Lack of Lipopolysaccharide-induced β-hexosaminidase and TNF-α Release from Human Mast Cells (HMC-1) and Rat Basophilic Cells (RBL-2H3)

Mast cells are important immune cells that are able to degranulate potent mediators, and participate in infections and inflammatory responses. The process of mast cell degranulation is complex and still partly unknown, especially in bacterial infections caused by endotoxins such as lipopolysaccarides. In this study, we have investigated lipopolysaccharide-induced degranulation of β-hexosaminidase and tumor necrosis factor α in a human mast cell line, HMC-1, and a rat basophilic leukemia cell line, RBL-2H3. We investigated whether the cells expressed the required Toll-like receptor 4 through which lipopolysaccaride activates the mast cell. By using RT-PCR we show that the Toll-like receptor 4 gene is actively transcribed in both cell lines, indicating that the cells could be able to respond to lipopolysaccaride. To analyse the degranulation of β-hexosaminidase, the cells were stimulated with different concentrations of lipopolysaccaride and the extracellular enzyme activity was measured spectrophotometrically. Our results showed that no release could be measured using this method in neither of the cell lines. The release of tumor necrosis factor α was analysed by using enzyme-linked-immunosorbent-assay, and the results indicated that neither lipopolysaccharide, ionomycin, nor 5’-(N-ethylcarboxamido) adenosine had any effect on this process. In conclusion, the HMC-1 cell line is not a useful model to study mast cell degranulation in oral infections, and a more reliable in vitro method is needed to investigate the involvement of human mast cells in pathological conditions and to screen for new therapeutic drugs