Immune response antigen binding

An epitope is an antigenic determinant of the pathogen. It consists of certain chemical groups that are antigenic, which means that it will elicit a specihc immune response by binding to antibodies. 

To initiate a T-cell immune response, antigen presenting cells have to display antigenic peptides com-plexed with the major histocompatibility complex (MHC) on their cell surface. The T-cell receptor of CDS cells is specific for the peptide-MHC class I complex while the CD4 cell receptor binds the peptide-MHC class II complex. This binding of the peptide-MHC II complex stimulates CD4 cell proliferation and subsequent lymphokine release. This CD4 cell response can initiate a delayed hypersensitivity reaction. However CD4 activation and the production of various lymphokines is also needed for the generation of cytotoxic T-cells and for the differentiation of plasma cells from B-lymphocytes and the antibody response by these plasma cells. For their role in also the humoral immune response CD4 cells are called T-helper cells. 

Fig. 11.1. Principle of an immunological synapse. Possibilities for communication between B and T cells during an immune response. Antigenic peptides are presented by the MHC complex class II at the surface of the B cell. The antigens are recognized and bound by T cell receptors of the T cell. The T cell receptor is activated and sets a signal chain in motion that leads to activation of the expression of cytokines, such as IL-2. The cytokine is secreted, and binds and activates a cytokine receptor on the B cell. TNFa is shown as another example of a ligand-receptor system. TNFa communicates, as a membrane-bound ligand, with a corresponding receptor on the surface of the B cell. The interactions shown take place in a narrow spatial region between B and T cells, which is why this system is referred to as an immunological synapse. TNF tumor necrosis factor MHC major histocompatibility complex IL-2 interleukin 2.

An antigen injected into a test animal elicits an immune response by binding to determinant specific receptor sites on two types of small lymphocytes denoted B and T. These receptor sites have been shown to be immunoglobulins integrated into the lymphocyte cell membrane, which accounts for their determinant specificity. A few characteristics of B and T lymphocytes are listed in Table 8-2, but their ontogeny, function, and interactions are immensely more complex than such a casual description... 

Haptens, a special class of antigen, are small molecules that induce specific antibody production when they are attached to a protein that acts as a carrier. Phosphorylcholine is one such hapten that has been widely used in the investigation of immune responses. The specific binding of this hapten... 

A cascade of proteins of the immune response that can be triggered by antigen-antibody complexes and by the innate immune system (e.g. exposure to microbial polysaccharides) to raise the immune response. Complement proteins can detect and bind to foreign material or immune complexes and label them for phagocytosis. They can also cause inflammation by directly degranulating mast cells and releasing chemokines to recruit other immune cells into the affected area. 

L. inocua ferritin site however, is the first described so far that has ligands belonging to two different subunits, and is not contained within a four-helix bundle. Recently it has been suggested that the neutrophil-activating protein of Helicobacter pylori, the major antigen of the immune response in infected individuals, is also a dodecameric ferritin, capable of binding up to 500 iron atoms per oligomer (Tonello et ah, 1999). 

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