IL-4 upregulates Fc epsilon RI alpha-chain messenger RNA in eosinophils

By using the reverse transcription polymerase chain reaction and Southern blot hybridization, we demonstrated that Fc epsilon RI alpha-chain (Fc epsilon RI alpha) messenger RNA was expressed in eosinophils purified from the peripheral blood of patients with allergic rhinitis and that this expression was enhanced by IL-4. However, studies in which flow cytometry or immunostaining was used did not reveal the expression of Fc epsilon RI alpha protein on eosinophils from peripheral blood. Neither IL-4 alone nor the combination of IL-4 and other cytokines could induce detectable Fc epsilon RI alpha protein; nevertheless, they do express Fc epsilon RI alpha mRNA. Double-labeling immunostaining on cryostat sections of nasal mucosa clearly demonstrated that some Fc epsilon RI alpha-positive cells were eosinophil cationic protein-positive, which confirms their eosinophilic nature. Not all the eosinophil cationic protein-positive cells express on Fc epsilon RI alpha signal. Considering that Fc epsilon RI alpha mRNA was detectable in four of five samples of eosinophils from those patients with nasal allergy and that only one of five eosinophil samples from normal subjects expressed Fc epsilon RI alpha mRNA, the level of Fc epsilon RI expression may be correlated with the activation of eosinophils. It seems very likely that some other unidentified factors are required for the process from the expression of Fc epsilon RI alpha mRNA to that of Fc epsilon RI as a protein.