination of immune responses |
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.
Immunology is a branch of medicine and biology that covers the medical study of immune systems in all organisms. In such we can see there is a difference of human immunology and comparative immunology in veterinary medicine and animal biosciences.
The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or T cells mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. The thymus is located in the upper front part of the chest, in the anterior superior mediastinum, behind the sternum, and in front of the heart. It is made up of two lobes, each consisting of a central medulla and an outer cortex, surrounded by a capsule.
Natural killer cells, also known as NK cells or large granular lymphocytes (LGL), are a type of cytotoxic lymphocyte critical to the innate immune system that belong to the rapidly expanding family of known innate lymphoid cells (ILC) and represent 5–20% of all circulating lymphocytes in humans. The role of NK cells is analogous to that of cytotoxic T cells in the vertebrate adaptive immune response. NK cells provide rapid responses to virus-infected cell and other intracellular pathogens acting at around 3 days after infection, and respond to tumor formation. Typically, immune cells detect the antigen presented on major histocompatibility complex (MHC) on infected cell surfaces, triggering cytokine release, causing the death of the infected cell by lysis or apoptosis. NK cells are unique, however, as they have the ability to recognize and kill stressed cells in the absence of antibodies and MHC, allowing for a much faster immune reaction. They were named "natural killers" because of the notion that they do not require activation to kill cells that are missing "self" markers of MHC class 1. This role is especially important because harmful cells that are missing MHC I markers cannot be detected and destroyed by other immune cells, such as T lymphocyte cells.
The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. It is part of the innate immune system, which is not adaptable and does not change during an individual's lifetime. The complement system can, however, be recruited and brought into action by antibodies generated by the adaptive immune system.
Acute-phase proteins (APPs) are a class of proteins whose concentrations in blood plasma either increase or decrease in response to inflammation. This response is called the acute-phase reaction. The acute-phase reaction characteristically involves fever, acceleration of peripheral leukocytes, circulating neutrophils and their precursors. The terms acute-phase protein and acute-phase reactant (APR) are often used synonymously, although some APRs are polypeptides rather than proteins.
In biochemistry and pharmacology, receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems. These signals are typically chemical messengers which bind to a receptor and produce physiological responses such as change in the electrical activity of a cell. For example, GABA, an inhibitory neurotransmitter inhibits electrical activity of neurons by binding to GABAA receptors. There are three main ways the action of the receptor can be classified: relay of signal, amplification, or integration. Relaying sends the signal onward, amplification increases the effect of a single ligand, and integration allows the signal to be incorporated into another biochemical pathway.
Interleukins (ILs) are a group of cytokines that are expressed and secreted by white blood cells (leukocytes) as well as some other body cells. The human genome encodes more than 50 interleukins and related proteins.
The adaptive immune system, also known as the acquired immune system, or specific 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.
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.
In immunology, a Fc receptor is a protein found on the surface of certain cells – including, among others, B lymphocytes, follicular dendritic cells, natural killer cells, macrophages, neutrophils, eosinophils, basophils, human platelets, and mast cells – that contribute to the protective functions of the immune system. Its name is derived from its binding specificity for a part of an antibody known as the Fc region. Fc receptors bind to antibodies that are attached to infected cells or invading pathogens. Their activity stimulates phagocytic or cytotoxic cells to destroy microbes, or infected cells by antibody-mediated phagocytosis or antibody-dependent cell-mediated cytotoxicity. Some viruses such as flaviviruses use Fc receptors to help them infect cells, by a mechanism known as antibody-dependent enhancement of infection.
Co-stimulation is a secondary signal which immune cells rely on to activate an immune response in the presence of an antigen-presenting cell. In the case of T cells, two stimuli are required to fully activate their immune response. During the activation of lymphocytes, co-stimulation is often crucial to the development of an effective immune response. Co-stimulation is required in addition to the antigen-specific signal from their antigen receptors.
Immune tolerance, or immunological tolerance, or immunotolerance, is a state of unresponsiveness of the immune system to substances or tissue that would otherwise have the capacity to elicit an immune response in a given organism. It is induced by prior exposure to that specific antigen and contrasts with conventional immune-mediated elimination of foreign antigens. Tolerance is classified into central tolerance or peripheral tolerance depending on where the state is originally induced—in the thymus and bone marrow (central) or in other tissues and lymph nodes (peripheral). The mechanisms by which these forms of tolerance are established are distinct, but the resulting effect is similar.
In immunology, an immunological synapse is the interface between an antigen-presenting cell or target cell and a lymphocyte such as a T/B cell or Natural Killer cell. The interface was originally named after the neuronal synapse, with which it shares the main structural pattern. An immunological synapse consists of molecules involved in T cell activation, which compose typical patterns—activation clusters. Immunological synapses are the subject of much ongoing research.
The interleukin-2 receptor (IL-2R) is a heterotrimeric protein expressed on the surface of certain immune cells, such as lymphocytes, that binds and responds to a cytokine called IL-2.
The general visceral afferent (GVA) fibers conduct sensory impulses from the internal organs, glands, and blood vessels to the central nervous system. They are considered to be part of the visceral nervous system, which is closely related to the autonomic nervous system, but 'visceral nervous system' and 'autonomic nervous system' are not direct synonyms and care should be taken when using these terms. Unlike the efferent fibers of the autonomic nervous system, the afferent fibers are not classified as either sympathetic or parasympathetic.
Lymphotoxin is a member of the tumor necrosis factor (TNF) superfamily of cytokines, whose members are responsible for regulating the growth and function of lymphocytes and are expressed by a wide variety of cells in the body.
Adrenergic means "working on adrenaline (epinephrine) or noradrenaline (norepinephrine)". When not further qualified, it is usually used in the sense of enhancing or mimicking the effects of epinephrine and norepinephrine in the body.
Immune adherence was described by Nelson (1953) for an in vitro immunological reaction between normal erythrocytes and a wide variety of microorganisms sensitized with their individually specific antibody and complement; erythrocytes were observed to adhere to microorganisms. It was later recognized to occur in vivo.
Killer Activation Receptors (KARs) are receptors expressed on the plasmatic membrane of Natural Killer cells. KARs work together with inhibitory receptors, which inactivate them in order to regulate the NK cells functions on hosted or transformed cells. These two kinds of specific receptors have some morphological features in common, such as being transmembrane proteins. The similarities are specially found in the extracellular domains and, the differences tend to be in the intracellular domains. KARs and KIRs can have tyrosine containing activatory or inhibitory motifs in the intracellular part of the receptor molecule.