Lung Fibrosis Increases Levels of Specific Surface Proteins, Suggests Disease Markers

A recent study published in the journal PLOS One, found two members of a class of proteins called surfactant proteins (SPs) at increased levels as a result of lung fibrosis and suggests that future studies could reveal the proteins, SP-A and SP-D,  as markers of disease severity.

Pulmonary emphysema and idiopathic pulmonary fibrosis (IPF) are defined by distinct clinical, functional, radiological, and pathological criteria. But both conditions can co-exist and define a condition known as combined pulmonary fibrosis and emphysema (CPFE) which is characterized by upper lobe emphysema and lower lobe pulmonary fibrosis.

Previous reports already determined that the SP-A and SP-D are increased in the blood of patients with chronic obstructive pulmonary disease (COPD), when compared to smokers and non-smoking controls; and that SPs may play a role in the development of interstitial lung diseases.

For the study,“Serum Levels of Surfactant Proteins in Patients with Combined Pulmonary Fibrosis and Emphysema (CPFE),” a team of researchers hypothesized that in CPFE patients, SP levels are probably altered when compared to patients with only IPF and patients with only emphysema and that the alterations may correlate with disease activity. Then researchers measured the levels of the four types of SPs – A, B, C and D – in four groups: patients with CPFE, emphysema only, IPF only, and healthy controls. Additionally, the team tested how the levels of SPs may associate with pulmonary function, disease severity, and survival.

The study included 122 patients (31 with emphysema, 62 with IPF, 29 with CPFE) and 25 healthy controls who underwent blood analysis for SPs, pulmonary function tests (PFTs), and other tests. Patients were followed for one year.

The analysis showed that when fibrosis is present, either alone or co-existing with other conditions, the levels of both SP-A and SP-D in patients’ blood is higher. These results suggest that circulating SP levels correlate with damage in fibrotic lungs, and that the increase may be due to local overproduction as a result of damage of lung alveoli or overleakage towards the systemic blood circulation.

Researchers concluded that the role of SP-A and SP-D, as markers of disease severity, should be investigated in future studies.