A blood test to measure levels of the immune signaling protein interleukin-32 (IL-32) may be a useful biomarker to diagnose and assess the severity of chronic obstructive pulmonary disease (COPD), a new study suggests.
The study, “Correlation between serum IL-32 concentration and clinical parameters of stable COPD: a retrospective clinical analysis,” was published in the journal Nature Scientific Reports.
Chronic inflammation in the lungs is a hallmark of COPD. The imbalance of various inflammatory mediators, including immune system signaling proteins — known as cytokines — play an essential role in small airway inflammation.
IL-32 is an inflammatory cytokine secreted by a variety of immune cells. Studies have shown that IL-32 is produced at high levels in the lungs of people with COPD and participates in the inflammatory process.
The prevalence of COPD has increased among Chinese people year by year, primarily due to environmental pollution and an aging population. Thus, researchers based at the Xi’an Medical University, in China, along with investigators at local hospitals, examined the levels of IL-32 in people with stable COPD and explored the relationship between IL-32 and clinical parameters.
The team analyzed the medical records of 116 people with stable COPD — defined as patients who are in stable condition with mild symptoms of infrequent cough and shortness of breath. A total of 70 healthy people were included as controls.
The patients were included if they had a lung function test within three days before enrollment, and had not had a lung infection or received antibiotics, glucocorticoids, or the bronchodilator theophylline within two weeks.
The severity of COPD was based on the diagnostic criteria of the Global Initiative for Chronic Obstructive Lung Disease (GOLD). Those at the GOLD-1 level had mild disease, while those at GOLD-2 were considered moderate. GOLD-3 patients had a severe illness, and GOLD-4 had very severe disease.
The results revealed that, overall, patients with stable COPD had significantly higher levels of IL-32 in their blood (169.9 picograms (pg)/mL) compared with healthy individuals (105.1 pg/mL).
IL-32 levels were highest in those at the GOLD-3 and GOLD-4 levels, compared with patients at GOLD-1 and GOLD-2, and significantly increased with disease duration.
The researchers also used the mMRC score, a five-point (0-to-4) scale that reflects the severity of shortness of breath, called dyspnea. Patients with an mMRC score of 4 — meaning more severe shortness of breath — had significantly higher levels of IL-32 than those with lower mMRC scores.
These findings suggested that “IL-32 might be a molecular biomarker that reflects the severity of COPD,” the researchers wrote.
No associations between the protein levels and gender, smoking, or body mass index were identified.
The serum concentration of IL-32 was negatively correlated with lung function, in which patients with the highest levels of IL-32 scored the lowest on lung function tests as measured by spirometry (FEV1/FVC and FEV1% predicted). In that test, a machine called a spirometer measures how much air a person can breathe in, and then how much and how forcefully the individual can exhale that air back out in a set matter of seconds. The results are reported as forced vital capacity (FVC) and forced expiratory volume (FEV-1).
A more detailed statistical analysis found that COPD grading, disease duration, and FEV1/FVC significantly influenced the levels of IL-32, in which FEV1/FVC was the greatest influence.
Finally, a serum IL-32 concentration of 105 pg/mL was calculated to be the threshold value to distinguish COPD patients from healthy individuals, with a sensitivity of 85.34% and a specificity of 64.29%. Of note, in this case, sensitivity refers to the ability to correctly diagnose COPD, while specificity refers to the ability to correctly identify cases that are not of COPD.
Overall, the results indicated that “increased IL-32 is involved in the chronic disease progression of COPD, suggesting that IL-32 may be a molecular biomarker that reflects the severity of COPD and contributes to the disease diagnosis,” the researchers concluded.
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