PHENOTYPIC CHANGES AMONG HYBRID RAT MAST-CELLS

Rat peritoneal mast cells and 6-thioguanine-resistant rat basophilic l eukemia cells, representative of connective tissue-type (CTMC) and muc osal (MMC) mast cells, respectively, were fused using polyethylene gly col. 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, we re selected for further study. Among these, the phenotype was also con firmed by analysis for rat mast cell protease I and by mediator releas e triggered by compound 48/80 and ionophore A23187. The CTMC phenotype disappeared after culturing cells for 2 weeks. The change in phenotyp e did not significantly alter the mediator release due to calcium iono phore 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 pe riod of CTMC phenotype loss, a drop in cellular DNA content occurred, suggesting that chromosome instability may, at least partially, have b een responsible for the phenotypic changes.