Expression of pro-inflammatory cytokines by flow-sorted alveolar macrophages in severe pneumonia

Abstract

The aim of the present study was to further characterize the role of alveolar macrophages (AM) in acute human lung inflammation by evaluating their capacity to produce pro-inflammatory cytokines such as tumour necrosis factor (TNF)-alpha, interleukin (IL)-6 and IL-8. Patients with severe community-acquired pneumonia (CAP; n=12) and healthy volunteers (n=10) underwent bronchoalveolar lavage (BAL). AM were separated to high purity (>96%) using fluorescence-activated cell sorting. We determined the TNF-alpha, IL-6 and IL-8 cytokine gene expression in AM ex vivo using semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR). Moreover, we measured in vitro unstimulated, lipopolysaccharide (LPS)- and LPS/interferon-gamma inducible TNF-alpha, IL-6 and IL-8 cytokine release and evaluated samples of BAL fluids for the same pro-inflammatory cytokines using an enzyme-linked immunosorbent assay (ELISA). We found increased TNF-alpha, IL-6 and IL-8 messenger ribonucleic acid (mRNA) levels in AM from CAP patients that were significantly elevated only for IL-8. When challenged with endotoxin in vitro, AM obtained from CAP patients showed a strongly reduced potential to release TNF-alpha and IL-6 compared to healthy controls, whereas IL-8 secretion did not differ significantly between groups. Moreover, stimulation of AM from CAP patients with LPS plus IFN-gamma augmented TNF-alpha and IL-6 cytokine release to near normal levels. Interestingly, no TNF-alpha protein was measured in BAL samples from CAP patients, whereas IL-6 and IL-8 protein levels were found to be significantly increased. Together, highly purified alveolar macrophages from community-acquired pneumonia patients show relatively low ex vivo tumour necrosis factor-alpha and interleukin-6 but not interleukin-8 messenger ribonucleic acid levels that are associated with a decreased pro-inflammatory cytokine release in vitro which, however, can be restored by concurrent interferon-gamma stimulation.