Ubiquitin-positive pneumocytes and inclusion bodies are present in secondary organizing pneumonia.

Objective: We previously reported that various types of interstitial pneumonia (IP) patterns contain intracytoplasmic eosinophilic inclusions or Mallory bodies (inclusions) that are ubiquitin positive (Ub+). In the present study, we examined tissues with the organizing pneumonia pattern (OP) to determine if they contain inclusions and Ub+ pneumocytes using lobectomized specimens.

Methods: Tissues from 34 patients with secondary OP, which appeared in 33 carcinomas and 1 pulmonary abscess, were histologically evaluated for the type of intraluminal granulation tissue and the presence of erosions and inclusions. Granulation tissues were classified into polypoid, mural and occluded subtypes according to Basset's criteria and scored.

Results: Inclusions were noted in 5.9% of the secondary OP cases with light microscope. Ub+ pneumocytes were detected after immunostaining and all inclusions were Ub+. Ub+ pneumocytes (inclusions) were noted in 14.7% of the secondary OP cases. OP contained pneumocyte erosions and inflammatory cell infiltration without a significant difference in the Ub+ and Ub- subgroups. Although there was no significant difference in the polypoid type of granulation tissue between the Ub+ and Ub- negative (Ub-) subgroups, the Ub+ subgroup had significant increases (p<0.05) in the mural-occluded type of granulation tissue (Ub+: 1.76±0.64, n=5 vs. Ub-: 0.72±0.87, n=29) as compared to the Ub- subgroup.

Conclusion: Some patients with secondary OP had Ub+ inclusions as pneumocyte injury.