CD28B7Liganden

CD28B7Liganden are the B7 family ligands that bind to the CD28 receptor on T cells. The principal ligands are B7-1 (CD80) and B7-2 (CD86), expressed on professional antigen-presenting cells such as dendritic cells, macrophages, and B cells. Their expression is upregulated during activation and inflammatory signaling, providing a critical second signal that complements T cell receptor engagement.

Binding of CD28 by B7-1 or B7-2 delivers a costimulatory signal that supports full T cell activation, clonal expansion, and cytokine production, notably interleukin-2. This costimulation integrates with TCR signaling to enhance cell survival and differentiation. In the absence of CD28 engagement, T cells may become anergic or fail to proliferate effectively.

Regulation of this axis involves CTLA-4 (CD152), an inhibitory receptor that also binds B7 ligands with higher affinity. The competition between CD28 and CTLA-4 for B7 ligands shapes the magnitude and duration of T cell responses. Therapeutic approaches include CTLA-4–Ig fusion proteins (abatacept, belatacept) that block B7-CD28 interactions to dampen autoimmunity or prevent transplant rejection.

Clinical and research relevance centers on the CD28–B7 axis as a major target in immunotherapy. Blocking this interaction can reduce autoreactive or alloimmune responses, while selective enhancement of costimulation can boost anti-tumor T cell activity in certain settings, albeit with autoimmune risk. The canonical B7 ligands for CD28 are CD80 and CD86; other B7 family members engage different receptors, such as ICOS-L for ICOS, and do not directly bind CD28.