Studies of circulating microparticle release in peripheral blood after pancreatic islet transplantation.

The loss of graft function after intraportal islet transplantation is likely multifactorial involving allogeneic rejection, recurrent autoimmunity, graft exhaustion due to a marginally implanted islet mass, immunosuppressant toxicity, and impaired β-cell regeneration. Because early markers of the loss of β-cell mass or function are lacking, monitoring of islet function remains a challenging issue. We have reported herein monitoring of membrane procoagulant microparticles (MPs) as markers of cell stress in the plasma of three recipients with various clinical histories. Early kinetics of C-peptide and MPs followed identical patterns during the first weeks after transplantation; a major increase probably reflected processes related to cell infusion and islet engraftment. Importantly in the case of rejection, MPs and C-peptide showed opposite patterns. A fall in C-peptide was associated with enhanced insulin needs. Our results suggested that a peak in MP levels might indicate rejection with prognotic value. Treatment of the loss of islet function by a new islet infusion or steroid therapy returned MP and C-peptide levels to their baselines with concomitant restoration of islet function. In the patient with suspected acute cellular rejection, MPs also appeared to be sensors of immunosuppressive steroid therapy.