Carp (Cyprinus carpio) hematopoietic cells collected from the kidney were cultured in vitro in 35 mm-diameter tissue culture dishes using 1 mlof RPMI-1640 medium, 20% fetal calf serum, varying concentrations of carp serum and 0.3% agarose. The cells at a concentration of 2 × 10
5 cells/ml in agar-medium were incubated for 7-10 days at 30°C with 5% CO
2.
Many small aggregates constituting 3 to 10 cells were observed 3 or 4 days after incubation. Most aggregates grew and formed colonies which were made up of 50 to 100 cells. In contrast, when cultured without carp serum, most of the cells did not multiply and disappeared by day 7. To investigate the colony-forming cell types, agar cultures were dried and stained with May-Grünwald Giemsa. It was found that the colonies containd blast cells, of granulocytes several developmental stages and mature granulocytes. The mature cells had a weakly acidophilic or chromophoric cytoplasm and a single oval or kidney shaped nucleus, and were positive for peroxidase reaction. Electron microscopy showed many granules containing electron-dense materials in the cytoplasm of the matured cells.
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