The diagnosis of antibody mediated rejection (AMR) of the lung allograft still represents a diagnostic challenge for pathologist and transplant physicians alike. The morphologic and immunohistochemistry interpretation of lung allograft biopsies with antibody-mediated rejection is not yet well defined. We investigate this question in 51 patients who underwent lung allograft transbronchial biopsies from 6/12/13 to 8/15/13. There were a total of 32 males and 19 patients. All of them were tested for Donor Specific Antibodies (DSA) by Luminex and all biopsies were tested by C4d immunohistochemistry on paraffin sections. We found 21% patients that showed acute cellular rejection (ACR) whereas 12% showed other morphologic findings not associated with ACR (organizing pneumonia, diffuse alveolar damage and acute fibrinod organizing pneumonia). DSA were present in 36% of C4d+ biopsies in interstitial capillaries, 61.5% in stromal areas, 76.9% in endothelium of large vessels, 24% in the wall of arteries and 42%in mucosal/submucosal locations. Fisher exact test suggests a correlation of DSA and C4d for biopsies positive for C4d in the stroma and mucosal/sub-mucosal locations. These findings propose a more detailed morphologic evaluation of C4d-stained lung allograft biopsies for the diagnosis of AMR in lung transplant.

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