INFLUENCE OF GENETIC AND ENVIRONMENTAL-FACTORS ON SURFACE EXPRESSION AND OCCUPANCY OF IGE RECEPTORS AND ON HISTAMINE RELEASABILITY OF MAST-CELLS

The relationship between the IgE load on mast cells and their secretor y capacity when challenged with anti-IgE was studied in peritoneal cel ls obtained from rats of three different strains, Hooded Lister (HL), Wistar Kyoto (WKY) and Sprague-Dawley (SD). IgE was determined cytoflu orometrically after labelling with FITC-conjugated anti-IgE before and after the saturation of the IgE receptors to provide a measure of the surface expression of IgE receptors (number of receptors available fo r bindings) as well as the IgE occupancy of the receptors (native IgE content). The secretory capacity of the mast cells was examined in vit ro in terms of histamine release as a function of anti-IgE concentrati on. Mast cells obtained from HL and WKY rats were found to carry signi ficantly higher levels of IgE receptors and IgE than the mast cells of SD rats bred and raised under the same conventional laboratory condit ions. The mast cells of SD rats kept under barrier-maintained conditio ns carried significantly less IgE than the mast cells obtained from SD rats kept under conventional conditions, but their IgE receptor level s were similar. The IgE-mediated histamine-releasing capacity of the m ast cells, evaluated in terms of maximum release or of the slopes of r egression lines (histamine release versus anti-IgE concentration), was positively correlated to the levels of native IgE and IgE receptors i n the three strains of rat combined. The mast cells obtained from WKY rats showed the highest secretory capacity in the three strains of rat examined, significantly higher than the mast cells of HL rats, even t hough the latter displayed similar levels of IgE and IgE receptors. Th ese findings indicate that under basal conditions in these strains of rat the number of IgE receptors available for binding as well as the I gE occupancy is determined by both the genetic background and the envi ronment. The IgE-mediated histamine release appeared to be largely, bu t not exclusively a function of the number of IgE-receptor complexes o n the mast-cell surface. The difference in histamine-releasing capacit y between WKY and HL rats suggests that genetic factors may control th e secretory capacity of the mast cells also through mechanisms other t han those involving the expression of IgE receptors and the binding of IgE by the mast cells.