Kuppe et al. Allergy, Asthma & Clinical Immunology 2012, 8:6 http://www.aacijournal.com/content/8/1/6 Page 3 of 6 Figure 2 Routine and immunohistochemical stainings of biopsies from cubital veins and bone marrow. (A-B) Biopsies of cubital veins showed complete loss of normal vein architecture with massive infiltration of lymphocytes (arrows in A), histiocytes (arrows in B), macrophages and fibroblasts. (C-D) Further immunohistochemical analysis revealed massively increased numbers of proliferating Ki-67+/CD68+ macrophages (arrows in C and D). (E-G) Bone marrow biopsies of the patient revealed haemophagocytosis, the defining criterion of MAS. Characteristically, the histiocytes showed degenerated and nucleated proerythoblasts within their cytoplasm (arrows E-G). positron emission tomography (PET) CT scan showed no hypermetabolic region. Finally, histological evaluation of a second bone marrow biopsy showed haemophagocytic histiocytes (Figure 2, E-G). Flow cytometric analysis revealed the absence of NKT cells and an increased expression of CD163 on all bone marrow cells. CD163, a receptor for haemoglobin- haptoglobin complexes, is involved in clearance and endocytosis of haemoglobin/haptoglobin complexes by macrophages and may thereby protect tissues from free haemoglobin-mediated oxidative damage. The plasma levels of soluble CD163 in HLH are considerably higher than those found in infections or autoimmune diseases [11]. In the peripheral blood, we also found a slight in- crease of the relative amount of B-lymphocytes as well as an increased expression of CD63 (degranulation mar- ker) and CD11b (migration marker on neutrophils) on bone marrow cells (Figure 3, A-I). One week after admission, an immunosuppressive regimen was started including 1 mg/kg body weight methylprednisolone and 5 mg/kg body weight ciclos- porin. The fever decreased over several days after initi- ation of therapy and laboratory values normalized (Table 1). After two weeks of therapy, the cytokine levels