antigen processing and presentation of exogenous peptide antigen

Definition

Target type: biologicalprocess

The process in which an antigen-presenting cell expresses a peptide antigen of exogenous origin on its cell surface in association with an MHC protein complex. The peptide is typically a fragment of a larger exogenous protein which has been degraded within the cell. [GOC:add, ISBN:0781735149]

Antigen processing and presentation of exogenous peptide antigen is a critical process in adaptive immunity that enables the immune system to recognize and respond to foreign invaders. This complex process involves a series of steps that ultimately lead to the display of peptide fragments derived from exogenous antigens on the surface of antigen-presenting cells (APCs) for recognition by T lymphocytes.

1. **Antigen Uptake:** The process begins with the uptake of exogenous antigens by APCs, such as macrophages, dendritic cells, and B cells. These cells possess specialized receptors that can bind to and internalize antigens, including pathogens, toxins, and foreign proteins.

2. **Antigen Degradation:** Once internalized, the antigen is transported to specialized compartments within the APC called endosomes. Within these compartments, the antigen is subjected to a series of enzymatic degradation steps.

3. **Proteolysis by Proteasomes:** In the cytosol, the antigen is degraded into smaller peptides by a large protein complex called the proteasome. This complex contains multiple proteolytic enzymes that cleave the antigen into peptides of varying lengths.

4. **Transport into Endosomes:** The generated peptides are then transported from the cytosol into the endosome via a specialized transporter protein called TAP (transporter associated with antigen processing). TAP recognizes specific peptide motifs and facilitates their translocation across the endoplasmic reticulum (ER) membrane.

5. **Loading onto MHC II Molecules:** Within the endosome, the peptides associate with MHC II molecules. MHC II molecules are specialized proteins expressed on the surface of APCs that are responsible for presenting exogenous antigens to CD4+ T cells.

6. **MHC II Maturation:** The MHC II molecules undergo a maturation process within the endosome, where they are loaded with the peptide antigen. The peptide-MHC II complex then translocates to the cell surface.

7. **Presentation to T Cells:** Once on the cell surface, the peptide-MHC II complex is displayed for recognition by CD4+ T cells. These T cells express T cell receptors (TCRs) that specifically recognize and bind to the presented peptide-MHC II complex.

8. **T Cell Activation:** Upon recognition, the T cell becomes activated, leading to the release of signaling molecules and the differentiation of effector T cells. These effector T cells can then target and eliminate cells that are displaying the same peptide-MHC II complex, thus effectively controlling the infection.

The antigen processing and presentation of exogenous peptide antigen is a highly regulated and coordinated process that plays a crucial role in the adaptive immune response. This process ensures that the immune system can effectively recognize and eliminate a wide range of foreign invaders, thereby protecting the organism from disease.'
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Proteins (1)

Compounds (4)