Elevation of antidonor immunoglobulin M levels precedes acute lung transplant rejection

Background: No useful noninvasive biomarker exists for diagnosing acute rejection after lung transplantation (LTx). In this study, antidonor T-cell antibodies were monitored daily in living-donor lobar LTx recipients to determine whether they are correlated with the onset of steroid-responsive typical acute rejection. Methods: Ten nonsensitized patients who underwent bilateral living-donor lobar LTxs donated from 2 persons were analyzed. In 5 patients, unilateral acute rejection developed during the first 14 days after LTx and responded to subsequent pulse steroid therapies. The other patients experienced no rejection episodes during the period. Immunoreactivity against T cells from each lobe of the donors was monitored daily by detecting antidonor immunoglobulin (Ig) M and IgG using flow cytometry crossmatching for 14 days after LTx. Results: There was a remarkable increase in IgM levels against rejected grafts around the onset of acute rejection, but this increase was not observed against nonrejected grafts. The mean IgM levels against rejected grafts 14 days after transplantation was significantly higher than that against nonrejected grafts in the acute rejection group (p = 0.009) and the no rejection group (p = 0.010). In the acute rejection group, the IgM level against rejected grafts became significantly higher than those against nonrejected grafts 2 days before the clinical onset of acute rejection. These trends were statistically marginal or not detected for IgG levels. Conclusions: Significant immunoreactivity of IgM, but not IgG, preceded the clinical onset of acute rejection. Antidonor IgM monitoring can contribute to the early detection of steroid-responsive acute rejection.