5.0 RBL-2H3 cell line
In mast cell research, the most common animal cell line used is the RBL-2H3 cell line59. The RBL cells were generated from rats that were injected with the chemical carcinogen β-chlorethylamine to induce basophilic leukemia 60. The RBL cells were adapted to suspension cell culture (named RBL-1) and can specifically bind IgE to their surface membrane 61,62. Nevertheless, neither an IgE/antigen trigger nor chemical stimulation by a Ca2+ionophore were able to cause RBL-1 to release histamine63. A responsive subline known as RBL-2H3 that degranulated in response to an IgE trigger was successfully isolated from subsequent cloning of RBL cells in 1981 64. These cells were a great model for understanding the FcεRI signaling cascades as they could be cultured in huge numbers to examine the characteristics and binding properties of IgE which will lead to the signaling pathways involved in degranulation 65.
RBL-2H3 cells were widely employed as a mast cells model shortly after they were formed. Unquestionably, RBL-2H3 cells have the advantage of being a cell line that is simple to cultivate due to its short doubling time (18-24 h), enabling researchers to obtain a high number of homogenous cells easily. However, their suitability and credibility were eventually questioned 66,67. In the early years of RBL cells establishment, a variant with impaired cromoglycate binding had been identified in a population of RBL-2H3 which suggest that the cell line may not be fully homogenous 68. Although research reports frequently referred to RBL cells as mast cell line, it was in fact derived from basophils. Additionally, the cell line was lack of consistency as to the physiology of basophils or mast cells as well as findings between other research groups utilizing the same cell line66. Mast cells and basophils are two different but functionally related cell types that are essential in type I hypersensitivity. Granulocyte basophils circulate, whereas mature mast cells are only found in tissues at the interfaces with external environment, such as the lungs, skin, and mucosal surfaces69. Despite their similarities, it was suggested that the two cell types descended from distinct lineages70,71. Nonetheless, numerous arguments suggested that they may share a common origin 72,73.
Nevertheless, RBL-2H3 cells have been successfully used in investigations on IgE binding to FceRI receptors and subsequent downstream processes 66,74. The expression of rat mast cell protease II (RMCP-II) 75 and a similar expression of the c-kit receptor tyrosine kinase 76 in RBL-2H3 cells comparative to human HMC-1 and murine P-815 mast cells were one of the few aspects of mast cell physiology that supports the notion that RBL-2H3 cells can model mast cells. Moreover, numerous studies have found similarities between the exocytosis mechanisms of bone marrow mast cells and RBL cells involving SNARE proteins, designating RBL cells as a suitable model for research on MC exocytosis 59.