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Pulmonary Pathology: Poster#294 ROLE OF A CD21+ FOLLICULAR DENDRITIC CELLS IN DISTINGUISHING BRONCHUS-ASSOCIATED LYMPHOID TISSUE FROM LUNG ACUTE CELLULAR REJECTION

Introduction: Bronchus-associated lymphoid tissue (BALT) is part of the lung immune system that consists of small aggregates of lymphoid cells at the bifurcation of the airways and along the lymphatic routes. While in animal models it plays a role in allograft response, that relationship has never been established in humans. BALT is often seen in lung transplant biopsies evaluated for rejection especially in A0 and A1 rejection. In early post-transplant biopsies (first 180 days) it is more commonly seen with A2 and A3 rejection. Irrespective of its role in allograft response in humans, morphologically BALT can occasionally be difficult to distinguish from rejection. Methods: We analyzed 33 transbronchial transplant lung biopsies, 25 with BALT and 8 with rejection for presence of CD21 positive dendritic cells to determine if their presence can distinguish BALT from the acute rejection. Fisher's exact test was used to evaluate statistical significance. Results: Of the 25 biopsies with BALT, 20 (80%) stained positive for CD21, while none of the 8 biopsies with acute rejection stained positive for CD21 (0%), a significant difference (p value <0.0001). Discussion: The results of the study showed that CD21 antibody may be helpful in distinguishing BALT from acute rejection in difficult cases.