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. 2010 Feb;18(2):81–89. doi: 10.1016/j.tim.2009.12.001

Figure 2.

Figure 2

Induction of cell-mediated immune response by CD4+ T cells. There are three signals that are important during T cell activation: antigen presentation (TCR:Peptide-MHC class II ligation), co-stimulation (CD40:CD40L and CD80/CD86:CD28) and polarising signals (cytokine milieu). Professional antigen-presenting cells (dendritic cells, B cells and macrophages) present antigens to T cells in the context of MHC class II via the TCR (T cell receptor). This induces upregulation of CD40L and CD28 on the T cells, which bind to their receptors CD40 and CD80/CD86, respectively, on APCs, in a process called co-stimulation. These events lead to the production of polarising cytokines by APCs which include IL-12 from macrophages and dendritic cells, and IL-23 from dendritic cells. The polarising cytokines are important because they dictate the fate of T cells on whether to differentiate into Th1, Th2 or Th17.