Megakaryocyte interaction with subendothelial extracellular matrix is associated with adhesion, platelet-like shape change, and thromboxane A2 production

We have examined the morphological and secretory behavior of rat and guinea pig megakaryocytes exposed for up to 24 hours to extracellular matrix produced by cultured bovine endothelial cells. By phase-contrast microscopy of living cells and in more detail by scanning electron microscopy, the megakaryocytes showed a nonreversible adherence, an extensive formation of filopodia around the periphery like the rays of the sun, and a tendency toward flattening. These filopodia were generally linear with attenuated tips and were larger than, but resembled the filopodia of, rat or guinea pig platelets exposed to this extracellular matrix. In contrast, isolated megakaryocytes on glass or on uncoated plastic surfaces did not show these responses; adherence, in the face of gentle agitation before fixation, was minimal, with rare filopodia and no flattening. Megakaryocytes that interacted with the extracellular matrix produced significant amounts of thromboxane A2, but this did not occur on uncoated surfaces and could not be attributed to other contaminating cells in the megakaryocyte suspensions. The appearance in megakaryocytes of these typical platelet responses indicates that megakaryocytes acquire the functional capabilities of platelets by the synthesis and assembly of platelet substances and organelles. Thromboxane production by megakaryocytes stimulated by the extracellular matrix is a readily quantifiable measure of this capacity.     

Challenges of establishing the correct diagnosis of outbreaks of acute febrile illnesses in Africa: the case of a likely Brucella outbreak among nomadic pastoralists, northeast Kenya, March-July 2005

An outbreak of acute febrile illness was reported among Somali pastoralists in remote, arid Northeast Kenya, where drinking raw milk is common. Blood specimens from 12 patients, collected mostly in the late convalescent phase, were tested for viral, bacterial, and parasitic pathogens. All were negative for viral and typhoid serology. Nine patients had Brucella antibodies present by at least one of the tests, four of whom had evidence suggestive of acute infection by the reference serologic microscopic agglutination test. Three patients were positive for leptospiral antibody by immunoglobulin M enzyme-linked immunosorbent assay, and two were positive for malaria. Although sensitive and specific point-of-care testing methods will improve diagnosis of acute febrile illness in developing countries, challenges of interpretation still remain when the outbreaks are remote, specimens collected too late, and positive results for multiple diseases are obtained. Better diagnostics and tools that can decipher overlapping signs and symptoms in such settings are needed.