Humoral immunity depends on lymphocytes to confer protection against infection through antibody-mediated functions , but it is not the only form of adaptive immunity that involves bone marrow lymphocytes. What is humoral immunity? Humoral immunity is an antibody-mediated response that occurs when foreign material - antigens - are detected in the body.
This foreign material typically includes extracellular invaders such as bacteria This mechanism is primarily driven by B cell lymphocytes , a type of immune cell that produces antibodies after the detection of a specific antigen.
What is an antibody? Antibodies are heavy proteins that are approximately 10 nanometers in size. These molecules are produced by B cells in order to identify and neutralize harmful agents such as infectious bacteria, fungi, and viruses.
These Y-shaped proteins contain antigen-binding sites that specifically bind to their target antigens. Instead, the cellular immune response must take over. Lymphocytes of the adaptive immune response must interact with antigen-embedded MHC class II molecules to mature into functional immune cells. The T H lymphocytes function indirectly to tell other immune cells about potential pathogens, while cytotoxic T cells T C are the key component of the cell-mediated part of the adaptive immune system which attacks and destroys infected cells.
T C cells are particularly important in protecting against viral infections because viruses replicate within cells where they are shielded from extracellular contact with circulating antibodies.
Once activated, the T C creates a large clone of cells with one specific set of cell-surface receptors, similar to the proliferation of activated B cells.
The resulting active T C cells then identify infected host cells. T C cells attempt to identify and destroy infected cells by triggering apoptosis programmed cell death before the pathogen can replicate and escape, thereby halting the progression of intracellular infections. To recognize which cells to pursue, T C recognize antigens presented on MHC I complexes, which are present on all nucleated cells.
MHC I complexes display a current readout of intracellular proteins inside a cell and will present pathogen antigens if the pathogen is present in the cell. T C cells also support NK lymphocytes to destroy early cancers. Cytokines are signaling molecules secreted by a T H cell in response to a pathogen-infected cell; they stimulate natural killer cells and phagocytes such as macrophages.
Phagocytes will then engulf infected cells and destroy them. Cytokines are also involved in stimulating T C cells, enhancing their ability to identify and destroy infected cells and tumors.
A summary of how the humoral and cell-mediated immune responses are activated appears in. Depending on the cytokines released, this activates either the humoral or the cell-mediated immune response. Regulatory T cells are a subset of T cells which modulate the immune system and keep immune reactions in check. Regulatory T cells are a component of the immune system that suppress immune responses of other cells.
These cells are involved in shutting down immune responses after they have successfully eliminated invading organisms, and also in preventing autoimmunity. CD25 is a component of the IL2 receptor : Interleukin 2 receptor is composed of three subunits alpha, beta, and gamma. CD25 constitutes the alpha chain of the IL2 receptor. The contribution of these populations to self- tolerance and immune homeostasis is less well defined.
An additional regulatory T cell subset, induced regulatory T cells, are also needed for tolerance and suppression. Though iTreg and nTreg cells share a similar function iTreg cells have recently been shown to be an essential non-redundant regulatory subset that supplements nTreg cells, in part by expanding TCR diversity within regulatory responses. Acute depletion of the iTreg cell pool in mouse models has resulted in inflammation and weight loss.
The contribution of nTreg cells versus iTreg cells in maintaining tolerance is unknown, but both are important. Epigenetic differences have been observed between nTreg and iTreg cells, with the former having more stable Foxp3 expression and wider demethylation.
T lymphocytes have a dual specificity: they recognize polymorphic residues of self major histocompatibility complex MHC molecules, which accounts for their MHC restriction; they also recognize residues of peptide antigens displayed by these MHC molecules, which is responsible for their specificity.
Clones of T cells with different specificities express different TCRs. The biochemical signals that are triggered in T cells following antigen recognition are transduced not by the TCR itself, but by invariant proteins CD3, and zeta , which are non-covalently linked to the antigen receptor to form the TCR complex. The physiologic role of some accessory molecules is to deliver signals to the T cells that function in concert with signals from the TCR complex to fully activate the cell.
The antigen receptor of MHC-restricted CD4 helper T cells and CD8 cytolytic T cell is a heterodimer consisting of two transmembrane polypeptide chains, designated alpha and beta, covalently linked to each other by disulfide bonds. Each alpha and beta chain consists of one variable domain V , one constant domain C , a hydrophobic transmembrane region, and a short cytoplasmic region.
The V regions of the TCR contain short stretches of amino acids where the variability between different TCRs is concentrated, and these form the hypervariable or complementarity-determining regions CDRs. Prion-affected tissue : This micrograph of brain tissue reveals the cytoarchitectural histopathologic changes found in bovine spongiform encephalopathy. The presence of vacuoles, i. T cell receptor : T cell receptor consists of alpha and beta chains, a transmembrane domain, and a cytoplasmic region.
Adaptive immunity is stimulated by exposure to infectious agents and recruits elements of the immunoglobulin superfamily. Describe the role of immunoglobulins in the adaptive immune response, specifically in humoral immunity.
Adaptive immunity is stimulated by exposure to infectious agents and increases in magnitude and defensive capabilities with each successive exposure to a particular microbe.
The components of adaptive immunity are lymphocytes and their products. There are two types of adaptive immune responses: humoral immunity and cell-mediated immunity. These are driven by different elements of the immune system and function to eliminate different types of microbes. Antibodies or Immunoglobulins bind antigens in the recognition phase and the effector phase of humoral immunity.
Immunoglobulins are produced in a membrane -bound form by B lymphocytes. These membrane molecules function as B cell receptors for antigens. Because passive immunity is short-lived, vaccination is often required shortly following birth to prevent diseases such as tuberculosis, hepatitis B, polio, and pertussis; however, maternal antibodies can inhibit the induction of protective vaccine responses throughout the first year of life. This effect is usually overcome by secondary responses to booster immunization.
Passive immunity is also provided through the transfer of IgA antibodies found in breast milk, which are transferred to the gastrointestinal tract of the infant, protecting against bacterial infections until the newborn has produced enough matured B cells to synthesize its own antibodies.
Artificially-acquired passive immunity is a short-term immunization achieved by the transfer of antibodies, and can be administered in several forms: as human or animal blood usually horse plasma or serum, as pooled human immunoglobulin for intravenous IVIG or intramuscular IG use, and as monoclonal antibodies MAb.
Passive transfer is used to help treat those with immunodeficiency and for several types of severe acute infections that have no vaccine, such as the Ebola virus.
Immunity derived from passive immunization lasts for only a short period of time, and there is potential risk for hypersensitivity reactions and serum sickness, especially from gamma globulin of non-human origin. Passive immunity provides immediate protection, but the body does not develop memory; therefore, the patient is at risk of being infected by the same pathogen later.
Innate and adaptive immunity in the immune system : This chart depicts the different divisions of immunity, including adaptive, innate, natural, artificial, passive maternal , active infection , passive antibody transfer and active immunization. Privacy Policy. Skip to main content. Immune System.
Search for:. Cell-Mediated Immune Response. Clonal Selection and T-Cell Differentiation Antigens are selected to form clones of themselves, both memory and effector. Learning Objectives Describe clonal selection and T cell differentiation. Key Takeaways Key Points All T cells originate from hematopoietic stem cells in the bone marrow and generate a large population of immature thymocytes. Clonal selection is used during negative selection to destroy lymphocytes that may be able to bind with self antigens.
Clonal selection is the theory that specific antigen receptors exist on lymphocytes before they are presented with an antigen due to random mutations during initial maturation and proliferation. After antigen presentation, selected lymphocytes undergo clonal expansion because they have the needed antigen receptor. Clonal selection may explain why memory cells can initiate secondary immune responses more quickly than the primary immune response, due to increased binding affinity from clonal expansion.
During T cell differentiation, the naive T cell becomes a blast cell that proliferates by clonal expansion and differentiates into memory and effector T cells. Many subsets of helper T cells are created during T cell differentiation and perform vastly different functions for the immune system. Key Terms Clonal selection : The idea that lymphocytes have antigen-specific binding receptors before they encounter with an antigen, and are selected to proliferate because they have the specific antigen receptor needed during an adaptive immune response.
Specific T-Cell Roles T helper cells assist the maturation of B cells and memory B cells while activating cytotoxic T cells and macrophages. Learning Objectives Distinguish between the different types of T cell roles. Key Takeaways Key Points Helper T cells secrete small proteins called cytokines that regulate or assist in the active immune response by activating other immune cells. They also present antigens to B cells. Cytotoxic T cells TC cells, or CTLs destroy virus-infected cells and tumor cells, and are implicated in transplant rejection and autoimmune disease.
Memory T cells persist long-term after an infection has resolved. Regulatory T cells are crucial for the maintenance of immunological tolerance, because they play a role in suppressing overactive immune responses.
Natural killer NK T cells bridge the adaptive immune system with the innate immune system by producing cytokines and binding to non-MHC or protein bound antigens, such as glycolipids and lipids. Key Terms Natural Killer T cells : A heterogeneous group of T cells that shares properties of both T cells and natural killer NK cells, and recognizes the non-polymorphic CD1d molecule, an antigen-presenting molecule that binds self- and foreign lipids and glycolipids instead of MHC.
Active and Passive Humoral Immunity The humoral immune response is the aspect of immunity mediated by secreted antibodies. Learning Objectives Distinguish between active and passive humoral immunity. Key Takeaways Key Points Passive immunity is the transfer of active humoral immunity in the form of ready-made antibodies from one individual to another.
Naturally-acquired passive immunity includes antibodies given from the mother to her child during fetal development or through breast milk after birth.
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