Question

How does the cytotoxic T lymphocyte neutralize the pathogen (such as some viruses) that has entered the body?

Answer 1

Cytotoxic T lymphocyte is also known as killer T cell . They directly kill the cells that display foreign antigen on the surface.When there is a intracellular viral infection , dendritic cells from the site of infection reaches the nearest lymph node and present the viral antigen in the form of MHC I. CD8+ T cells identify the antigen and the helper T cells start secreting interleukins. These two responses activate the T cells which proliferates and differentiates to form  Cytotoxic T lymphocytes and memory T cells.Cytotoxic T lymphocytes secretes more and becomes self stimulating. these cells now move from lymph node to the site of infection and tag the virus infected cells. They bind with with MHC of the virus infected cells and undergo granulation to form granules cotaining cytotoxic proteins like perforin, granulysin etc aided by CD8 cells.

Perforin forms pores on the cell surface of target cells and make it easy for the other cytotoxic granules to pass through into the cell. Granzymes cause apoptosis or programmed cell death by activating nucleases and damaging the mitochondria leading to degradation of target cells. The damaged target cells are now ingested by phagocytes.

Cytotoxic T lymphocytes secrete cytokines like interferons and necrosis factors which recruits macrophages at the site of infection.