Cultured human mast cells are heterogeneous for expression of the high-affinity IgE receptor FcεRI.

OBJECTIVE: We determined the density of FcεRI on mast cells cultured from cord (CBMC) and peripheral blood (PBMC) and studied the kinetics of the response through FcεRI.
METHODS: Mast cells were cultured from CD133+ progenitors from peripheral or cord blood. FcεRI was stabilized by culture with 2 μg/ml IgE. Cells were activated by addition of anti-FcεRI antibody (1 ng/ml-10 μg/ml). Maximal activation, sensitivity, and cooperativity were determined.
RESULTS: All cultures were homogeneous for tryptase and metachromasy. All cells expressing FcεRI could be activated by cross-linking FcεRI to upregulate CD63. PBMC bind 203,000 molecules of IgE/cell. Stabilization of FcεRI with IgE doubled the number of CD63+ cells (p = 0.0001) and increased the sensitivity (from 0.083 to 0.013 μg/ml anti-FcεRI) and the slope factor (from 10.8 to 68) of PBMC but not of CBMC. Anti-IgE reversed these effects (p = 0.0002) but did not reduce activation levels below that of cell lines not stabilized with IgE.
CONCLUSION: Baseline expression of FcεRI is independent of anti-IgE. The fraction of PBMC that binds high levels of IgE can be activated through FcεRI.