Roflumilast prevents the increase in inflammatory cells in the lungs of mice chronically exposed to cigarette smoke: an immunohistochemical study

RATIONALE We have previously reported that roflumilast, an investigational phosphodiesterase 4 (PDE4) inhibitor, fully prevented the development of emphysema in C57BL/6J mice chronically exposed to cigarette smoke (AJRCCM 2005; 172: 848-53). In the present study, we investigated the effect of roflumilast on changes in inflammatory cell volume density (VV) in mice exposed to cigarette smoke for 7 months. METHODS C57BL/6J mice were either exposed to room air (N=5) or cigarette smoke for 7 months (N=5). Additionally, a group of cigarette smoke exposed animals received roflumilast 5 mg/kg per os (N=5). VV was assessed immunohistochemically and by point counting. Neutrophils were marked with myeloperoxidase antibody, macrophages with Mac-3 antibody, dendritic cells with fascin antibody, B-lymphocytes with B220 antibody, and CD4+ T-cells with CD4+ antibody. RESULTS Chronic cigarette smoke exposure of mice, as compared to air exposure, increased neutrophil VV (2.3±0.3 x 10-4 mL/g vs 1.2±0.2 x 10-4 mL/g, p<0.01), macrophage VV (14.4±0.4 x 10-4 mL/g vs 8.0±0.5 x 10-4 mL/g, p<0.01), dendritic cell VV (6.1±0.4 x 10-4 mL/g vs 1.9±0.3 x 10-4 mL/g, p<0.01), B-lymphocyte VV (3.4±0.4 x 10-4 mL/g vs 0.6±0.3 x 10-4 mL/g, p<0.01), and CD4+ T-cell VV (6.7±1.0 x 10-4 mL/g vs 1.1±0.3 x 10-4 mL/g, p<0.01). Roflumilast prevented the increase in neutrophil VV by 78% (p<0.05), macrophage VV by 70% (p<0.01), dendritic cell VV by 48% (p<0.01), B-lymphocyte VV by 100% (p<0.01), and CD4+ T-cell VV by 98% (p<0.01). CONCLUSIONS These results indicate that chronic cigarette smoke exposure in mice elicits an increase of cells involved in both the innate and adaptive immune responses. Roflumilast administration significantly prevented the recruitment of these cells.