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In all vertebrates except Agnatha, B cells and T cells are produced by stem cells in the bone marrow. [6] T cell progenitors then migrate from the bone marrow to the thymus, where they develop further. In an adult animal, the peripheral lymphoid organs contain a mixture of B and T cells in at least three stages of differentiation: [citation ...
Some memory B cells can be activated without T cell help, such as certain virus-specific memory B cells, but others need T cell help. [26] Upon antigen binding, the memory B cell takes up the antigen through receptor-mediated endocytosis, degrades it, and presents it to T cells as peptide pieces in complex with MHC-II molecules on the cell ...
Step 3: A T helper cell binds to the macrophage and becomes an activated T helper cell. Step 4: The activated T helper cell binds to a B cell in order to activate the B cell. Step 5: When the B cells are activated, some B cells turn into plasma cells and are released in the blood, while other B cells become B memory cells that quicken response ...
When B cells and T cells are activated and begin to replicate, some of their offspring become long-lived memory cells. Throughout the lifetime of an animal, these memory cells remember each specific pathogen encountered and can mount a strong response if the pathogen is detected again.
Activated effector T cells can be placed into three functioning classes, detecting peptide antigens originating from various types of pathogen: The first class being 1) Cytotoxic T cells, which kill infected target cells by apoptosis without using cytokines, 2) T h 1 cells, which primarily function to activate macrophages, and 3) T h 2 cells ...
These T cells bind to the MHC II-antigen molecule and cause activation of the B cell. This is a type of safeguard to the system, similar to a two-factor authentication method. First, the B cells must encounter a foreign antigen and are then required to be activated by T helper cells before they differentiate into specific cells. [8]
Co-stimulation of the B cell by activated T cell resulting in its complete activation. Proliferation [note 4] of B cells with resultant production of soluble antibodies. Steps in production of antibodies by B cells: 1. Antigen is recognized and engulfed by B cell 2. Antigen is processed 3. Processed antigen is presented on B cell surface 4.
Activation of T cells without co-stimulation may lead to the unresponsiveness of the T cell (also called anergy), apoptosis or the acquisition of the immune tolerance. [ 3 ] The counterpart of the co-stimulatory signal is a (co-)inhibitory signal, where inhibitory molecules interact with different signaling pathways in order to arrest T cell ...