Figure 3. B7–CD28 family and newly discovered interactions.
In addition to known interactions (see Fig. 1), B7 homolog 1 (B7H1) was recently found to interact with and deliver a negative signal through B7.1, which is expressed on activated T cells. Human B7H2 — also known as inducible co-stimulator ligand (ICOSL) — was identified to engage both CD28 and cytotoxic T lymphocyte antigen 4 (CTLA4) to modulate T cell activation in addition to ICOS. APC, antigen-presenting cell.