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 Fc epsilon RI mRNA (alpha-, beta- and gamma-chains), the alpha-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 number of mRNA+ cells for the alpha-, beta- and gamma-chains for Fc epsilon RI at all time-points (6, 24 and 48 hr) after allergen challenge (P < 0.01). By double IHC/ISH significant increases in alpha-, beta- and gamma-chain mRNA+ macrophages, eosinophils, mast cells and CD1a+ cells were also observed after allergen challenge (P < 0.05). The distribution of Fc epsilon RI subunit (alpha-, beta-, or gamma-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 Fc epsilon RI protein+ cells (P < 0.01) were observed 24 and 48 hr after allergen challenge. Double IHC showed that the distribution of Fc epsilon RI+ 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 Fc epsilon RI on eosinophils, macrophages, mast cells and Langerhans' cells.