Fig. 3

T cell activation in the lymph node. a Both immunological signal 1 (T cell receptor (TCR) recognition of antigens) and immunological signal 2 (stimulation of CD28 by B7 costimulatory molecules) are required for T cell activation in the lymph node. The interaction between the cytotoxic T lymphocyte-associated protein 4 (CTLA-4) receptor and B7 expressed on T cells and antigen presenting cells, respectively, prevents T cells from becoming fully activated by blocking immunologic signal 2. b Antibodies that block the CTLA-4 pathway (e.g. ipilimumab) permit T cell activation by derepressing signaling by CD28. MCH, Major histocompatibility complex. (Adapted from [77])