Combination IL-2 and IL-4 reduces glucocorticoid receptor-binding affinity and T cell response to glucocorticoids

The mechanisms contributing to persistent T cell activation and poor response to glucocorticoids in chronic inflammatory illnesses such as steroid resistant (SR) asthma are poorly defined. We examined the possibility that certain cytokines, specifically IL-2 and IL-4, could affect T cell response to glucocorticoids. A [3H]dexamethasone radioligand-binding assay was used to measure the number of glucocorticoid receptors (GR) and dissociation constant (Kd) in PBMC from normal donors and patients with SR asthma, cultured in the absence and presence of these cytokines. PBMC from normal donors incubated for 48 h in the presence of combination IL-2 + IL-4 had nuclear GR with significantly reduced binding affinity (GR Kd = 36.1 +/- 1.63 nM, mean +/- SEM; p = 0.0001) as compared with PBMC incubated with medium alone (GR Kd = 6.74 +/- 0.46 nM). The cytosolic GR Kd remained unchanged. However, when PBMC were incubated with IL-2 alone or IL-4 alone, no change in GR-binding affinity was observed. Furthermore, when T cells and non-T cells were individually stimulated with combination IL-2 + IL-4, a significant reduction in GR-binding affinity was observed only in the T cell population (p = 0.0001). The IL-2 + IL-4-induced alteration in PBMC GR Kd was associated with an increase in GR number (8348 +/- 964 vs 1710 +/- 228 sites/cell; p = 0.0003). More importantly, the alteration in PBMC GR-binding affinity with IL-2 + IL-4 was associated with a functional change in T cell response to methylprednisolone MPN, i.e., a reduced inhibitory effect of MPN on PMA/ionomycin-induced T cell proliferation. These effects of IL-2 + IL-4 on PBMC GR affinity and response to MPN were blocked by co-incubation with IFN-gamma. Freshly isolated PBMC from four patients with SR asthma had a significantly reduced GR-binding affinity (Kd = 40.0 +/- 2.68 nM; p = 0.0001) when compared with seven normal subjects (7.15 +/- 0.41 nM). The altered PBMC GR binding from patients with SR asthma reversed to normal when incubated with medium alone, but was sustained with IL-2 + IL-4. These observations suggest that with persistent inflammation certain cytokines may contribute to an impaired response to glucocorticoids. Furthermore, the effects of IL-2 and IL-4 were blocked by IFN-gamma.