Figure 2.

CD28 is constitutively expressed on T cells and CD86 is expressed on antigen-presenting cells (APCs). (a) Upon activation CD80 is also expressed on the APC and CD86 is further upregulated. (b) Cytotoxic T lymphocyte-associated antigen (CTLA)4 expression is induced later during activation, and out-competes CD28 for the interactions, thereby inducing a downregulation in immune response.