Macrophage Cholesterol Depletion and Its Effect on the Phagocytosis of Cryptococcus neoformans

Summary

In this article, a protocol for infection of macrophages with Cryptococcus neoformans is described. Also, a method for sterol depletion from the macrophages is explained. These protocols provide a guide to study fungal infections in vitro and examine the role of sterols in such infections.

Abstract

Cryptococcosis is a life-threatening infection caused by pathogenic fungi of the genus Cryptococcus. Infection occurs upon inhalation of spores, which are able to replicate in the deep lung. Phagocytosis of Cryptococcus by macrophages is one of the ways that the disease is able to spread into the central nervous system to cause lethal meningoencephalitis. Therefore, study of the association between Cryptococcus and macrophages is important to understanding the progression of the infection. The present study describes a step-by-step protocol to study macrophage infectivity by C. neoformansin vitro. Using this protocol, the role of host sterols on host-pathogen interactions is studied. Different concentrations of methyl--cyclodextrin (MCD) were used to deplete cholesterol from murine reticulum sarcoma macrophage-like cell line J774A.1. Cholesterol depletion was confirmed and quantified using both a commercially available cholesterol quantification kit and thin layer chromatography. Cholesterol depleted cells were activated using Lipopolysacharide (LPS) and Interferon gamma (IFNγ) and infected with antibody-opsonized Cryptococcus neoformans wild-type H99 cells at an effector-to-target ratio of 1:1. Infected cells were monitored after 2 hr of incubation with C. neoformans and their phagocytic index was calculated. Cholesterol depletion resulted in a significant reduction in the phagocytic index. The presented protocols offer a convenient method to mimic the initiation of the infection process in a laboratory environment and study the role of host lipid composition on infectivity.

Introduction

Phagocytosis is a process by which extracellular entities are internalized by host cells. It is a key weapon in the immune system’s arsenal to defend against pathogens, but the process may often be subverted by pathogens to allow for internalization and spreading throughout the body¹. Phagocytosis is mediated by several signaling events that result in attachment and engulfment via rearrangements of the host cell’s cytoskeleton. ‘Professional’ phagocytes are able to recognize and bind to opsonins on the surface of the invading pathogen to signal for attachment and the formation of lamellipodia, which engulf the pathogen and form a pha....

Protocol

1. Cholesterol Depletion of J774A.1 Cells with MβCD

1. In a sterile biosafety cabinet, seed 10⁵ J774A.1 macrophage-like cells per well on a 96-well cell culture plate in 200 μl of Dulbecco’s Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum (FBS) and 1% penicillin/streptomycin (P/S). Incubate at 37 °C and 5% CO₂ O/N.
2. Remove media from the cell monolayer and wash the cells twice with 1x phosphate buffered saline (PBS) that has been filtered or autoclaved.
3. Add 200 μl of MβCD solution at the desired concentration (10 mM or 30 mM in PBS) or 1x PBS as a control and incubat....

Results

Cholesterol Depletion

Analysis of the supernatant reserved in step 1.3 of the protocol by following the manufacturer’s instructions in the Amplex Red Cholesterol Assay kit yields an elevated concentration of cholesterol in MβCD treated sample as compared to the 1x PBS control. Depending on cell type and MβCD concentration used cholesterol depletion may vary. For J774 treated with 10 mM MβCD, a depletion of approximately 50% was observed. Depletion can be calculated using values obtained from the .......

Discussion

In working with this protocol it is important to obtain accurate cell counts when plating mammalian cells and opsonizing C. neoformans cells. This minimizes variation between trials and ensures an accurate 1:1 target to effector ratio throughout the study. It is also critical to coordinate the timing of the cholesterol depletion and infection to prevent the opsonized yeast cells or treated macrophage cells from resting at RT in between the procedures. Long waiting periods could lead to loss of antibody opsonizat.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Class II type A2 Biosafety Cabinet	Labconco	3460009
J774A.1 cell line	ATCC	TIB-67	Arrives Frozen. See ATCC instructions for culturing.
Dulbecco’s Modified Eagle Medium	Gibco	11995-065	Store at 4 °C and warm to 37 °C prior to use
HI Fetal Bovine Serum Performance Plus	Gibco	10082-147	Keep frozen at -20 °C and thaw before adding to DMEM
Penicillin-Streptomycin (10,000 U/ml)	Gibco	15140-122	Used to suplement DMEM
Isotemp Cell culture incubator	Fisher Scientific		Model # 3530
96-Well culture dish	Corning Inc. Costar	3595
10x Phosphate Buffered Saline	Fisher Scientific BioReagents	BP3994	Dilute to 1x and filter or autoclave prior to use.
Methyl-β-cyclodextrin	Sigma Life Science	C4555-10G	Dissolve in 1x PBS to make solutions of 10 mM and 30 mM concentrations
Orbital shaker	Labline
Amplex Red Cholesterol Assay Kit	Life Technologies Molecular Probes	A12216	All reagents for Cholesterol Assay are contained within the kit. Follow Manufacturer instructions.
96-Well Black Assay plate	Corning Inc. Costar	3603
FilterMax microplate reader	Molecular Devices		Model F5
TLC chamber	Sigma-Aldrich	Z126195-1EA
Chloroform	Sigma-Aldrich	650498-4L
Methanol	Sigma-Aldrich	34860-2L-R
TLC Paper	Whatman	3030917	Cut down to size needed for TLC tank
Fume hood			Any fume hood that complies with AIHA/ANSI Standards
6-Well plate	Corning Inc. Costar	3506
Trypsin-EDTA	Gibco	25300-054
Cell scraper	Corning Inc. Costar	3010
Hemocytometer	Hausser Scientific	1490
Centrifuge	Beckman Coulter		Model Alegra x-30R
Votex mixer	Fisher Scientific	12-812
Balance	Mettler Toledo		Model # MS104S meaures down to 0.1 mg
Glass Pasteur pipette	Fisherbrand	13-678-20A
Cholesterol	Avanti Polar Lipids	700000
SpeedVac concentrator	Thermo Scientific		Model # SPD2010
Petroleum ether	Fisher Scientific	E139-1
Diethyl ether	Sigma-Aldrich	309966
Acetic acid	Sigma-Aldrich	320099
TLC Silica Gel 60 with concentrating zone	Analytical Chromatograhy Millipore	1.11845.0001
Iodine chips	Sigma-Aldrich	376558-50G
Sulfuric acid	Sigma-Aldrich	320501
Manganese chloride	Sigma-Aldrich	244589
UVP EC3 Imaging System	Ultra-Violet Products Ltd.		Use the Vision Works LS software for densitometry analysis
Glass bottom confocal dish	MatTek	P35G-1.5-10C	www.glassbottomdishes.com
Cryptococcus neoformans (H99)			Obtained from Duke University Medical Center
YNB	BD	239210	See manufacturer for preparation instructions. Use a glucose concentration of 20 g/L.
Lipopolysaccharide	Sigma	L4391-1MG	Dissolve in 1x PBS to make 1 mg/ml stock. Store at -20 °C.
Interferon gamma	Sigma	I4777	Dissolve in 1x PBS to make 0.1 mg/ml stock solution
Glucuronoxylomannan antibody (anti-GXM)			Gift from Arturo Casadevall's Lab concentration is 1.98 mg/ml
Giemsa	MP Biomedicals	194591	Dissolve 0.8 g of Giemsa in 25 ml of glycerol and heat to 60 °C for 1 hr. Add 25 ml of methanol to the solution and allow to age at room temperature for at least 1 month.
Microscope	Zeiss		Observer.D1 microscope with AxioCam MRm for taking images