Figure 1.

(T)cell activation patterns. (A) A typical primary T cell activation requires 3 signals to occur in sequence and depends on: 1). antigen recognition by TCR engagement and the strength of the signal received, 2). ligation of co-stimulatory molecules to their ligands and 3). cytokine mediated expansion and differentiation of cells to effector cells. (B) Cytokine exposure alone causes an antigen non-specific “bystander activation” expansion of memory T cells which exhibit broad lytic capabilities in comparison to antigen specfic activated T cells.