We studied a male patient with cyclic thrombocytopenia whose bone marrow megakaryocyte count showed cyclic fluctuations in synchrony with cyclic changes of platelet count. He failed to respond to either prednisolone or bolus methylprednisolone therapy, but subsequently he was successfully treated with azathioprine. To investigate the underlying pathogenesis of the cyclic fluctuations in the platelet count, we studied the kinetics of megakaryocyte progenitor cells (CFU-Meg) and the effects of the patient's peripheral blood mononuclear cells on CFU-Meg. In one cycle of the platelet fluctuation, the increase in the CFU-Meg number preceded an increase in the bone marrow megakaryocyte count and then the platelet count. In the latter half of the cycle, CFU-Meg, bone marrow megakaryocytes and platelets began to decrease in that order. Peripheral blood mononuclear cells obtained from the patient in the thrombocytopenic phase suppressed megakaryocyte colony formation from normal bone marrow cells in a dose-dependent manner. In contrast, these cells obtained in the phase of a normal platelet count did not suppress megakaryocyte colony formation at all. These findings indicate that the cause of platelet fluctuation is periodic failure of megakaryocytopoiesis at the stage of CFU-Meg and that the patient's peripheral mononuclear cells are responsible for periodically suppressing the CFU-Meg.

The Philadelphia (Ph1) chromosome, in which the hybrid bcr-abl gene is formed, is thought to be the initial event in chronic myelogenous leukemia (CML). The position of the breakpoint within the breakpoint cluster region (bcr) on Ph1 chromosome and the splicing pattern determine the species of the fused bcr-abl messenger RNA (mRNA). We tried to detect the two types of fused mRNAs in 57 chronic-phase cases of Ph1-positive CML using the polymerase chain reaction procedure (RT- PCR). The bcr exon 2/abl exon 2 fused mRNA (b2-a2) was detected in 17 patients, the bcr exon 3/abl exon 2 fused mRNA (b3-a2) was detected in 34 patients, and both types of mRNA were detected in six patients. The platelet counts of patients who expressed b3-a2 mRNA or both types were significantly higher than those of patients who expressed only b2-a2 (841.5 v 373.5 x 10(9)/L; P less than .015), although there was no significant difference in the white blood cell counts or hemoglobin. This finding suggests a possibility that the type of bcr-abl mRNA may affect the thrombopoietic activity in CML.

Two new myeloid cell lines (K051 and K052) were established from a patient with multilineage CD7-positive acute leukemia. The K051 and K052 were established from the patient's bone marrow cells at diagnosis and at relapse, respectively. The K051 cell expressed myeloid- associated antigens (CD13 and CD33), a platelet-associated antigen (CD41), and an erythroid antigen (glycophorin A). The K052 cell expressed myeloid-associated antigens (CD13, CD14, and CD33), lymphoid markers (CD2, CD5, and CD7), and HLA-DR. Chromosome analysis of both cell lines showed a 17p- chromosome. Both cell lines were investigated for aberrations of the p53 gene and the N-ras gene. A p53 mutation detected in both cell lines consisted of a C-->T substitution in codon 248. An N-ras mutation detected only in the K052 cell consisted of a G-- >C substitution in codon 13. Expression of the multidrug resistance gene (MDR1) was also investigated by the semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). MDR1-mRNA was more highly expressed by the K052 cell than the K051 cell, being equivalent to that in HEL cells. The functional MDR1-protein against vincristine was also observed, and its function was inhibited by verapamile and Cyclosporin A. The K052 cells were capable of phenotypic or morphologic differentiation after being incubated with granulocyte colony- stimulating factor, interleukin-2, phorbol 12-myristate 13-acetate, or 1,25-dihydroxy-vitamin D3. In contrast, the K051 cells responded phenotypically to retinoic acid. Thus, the K051 and K052 cell lines will be useful for investigating the cellular and molecular events in leukemogenesis and differentiation, and the mechanism of expression of the MDR1 gene.