Lymphocyte senescence and GC resistance have been described in several other inflammatory conditions such as cardiovascular disease [
18], autoimmune disease [
19], arthritis [
20], IBD [
21] associated with aging [
22] and aging with associated inflammation in COPD [
23]. This is the first study to show that lymphocyte senescence in COPD is associated with a loss of GCR from both T and NKT-like cells. Importantly, the loss of GCR by increased numbers of senescent CD8 + CD28null T cells and NKT-like cells was shown to correlate with COPD disease severity.
We have previously shown an increase in pro-inflammatory CD8+ T cells in peripheral blood and lungs [
3] and an increase in cytotoxic NKT-like and NK cells in the airways in COPD patients compared to healthy and never-smokers [
9]. Consistent with this we identified increased CD8/CD28null cells in both current and ex-smoker COPD groups [
5]. Senescent CD28null T and NKT-like cells have been shown to be more pro-inflammatory and cytotoxic than their CD28 positive counterparts [
5,
9], and exhibit a relative resistance to corticosteroids [
10]. The mechanism for this resistance was at least partially explained by our findings of an increase in the drug efflux pump Pgp1 in pro-inflammatory peripheral blood T and NKT-like cells [
11]. However, we did not differentiate Pgp1 expression on CD28+ and CD28null T and NKT-like cells in this previous study. We also hypothesized that steroid resistant senescent lymphocytes may have decreased levels of GCR. There have been reports of reduced GCR number in PBMC in patients with steroid resistant asthma [
24] and importantly, reduced GCRα protein expression in the peripheral lung of patients with COPD and smokers with normal lung function [
25]. However, there have been no reports of decreased GCR expression in the peripheral blood of patients with COPD, or in the various lymphocyte subsets. Our current study shows there is a significant loss of GCR expression in CD28null T and NKT-like subsets, with the greatest loss demonstrated in CD8 + CD28null cells, the senescent and most pro-inflammatory subset [
5]. Importantly, these GCR deficient lymphocytes were shown to be present in the systemic circulation of COPD patients. Barnes et al. proposed a spillover of cells from the lungs into the systemic circulation [
2], which suggest these GCR deficient cells may have originated in the lung. There have been conflicting reports that either support or dispute this concept. One report showed no difference in GCR expression in lung follicular CD8 cells between COPD patients and smokers [
26] using immunofluorescence techniques. This study did not however differentiate between GCR expression in CD28+ and CD28null subsets of CD8 T cells. Another study of patients with interstitial lung disease showed decreased expression of GCR mRNA in lung tissue from steroid resistant compared with steroid sensitive patients [
27].
We then investigated the intracellular localization of GCR in the various lymphocyte subsets and showed reduced cytoplasmic and nuclear GCR expression in CD28null compared with CD28+ T and NKT-like cells. Following stimulation there was a similar proportion of GCR in the cytoplasm and nucleus of both CD28null and CD28+ CD8+ T cells from both COPD patients and control subjects, suggesting there is no defect in nuclear translocation of the GCR between these subsets. Interestingly, our present study showed that a loss of GCR expression by CD28null T and NKT-like cells was also observed in healthy control subjects although at decreased numbers compared with patients with COPD ie., GCR expression was the same in CD28null T and NKT-like cells from both subject groups. One could speculate that these cells may be the precursors to potential inflammatory diseases. Our findings suggest that the relative GC resistance of the CD28null inflammatory lymphocytes need to be considered with any therapeutic approaches, and alternative therapies to GC may be required to avoid susceptibility to inflammatory diseases. To our knowledge, there have been no treatments to date that have increased lymphocyte GCR expression, although there has been a report of successful pitavastatin treatment of acute lung injury in septic mice with associated increase in GCR in alveolar macrophages [
28] and in studies using selective GCR agonists in the treatment of inflammatory bowel disease [
29]. Investigation of the possible effects of these therapeutics on GCR expression in CD28null CD8+ T cells would be worthwhile. We have previously shown CD137 is increased in CD28null T and NKT-like cells in COPD [
30]. In this previous study there was a significant decrease in the percentage of CD28null T and NKT-like cells producing IFNγ and TNFα in the presence of anti-CD137 blocking antibody compared with CD28+ T and NKT-like counterparts suggesting these pro-inflammatory cells may be targeted therapeutically. In conclusion, lymphocyte senescence in COPD is associated with loss of GCR in CD28null T and NKT-like cells. This loss is related to disease severity in COPD, thus therapies aimed at increasing GCR expression in pro-inflammatory senescent lymphocytes are warranted.