<P> A simple activation of naive CD8 T cells requires the interaction with professional antigen - presenting cells, mainly with matured dendritic cells . To generate longlasting memory T cells and to allow repetitive stimulation of cytotoxic T cells, dendritic cells have to interact with both, activated CD4 helper T cells and CD8 T cells . During this process, the CD4 helper T cells "license" the dendritic cells to give a potent activating signal to the naive CD8 T cells . </P> <P> While in most cases activation is dependent on TCR recognition of antigen, alternative pathways for activation have been described . For example, cytotoxic T cells have been shown to become activated when targeted by other CD8 T cells leading to tolerization of the latter . </P> <P> Once activated, the T cell undergoes clonal expansion with the help of the cytokine Interleukin - 2 (IL - 2), which is a growth and differentiation factor for T cells . This increases the number of cells specific for the target antigen that can then travel throughout the body in search of antigen - positive somatic cells . </P> <P> When exposed to infected / dysfunctional somatic cells, T cells release the cytotoxins perforin, granzymes, and granulysin . Through the action of perforin, granzymes enter the cytoplasm of the target cell and their serine protease function triggers the caspase cascade, which is a series of cysteine proteases that eventually lead to apoptosis (programmed cell death). </P>

Describe some ways in which cytotoxic t cells destroy target cells