<prompt> Berbecks granules are seen inLangerhan cellsLymphocytesNeutrophilsBasophils  <response>: Ans. a Langerhan cells. Ref. Robbins, Pathologic Basis of Disease 6thpg.685HISTIOCYTOSIS Histiocytosis represents clonal proliferation of antigen- presenting dendritic cells. It is of two types:- Localized histiocytosis 70 i.e. Eosinophilic granuloma. It is the most benign variety of langerhans cell histiocytosis.- Disseminated histiocytosis 30i. Hand - Schuller - Christian disease chronicii. Letterer-Siwe disease fulminant Age: 5-10 years most common Location: Bone in children or lung in adults most commonly involved. Sites of infection:- Flat bones: calvarium mandible ribs pelvis vertebrae- Long bones- Skull: Diplopic space of parietal bone most common affected.i. Roundovoid punched out lesion with beveled edge Hole within hole appearance with sharply marginated without the sclerotic rim with button sequestrum with soft tissue mass overlying lesion geographic skull.- Jaw: Floating tissue mass overlying lesion- Vertebra plana- Painful diaphyseal expansile lytic long bone lesions. Pathology:- Birbecks granulesHX bodies are characteristic pathologic feature of histiocytosis X, noted in cytoplasm of Langerhan cells.- On electron microscope they have tennis-racket appearance.- These tumor cells typically express HLA-DR and CDla.DISEASESCELLULAR CHARACTERISTICS OF THE LESIONSTREATMENTClass 1Langerhans cell histiocytosis Langerhans cells CDla positive with Birbeck granulesLocal therapy for isolated lesions; chemotherapy for disseminated disease.Class IIInfection-associated hemophagocytic syndromeMorphologically normal reactive macrophages with prominent erythrophagocytosisChemotherapy; allogeneic bone marrow transplantation.Class III Malignant histiocytosisNeoplastic proliferation of cells with characteristics of monocytes macrophages or their precursors iAntineoplastic chemotherapy, including - methotrexate, vincristine, etoposide, imatinib...are being tried. 