Figure 1.

T cell activation alternative methods. Classic 2 signal activation involves T cell interaction with antigen presenting cell. Signal one is antigen dependent and delivered to the T cell receptor by MHC/HLA and antigen. The costimulus can include CD28 interacting with B71 or B72; that outcome creates activation leading to cytokine production. When a source of CD154 is available, including from the newly activated T cells, other T cells receive a different second signal costimulus to produce inflammatory type cytokines. CD28 signals favor more regulatory type cytokines.