Neutrophil Lifespan Extension with CLON-G and an In Vitro Spontaneous Death Assay

Summary

This protocol details the preparation of CLON-G to extend the neutrophil lifespan to greater than 5 days and provides a reliable procedure for evaluating neutrophil death with flow cytometry and confocal fluorescence microscopy.

Abstract

The average lifespan of a neutrophil is less than 24 h, which limits basic research on neutrophils and the application of neutrophil studies. Our previous research indicated that multiple pathways could mediate the spontaneous death of neutrophils. A cocktail was developed by simultaneously targeting these pathways, caspases-lysosomal membrane permeabilization-oxidant-necroptosis inhibition plus granulocyte colony-stimulating factor (CLON-G), which prolonged the neutrophil lifespan to greater than 5 days without significantly compromising the neutrophil function. Concurrently, a reliable and stable protocol for assessing and evaluating neutrophil death was also developed. In this work, we show that CLON-G can prolong the neutrophil lifespan in vitro to more than 5 days, and we exhibit the lengthening of the neutrophil lifespan with FACS and confocal fluorescence microscopy. This report introduces procedures for the preparation of CLON-G and showcases an in vitro spontaneous death assay of neutrophils, which can be used for the study of neutrophils and for subsequently interrogating neutrophil death, thus providing a reliable resource for the neutrophil community.

Introduction

Neutrophils are known to comprise an arsenal of abundant cytoplasmic granules, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, antimicrobial enzymes, and various organelles that defend against invading microbes; additionally, they are highly motile and are the first cells recruited to the inflammation site, meaning neutrophils are the first line of defense of the innate immune system^1,2. Granulocyte transfusion therapy has hence become a promising clinical treatment for neutropenia-related infections to transiently boost neutrophil immunity^3,4

Protocol

The Boston Children's Hospital and State Key Laboratory of Experimental Hematology (SKLEH) Animal Care and Use Committee approved and monitored all the procedures. Figure 1 depicts a flow chart of neutrophil culturing with CLON-G and the in vitro death assay.

1. Neutrophil lifespan extension with CLON-G

NOTE: All the mentioned operations and materials must be sterile. Ensure all the solutions are well mixed and distributed evenly.

1. Preservation of the CLON-G components
   1. Dissolve 50 mg of Q-VD-oph (see Table of Materials

Results

The Wright-Giemsa-stained morphology (Figure 2A-D) and FACS phenotypes (Figure 2E-J) of the CLON-G treated neutrophils were not affected. The viability of the CLON-G treated neutrophils at 24 h was about 90%+ based on flow cytometry analysis (Figure 3) and the fluorescent image assays (Figure 4). Lower viability could result from improp.......

Discussion

Neutrophils play vital roles in innate and adaptive immunity, and their homeostasis is tightly regulated. Neutrophils are the most abundant leukocytes in human peripheral blood, and they have a robust and fast turnover. A healthy adult can release 1 x 10⁹ neutrophils/kg daily from the bone marrow²⁸. The death of neutrophils has hence become one of the puzzling enigmas of this field, and much effort has been dedicated to better understanding them. Caspase^29,<.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.2 µm syringe filter	Pall Corporation	4612	Filtrate prepared CLON-G components.
1.5 mL micro centrifuge tube	LABSELECT	MCT-001-150	Lab consumable.
15 mL Centrifuge Tubes	LABSELECT	CT-002-15	Lab consumable.
24 well cell culture plate	Falcon	351147	Neutrophil culture plate.
50 mL Centrifuge Tubes	LABSELECT	CT-002-50	Lab consumable.
BD LSRII	BD		Instrument for flow cytometry analysis of neutrophil death.
Calcium chloride (CaCl2)	Sigma Aldrich	C4901	Assitant of Annexin-V binding  to phosphatidylserine.
Confocal microscope	Perkinelmer	UltraVIEW VOX	Instrument for fluorescent analysis of neutrophil death.
Confocal plate	NEST	801001-20mm	Lab consumable for fluorescent image assay.
Counting beads	Thermo Fisher	C36950	Quantification in flow cytometry analysis of neutrophil death.
DFO	Sigma Aldrich	D9533	Component of CLON-G. LMP inhibitor.
Dimethyl sulfoxide ( DMSO)	Sigma Aldrich	D2650	Solvent for Q-VD-oph and Nec-1s.
Fetal Bovine Serum	Gibco	10099141C	Component of neutrophil culture basic medium. Nutrition supply.
FITC-Annexin-V	BD	51-65874X	Annexin-V can bind to phosphatidylserine of aged cells.This is at FITC channel.
Hsp70	Abcam	ab113187	Component of CLON-G. LMP inhibitor.
NAC	Sigma Aldrich	A9165	Component of CLON-G. Antioxidant.
Nec-1s	EMD Millipore	852391-15-2	Component of CLON-G. Necroptosis inhibitor.
Penicillin-Streptomycin Solution (PS)	Gibco	15070063	Component of neutrophil culture basic medium. Antibiotics to protect cells from bacteria comtamination.
Propidium Iodide (PI)	BioLegend	421301	For neutrophil death assay. A small fluorescent molecule that binds to DNA  but cannot passively traverse into cells that possess an intact plasma membrane.
Q-VD-oph	Selleck chem	S7311	Component of CLON-G. Pan-caspase inhibitor.
Recombinant Human Granulocyte Colony-stimulating Factor for Injection (CHO cell)(G-CSF)	Chugai Pharma China	GRANOCYTE	Component of CLON-G.  Promote neutrophil survival through Akt pathway.
Round-Bottom Polystyrene Tubes	Falcon	100-0102	Lab consumable for flow cytometry analysis.
RPMI1640	Gibco	C11875500BT	Component of neutrophil culture basic medium.
Saline	LEAGENE	R00641	Solution for flow cytometry analysis of neutrophil death.
Sodium hydroxide (NaOH)	FENG CHUAN	13-011-00029	pH adjustion for NAC.
Wright-Giemsa Stain Solution	Solarbio	G1020	Neutrophil cytospin staining.