LCH is characterized by the presence of Langerhans cells juxtaposed against a backdrop of hematopoietic cells, including T-cells, macrophages, and eosinophils. The investigated material included open lung biopsy samples taken from seven patients (four males and three females) at the mean age of 23.2 years. They were all smokers. The intensity of the histological lesions was semiquantitatively measured, differentiating three intensity grades: mild, moderate and intense. In most cases (3/7), the interalveolar septa were focally and intensively thickened. The inÀ ammatory in¿ ltrates in the septa were focal, intense in 3/7, moderate in 1/7, and mild in 1/7 specimens. Lymphocytes prevailed, followed by macrophages, eosinophil granulocytes, and plasma cells. The lumen of the alveoli was occupied by a few macrophages and lymphocytes, sparse plasma cells and few eosinophil granulocytes. The alveolar cells were focally cuboid in 7 cases. Histiocyte aggregates were detected in all specimens, most frequently localized peribronchiolarly (7/7) and in the intraalveolar septa (4/7). The aggregates had either a clear (15/25), or a relatively clear (10/25) demarcation line against the periphery. The aggregates were predominantly composed of Langerhans’ cells (7/7, abundant), followed by eosinophil granulocytes (abundant in 4/25, moderate in 8/25, sparse in 13/25), lymphocytes (sparse in 10/25 and moderate in 15/25 cases), and plasma cells (sparse in 10/25). The Langerhans’ cells were CD1a and S 100 positive. Histiocyte aggregates were registered in all biopsy samples; the Langerhans’ cells were CD1a and S100 positive.

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