Label-free Neutrophil Enrichment from Patient-derived Airway Secretion Using Closed-loop Inertial Microfluidics
Summary
In this research, we demonstrate a label-free neutrophil separation method from clinical airway secretions using closed-loop operation of spiral inertial microfluidics. The proposed method would expand the clinical in vitro assays for various respiratory diseases.
Abstract
Airway secretions contain a large number of immune-related cells, e.g., neutrophils, macrophages, and lymphocytes, which can be used as a major resource to evaluate a variety of pulmonary diseases, both for research and clinical purposes. However, due to the heterogeneous and viscous nature of patient mucus, there is currently no reliable dissociation method that does not damage the host immune cells in the patient airway secretion. In this research, we introduce a sample preparation method that uses inertial microfluidics for the patient's immune assessment. Regardless of the heterogeneous fluidic properties of the clinical samples, the proposed method recovers more than 95% of neutrophils from airway secretion samples that are diluted 1,000-fold with milliliters of clean saline. By recirculating the concentrated output stream to the initial sample reservoir, a high concentration, recovery, and purity of the immune cells are provided; recirculation is considered a trade-off to the single-run syringe-based operation of inertial microfluidics. The closed-loop operation of spiral microfluidics provides leukocytes without physical or chemical disturbance, as demonstrated by the phorbol 12-myristate 13-acetate (PMA)-induced elastase release of sorted neutrophils.
Introduction
Since cells are encapsulated in a large amount of mucus in airway secretions, the functional assessment of leukocytes by an in vitro assay has been hindered. Dithiothreitol (DTT) is the most common lysis buffer to dissociate and homogenize the sputum for cytological analysis and detection of mediators while providing tolerable viability of isolated cells1,2. However, DTT can interfere with surface-bound antigens of airway neutrophils, resulting in the disruption of neutrophil function such as elastase and myeloperoxidase (MPO) release2,3.Therefore, few studies of human airway neutrophil function have been conducted with peripheral blood neutrophils, which may not reveal the physiological characteristics of pulmonary4. Meanwhile, inertial microfluidics has made advances in isolating cells from various patient biomatrices5,6.The equilibrium between inertial lift forces and Dean drag aligns the particle/cell according to their size, which allows label-free particle separation7. Our group previously introduced a sample preparation method for circulating tumor cells8,9, pathogens in blood8, cells from a suspension culture10,11,12, and polymorphonuclear leukocytes (PMNs) from blood13,14.
Here, we introduce a protocol to prepare immune cells from a patient's airway secretions using closed-loop inertial microfluidics for a downstream in vitro assay, such as the neutrophil elastase (NE) assay. This method provides both high concentration and recovery, especially when there is a significant overlap in the lateral direction of the cell/particle from which the cell/particle-of-interest is to be removed, which is commonly observed in clinical samples. By recirculating the Inner wall (IW)-focused large particles or cells back to the input sample tube, the particle or cell-of-interest concentrates in the original reservoir, while background fluids with small mucin aggregates pass through the waste reservoir. Despite the heterogeneous fluidic properties of clinical samples, the proposed method recovers consistently above 95% of neutrophils from airway secretion samples that are diluted 1,000-fold with a clean saline solution (~1 mL). By contrast, the lysis method presents a wide range of PMNs recovery rates depending on the sample condition. The proposed protocol captures leukocytes in a label-free manner with no physical or chemical disruption, which provides the possibility to harvest delicate cells from clinically challenging biometrics with minimally invasive procedures.
Protocol
Representative Results
Discussion
In inertial microfluidics, particle and cells localize at a certain lateral position in a micro-channel based on their size5,18,19,20. Due to the combined effect of the Dean drag force and the inertial lift force in the curved microchannel, large particles or neutrophils (>10 µm) are located inside the channel and small particles, mucus aggregates, and debris smaller than 6 µm are…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was supported by NIH/NIAID (R21AI119042) as well as NIH U24 Sample Sparing assay program (U24-AI118656).
Materials
| PDMS precursor | Dow corning | 184 SIL ELAST KIT 3.9KG | 10:1 ratio of base and curing agent |
| VWR gravity convection oven | VWR | 414005-128 | PDMS precursor to be cured in 90 deg. |
| 100mm petri dish | VWR | 89000-324 | Fabrication of PDMS Supporting layer |
| Harris Uni-core puncher | Sigma-aldrich | WHAWB100076 | 2mm diameter or other depending on the tubing size |
| Air plasma machine | Femto Science | Cute | Surface plasma treatment for PDMS device to bottom base. |
| 2” x 3” glass slide | TED PELLA, INC. | 2195 | To support PDMS device |
| Masterflex spooled platinum-cured silicone tubing, L/S 14 | Cole-Parmer | EW-96410-14 | Tubing for microfluidics and peristlatic pump |
| 1/16 inch Luer connector, male | Harvard apparatus | PC2 72-1443 | Connector for fluid guide |
| 50mL Falcon tube | Corning | 21008-940 | sample collection & preparation |
| Phosphate-Buffered Saline, 1X Without Calcium and Magnesium | Corning | 45000-446 | Buffer solution to dilute sample |
| Halyard Closed suction Catheter, Elbow, 14F/ channel 4.67mm | HALYARD HEALTH | 22113 | Tracheal seceation suction catheter |
| 0.9% Sterile Normal saline, 10mL pre-filled syringe | BD PosiFlush | NHRIC: 8290-306547 | For tracheal seceation collection from the patients |
| SecurTainer™ III Specimen Containers, 20mL | Simport | 1176R36 | Sterile sputum (airway secretion) collection container |
| Syringe with Luer-Lok Tip, 10mL | BD | BD309604 | To pipette homogenize the mucus sample and reach the bottom of sample tube |
| BD Blunt Fill Needle, with BD Luer-Lok Tip | BD | To pipette homogenize the mucus sample and reach the bottom of sample tube | |
| 40µm nylon cell strainer | Falcon | 21008-949 | To remove large chunk or blood clots, which can block the microfluidics access hole or the channel. |
| Peristaltic pump (Masterflex L/S Digital Drive) | Cole-Parmer | HV-07522-30 | operation of microfluidics |
| BD LSR II flow cytometer | BD Bioscience | LSR II flow cytometer | Quantification of cell recovery ratio |
| Fluorescein isothiocyanate (FITC)-conjugated mouse anti-human CD66b monoclonal antibody | BD Bioscience | 561927 | Immunostaining of neutrophils for Flow cytometer analysis |
| Allophycocyanin (APC)-conjugated mouse anti-human CD45 monoclonal antibody | BD Bioscience | 561864 | Immunostaining of neutrophils for Flow cytometer analysis |
| Plate reader | Thermo Fisher scientific | Varioskan | Plate reader for neutrophil elastase assay, ex485/em525 |
| Neutrophil elastase assay kit | Cayman Chemical | 600610 | Neutrophil functionality assessment |
| Fluoresbrite YG Microspheres 10.0µm | PolyScience, Inc. | 18140-2 | Fluorescent particles to express white blood cell trajectory in microfluidics |
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