title: The complement dependent cytotoxicity (CDC) immune effector mechanism contributes to anti-CD154 induced immunosuppression.
abstract: BACKGROUND
  In many situations, anti-CD154 (CD40 ligand) monoclonal antibody (mAb) treatment is very potent in producing allograft tolerance. In accordance to our previously reported results, combined donor specific transfusion (DST)3 plus anti-CD154 mAb (MR1) treatment enables the permanent engraftment of DBA/2 (H-2(d)) islets into B6AF1 (H-2(b/kd)) recipients in all cases. It has been widely assumed that the MR1 anti-154 is a noncytolytic neutralizing mAb, and it exerts immune suppressive effects by blockade of CD40/CD154 signal pathway. In this study, we sought to test the role of complement dependent cytotoxicity (CDC) immune effector mechanism in MR1 anti-CD154 induced immunosuppression.
  
  
  METHODS
  We have evaluated the contributions of CDC in the context of the potent tolerizing effects of DST plus anti-CD154 mAb treatment regiment in recipients of islet allografts. We have used CD40 knockout (KO) mice and complement C5 deficient mice DBA/2 as islet allograft recipients as well as cobra venom factor (CVF), a complement blocker, treatment.
  
  
  RESULTS
  The absence of direct and indirect CD40/CD154 pathway signals does not prevent islet allograft acute rejection. Interestingly, MR1 anti-CD154 induces islet allograft tolerance in the absence of CD40/CD154 pathway. In a wild-type major histocompatibility complex (MHC) mismatched strain combination, DST results in accelerated islet allograft rejection. Combination of DST and MR1 anti-CD154 treatment prevents presensitization and permits permanent engraftment. However, administration of CVF abolishes the tolerance induction. Moreover, DST plus MR1 anti-CD154 regiment, a potent tolerizing therapy, does not prevent acute islet allograft rejection when complement C5 deficient DBA/2 mice are used as recipients. Thus, the mechanisms of the tolerizing effects by MR1 anti-CD154 are not limited to blockade of CD40/CD154 signals. The CDC immune effector mechanism contributes to MR1 anti-CD154 induced immunosuppression.
mesh_terms: D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D001803:Blood Transfusion; D019013:CD40 Antigens / Q000502:physiology; D023201:CD40 Ligand / Q000502:physiology*; D003165:Complement System Proteins / Q000502:physiology*; D003602:Cytotoxicity, Immunologic; D006801:Humans; D007166:Immunosuppressive Agents / Q000627:therapeutic use*; D016381:Islets of Langerhans Transplantation; D014184:Transplantation, Homologous
chemical_list: D000911:Antibodies, Monoclonal; D019013:CD40 Antigens; D007166:Immunosuppressive Agents; D023201:CD40 Ligand; D003165:Complement System Proteins