B7 is a peripheral membrane protein presented by activated antigen-presenting cells (APC). B7, upon binding of CD28 or CD152 (CTLA-4) epitopes on T cells, can generate a costimulatory signal or a co-inhibitory signal to enhance or decrease the activity of an MHC-TCR signal between the APC and the T cell. Binding of the B7 protein of APC to CTLA-4 of T cells causes inhibition of the activity of T cells.
There are two variants of B7 proteins:
- B7-1 (CD80)
- and
- B7-2 (CD86).
It is not known whether they are significantly different from each other both protein variants. So far, CD80 is found on dendritic cells, macrophages and activated B cells, CD86 (B7-2) on B cells. The epitopes CD28 and CD152 (CTLA-4) expressed by T cells each interact with both B7-1 and B7-2.