Interstitial lung disease (ILD) is a group of lung disorders characterized by inflammation and scarring of the lung tissue. ILD effects the interstitium of the lung, which is the area of the lung between the air sacs (alveoli) where gas exchange takes place. The scarring and inflammation in ILD can cause the lungs to become stiff and less able to expand and contract, leading to difficulty breathing and reduced oxygen uptake.
There are several different types of ILD, including an ILD associated with rheumatoid arthritis (RA). RA-associated ILD (or RA-ILD) effects 5-10% of patients with RA. Unfortunately, RA-ILD is associated with poor quality of life and early death. Treatment options for RA-ILD are extremely limited, and more research is desperately needed to better understand the cause of RA-ILD so that more effective treatments can be identified and implemented.
Our team recently made a new discovery that a particular antibody in the blood called anti-peptidylarginine deiminase-4 (PAD4) is associated with less severe RA-ILD. When anti-PAD4 antibodies were present in the blood of patients with RA-ILD, they had less lung fibrosis, better lung function and had improved survival compared to RA-ILD patients who were negative for the anti-PAD4 antibody. This novel finding suggests that this antibody could be useful to better characterize prognosis in patients with RA-ILD. Importantly, our ongoing work is investigating what effect this antibody has on cells in the lung to better understand how it is associated with more favorable outcomes in RA-ILD.
Idiopathic pulmonary fibrosis (IPF) is another form of ILD that occurs in people without RA. The cause of IPF is unknown, but our work has identified a subset of IPF patients (approximately 25%) who have RA-associated autoantibodies in their blood. This important finding suggests that a subset of IPF patients may have a lung disease more similar to patients with RA-ILD. Our ongoing work in this area is investigating whether other RA features, such as increased neutrophil extracellular trap (NET) formation in the lung, are present in the lungs of patients with IPF.