| Abstract
| - Abstract. Cells from the spleen and head kidney of rainbow trout (Oncorhynchus mykiss) were cultured in vitro. The cells were held in culture for more than three months. Spleen cells lived only a few days if cultured between October and May, but long-term cultures were possible in late spring and summer. This variation is assumed to be due to seasonal variations in the content of precursor cells. An adherent cell layer (stroma) was found, which was occupied by other cells on the surface or in niches of the stromal network. Various cell types could be identified by different cytochemical methods and electron microscopy: macrophages, blast cells, fibroblastoid and epitheloid cells, adipocytes and multinucleated cells. About 20% of stromal cells were found to be capable of phagocytosis. Living cells were found in the supernatant of cultures: granulocytes, lymphocytes, blast cells, multinucleated cells. The admixture of phytohaemagglutinin (PHA) or horse serum (HS) was necessary for development of the stroma-like network. It is supposed, that PHA promotes the release of growth factors, and that HS could also produce the same effects. HS also causes strong growth of stromal structures and therefore the release of growth factors by the stroma.
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