Activation of Human CD8+ T Cells Results in a Highly Selective and Very Potent Upregulation of Interferon-r, TNF-a, IL-2 and Granzyme B, But Not of Other Granzymes and Perforin

Cytotoxic T cells are fully immunocompetent only after full activation. In order to study this activation process and to identify the major changes in gene expression upon activation, human peripheral blood CD8+ T cells were purified and activated in vitro by anti-CD2, CD3 and CD28 coupled beads alone or in combination with recombinant IL-12 and IL-18. The changes in the transcriptomes were then analyzed by quantitative transcriptomics during the first 24 hours of stimulation. Major changes in expression were only seen in a remarkably low number of genes including primarily granzyme B (GZMB) and a few inflammatory cytokines and chemokines. GZMB increased 30-40 fold already after 4-hours stimulation whereas the other four human granzymes remained unchanged or even decreased in expression. This stimulation of GZMB was further increased 2-3 times by the addition of IL-18 and IL-12. Interestingly, there was only a minor 2-fold increase in the expression of perforin, the pore forming molecule enabling the entry of the granzymes into the target cell. In sharp contrast, a remarkably strong increase was detected for a few inflammatory cytokines and chemokines: 1000-fold increase for Interferon- (IFN-, almost 1500-fold for IL-2, >100-fold for TNF-, >10-fold for CCL3 and 30-100-fold for CCL4. A minor increase in the levels of IL-3, IL-4, IL-5, IL-10, and IL-13 were also seen and a quite strong increase in IL17F at 4 hours which then rapidly dropped almost to preincubation levels by 24 hours. A quite dramatic 100-fold increase was also seen in one of the micro RNAs, the MIR155HG. These findings strongly support the notion that GZMB is the major player in the apoptosis induction in target cells and that the other granzymes may primarily have other functions in T cell mediated immunity, unrelated to apoptosis. It also shows that cytotoxic T cells, upon activation, are major producers of a selective array of proinflammatory cytokines and chemokines.