CD8+ Cells

 

 

Introduction

CD8+ cells are T lymphocytes that play a central role in cell-mediated immunity.

CD8+ cells develop following cytokine stimulation from CD4+ cells and recognition of antigen presented on MHC Class I molecules. This causes differentiation into Cytotoxic T Lymphocytes (CTL), which does not secrete many cytokines but instead exhibits cell-killing abilities.

CTLs have a vital function in monitoring cells of the body and is vitally involved in viral infections, neoplastic clearance, and tissue graft rejection.

 

 

 

Development and Activation

Naive CD8+ cells reside in the lymph nodes, where they await antigen presentation on MHC class I molecules by APCs. Along with antigen presentation, CTL development depends on CD4+ cell expression of IL-2, which normally takes place at the site of viral infection. Resting CD8+ cells do not express IL-2 R, requiring antigen stimulation for their expression.

 

 

CTL Function

CD8+ cells recognize antigen presented in MHC I molecules with their TCRs, leading to cytotoxic killing of neoplastic cells or those infected with viruses or intracellular pathogens.

 

 

Response to Virally Infected Cells

MHC I presentation by virus-infected cells induces CD8+ cell binding via its TCR. This induces release of granules from CTLs.

Perforin creates pores for entry by granzyme, which leads to caspase activation and apoptosis.

CTL-expressed Fas also induces apoptosis by binding to FasL.