Immunohistochemical diagnosis of pulmonary eosinophilic granuloma on lung biopsy

S-100 protein immunostaining has been advocated to identify the characteristic Langerhans' cells in the histologic diagnosis of PEG. Reliable demonstration of an increased number of Langerhans' cells is essential in difficult biopsy cases, since occasional Langerhans' cells can be found in other pulmonary lesions. We examined the S-100 protein labeling pattern in three cases of PEG and a variety of controls. Non-Langerhans' histiocytes were labeled for lysozyme antigen on the same histologic sections using a combined ABC and PAP technique. This verified that the S-100 protein-negative histiocytes were indeed a separate population from the S-100 protein-positive histiocytes and did not represent Langerhans' cells which failed to label with antiserum to S-100 protein. This technique confirms the usefulness of S-100 protein staining in the diagnosis of PEG and offers a means to verify the reliability of the S-100 protein labeling in questionable cases.