Lung cells of patients with idiopathic pulmonary fibrosis (IPF) have higher than normal levels of two cytokines, small proteins crucial to the functioning of the immune system, according to a study.
The researchers also discovered higher than normal levels of the cytokines interleukin 33 (IL-33) and thymic stromal lymphopoietin (TSLP) in mouse models of IPF.
This suggested there is a link between innate immune response — that is, the response of the cells and mechanisms that defend the body against infection — and the development of IPF. It also suggested that animals are important in the study of lung diseases.
The study, “Upregulation of interleukin-33 and thymic stromal lymphopoietin levels in the lungs of idiopathic pulmonary fibrosis,” was published in the journal BMC Pulmonary Medicine.
The epithelium in our respiratory tract is a large surface that is in contact with the outside environment through the air we breath. Lung epithelial cells contain several cytokines, which regulate cells’ movement toward sites of inflammation, infection and trauma.
Three cytokines are particularly relevant to lung epithelial cells’ immune defense: IL-33, IL-25 and TSLP. The immune responses they mediate play an important role in the immune response of pulmonary fibrosis animal models, such as the bleomycin-induced lung fibrosis mouse model.
However, “despite the relations of the pulmonary fibrosis with IL-25, IL-33, and TSLP, the clinical implications of these cytokine remain poorly defined due to the small number of subjects (less than 15) examined in the previous studies,” researchers wrote.
So the team decided to investigate how levels of the cytokines influence the clinical outcomes of patients with lung fibrosis. They measured IL-25, IL-33, and TSLP levels in bronchoalveolar lavage (BAL) fluid extracted from 100 patients with IPF and 40 healthy controls.
They also measured levels of the three proteins in patients with other interstitial lung diseases, including non-specific interstitial pneumonia, hypersensitivity pneumonitis, and sarcoidosis.
Researchers observed that levels of TSLP and IL-33 were significantly higher in IPF patients than in controls and patients with other lung diseases. Levels of IL-25 were about the same in all three groups.
“These observations strongly support the notion of accentuated innate immune activation in the development of IPF, an effect commonly seen in animal models of acute lung injury and fibrosis,” the scientists wrote.
They also suggested that levels of IL-33 and TSLP in BAL fluids might be used to distinguish patients with IPF from those with other chronic interstitial lung diseases.
Overall, the results suggest that the development of IPF may be associated with the activation of certain innate immune responses, particularly those mediated by IL-33 and TSLP.