Background Previous observations have established that IFN-γ production is depressed in CD4+ T cells from atopic asthmatics compared with non-asthmatics.
Objective The aim of this study was to determine if decreased IFN-γ production could be due to a dissociation between levels of apoptosis within the T cell subsets of the asthmatic bronchial wall.
Methods Twenty asthmatics (10 atopic and 10 non-atopic) and eight non-atopic non-asthmatics underwent bronchoscopy. Cryostat sections of these biopsies were investigated using immunohistological techniques to determine the relative number of CD4/FAS+ and CD4/Bcl-2+ cells. Detection of IFN-γ+ and IL-4+ was combined with TUNEL staining to determine the proportions of the Th1 and Th2 cells undergoing apoptosis.
Results Experiments revealed raised proportions of activated CD4+ T cells as assessed by expression of HLA-DR and CD25+ expression in the asthmatic samples. Expression of Bcl-2 by the CD4+ cell population was significantly reduced in the asthmatic compared with the control group (P = 0.002). There was no significant difference in the expression of CD4+ Fas-ligand or the number of CD4+ undergoing apoptosis in the asthmatic and non-asthmatic groups. However, the IFN-γ+ (P = 0.04) but not IL-4+ T cells in the asthmatic biopsies had significantly higher proportions of apoptotic cells compared with the control group.
Conclusion The evidence supports the hypothesis that Th1/Th2 imbalance in asthmatic inflammation may be a result of premature apoptosis within the Th1 subset.