Summary. The pathogenesis of haemophagocytic lymphohistiocytosis (HLH) in children without a known familial pattern of inheritance is often dif®cult to establish. Splenic enlargement, one of the main clinical ®ndings in this disorder, has led to the use of splenectomy for uncontrollable coagulopathy, persistent cytopenia or both. This procedure is also thought to be a useful tool in making a differential diagnosis in cases of the immunochemotherapy-resistant HLH. We report here ®ve cases of splenectomized childhood HLH, in which subsets of mononuclear spleen cells were analysed either by¯ow cytometry or immunohistochemistry, and the results were compared with those from cases of hereditary spherocytosis (controls). There was a statistically signi®cant depletion of CD19 B cells in the HLH cases (3´8 6 3´2% vs. 52´6 6 4´5%, P < 0´0001) associated with an increase of T cells in three cases and of natural killer cells in another. The histopathological ®ndings included atrophic white pulps, B-cell depletion with ®brosis and haemosiderosis in all ®ve cases. Despite temporary therapeutic bene®ts, three of the HLH patients had a rapidly deteriorating post-splenectomy course and all three eventually died. These results demonstrate striking depletion of B cells in the enlarged spleens of children with HLH, which may be an intrinsic feature of HLH pathogenesis. Further study is needed to establish the therapeutic value of splenectomy in this disease.

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We report a case of acute megakaryoblastic leukemia (AMKL) with antiplatelet antibody in a boy with Down syndrome. When the patient was admitted, his platelet count was 1.3 x 104/mm3 and antiplatelet antibody in the plasma was detected. Two months after admission, blasts, which showed positive reaction to both antiplatelet monoclonal antibody and platelet peroxidase, increased.acute megakaryoblastic leukemia ; Down syndrome ; antiplatelet antibody It is well known that children with Down syndrome are at increased risk of acute megakaryoblastic leukemia (AMKL). A number of such reported cases exhibited a preleukemic phase, characterized by thrombocytopenia (Beven and Rose 1982;Hayashi et al. 1986;Peeters and Poon 1987), but the etiology of thrombocytopenia has been unknown. We describe a case of AMKL in a boy with Down syndrome, following thrombocytopenia with antiplatelet antibody.The patient displayed physical stigmata of Down syndrome at birth, and chromosome analysis showed the. karyotype as 47,XY, + 21. At 20 months of age, he was admitted because of fever and generalized purpura. He had no history of blood transfusion. The results of hematologic examination were : red blood cells 323 x 104/mm3 ; platelets 1.3 x 104/mm3 ; white blood cells 4,400/mm3 with 19% blasts. In the bone marrow there were 8% blasts and a few (1/mm3) megakaryocytes, and we could not determine whether the blasts were leukemic or not. Bleeding time was prolonged (>5 min), but the results of coagulation studies were normal. Platelet associated IgG (PAIgG), measured by enzymelinked immunosorbent assay (Schiffer and Young 1983), was 181 ng/10' platelets. Antiplatelet antibody was detected by mixed passive hemagglutination test (Shibata et al. 1984) ( Table 1). And microlymphocytotoxicity test (Terasaki et al. 1978) showed negative reaction. Two months after admission, the blasts suddenly increased to 56% in the