Understanding the Cytosolic Pathway: Degradation of Viral Antigens and Presentation on Class I MHC Molecules

In the _________ pathway, viral antigens are degraded in proteasomes and antigenic peptides are loaded on class ___ MHC molecules

In the cytosolic pathway, viral antigens are degraded in proteasomes and antigenic peptides are loaded on class I MHC molecules

In the cytosolic pathway, viral antigens are degraded in proteasomes and antigenic peptides are loaded on class I MHC molecules.

When a virus infects a cell, it replicates and produces viral proteins that can be recognized by the immune system as foreign antigens. These viral antigens need to be presented to the immune cells, such as CD8+ T cells, to trigger an immune response.

In the cytosolic pathway, viral antigens are degraded within the cytosol of the infected cell by large protein complexes called proteasomes. Proteasomes act as molecular shredders that break down proteins into smaller peptides. Specific viral proteins are targeted for degradation by the proteasomes.

The degraded viral proteins are then transported into the endoplasmic reticulum (ER), where they encounter a protein complex called the transporter associated with antigen processing (TAP). The role of TAP is to transport the viral peptides from the cytosol into the ER lumen.

Within the ER, the viral peptides are loaded onto the groove of class I major histocompatibility complex (MHC) molecules. Class I MHC molecules are membrane-bound proteins that are found on the surface of virtually all nucleated cells. They function by presenting antigenic peptides derived from intracellular pathogens, including viruses, to the immune system.

Once the viral peptides are loaded onto the class I MHC molecules, the MHC-peptide complex is transported to the cell surface. CD8+ T cells, also known as cytotoxic T cells, patrol the body and are specialized in recognizing and killing cells displaying foreign antigens on their surface. CD8+ T cells bind specifically to the viral peptide-class I MHC complex, leading to the activation and proliferation of the CD8+ T cells. These activated T cells then mount an immune response against the infected cell, helping to eliminate the virus.

In summary, in the cytosolic pathway, viral antigens are degraded in proteasomes within the infected cell’s cytosol, and the resulting antigenic peptides are loaded onto class I MHC molecules, which present them on the cell surface to trigger an immune response.

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