Microfluidic Device Allows Collection, Analysis of Hard-to-Handle Immune Cells

Scientists have developed a new microfluidic tool for isolating rapidly and effectively neutrophils from small blood samples, an achievement that could provide information essential to determine better the immune system's response to traumatic injury. The system can also be modified to isolate almost any type of cell.

The research was published in August 2010 in advance online release in the journal Nature Medicine. "Neutrophils are currently garnering a lot of interest from researchers and clinicians, but collecting and processing them has been a real challenge,” said Kenneth Kotz, Ph.D., of the Massachusetts General Hospital (MGH; Boston, USA) Center for Engineering in Medicine, and lead author of the study. "This tool will allow a new range of studies and diagnostics based on cell-specific genomic and proteomic signatures.”

Part of the body's first-line defense against injury or infection, neutrophils were long thought to play fairly simple roles, such as releasing antimicrobial proteins and ingesting pathogens. However, recent studies find their actions to be more complex and critical to both chronic and acute inflammation, particularly the activation of the immune system in response to injury.

Examining patterns of gene expression and protein synthesis in neutrophils could reveal fundamental information about the immune response, but collecting the cells for analysis has been a challenge. Conventional isolation procedures take more than two hours and require comparatively large blood samples. Neutrophils also are sensitive to handling and easily become activated, changing the molecular patterns of interest, and they contain very small amounts of messenger RNA, which is required for studies of gene expression.

Building on their experience developing silicon-chip-based devices that capture CD4 T cells for HIV diagnosis or isolate circulating tumor cells, Dr. Kotz's team developed a system that gathers a neutrophil-rich sample from microliter-sized blood samples in less than five minutes, reducing the risk of disturbing cells in the process. To meet the requirements for speed and precision, the researchers totally redesigned the geometry, antibody-based coating, and other features of the cell-capture module at the heart of the device. The samples gathered were successful in revealing differences in gene and protein activity relevant to the cells' activation status.

While the laboratory tests were encouraging, samples from critically injured patients need to be handled and processed in real-world clinical environments. Through the efforts of study coauthor Lyle Moldawer, Ph.D., of the University of Florida College of Medicine, the devices were tested at six sites participating in a major U.S. National Institutes of Health (Bethesda, MD, USA)-sponsored study of the immune response to injury, led by Ronald Tompkins, M.D., Sc.D., chief of the MGH Burns Service and also a study coauthor. Analyzing samples from 26 patients with serious burns or other traumatic injuries revealed complicated gene expression patterns that shifted during the 28 days after injury, most likely reflecting complex interactions between various immune system components.

Dr. Kotz stated, "Until now, it's been logistically impossible to study neutrophils to the extent we have in this paper.” He noted that their analysis of neutrophil samples from trauma patients is the largest such study to date and added, "This technology--which is much faster and gentler than current approaches to isolating cells--can be scaled and modified to capture just about any cell type, and we're working to apply it to other cell-based assays.”

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