DYSREGULATION OF INTERLEUKIN-4, INTERLEUKIN-5, AND INTERFERON-GAMMA GENE-EXPRESSION IN STEROID-RESISTANT ASTHMA

In steroid-resistant (SR) asthma, there is a lack of clinical responsiveness to oral prednisone. Previous studies indicate that this may be explained by the effect of the combination of interleukin 2 (IL-2) and IL-4 on glucocorticoid-receptor binding affinity. By contrast, steroid-sensitive (SS) asthmatics respond well to glucocorticoids, and this is accompanied by a decrease in the numbers of bronchoalveolar lavage (BAL) messenger RNA(+) (mRNA(+)) cells expressing IL-4 and IL-5, and an increase in interferon gamma (IFN-gamma) transcripts. In the present study, we hypothesized that SR asthma is associated with alterations in T helper types 1/2 (Th2/Th1)-type cytokine gene expression. BAL was performed in six SR asthmatics and six SS asthmatics, before and after a 1-wk course of 40 mg daily prednisone. mRNA(+) cells for IL-2, IL-4, IL-5, and IFN-gamma was measured by in situ hybridization using S-35-labeled RNA probes. Before prednisone therapy, there were significantly greater numbers of BAL cells (per 1,000) expressing IL-2 mRNA (p <0.01) and IL-4 mRNA (p <0.05) in SR asthmatics as compared with SS asthmatics, but no differences between the two groups in the numbers of BAL cells expressing IFN-gamma or IL-5 mRNA expression were observed. After a 1-wk course of prednisone, IL-2 expression was not altered in either group. However, SS asthmatics had a significant decrease in the numbers of BAL cells expressing mRNA for IL-4 (p <0.01) and IL-5 (p <0.001), and a rise in the numbers of IFN-gamma mRNA(+) cells (tr <0.01). In contrast, after prednisone treatment, SR asthmatics had no significant change in either the number of BAL cells expressing mRNA for IL-4 or IL-5. Of note, there was an unexpected decrease in the numbers of IFN-gamma mRNA(+) cells (p = 0.05). Our current findings indicate that SR asthma is associated with a dysregulation of the expression of the genes encoding for Th2/Th1 cytokines in airway cells and is compatible with the concept that a combination of IL-2 and IL-4 induce glucocorticoid (GR) binding affinity and T cell responsiveness to glucocorticoids.