Rabbit Anti-Human CTLA-4 monoclonal antibody for FC, ICC, IF,. CTLA4 (Cytotoxic T-Lymphocyte Antigen 4) is a CD28-family receptor expressed on mainly CD4+ T cells. It binds the same ligands as CD28 (CD80 and CD86 on B cells and dendritic cells), but with higher affinity. However, in contrast to CD28 which enhances cell function when bound at the same time as the T cell receptor, CTLA4 inhbits the T cell and prevents it from functioning. Intracellular CTLA4 is also found in regulatory T cells and may be important to their function.