Blocking the B7-CD28 costimulation pathway by CTLA4 Ig, a recombinant fusion protein, containing the extracellular domain of human CTLA4 (a homologue of CD28), resulting in T cell anergy, ameliorated renal dysfunction and decreased mononuclear cell infiltration in a model of renal cold ischemia [28]. Here, CTLA4 is linked to ischemia.