Normal neutrophil maturation is associated with selective loss of MAP kinase activation by G-CSF.

Although both GM-CSF and G-CSF activate p42/44 MAPK in neutrophil progenitors, the ability of G-CSF to cause MAPK activation is lost in mature neutrophils, while GM-CSF exposure still causes activation. The mechanism of this differential effect related to maturation status has not been explored. We verified that G-CSF and GM-CSF receptors remain functional on purified mature neutrophils by demonstrating that both cytokines caused phosphorylation of STAT3. However, only GM-CSF was capable of activating MAPK as assessed by gel shift and in vitro kinase assay. Both G-CSF and GM-CSF caused activation of p21 ras in neutrophils, demonstrating that early events in the ras-MAPK pathway remain functional after stimulation by either cytokine. Inhibition of tyrosine phosphatase activity by pervanadate restored the ability of G-CSF to activate MAPK in mature neutrophils. Specific inhibition of the SHP-1 phosphatase, known to be activated by G-CSF but not GM-CSF also restored the ability of G-CSF to activate MAPK in neutrophils. These studies suggest that G-CSF activation of SHP-1 may be an important regulatory step for permitting optimal terminal differentiation during neutrophil production and add to our knowledge of the instructional role of G-CSF and GM-CSF for balancing proliferation and differentiation of neutrophil progenitor cells. This information may prove useful for the understanding of conditions in which neutrophil proliferative/differentiative balancing is dysregulated, such as myeloid leukemia and myelodysplastic disorders.

Thrombotic thrombocytopenic purpura associated with bone marrow metastasis and secondary myelofibrosis in cancer.

To examine the relationship between cancer and development of thrombotic microangiopathy (TM), the medical records of patients with known TM were examined in one institution from January 1981 to December 2002. Nine out of 93 patients with the established diagnosis of TM had active cancer. All nine of those patients had thrombotic thrombocytopenic purpura (TTP). Among those patients, two patients received chemotherapy prior to the development of TTP. Six of the seven patients who received no chemotherapy had extensive bone marrow metastasis and secondary myelofibrosis. There were two patients each with breast cancer, lung cancer, and stomach cancer. Severe anemia and thrombocytopenia with leukoerythroblastosis were prominent clinical features in all six patients. Four patients had neurological (mental) changes and three developed fever, but none had significant renal dysfunction. Upon establishing the diagnosis of TTP, four patients were treated with exchange plasmapheresis (EP) and two patients were treated with chemotherapy because there were no neurological changes. Three patients achieved complete remission of TTP, one with EP alone and two with chemotherapy. The one patient who achieved remission with EP alone was later treated with chemotherapy and survived for 2 1/2 years. The other three patients treated with EP alone died within 2 months after the diagnosis of TTP. Since TTP occurred in association with bone marrow metastasis and myelofibrosis in six patients among seven chemotherapy-untreated cancer patients, this marrow change was considered to be the possible cause of the development of TTP. It is recommended that all cancer patients with unexplained anemia and thrombocytopenia be evaluated for the coexistence of bone marrow metastasis and TTP.

Acute thrombotic thrombocytopenic purpura following orthopedic surgery.

Release of unusually large von Willibrand factor (UL vWF) multimers and a deficiency of vWF metalloprotease may result in thrombotic thrombocytopenic purpura (TTP), a life threatening disease. Surgery has been associated with TTP, probably by releasing massive amounts of UL vWF. An association between TTP and orthopedic surgery has never been reported in the literature. We report a case of TTP following a total knee replacement surgery in which prior use of ticlopidine might have played a role.