Peripheral-type benzodiazepine receptors in bronchoalveolar lavage cells of patients with interstitial lung disease

Abstract

PK11195 is a ligand with high affinity for peripheral benzodiazepine receptors (PBRs), which are present in large numbers in macrophages. PBRs play a role in antioxidant pathways and apoptosis, key factors in control of lung health. Intrapulmonary PBRs, assessed in vivo by positron emission tomography (PET), are decreased in interstitial lung disease (ILD) despite increased macrophage numbers. We wished to ascertain whether the observed decrease in in vivo expression of PBRs in the PET scans could be accounted for by a reduction in PBRs per cell by saturation-binding assays of R-PK11195 in cells obtained by bronchoalveolar lavage (BAL). We performed receptor saturation-binding assays with [(3)H]-R-PK11195 on a mixed population of cells recovered by BAL to quantify the number of R-PK11195 binding sites per macrophage in 10 subjects with ILD and 10 normal subjects. Receptor affinity [dissociation constant (Kd)] was similar in ILD patients and controls. However, R-PK11195 binding sites per cell [(maximal binding sites available (B(max))] were decreased in macrophages obtained by BAL from subjects with ILD compared to normal (P<.0005). Microautoradiography confirmed localization of R-PK11195 to macrophages in a mixed inflammatory cell population obtained by BAL. These results demonstrate that in vitro PBR expression per cell on macrophages obtained by BAL is reduced in patients with ILD indicating a potentially functionally different macrophage phenotype. As PBRs are involved in the orchestration of lung inflammatory responses, this finding offers further insight into the role of macrophages in the pathogenesis of ILDs and offers a potential avenue for pharmacological strategy.