Question

What is the major role of CD8+ cells? How do they kill (what are the 2 ways)?

Answer 1

Ans . CD8+ cells are cytotoxic cells that induce apoptosis in cells, which present the cognate antigen on MHC class I.

CD8+ cells are very important for immune defence against intracellular pathogens , including viruses and bacteria and for tumor surveillance.

When CD8+ cells recognises its antigen and becomes activated then it has following two mechanisms to kill infected or malignant cells:-

1) The first is secretion of cytokines, primarily TNF- and IFN - , which have anti-tumor and anti-viral microbial effects.

2) The second major function is the production of and release of cytotoxic granules. These granules , also found in NK cells , contain two families of proteins, perforin and granzymes.

When CD8+ cells - by interaction between TCR on CD8+ cells and the peptide on MHC class I molecule of target cell - are stimulated to attack target cells , they release perforin , a molecule that produces channels in the plasma membrane of target cells leading to lysis.

CD8+ cells also secrete granzymes (serine proteases) , which pass through the channels in the target cells and trigger apoptosis.