Systemic immune cell activation in a subgroup of patients with idiopathic pulmonary fibrosis

Abstract

Background: The prognosis of idiopathic pulmonary fibrosis (IPF/UIP) is poor and its immunopathogenesis is insufficiently understood.

Objectives: The aim of our study was to elucidate the compartmentalization of cell activation and the influence of corticosteroid therapy upon this activation in IPF/UIP. We determined the concentrations of proinflammatory cytokines released by bronchoalveolar lavage (BAL) cells and peripheral blood mononuclear cells (PBMNC) in treated and untreated patients with IPF/UIP. We chose tumor necrosis factor-alpha (TNFalpha) since it is a cytokine predominantly secreted by cells of the monocyte/macrophage lineage and interleukin-2 (IL-2) exclusively by T lymphocytes.

Methods: The release of TNFalpha and IL-2 by BAL cells and PBMNC was measured in cell culture supernatants of 72 treated and untreated IPF/UIP patients. Additionally, in the blood compartment serological parameters reflecting the monocyte/macrophage and lymphocyte activation, such as neopterin and soluble IL-2 receptor (sIL-2R), were determined.

Results: The TNFalpha release by BAL cells was significantly elevated in both groups compared to controls but did not differ between treated and untreated patients with IPF/UIP. In 7 of 19 untreated patients with IPF, PBMNC were activated and released increased amounts of TNFalpha. In only 1 of 17 treated patients with IPF, TNFalpha release by PBMNC could be found. The serum level of neopterin, a marker of cell activation of the monocyte/macrophage lineage did not differ between treated and untreated patients. The BAL lymphocyte and PBMNC IL-2 release was significantly elevated in IPF/UIP patients without therapy compared to controls (p < 0.05). In contrast, no IL-2 release of BAL cells or PBMNC was observed in treated IPF/UIP patients. Lymphocyte activation was furthermore identified in untreated IPF patients by elevated soluble IL-2 receptor serum concentrations (p < 0.0001).

Conclusions: Cells of the monocyte/macrophage lineage and T lymphocytes are activated in BAL cells and PBMNC of patients with IPF/UIP. During treatment, the systemic and local activation of T cells is suppressed. BAL macrophages, however, maintain their activated status, which might be the cause for the frequent chronic progression of the disease.