The ongoing clinical syndrome coronavirus disease 2019 (COVID-19) pandemic has elicited a flurry of scientific research focused on characterizing the disease’s pathology and developing more effective diagnostics and therapies.
Changes in the physical properties of blood cells can contribute to dysfunctional vascular flow—one of COVID-19’s many effects on the human body. Moreover, certain diseases can be diagnosed and their progression monitored through measurement of the physical properties of blood cells, such assize and mechanical properties. Accordingly, a team led by the Guck Lab at the Max Planck Institute hypothesized that the physical properties of blood cells might provide insight into the pathology of COVID-19. They reported their findings in the July 20, 2021 special issue of Biophysical Journal entitled “Biophysicists Address Covid-19 Challenges II.”
The physical properties of blood cells were measured by using real-time deformability cytometry. In this technique, blood cells flowing through the channel of a microfluidic device are observed via microscopy; these conditions mimic in vivo blood flow through a small vessel. Physical properties like cell cross-section, volume, deformability, and Young’s modulus can then be calculated from the cell’s response to the physical forces of flow.
The study examined blood cells collected from hospitalized COVID-19 patients, recovered COVID-19 patients ~7 months after hospitalization, and healthy volunteers. The results show changes in the physical properties of four types of blood cells:
- Erythrocytes: Red blood cells in COVID-19 patients were smaller and more deformable than those in healthy volunteers, which may be indicative of the cell damage reported in previous studies. These changes were partly retained in recovered COVID-19 patients.
- Lymphocytes: The stiffness of lymphocytes, measured via deformability and Young’s modulus, was lower in COVID-19 patients than in healthy volunteers. This metric returned to baseline in recovered patients.
- Monocytes: Monocytes were bigger—as measured by both cross-sectional area and volume—in COVID-19 patients than in healthy volunteers and recovered patients. This observation may be consistent with the emergence of a phagocytic phenotype and supports the results of previous research.
- Neutrophils: Neutrophils in COVID-19 patients were larger and more deformable than those in healthy volunteers. These changes, consistent with cell activation, might disrupt blood flow through vessels and were partly retained in recovered patients.
Real-time deformability cytometry is a rapid, inexpensive, and label-free technique that can differentiate between blood cells in COVID-19 patients and healthy volunteers and might form the basis of a new diagnostic technique. To realize this goal, future studies must validate the findings of this report in a large, heterogeneous patient population with a range of COVID-19 symptom severity. Additionally, the results must be compared against those in other common infectious diseases, which can also alter the physical properties of blood cells.