S1P Contributes to Endotoxin-enhanced B-Cell Functions Involved in Hypersensitivity Pneumonitis.

In a proportion of patients with hypersensitivity pneumonitis, the biological and environmental factors that sustain inflammation are ill defined, resulting in no effective treatment option. Bioaerosols found in occupational settings are complex and often include Toll-like receptor ligands, such as endotoxins. How Toll-like receptor ligands contribute to the persistence of hypersensitivity pneumonitis, however, remains poorly understood. In a previous study, we found that an S1P (sphingosine-1-phosphate receptor 1) agonist prevented the reactivation of antigen-driven B-cell responses in the lung. Here, we assessed the impact of endotoxins on B-cell activation in preexisting hypersensitivity pneumonitis and the role of S1P in this phenomenon. The impact of endotoxins on pre-established hypersensitivity pneumonitis was studied . S1P levels were tracked on B cells in the course of the disease using S1P-eGFP knockin mice, and the role of S1P on B-cell functions was assessed using pharmacological tools. S1P was found on B cells in experimental hypersensitivity pneumonitis. Endotoxin exposure enhanced neutrophil accumulation in the BAL of mice with experimental hypersensitivity pneumonitis. This was associated with enhanced CD69 cell-surface expression on lymphocytes in the BAL. In isolated B cells, endotoxins increased cell-surface levels of costimulatory molecules and CD69, which was prevented by an S1P agonist. S1P modulators also reduced TNF production by B cells and their capacity to trigger T-cell cooperation . An S1P ligand directly inhibited endotoxin-induced B-cell activation.