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The discussion that follows now concerns alpha/beta T cells. The TCR (of αβ T-cells) binds a bimolecular complex displayed at the surface of some other cells called an antigen-presenting cell (APC). This complex consists of: a fragment of an antigen lying within the groove of a histocompatibility molecule. The complex has been compared to a ...
Professional APCs specialize in presenting antigens to T cells. [5] They are very efficient at internalizing antigens, either by phagocytosis (e.g. macrophages), or by receptor-mediated endocytosis (B cells), processing the antigen into peptide fragments and then displaying those peptides (bound to a class II MHC molecule) on their membrane. [1]
The immune system identifies and attacks "non-self" external antigens. Antibodies usually do not react with self-antigens due to negative selection of T cells in the thymus and B cells in the bone marrow. [5] The diseases in which antibodies react with self antigens and damage the body's own cells are called autoimmune diseases. [6]
The universal structure of antibody includes the constant regions part of the fragment crystallizable(Fc) region of the antibody (shown in dark blue). It also includes the fragment antigen binding which is composed of one heavy and one light chain (shown as L for light and H for heavy).
Because T cells recognize only fragmented antigens displayed on cell surfaces, antigen processing must occur before the antigen fragment can be recognized by a T-cell receptor. Specifically, the fragment, bound to the major histocompatibility complex (MHC), is transported to the surface of the antigen-presenting cell, a process known as ...
Complementarity-determining regions (CDRs) are polypeptide segments of the variable chains in immunoglobulins (antibodies) and T cell receptors, generated by B-cells and T-cells respectively. CDRs are where these molecules bind to their specific antigen and their structure/sequence determines the binding activity of the respective antibody.
The fragment antigen-binding region (Fab region) is a region on an antibody that binds to antigens. It is composed of one constant and one variable domain of each of the heavy and the light chain . The variable domain contains the paratope (the antigen-binding site), comprising a set of complementarity-determining regions , at the amino ...
The fragment crystallizable region (Fc region) is the tail region of an antibody that interacts with cell surface receptors called Fc receptors and some proteins of the complement system. This region allows antibodies to activate the immune system , for example, through binding to Fc receptors .