High-affinity immunoglobulin E receptor (FcεRI)-bearing eosinophils, mast cells, macrophages and Langerhans' cells in allergen-induced late-phase cutaneous reactions in atopic subjects

We have used in situ hybridization (ISH) and immunohistochemistry (IHC) to investigate the kinetics of the expression for FcεRI mRNA (α-, β- and γ-chains), the α-chain protein product, as well as the phenotype of the mRNA- or protein-positive cells in allergen-induced late-phase skin reactions in atopic subjects. Compared with diluent controls, there were significant increases in the total numbers of mRNA⁺ cells for the α-, β-and γ-chains for FcεRI at all time-points (6, 24 and 48 hr) after allergen challenge (P<0.01). By double IHC/ISH significant increases in α-, βand γ-chain mRNA⁺ macrophages, eosinophils, mast cells and CD1a⁺ cells were also observed after allergen challenge (P<0.05). The distribution of FcεRI subunit (α-, β-, or γ-chain) mRNA⁺ co-localization was CD68⁺ macrophages (42-47%), EG2⁺ eosinophils (33-39%), tryptase⁺ mast cells (5-11%) and CD1a⁺ Langerhans' cells (2-4%). Using single IHC, significant increases in the total number of FcεRI protein⁺ cells (P<0.01) were observed 24 and 48 hr after allergen challenge. Double IHC showed that the distribution of FcεRI⁺ cells was tryptase⁺ mast cells (33%), CD68⁺ macrophages (36%), EG2⁺ eosinophils (20%), CD1a⁺ Langerhans' cells (4%) and unidentified cells (7%), at the 24-hr allergen-challenged sites. These observations suggest that the cutaneous late-phase reaction in man is associated with up-regulation of FcεRI on eosinophils, macrophages, mast cells and Langerhans' cells.