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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

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 simultaneously1,2,3,4. 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 cancers6,7

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.......

Representative Results

This protocol was developed with a clinical laboratory setting in mind. The focus during the development of the protocol was on simplicity, efficiency, and reproducibility. It was found that the most time-consuming step in the processing of sputum was counting the cells. Therefore, the protocol is set up in such a way that sputum processing and cell labeling can be performed independently from cell counting without loss of time. An accurate cell count, which is still necessary to dilute the sample appropriately for an un.......

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.......

Acknowledgements

We want to thank David Rodriguez for his assistance with the figure preparation. Sputum samples were run on the BD LSR II at the UT Health San Antonio Flow Cytometry Shared Resource Facility, supported by UT Health, NIH-NCI P30 CA054174-20 (CTRC at UT Health) and UL1 TR001120 (CTSA grant).

....

Materials

NameCompanyCatalog NumberComments
1% Paraformaldehyde Flow-FixPolysciences25037
100 µM nylon cell strainers, Falcon #352360Fisher Scientific08-771-19
3 M NaOHEMDSX0593-1
50 mL conical falcon tubeFisher Scientific14-432-22
Alexa488 anti-human CD19BioLegend302219
Alexa488 anti-human CD3BioLegend300415
Alexa488 anti-human cytokeratinBioLegend628608
Alexa488 PanCK, CD3, and CD19 IsotypeBioLegend400129
BV510 anti-human CD45BioLegend304036
CD66b FITC isotypeBD Biosciences555748
CompBead Plus Compensation BeadsBD Biosciences560497
Corning Polystyrene dispoable sterile bottle 250 mLFisher Scientific09-761-4
Corning Polystyrene dispoable sterile bottle 500 mLFisher Scientific09-761-10
CS&T beadsBD Biosciences655051
DTTFisher ScientificBP172-5
FITC anti-human CD66bGeneTexGTX75907
Fixable Viability StainBD Biosciences564406
FlowCheckBeckman CoulterA69183
FlowSetBeckman CoulterA69184
HBSSFisher Scientific14-175-095
NACSigma-AldrichA9165
NIST Beads, 05 μMPolysciences64080
NIST Beads, 20 μMPolysciences64160
NIST Beads, 30 μMPolysciences64170
PE anti-human CD45BioLegend304039
PE-CF594 anti-human EpCAMBD Biosciences565399
PE-CF594 CD206/EpCAM IsotypeBD Biosciences562292
PE-CR594 anti-human CD206BD Biosciences564063
Sodium citrate dihydrateEMDSX0445-1
Trypan Blue solution, 0.4%Fisher Scientific15250061

References

  1. Lugli, E., Roederer, M., Cossarizza, A. Data analysis in flow cytometry: the future just started. Cytometry. Part A: The Journal of the International Society for Analytical Cytology. 77 (7), 705-713 (2010).
  2. Perfetto, S. P., Chattopadhyay, P. K., Roederer, M.

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