Quality-Controlled Sputum Analysis by Flow Cytometry

Summary

This protocol describes an efficient method for dissociating sputum into a single cell suspension and the subsequent characterization of cellular subsets on standard flow cytometric platforms.

Abstract

Sputum, widely used to study the cellular content and other microenvironmental features to understand the health of the lung, is traditionally analyzed using cytology-based methodologies. Its utility is limited because reading the slides is time-consuming and requires highly specialized personnel. Moreover, extensive debris and the presence of too many squamous epithelial cells (SECs), or cheek cells, often renders a sample inadequate for diagnosis. In contrast, flow cytometry allows for high-throughput phenotyping of cellular populations while simultaneously excluding debris and SECs.

The protocol presented here describes an efficient method to dissociate sputum into a single cell suspension, antibody stain and fix cellular populations, and acquire samples on a flow cytometric platform. A gating strategy that describes the exclusion of debris, dead cells (including SECs) and cell doublets is presented here. Further, this work also explains how to analyze viable, single sputum cells based on a cluster of differentiation (CD)45 positive and negative populations to characterize hematopoietic and epithelial lineage subsets. A quality control measure is also provided by identifying lung-specific macrophages as evidence that a sample is derived from the lung and is not saliva. Finally, it has been demonstrated that this method can be applied to different cytometric platforms by providing sputum profiles from the same patient analyzed on three flow cytometers; Navios EX, LSR II, and Lyric. Furthermore, this protocol can be modified to include additional cellular markers of interest. A method to analyze an entire sputum sample on a flow cytometric platform is presented here that makes sputum amenable for developing high-throughput diagnostics of lung disease.

Introduction

Technical advancements in the hardware and software of flow cytometers have made it possible to identify many distinct cell populations simultaneously^1,2,3,4. The utilization of the flow cytometer in hematopoietic cell research, for example, has led to a much better understanding of the immune system² and the cellular hierarchy of the hematopoietic system⁵, as well as the diagnostic distinction of a multitude of different blood cancers^6,7

Protocol

All steps of the sputum processing are performed in a biological safety cabinet with appropriate personal protective equipment.

1. Reagent preparation before starting sputum dissociation

1. Thaw 1% Paraformaldehyde (PFA), 25 mL per sample on ice, and keep cold until use.
   CAUTION: PFA is toxic by inhalation and skin contact. Prepare the fixative according to the manufacturer's instructions and freeze at -20 °C in 25 mL aliquots until use.
2. Approximate the weigh.......

Discussion

The cellular content of sputum includes a large variety of wide-ranging cells, often accompanied by a lot of debris³⁷. In addition, sputum analysis requires a quality control that confirms the sample is collected from the lung instead of the oral cavity³⁸. Therefore, it is not as simple to analyze sputum by flow cytometry as it is for blood, for example, which releases a much cleaner and homogeneous cell suspension. This protocol has addressed all these issues: providing in.......

Materials

Name	Company	Catalog Number	Comments
1% Paraformaldehyde Flow-Fix	Polysciences	25037
100 µM nylon cell strainers, Falcon #352360	Fisher Scientific	08-771-19
3 M NaOH	EMD	SX0593-1
50 mL conical falcon tube	Fisher Scientific	14-432-22
Alexa488 anti-human CD19	BioLegend	302219
Alexa488 anti-human CD3	BioLegend	300415
Alexa488 anti-human cytokeratin	BioLegend	628608
Alexa488 PanCK, CD3, and CD19 Isotype	BioLegend	400129
BV510 anti-human CD45	BioLegend	304036
CD66b FITC isotype	BD Biosciences	555748
CompBead Plus Compensation Beads	BD Biosciences	560497
Corning Polystyrene dispoable sterile bottle 250 mL	Fisher Scientific	09-761-4
Corning Polystyrene dispoable sterile bottle 500 mL	Fisher Scientific	09-761-10
CS&T beads	BD Biosciences	655051
DTT	Fisher Scientific	BP172-5
FITC anti-human CD66b	GeneTex	GTX75907
Fixable Viability Stain	BD Biosciences	564406
FlowCheck	Beckman Coulter	A69183
FlowSet	Beckman Coulter	A69184
HBSS	Fisher Scientific	14-175-095
NAC	Sigma-Aldrich	A9165
NIST Beads, 05 μM	Polysciences	64080
NIST Beads, 20 μM	Polysciences	64160
NIST Beads, 30 μM	Polysciences	64170
PE anti-human CD45	BioLegend	304039
PE-CF594 anti-human EpCAM	BD Biosciences	565399
PE-CF594 CD206/EpCAM Isotype	BD Biosciences	562292
PE-CR594 anti-human CD206	BD Biosciences	564063
Sodium citrate dihydrate	EMD	SX0445-1
Trypan Blue solution, 0.4%	Fisher Scientific	15250061