Antibodies are the agents of humoral immunity. An antibody, also known as an immunoglobulin (Ig), is a protein that is produced by plasma cells after stimulation by an antigen. The plasma cells, on the other hand, produce and secrete large quantities, up to 100 million molecules per hour, of antibody molecules. The memory B cells remain inactive at this point, until another later encounter with the antigen, caused by a reinfection by the same bacteria or virus, results in them dividing into a new population of plasma cells. These daughter cells become either plasma cells or memory B cells. The helper T cell binds to the antigen-MHC class II complex and is induced to release cytokines that induce the B cell to divide rapidly, which makes thousands of identical (clonal) cells. The helper T cell must already have been activated through an encounter with the antigen (discussed below). In most cases, the sensitized B cell must then encounter a specific kind of T cell, called a helper T cell, before it is activated. When this process is complete, the B cell is sensitized. When a B cell encounters the antigen that binds to its receptor, the antigen molecule is brought into the cell by endocytosis and reappears on the surface of the cell bound to an MHC class II molecule. Once the B cells mature in the bone marrow, they migrate to lymph nodes or other lymphatic organs. Some B cells are transformed into memory cells, allowing for a faster antibody-mediated immune response upon future infection.\): B cell receptors are embedded in the membranes of B cells and bind a variety of antigens through their variable regions.Įach B cell has only one kind of antigen receptor, which makes every B cell different. B cells change into plasma cells, secreting large quantities of finely tuned antibodies specific to the foreign agent. T cells then bind to the MHC complex on B cells, leading to B cells' proliferation and differentiation. The antigen-MHC II complex allows Th cells to bind to the APC, leading to a proliferation of Th cells and cytokine release. There are two types of MHC molecules: MHC class I, expressed on the surfaces of most cells, and class II, expressed exclusively on APCs' surfaces. The antigen's fragments will appear on the APC's surface attached to a cell surface glycoprotein known as MHC II (major histocompatibility complex). Infectious agent antigens are engulfed and partially degraded by antigen-presenting cells (APCs), such as macrophages, Langerhans cells, dendritic cells, lymph nodes, and monocytes. Learn more about K D and how it affects antibody performanceĪn antibody response is the culmination of a series of interactions between macrophages, T lymphocytes, and B lymphocytes. Avidity measures the overall stability of the complex between antibodies and antigens. Affinity measures the strength of the epitope's binding to an antibody and is often represented by the dissociation constant K D. The region of an antigen that interacts with an antibody is defined as an epitope. The region of the antibody that reacts with the antigen is called the paratope. The antibody-antigen interaction forms the basis of all immunoassays but is also the basis for the immune response. View our poster on human T cell development The specificity of the immune system is impacted by the fact that one cell recognizes only one antigen. All antigen receptors are glycoproteins, and only one kind of receptor is synthesized within any one cell. All three types of lymphocytes carry cell surface receptors that can bind antigens. T h cells are involved in both responses through the release of cytokine proteins. The cell-mediated response involves binding TC cells to foreign or infected cells, followed by the lysis of these cells. B lymphocytes mediate the humoral response by releasing antibodies specific to the infectious agent. The adaptive immune response can be either humoral or cell-mediated. Most functions of the adaptive immune system can be described by grouping lymphocytes into three basic types:īrowse Abcam's products to study adaptive immunity Pathogens bound to antibodies are marked for clearance or destruction. The term antibody is used interchangeably with immunoglobulin. Any molecule that can bind to an antibody is called an antigen. These secreted proteins are known as antibodies. Lymphocytes synthesize cell surface receptors or secrete proteins that specifically bind to foreign molecules. Lymphocytes arise continuously from progenitor cells in the bone marrow. It consists of various cells and molecules, with lymphocytes and antibodies being the key elements. The adaptive immune system is activated when the innate system fails to clear pathogens from the body. The innate immune system's function and efficiency do not change with repeated exposure to foreign pathogens.īrowse Abcam's products to study innate immunity The adaptive immune system
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