Question

1) Describe how CD8 T-cells contribute to cell-mediated immunity. [Be sure to provide a short general overview first, and then provide specific ways in which T cells destroy their target cells].

Answer 1

Features	T cells
Site of development	Thymus
Distribution	Para-cortical area of Lymph nodes, Peri- arteriolar lymph sheath (PALS) of spleen
Antigen Receptor	TCRs
Surface receptors	CD3 CD4 ,CDs
Role in immune responce	As T cytotoxic cells plays important role in cell mediated immunity. As Th cells help in inducing humoral as well as cell mediated immunity

CD8+ (cytotoxic) T cells, are generated in the thymus and express the Tcell

receptor. These cells express a dimeric coreceptor, CD8, usually composed of one CD8α and one CD8β chain.

These are very important for immune defence against intracellular pathogens, including viruses and bacteria for tumour surveillance.

Activated CD8+ T cell acts by three major mechanisms to kill infected or malignant cells.

• By secretion of cytokines, primarily TNF-α and IFN-γ, which have anti-tumour and anti-microbial
• By the production and release of cytotoxic granules

These granules contain two families of proteins, perforin, and granzymes. Perforin forms a pore in the membrane of the target cell, similar to the membrane attack complex of complement. This pore allows the granzymes also contained in the cytotoxic granules to enter the infected or malignant cell. Granzymes are serine proteases which cleave the proteins inside the cell, shutting down the production of viral proteins and ultimately resulting in apoptosis of the target cell.

• The CD8 cells cause destruction of infected cells

Activated CD8+ T cells express FasL on the cell surface, which binds to its receptor, Fas, on the surface of the target cell.

Fas molecules on the target cell trimerize, which pulls together signalling molecules. These

signalling molecules result in the activation of the caspase cascade, which also results in

apoptosis of the target cell.

CD8+ T cells contribute to an excessive immune response that leads to immunopathology