CD28B7

CD28B7 is a term commonly used to describe the co-stimulatory interaction between the CD28 receptor on T cells and the B7 family ligands CD80 (B7-1) and CD86 (B7-2) on antigen-presenting cells. There is no separate protein universally recognized as “CD28B7”; rather, CD28B7 refers to the functional axis formed by CD28–B7 engagement that provides a key second signal for T cell activation.

In the immune response, T cell activation requires two signals: T cell receptor recognition of antigen and a co-stimulatory signal provided by B7 ligands binding to CD28. This co-stimulation promotes T cell proliferation, survival, and cytokine production, notably interleukin-2. B7 ligands are expressed by professional antigen-presenting cells such as dendritic cells, macrophages, and B cells, and their expression is upregulated in response to innate immune cues. Without co-stimulation, T cells may become anergic or undergo apoptosis, contributing to peripheral tolerance.

CD28 signaling engages multiple intracellular pathways, including PI3K–Akt, MAP kinase, and NF-κB, supporting metabolic changes and gene expression required for full T cell activation. The B7–CD28 axis is counterbalanced by CTLA-4, which binds B7 ligands with higher affinity and inhibits activating signals, contributing to immune regulation.

Clinically, modulation of the CD28–B7 axis has therapeutic relevance. Agents such as CTLA-4–Ig fusion proteins (e.g., abatacept) block B7–CD28 interactions to dampen immune responses in autoimmune diseases and transplantation, illustrating the axis’s importance in health and disease.