5.3 Humanized RBL cells
As discussed above, RBL cells
originated from rats. It was established that rat IgE can bind to human
IgE receptor 95, however rat IgE receptor did not
recognize human IgE 96. RBL cells expressing the high
affinity IgE receptor FcεRI implied that the cell line may be suitable
for the detection of allergen specific IgE and allergens59. Stable transfection of human FcεRI α chain in RBL
cells was achieved in the 90s with the receptor expressed mediated
antigen-induced signaling and mediator release97–100. These humanized RBL cells were then utilized
to investigate the ability of pure peanut allergens and other food
allergens to induce degranulation 101–104. RBL-SX38
is one of the commonly used humanized RBL cell lines that expresses α,
β, and γ chains of human FcεRI 105.
The addition of a reporter gene (firefly luciferase) to humanized RBL
cells paved the way for straightforward and extremely sensitive
detection of cellular activity via the IgE receptor59. The first and most common system was a
Nuclear Factor of Activated
T-cells (NFAT)-firefly luciferase reporter that is linked to IgE
dependent signal transduction named RS-ATL8 cells 106.
The calcium influx from stimulation of the cells activates calcineurin,
a phosphatase that dephosphorylates NFAT. This resulted in the unveiling
of the nuclear localization signal in the N-terminal and leads to
nuclear translocation. NFAT then attaches to specific promoter regions
and initiates gene transcription of the luciferase reporter gene107. By detecting luciferase activity with suitable
substrates and a luminescence detector, activation of these cells may be
detected 106. RS-ATL8 assay is very sensitive and well
suited for high throughput format. The assay had since been employed for
the identification of food or other allergens, as well as determining
the allergenicity of vaccines 108–110.
From our literature retrieval, we identified two articles using the
humanized RBL cells, RBL-SX38 111,112 and one article
using the reporter humanized cells, RS-ALT8 113 to
investigate the release of β-hexosaminidase. RBL-SX38 was obtained from
a research group in Harvard Medical School, USA while the study using
RS-ALT8 did not specify the cells’ origin. Both RBL-SX38 and RS-ALT8
cells were grown in MEM supplemented with 10% FBS, L-glutamine and
antibiotics. One study using RBL-SX38 did not specify the culture
condition. In all three studies, cells were sensitized with allergen
specific human IgE and induced by their respective allergens.