This is the first study to show differential expression of the drug efflux pump Pgp1 by T, NKT-like and NK cells from COPD patients compared with healthy control subjects. COPD is a systemic disease  and we have previously shown increased IFNγ and TNFα by T cells , granzyme B by NK and NKT-like cells  and granzyme B by T cells  in the peripheral blood and lungs of COPD patients. Our novel findings that Pgp1 is up-regulated in NKT-like and NK cells in patients with COPD and that this is associated with increased pro-inflammatory and cytotoxic molecules in T, NKT-like and NK cells have important implications for treatment strategies to target these cells.
The relative lack of corticosteroid efficacy in COPD has been poorly understood and a major limiting factor in COPD treatment . We now show that production of IFNγ and TNFα and granzyme B by T and NKT-like subsets of lymphocytes are not inhibited with therapeutic doses of methylprednisolone, a commonly used corticosteroid in vitro, confirming clinical findings. Importantly we show that by targeting Pgp1 with a low dose of the inhibitor, cyclosporine A, production of the pro-inflammatory cytokines IFNγ and TNFα are significantly inhibited. Further, a combination of very low dose cyclosporine A (2.5 ng/mL) with standard dose methylprednisolone (10-6 M), results in synergistic inhibition of these pro-inflammatory cytokines known to have systemic effects in patients with COPD . The excellent negative correlation between efflux of Calcein-AM, previously shown to identify Pgp1 function in cells  and our findings of Pgp1 expression in T, NKT-like and NK cells confirms these novel findings.
Our group has undertaken pioneering work on the role of T-cell pro-inflammatory cytokines, particularly TNFα and IFNγ, and their role in COPD . T cells are a major inflammatory cell type present in the lung in COPD patients. Our findings in 2007 were the first comprehensive report of intracellular pro- and anti-inflammatory T cell cytokines in the separate compartments of blood, bronchoalveolar lavage and intraepithelial T cells from bronchial brushings from COPD subjects and smokers. Interestingly, T-cell derived TNFα has been shown to cause apoptosis of airway epithelial cells and impair the clearance of these cells by alveolar macrophages . Recently, TNFα has been described as the “driving force behind COPD” , and induction of TNFα in the lung has been shown to result in emphysema in the mouse model . TNFα has also been shown to induce IL-2Rs and IFNγ production by T cells and activate neutrophils, macrophages, endothelial cells and fibroblasts ; cells that play important roles in the pathogenesis of COPD . Recently it has been shown that fractalkine, a potent chemoattractant for monocytes and T cells produced by airway smooth muscle cells, was induced in the presence of both IFNγ and TNFα . Furthermore, increased TNFα levels have been shown to be increased in diseases associated with COPD such as cardiovascular disease and as such, systemic treatment with low dose Cyclosporin A and prednisolone may result in improvements of a broad range of inflammatory conditions associated with COPD .
An important extension of this work would be to study T, NKT-like and NK cells in both the airways and lung tissue of COPD patients as we have previously done [5, 15] to determine the role Pgp1 may play in steroid resistance in these compartments. If this hypothesis is correct, targeting the airways with inhaled low dose CsA combined with steroid may be the treatment of choice to inhibit these pro-inflammatory molecules associated with COPD disease.
It would also be of interest to study Pgp1 expression in lymphocyte subsets in the peripheral blood of smokers who have not progressed to COPD. Our previous findings of increased T-cell production of IFNγ and TNFα in the peripheral blood of COPD patients but not smokers without COPD suggests Pgp1 may not be upregulated in smokers who have not progressed to COPD. However, there may be a subset of susceptible smokers who do have increased Pgp1 in these cells who have an increased risk of developing COPD and further studies are warranted to investigate this hypothesis.
Our present findings show that there was a significant increase in Pgp1 expression by T and NKT-like cells compared with NK cells suggesting these subsets of lymphocytes may be the most resistant to effects of therapeutic drugs.
We showed that the cytotoxic molecule, granzyme B is unaltered by standard dose methylprednisolone and requires much higher concentrations of cyclosporine usually used for immunosuppression in patients such as those following lung transplantation . Our results suggest that patients with high levels of this cytotoxic molecule may require treatment with higher dose Cyclosporin A. Further, identification of patients with high levels of granzyme B and response following treatment may allow tailoring therapeutics to individual patients using these techniques, to optimize immunosuppression as to possibly avoid problems associated with over-immunosuppression (e.g., infection and malignancy) and under-immunosuppression with worsening of COPD symptoms.