Asthma is a chronic disease that inflames and narrows the airways of the lungs, causing recurring periods of wheezing, chest tightness, shortness of breath, and coughing. In the U.S., more than 25 million people are known to have asthma, and about 7 million of these are children.1
Despite its high prevalence, asthma is notoriously difficult to diagnose, characterize, and treat. Currently, there is no single test that doctors rely on to diagnose asthma. Instead, doctors take into account a patient’s history, symptoms, triggers, and allergies along with results from several breathing tests. The most common of these tests uses a spirometer to record the amount and the rate of air that a patient breathes in and out over a period of time. Patients may also undergo a bronchial challenge, in which a doctor attempts to trigger asthma by having a patient inhale certain drugs that cause the bronchioles, or air passages in the lungs, to constrict; patients with asthma generally become symptomatic at a lower dose of the drug. This test can also be reversed by giving patients drugs that dilate the bronchioles, and important information can be gleaned based on how quickly the patient returns to a normal state.
Yet these breathing tests can be challenging to administer to children or the elderly, which make up a large population of asthmatic patients. In addition, many of the tests rely partially on patients to be symptomatic at the time of their doctor’s visit, which, due to the intermittent nature of asthma, can easily result in a misdiagnosis. Furthermore, disease severity, expected clinical course, and risk of exacerbations are not easily determined with the tests that are currently available.
Cellular changes in asthma
Over the past several decades, significant progress has been made in identifying many of the cellular changes that occur in asthma patients. For example, the recruitment of white blood cells—such as eosinophils and neutrophils—to the lungs is believed to be a key factor in the development of asthma. With this knowledge, researchers have begun to explore new ways to diagnose asthma that are based on quantitative differences in cellular behavior rather than clinical observations.
Now, NIBIB-funded researchers led by David Beebe, Ph.D., Director of the Microtechnology, Medicine, and Biology lab at the University of Wisconsin, report that they have created a handheld device that can diagnose asthma from a single drop of blood within minutes. The device works by measuring a characteristic of neutrophils that is different in asthmatic versus non-asthmatic patients.
Neutrophils are white blood cells that quickly move to sites of infection where they are capable of ingesting invading micro-organisms. Neutrophils migrate to the lungs of asthmatic patients when other immune cells within the lung tissue become activated and begin to release chemokines, which are signaling proteins that attract neutrophils. Once inside the lung tissue, neutrophils release factors that cause the smooth muscle cells within the airways of the lungs to multiply, causing the airways to narrow and obstruct the passage of air.
Diagnosing asthma with blood
Beebe’s new handheld device is a microfluidic platform capable of assessing characteristics of neutrophils as they move in response to chemokines; this movement is known as chemotaxis. The device is the size of a microscope slide and made of two main components, a base and a lid. On the base, there are multiple tiny channels whose surfaces have been coated with a protein called P-selectin. When a patient’s blood is run through the channels, neutrophils bind to the P-selectin. Then, through a series of washes, the rest of the blood is removed, leaving only the neutrophils behind.
To initiate chemotaxis, a lid with a tiny amount of chemokines that attract neutrophils is placed on top of the base so that the chemokines come in contact with one end of the channels. As the neutrophils travel towards the chemokines, time lapse photos are taken of the neutrophils under a microscope.
In the final step, researchers use custom tracking software to automatically measure three sets of data: 1) the absolute migration speed (independent of the direction the cells move) 2) the chemotaxic index (displacement of the cell throughout time divided by its total path length) and 3) chemotaxis velocity (speed of the cell in the direction of the chemokine).
Testing in patients
Beebe and colleagues recently tested their diagnostic device in a small clinical trial of 34 subjects, 23 of whom had received a previous clinical diagnosis of mild asthma and 11 of whom had a diagnosis of non-asthmatic allergic rhinitis, a condition that causes cold-like symptoms but is distinct from asthma. The trial was led by Eric Sackmann, Ph.D., a former graduate student in Beebe's lab, and Sameer Mathur, M.D., Ph.D., Associate Professor of Medicine at the University of Wisconsin School of Medicine and Public Health. The results were published in the April 22, 2014 issue of PNAS.
The researchers found that while the absolute migration speed and the chemotaxic index did not vary between the two groups, the neutrophils of the asthmatic patients had a significantly lower chemotaxis velocity. The researchers used this as a biomarker to accurately identify 22 of the 23 asthmatic patients and 8 of the 11 non asthmatic patients.
Importantly, only one of the subjects was experiencing symptoms at the time of the test, highlighting the advantage of a diagnostic test that does not rely on clinical symptoms. In addition, the researchers point out that a simple finger prick requires minimal patient compliance and does not place a major physical stress on the patient, making it optimal for children and the elderly. The researchers also speculate that because the test provides a quantitative result, it could potentially be useful in determining asthma severity and for conducting routine assessments to determine how well the disease is being controlled and whether there is a risk for future exacerbation. Other strengths of the device are its ease-of-use, speed (the entire test can be run under 5 minutes), and its transportability. Finally, the researchers believe their device could be used to probe neutrophil function in other inflammatory diseases.
“Every day scientists make great strides in understanding the biological basis of disease. But simply knowing how we get sick is not enough. When we can combine this knowledge with technological innovation to design better, faster, cheaper, and easier-to-use diagnostic systems, then we’ve done something exceptional,” said Rosemarie Hunziker, Ph.D., a program director at NIBIB. “This device is another great example of NIBIB’s commitment to support the development of technologies that will have big impacts on healthcare.”
This research was supported in part by the National Institute of Biomedical Imaging and Bioengineering award #EB010039 and NIH Program Project Grant HL088584
Sackmann EK, Berthier E, Schwantes EA, Fichtinger PS, Evans MD, Dziadzio LL, Huttenlocher A, Mathur SK, Beebe DJ.
Characterizing asthma from a drop of blood using neutrophil chemotaxis.
Proc Natl Acad Sci U S A. 2014 Apr 22;111(16):5813-8.