Expression and Significance of Th17 and Treg Cells in Pulmonary Infections with Gram-Negative Bacteria

The aim of this study was to investigate the expression and significance of T helper type 17 (Th17) and regulatory T (Treg) cells in severe pulmonary infection with gram-negative bacteria (GNB). The peripheral venous blood (PVB) and bronchoalveolar lavage fluid (BALF) were collected from patients receiving mechanical ventilation in the intensive care unit (ICU) owing to: (1) pulmonary GNB infection (group I) and (2) nonpulmonary infection (group NI). Patients from the two groups were matched based on their Acute Physiology and Chronic Health Evaluation II (APACHE II) scores and were recruited in the same period. The levels of Th17 and Treg cells in the PVB and BALF were measured by flow cytometry. (1) The levels of Th17 and Treg cells in the PVB and BALF of the infection group (I) were significantly higher than those of the noninfection group (NI) (p < 0.01), and the levels decreased significantly after treatment (p < 0.01). (2) The Treg/Th17 cell ratio in the PVB and BALF of group I was significantly lower than those of group NI and after treatment (p < 0.01). (3) The levels of Th17 and Treg cells in the PVB and BALF could not predict the 28-day mortality (p > 0.05). The expression of Th17 and Treg cells was abnormal in patients with severe pulmonary GNB infection. Our data suggest an overactive immune response in the early stages of inflammation, but the levels of Treg and Th17 cells failed to predict the 28-day mortality.