Phenotypic Changes among Hybrid Rat Mast Cells

Abstract

Rat peritoneal mast cells and 6-thioguanine-resistant rat basophilic leukemia cells, representative of connective tissue-type (CTMC) and mucosal (MMC) mast cells, respectively, were fused using polyethylene glycol. Four out of 14 primary hybrid mast cell lines contained more than 50% of CTMC as demonstrated by histochemical staining. Two cell lines, one predominantly of the CTMC and the other of the MMC phenotype, were selected for further study. Among these, the phenotype was also confirmed by analysis for rat mast cell protease I and by mediator release triggered by compound 48/80 and ionophore A23187. The CTMC phenotype disappeared after culturing cells for 2 weeks. The change in phenotype did not significantly alter the mediator release due to calcium ionophore A23187. Repeated cloning of cells bearing the CTMC phenotype did not yield a cloned line of cells expressing the CTMC phenotype only, although it prolonged the persistence of this phenotype. During the period of CTMC phenotype loss, a drop in cellular DNA content occurred, suggesting that chromosome instability may, at least partially, have been responsible for the phenotypic changes.

Minimal Contribution of Marrow-Derived Endothelial Precursors to Tumor Vasculature

“…Given that marrow-derived endothelial cells integrating into angiogenic microvasculature appears to be a rare event, we attempted to determine whether the rare GFP ϩ endothelial cell was a result of cell fusion. Others have used DNA content analysis to determine the presence or absence of cell fusion, but this analysis can be misleading as fused cells have been shown to lose cellular DNA, which could potentially lead to inaccurate interpretation of results (22)(23)(24)(25). We thus used a transgenic double-reporter strategy to determine whether bone marrowderived endothelial cells observed in B6RV2 tumors arise by differentiation or fusion.…”