Altered phenotype of blood dendritic cells in patients with acute pneumonia

Dendritic cells (DCs) play a key role in the host defence against inhaled pathogens. However, the phenotype of blood DCs in patients with acute respiratory infections is unknown.

To investigate the number and the expression of function-associated molecules of blood DCs in patients with acute infectious pneumonia.

Sixteen patients with acute pneumonia and 19 controls without pneumonia were included in the study. The number as well as the expression of function-associated molecules of myeloid DCs (mDCs) and plasmacytoid DCs (pDCs) were analysed in peripheral blood using four-colour flow cytometry.

Elevated concentrations of procalcitonin (median: 0.55 ng/ml) and the rapid response to antibiotic treatment suggested a bacterial origin of the pneumonia in the patients. Total mDC (median: 27% of the controls) and pDC counts (median: 53% of the controls) were markedly reduced in patients with pneumonia, as compared to the controls. Percentages of blood mDCs, but not pDCs, were negatively correlated with serum concentrations of C-reactive protein. Patients with pneumonia were characterised by a significantly increased expression of Fc gamma receptors (CD32 and CD64) on mDCs and the Toll-like receptor 9 (TLR9) on pDCs.

Circulating DCs are markedly reduced in patients with pneumonia, and characterised by an up-regulation of molecules recognising pathogen-associated molecular patterns and opsonised antigens.