Unstimulated basophils in atopic and nonatopic subjects express intracellular interleukin-4: detection by flow cytometry

Background IgE-stimulated cultured basophils from atopic subjects are capable of secreting interleukin-4 (IL-4). We describe a flow-cytometric technique which identified intracellular IL-4 in unstimulated basophils unseparated from peripheral blood mononuclear cells (PBMC) in both atopic (AT) and nonatopic (NC) volunteers.
Methods Freshly isolated PBMC were fixed in 4% paraformaldehyde (PFA). Surface staining with 22E7, a noncompetitive anti-Fc-a antibody, allowed identification of basophils. Permeabilization by 0.1 % saponin allowed staining of intracellular cytokines with specific monoclonal antibodies (mAbs). Two series of experiments utilizing different protocols and anticytokine mAbs were performed. The first protocol required a two-stage fluorochrome staining technique. The availability of fluorochrome-conjugated mAbs allowed a simpler, one-stage labelling procedure for the second protocol.
Results With the first protocol, IL-4 (but not IFN-y), immunoreactivity was detectable in a majority (median 77%) of peripheral blood basophils from both AT and NC subjects (N = 8). Basophil IL-4 immunoreactivity was again evident in experiment 2 but did not differ significantly between AT and NC subjects - either evaluated as percentage of IL-4+ basophils (AT median=66%, NC median=38.4%, P=0.41) or lL-4-specific mean fluorescence (AT median=0.85, NC median=0.3, P=0.07).
Conclusions This simple technique allowed the study of intracellular cytokine expression in unstimulated blood basophils. It demonstrated constitutive basophil expression of lL-4 (but not IFN-y) in all subjects, with no significant increases in atopies.