Bioparticle Microarrays for Chemotactic and Molecular Analysis of Human Neutrophil Swarming in vitro

Summary

This protocol generates bioparticle microarrays that provide spatially controlled neutrophil swarming. It provides easy access to the mediators that neutrophils release during migration and allows for quantitative imaging analysis.

Abstract

Neutrophil swarming is a cooperative process by which neutrophils seal off a site of infection and promote tissue reorganization. Swarming has classically been studied in vivo in animal models showing characteristic patterns of cell migration. However, in vivo models have several limitations, including intercellular mediators that are difficult to access and analyze, as well as the inability to directly analyze human neutrophils. Because of these limitations, there is a need for an in vitro platform that studies swarming with human neutrophils and provides easy access to the molecular signals generated during swarming. Here, a multistep microstamping process is used to generate a bioparticle microarray that stimulates swarming by mimicking an in vivo infection. The bioparticle microarray induces neutrophils to swarm in a controlled and stable manner. On the microarray, neutrophils increase in speed and form stable swarms around bioparticle clusters. Additionally, supernatant generated by the neutrophils was analyzed and 16 proteins were discovered to have been differentially expressed over the course of swarming. This in vitro swarming platform facilitates direct analysis of neutrophil migration and protein release in a reproducible, spatially controlled manner.

Introduction

Neutrophils, the most abundant white blood cell in the bloodstream¹, are gaining attention as potential diagnostic and therapeutic targets^2,3 because they may be involved in a variety of medical conditions including gout⁴, sepsis³, trauma^5,6, cancer^1,7,8, and various autoimmune diseases^5,9. Neutrophil swarming is a multistage, tigh....

Protocol

The authors acknowledge the healthy volunteers who kindly donated their blood. Blood specimens were obtained after informed volunteer consent according to institutional review board (IRB) protocol #2018H0268 reviewed by the Biomedical Sciences Committee at The Ohio State University.

1. Microfabrication of bioparticle microarray

1. Using standard photolithography procedures, generate the master silicon wafer.
   1. Generate a proof of the desired design using a computer-aided des.......

Discussion

We developed a microstamping platform to generate uniform arrays of bioparticles to stimulate in vitro neutrophil swarming. The in vitro nature of our platform allows us to circumvent the complications that arise with in vivo swarming experiments, namely the poor ability to analyze mediators released by swarming neutrophils⁵. Additionally, in vivo models are typically performed in rodents^11,12,13,

Materials

Name	Company	Catalog Number	Comments
"The Big Easy" EasySep Magnet	STEMCELL Technologies	18001	Magnet to use with neutrophil isolation kit
Cell Incubator	Okolab	777057437 / 77057343	Okolab cage incubator for temperature and CO2 control
EasySep Human Neutrophil Isolation Kit	STEMCELL Technologies	17957	Kit for immunomagnetic negative selection of human neutrophils
Eclipse Ti2	Nikon Instruments	MEA54010 / MEF55037	Inverted research microscope
Escherichia coli (K-12 strain) BioParticles Texas Red conjugate	Invitrogen	E2863	Bioparticle powder, dissolve in water prior to addition to Zetag® array
Harris Uni-Core 8-mm biopsy punch	Sigma Aldrich	Z708925	To cut PDMS stamps
HetaSep	STEMCELL Technologies	7906	Erythrocyte aggregation agent for separating buffy coat from red blood cells in fresh human blood
Hoechst 33342	Life Technologies	H3570	Nucleus fluorescent stain
Human L1000 Array	Raybiotech Inc.	AAH-BLG-1000-4	High density array to detect 1000 human proteins
Human Serum Albumin (HSA)	Sigma Aldrich	A5843	Low endotoxin HSA, to prepare 2 % solutions in IMDM for isolated neutrophils
Iscove's Modified Dulbeccos' Medium (IMDM)	Thermo Fisher Scientific	12440053	To resuspend isolated neutrophils
K2-EDTA tubes	Thermo Fisher Scientific	02-657-32	Tubes for blood collection
Low Reflective Chrome Photomask	Front Range Photomask	N/A	Dimensions 5" x 5" x 0.09" (L x W x D)
Microarray Scanner	Perkin Elmer	ASCNGX00	Fluorescence reader of protein patterned microdomains
Microscopy Image Analsysis Software - Imaris	Bitplane	9.3.0	Software for automatic cell tracking analysis
NiS Elements Advanced Research Software Package	Nikon Instruments	MQS31100	Software for automatic live cell imaging and swarm size calculation
Poly-L-lysine fluorescein isothiocyanate (PLL-FITC)	Sigma Aldrich	P3069-10MG	30,000 - 70,000 MW PLL labeled with FITC, used to fluorescently label CP solution
SecureSeal 8-well Imaging Spacer	Grace Bio-Labs	654008	8-well, 9-mm diameter, adhesive imaging spacer
Silicon Wafer	University Wafer	590	Silicon 100 mm N/P (100) 0- 100 ohm-cm 500 μm SSP test
Spin Coater	Laurell	WS-650MZ-23NPPB	Used to spincoat a 40-µm layer of photoresist onto silicon wafer
SU-8 2025	MicroChem	2025	Negative photoresist to make silicon master wafer
SU-8 Developer	MicroChem	Y020100	Photoresist developer. Remove non-crosslinked SU-8 2025 from silicon wafer
Sylgard 184 (polydimethylsiloxane, PDMS)	Dow	1673921	2-part silicone elastomer kit for making microstamps and PDMS wells
UV Exposure Masking System	Kloé	UV-KUB 2	Used to crosslink photoresist on silicon wafer through chrome mask with UV light
Water	Thermo Fisher Scientific	A1287303	High quality water to dilute bioparticles
Zetag 8185	BASF	8185	Cationic polyelectrolyte (CP), powder, Copolymer of acrylamide and quaternized cationic monomer, forms "inking solution" for microstamping when dissolved in water
Zymosan A S. cerevisiae BioParticles Texas Red conjugate	Invitrogen	Z2843	Bioparticle powder, dissolve in water prior to addition to Zetag array