A new method is described for the large-scale purification of human pancreatic islets with a discontinuous gradient of bovine serum albumin formed on an IBM 2991 cell separator. Fifteen human pancreases were processed, and after density-gradient centrifugation, a mean of 2643 islets/ml pancreatic digest were recovered with a mean purity of 63% and contained in 430 microliter mean vol. Viability of gradient-isolated islets was compared with that of non-density-gradient islets (handpicked) and showed no difference in function. This technique allows isolation of intact, viable human islets of Langerhans of sufficient purity for potential human transplantation.
Megakaryocytopoiesis occurs in the hematopoietic (extravascular) compartment of marrow. Thus, platelets must traverse the wall of the vascular sinuses of marrow to enter the circulation. We have examined mouse and rat marrow, fixed by rapid immersion so as to maintain anatomical relationships as close to the natural state as possible. Quantitative transmission electron microscopy (TEM) of random transections of femurs established that megakaryocytes reside less than 1 mu from a marrow sinus wall with a probability unlikely to be the result of chance (P less than 0.001). An intimate relationship exists between the megakaryocyte periphery and the abluminal surface of the endothelial lining cell. At the time of platelet release megakaryocyte cytoplasm invaginates and penetrates the endothelial lining cell. The penetrating cytoplasm is detached and enters the marrow circulation. From their dimensions in comparison to circulating platelets, the released cytoplasm represents a packet of platelets that undergoes further fragmentation in the circulation. The parasinusoidal location of megakaryocytes and the process of sinus-wall penetration and platelet delivery was observed by TEM and scanning electron microscopy. These studies provided quantitative support for a specific anatomical arrangement of megakaryocytes in marrow. Moreover, the process of platelet release appears to be a physiological form of metastasis with invasion of vascular walls and vascular spread of cells, that are in this case amitotic.
Tumour cells from a squamous carcinoma (approximately 2.5 X 10(5)) were injected intraportally into a syngeneic strain of rats to produce liver metastases 14 days later. Kupffer cells were stimulated by Corynebacterium parvum (7 mg or 1 mg i.v.) and zymosan (10 mg intraportally). Kupffer cell activity was depressed by the administration of silica, gadolinium chloride or human red cells. The animals in each group were sacrificed at 14 days, the livers removed and the number of visible surface metastases counted and compared. (Mann-Whitney U-test). Kupffer cell stimulation significantly reduced the number of surface liver metastases in all animals (P 0.0048). In contrast depression of Kupffer cell activity significantly increased the number of metastases in all animals (P 0.0045), suggesting that the activity of these cells has an important effect on the development of liver metastases.
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