Question

Assume that someodies arodvally creat doon and are not replaced A ute that you have a cell infected with SARS Coy2 Below draw AND LABEL he cell in a timeline as it is encountered by a CDS T-cell in ench of the three steps detailed: 19 points) Draw recognition of your cell by a Cytotoxic Draw the virally infected cell. Show MHC I displaying endogenous and auto- antigens Draw the outcome of this recognition (include perforins and granzymes) MHC I, TCR, and CD8 proteins)

Answer 1

2 SARS COV-2 T-cell viral nucleic acid granenzyme and perforins secretory vesicle CD8 receptor TCR golgi apparatus viral protein TAP E5 MHCI МНС-І pores produced proteasome RER causing apoptosis target cell The adhesion phase: The CD8-TCR complex on a CTL binds to MHC I molecules on the target cell surface and an immunological synapse forms around the contact area. CD8 is only expressed on T cells that recognize processed endogenous antigens and that further attack and kill abnormal cells. It is a receptor for MHC I molecules. CD8+ T cells usually function as T cytotoxic cells. Viruses take over the protein-synthesizing machinery of the cell and use it to make new viral proteins. There is a system in place in normal living cells for presentation of endogenous peptides on MHC class Ia molecules on their surfaces. Cells routinely break down and recycle proteins. For this, proteins are first attached to several molecules of ubiquitin, a 76 amino acids polypeptide. Ubiquitinated proteins are recognized by a large enzyme complex called a proteasome, which breaks down these proteins into fragments of 8-15 amino acids. For about one in a million molecules, the peptides are rescued from further breakdown by attachment to transporter proteins, TAP1 and TAP2 (for transporter for antigen processing 1 and 2) which transports them into endosomes. Here they are shortened one amino acid at a time until they are completely degraded, unless an intermediate, 9 amino acid long peptide precisely fits the binding site on an empty MHC class la molecule. The MHC I- peptide complexes are carried to the cell surface and displayed there for many hours. This process of endogenous antigen presentation happens routinely irrespective of the presence of viruses inside the cell. When a cell is infected by a virus, some of the newly synthesized viral proteins are processed in this manner, leading to display of MHC I- viral peptide complexes on the cell surface. These antigen fragments are recognized by cytotoxic T cells (Tc cells) which become activated. A cell can express about 106 MHC-peptide complexes and about 200 of them displaying the same viral peptide are required to activate a Tc cell. The lethal hit: The cytoplasmic granules migrate to the immunological synapse and their contents are emptied on to target cell surface. Perforins are membrane perturbing glycoproteins. They insert themselves into the target cell membrane. Between 12-18 monomers aggregate to form a membrane attack complex (MAC) (as the complement component C9 does], permitting granzymes to enter target cells. Granzyme A causes nuclear damage in the target cell and granzyme B sets off apoptosis. Granulysin is an antibacterial peptide found in the granules. It kills any intracellular bacteria released during apoptosis. TNF-B secreted by some CTLs binds to its receptors on target cells and so triggers their apoptosis.