Confocal Laser Scanning Microscopy-Based Quantitative Analysis of Aspergillus fumigatus Conidia Distribution in Whole-Mount Optically Cleared Mouse Lung

Summary

We describe the method for quantitative analysis of the distribution of Aspergillus fumigatus conidia (3 µm in size) in the airways of mice. The method also can be used for the analysis of microparticles and nanoparticle agglomerate distribution in the airways in various pathological condition models.

Abstract

Aspergillus fumigatus conidia are airborne pathogens that can penetrate human airways. Immunocompetent people without allergies exhibit resistance and immunological tolerance, while in immunocompromised patients, conidia can colonize airways and cause severe invasive respiratory disorders. Various cells in different airway compartments are involved in the immune response that prevents fungal invasion; however, the spatio-temporal aspects of pathogen elimination are still not completely understood. Three-dimensional (3D) imaging of optically cleared whole-mount organs, particularly the lungs of experimental mice, permits detection of fluorescently labeled pathogens in the airways at different time points after infection. In the present study, we describe an experimental setup to perform a quantitative analysis of A. fumigatus conidia distribution in the airways. Using fluorescent confocal laser scanning microscopy (CLSM), we traced the location of fluorescently labeled conidia in the bronchial branches and the alveolar compartment 6 hours after oropharyngeal application to mice. The approach described here was previously used for detection of the precise pathogen location and identification of the pathogen-interacting cells at different phases of the immune response. The experimental setup can be used to estimate the kinetics of the pathogen elimination in different pathological conditions.

Introduction

On a daily basis, people inhale airborne pathogens, including spores of opportunistic fungi Aspergillus fumigatus (A. fumigatus conidia) that can penetrate the respiratory tract¹. The respiratory tract of mammals is a system of airways of different generations that are characterized by the different structures of the airway walls^2,3,4. Tracheobronchial walls consist of several cell types among which are ciliated cells that provide the mucociliary clearance⁵. In the alveoli, there are no ciliated cells and the p....

Protocol

All methods concerning laboratory animals described here have been approved by the Institutional Animal Care and Use Committee (IACUC) at the Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences (protocol number 226/2017).

1. A. fumigatus conidia application

1. To obtain fluorescently labeled A. fumigatus conidia, fix 5 × 10⁸ conidia by adding 1 mL of 3% paraformaldehyde to the conidia pellet. Incubate in a 50 mL test tube for 2 h on a shaker at room temperature.
2. Wash conidia with 20 mL of phosphate buffer saline (PBS): centrifuge at 1,000 x g for 15 mi....

Results

Following the protocol above, the 3D image showing the airways and A. fumigatus conidia in the lung lobe of a mouse was obtained (Figure 1A). Streptavidin (that was used for airway visualization) labeled bronchi and bronchioles¹⁵. Additionally, the large vessels, which are easily distinguishable from the airways by their morphology, and pleura are visualized in the airway channel (Figure 1A-C). The creation of th.......

Discussion

Whole-organ 3D imaging permits obtaining of the data without dissection of the specimen, which is of great importance for investigating the spatial aspects of the anatomical distribution of the pathogen in the organism. There are several techniques and modifications of tissue optical clearing that help to overcome the laser light scattering and allow whole-organ imaging^15,16,18,19. One of the c.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Alexa Fluor 594 NHS Ester	ThermoFisher	A20004
Aspergillus fumigatus conidia	ATCC	46645	The strain AfS150, a ATCC 46645 derivative
Benzyl alcohol	Panreac	141081.1611	98.0-100 %
Benzyl benzoate	Acros	AC10586-0010	99+%
C57Bl/6 mice	Pushchino Animal Breeding Centre (Russia)		Male. 12 - 30 week old.
Catheter	Venisystems	G715-A01	18G
Cell imaging coverglass-bottom chamber	Eppendorf	30742028	4 or 8 well chamber with coverglass bottom
Centrifuge	Eppendorf	5804R	Any centrifuge provided 1000 g can be used
Confocal laser scanning microscope	ZEISS	ZEISS LSM780
Dimethyl sulfoxide	Sigma-Aldrich	276855	≥99.9%
FIJI image processing package	FIJI		Free software
Forcep	B. Braun Aesculap	BD557R	Toothed
Forcep	B. Braun Aesculap	BD321R	Fine-tipped
Forcep	Bochem	1727	Smooth
Glass bottle	DURAN	242101304	With ground-in lid
Graphic Editor Photoshop	Adobe Inc		Adobe Photoshop CS
GraphPad Software	GraphPad		Prism 8
Imaris Microscopy Imaging Software	Oxford Instruments		Free trial is available https://imaris.oxinst.com/microscopy-imaging-software-free-trial
Isoflurane	Karizoo
NaHCO3	Panreac	141638
Objective	ZEISS	420640-9800-000	Plan-Apochromat, 10 × (NA = 0.3)
Paraformaldehyde	Sigma-Aldrich	158127
PBS	Paneco	P060Π
Pipette	ProLine	722020	5 to 50 μL
Powdered milk	Roth	T145.2
Sample mixer	Dynal	MXIC1
Scissors	B. Braun	BC257R	Blunt
Shaker	Apexlab	GS-20	50-300 rpm
Skalpel	Bochem	12646
Silk thread	B. Braun		3 USP
Streptavidin, Alexa Fluor 488 conjugate	ThermoFisher	S11223
Test tube	SPL Lifesciences	50050	50 mL
Tris (hydroxymethyl aminomethane)	Helicon	H-1702-0.5	Mr 121.14; CAS Number: 77-86-1
Triton X-100	Amresco	Am-O694-0.1
ZEN microscope software	ZEISS	ZEN2012 SP5	https://www.zeiss.com/microscopy/int/products/microscope-software/zen.html