The abnormal multimeric composition of plasma von Willebrand factor in type IIB von Willebrand's disease is transiently corrected after infusion of 1-deamino-[8-D-arginine]-vasopressin. However, the larger multimers released into the circulation disappear more rapidly in these patients than in type I von Willebrand's disease or normals. We demonstrate that the larger multimers of normal von Willebrand factor transfused into a type IIB patient are cleared from the circulation more slowly than multimers of similar size endogenously released from tissue stores. The rate of disappearance of large von Willebrand factor multimers after infusion of cryoprecipitate is similar in IIB, IIA, and severe homozygous-like von Willebrand's disease. Platelets from the IIB patient exhibited normal ristocetin-induced binding of normal von Willebrand factor. However, like normal platelets, they bound IIB von Willebrand factor at lower ristocetin concentrations than required for normal von Willebrand factor. These findings provide evidence that absence of the larger multimers from IIB plasma is related to a molecular abnormality of von Willebrand factor rather than to enhanced affinity of abnormal tissue or cellular binding sites, as is the case in the recently described “pseudo” von Willebrand's disease and “platelet-type” von Willebrand's disease.

One hundred-nine cases of autoimmune hemolysis were reviewed to determine the frequency of reticulocytopenia, the state of the erythroid marrow in reticulocytopenic cases, and the course of reticulocyte production indices with time and glucocorticoid treatment. The mean hematocrit at presentation was 24 mL/dL, but 30% of cases had an initial hematocrit less than 20 mL/dL. Median reticulocyte percentage at diagnosis was 9%, and median reticulocyte production index was 2.8 times basal. Twenty percent of cases had an initial reticulocyte count less than 4%, and 37% had an initial reticulocyte production index less than 2.0 times basal. These reticulocytopenic patients were nearly evenly distributed between warm and cold antibody- mediated cases and between primary and secondary cases. Fifty-four percent of reticulocytopenic cases had a bone marrow examination during hospitalization. Three-fourths of these marrows showed erythroid hyperplasia, and erythroid hypoplasia was seen in only one case. Eighty- eight cases had serial reticulocyte measurements, and in only 15% of patients did the reticulocyte production index remain less than 2.0 times basal. Thus, in most cases, the initially low reticulocyte production index may represent a lag in marrow responsiveness to hemolytic stress. In cases with persistent reticulocytopenia, ineffective erythropoiesis is suggested by the frequency of marrow erythroid hyperplasia. In the cases that were initially reticulocytopenic and demonstrated an increase in reticulocyte production index, the magnitude of this increase was significantly greater in glucocorticoid-treated patients than in those not so treated, indicating that a glucocorticoid sensitive component exists in the marrow erythropoietic response to hemolysis. Awareness of the frequency of an initial reticulocytopenia in cases of autoimmune hemolysis may be important in initial diagnosis and treatment.

We have established two human cell lines which elaborate colony- stimulating activity (CSA) for at least four species: man, mouse, rabbit, and dog. One, GCT, was isolated from a lung metastasis of a fibrous histiocytoma; the other, RC4, from a monocyte-enriched fraction of normal blood. Medium conditioned by either GCT or RC4 cells was more potent in stimulating human marrow growth in vitro than was monocyte-conditioned medium or human leukocyte feeder layers. Fractionation of cell-line-conditioned medium by Sephacryl S-200 chromatography indicated that the maximum activity of the CSA for human marrow cells is eluted within the range of 30,000–40,000 daltons. These cells lines provide a continuous source of large quantities of conditioned medium for purification of CSA. Moreover, the invariable growth-supporting activity for all species tested and the high potency of cell-line CSA facilitates studies of its elaboration and biologic effects.

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GCT, a human monocyte-like cell line, has been shown to release biochemically distinct colony-stimulating activities (CSAs) for mouse and human marrows. These appear to be periodate-sensitive proteins with critical disulfide bonds. One, of molecular weight 145,000 daltons, stimulates macrophagic colony growth and is related to a 30,000-dalton molecule that also stimulates mouse growth. A 30,000-dalton CSA for human marrow can be separated from the 30,000-dalton mouse CSA by isoelectric focusing and gradient polyacrylamide gel electrophoresis. This distinction agrees with our previous finding of differential neutralization with anti-human urinary CSF antibody. The 30,000-dalton CSAs stimulate neutrophil, neutrophil-monocyte, and eosinophil colony growth in human marrow but only neutrophil and neutrophil-monocyte colonies in the mouse. Subcellular fractionation of GCT cells indicates that there are pools of preformed CSAs primarily associated with the cell cytosol that have similar apparent molecular weights to their secreted counterparts.