Negative co-receptors on lymphocytes

The past year has seen significant advances in our understanding of critical roles of negative immunoregulatory signals delivered through the B7–CD28 superfamily in regulating T cell activation and tolerance. Structural data on CTLA-4 have provided novel insights into the inhibitory functions of CTLA-4. Initial characterization of the PD-1–PD-1-ligand pathway has revealed that this pathway can downregulate TCR- and CD28-mediated signals. Recent studies indicate that ICOS exerts distinct effects at different phases of an immune response: ICOS can inhibit as well as stimulate T cell responses.