Establishment of an In vitro System to Study Intracellular Behavior of Candida glabrata in Human THP-1 Macrophages
Summary
The current article outlines a protocol to establish an in vitro cell culture model system to study the interaction of a facultative intracellular human fungal pathogen Candida glabrata with human macrophages which will be a useful tool to advance our knowledge of fungal virulence mechanisms.
Abstract
A cell culture model system, if a close mimic of host environmental conditions, can serve as an inexpensive, reproducible and easily manipulatable alternative to animal model systems for the study of a specific step of microbial pathogen infection. A human monocytic cell line THP-1 which, upon phorbol ester treatment, is differentiated into macrophages, has previously been used to study virulence strategies of many intracellular pathogens including Mycobacterium tuberculosis. Here, we discuss a protocol to enact an in vitro cell culture model system using THP-1 macrophages to delineate the interaction of an opportunistic human yeast pathogen Candida glabrata with host phagocytic cells. This model system is simple, fast, amenable to high-throughput mutant screens, and requires no sophisticated equipment. A typical THP-1 macrophage infection experiment takes approximately 24 hr with an additional 24-48 hr to allow recovered intracellular yeast to grow on rich medium for colony forming unit-based viability analysis. Like other in vitro model systems, a possible limitation of this approach is difficulty in extrapolating the results obtained to a highly complex immune cell circuitry existing in the human host. However, despite this, the current protocol is very useful to elucidate the strategies that a fungal pathogen may employ to evade/counteract antimicrobial response and survive, adapt, and proliferate in the nutrient-poor environment of host immune cells.
Introduction
Candida species are the leading cause of life-threatening invasive fungal infections in immunocompromised patients1. Candida glabrata, an emerging nosocomial pathogen, is the second or third most frequently isolated Candida species from Intensive Care Unit patients depending upon the geographical location1-3. Phylogenetically, C. glabrata, a haploid budding yeast, is more closely related to the non pathogenic model yeast Saccharomyces cerevisiae than to pathogenic Candida spp. including C. albicans4. Consistent with this, C. glabrata lacks some key fungal virulence traits including mating, secreted proteolytic activity and morphological plasticity4-5.
Although C. glabrata does not form hyphae, it can survive and replicate in murine and human macrophages6-8 suggesting that it has developed unique pathogenesis mechanisms. Limited information is available about the strategies that C. glabrata employs to survive nutrient-poor intracellular macrophage environment and counteract oxidative and nonoxidative host responses mounted by host immune cells5. A pertinent macrophage model system is a prerequisite to delineate the interaction of C. glabrata with host phagocytic cells via functional genomic and proteomic approaches. Peripheral blood mononuclear cells (PBMCs) and bone marrow-derived macrophages (BMDMs) of human and murine origin, respectively, have earlier been used to study the interaction of C. glabrata with host immune cells7,9. However, difficulty in obtaining PBMCs and BMDMs, their limited life span and intrinsic variation among different mammalian donors restrict the utilization of these cells as versatile model systems.
Here, we describe a method for establishment of an in vitro system to study the intracellular behavior of C. glabrata cells in macrophages derived from human monocytic cell line THP-1. The overall goal of this protocol was to enact a simple, inexpensive, quick, and reproducible cell culture model system that can be easily manipulated to study different aspects of host-fungal pathogen interaction.
THP-1 cells have previously been used to decipher the host immune response against a wide range of pathogens including bacteria, viruses, and fungi10-12. Monocytic THP-1 cells are easy to maintain and can be differentiated, upon phorbol ester treatment, to macrophages which mimic monocyte-derived macrophages of human and express appropriate macrophage markers13. The main advantages of THP-1 macrophage model system are the ease-of-use and the lack of sophisticated equipment requirement.
The protocol presented here is easily adaptable to study the interaction of other human fungal pathogens with host immune cells. The current procedure can also be employed to identify virulence factors for the pathogen of interest using high throughput mutant screens. This proof-of-concept was exemplified by the successful use of THP-1 culture model system to identify a set of 56 genes that are required for survival of C. glabrata in human macrophages8.
Protocol
Representative Results
Discussion
Innate immune system plays an important role in the control of opportunistic fungal infections. Macrophages contribute to antifungal defense by ingestion and destruction of the fungal pathogen. Thus, elucidation of factors that are required for survival and/or counteracting the antimicrobial functions of macrophages will advance our understanding of fungal virulence strategies. In this context, we have established an in vitro cell culture model system using macrophages derived from a human monocytic cell line TH…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was supported by Innovative Young Biotechnologist Award BT/BI/12/040/2005 and BT/PR13289/BRB/10/745/2009 grant from Department of Biotechnology, Government of India and core funds of Centre for DNA Fingerprinting and Diagnostics, Hyderabad. MNR and GB are the recipients of Junior and Senior Research Fellowships of the Council of Scientific and Industrial Research towards the pursuit of a PhD degree of the Manipal University. SB is the recipient of Junior and Senior Research Fellowship of the Department of Biotechnology towards the pursuit of a PhD degree of the Manipal University.
Materials
| THP-1 | American Type Culture Collection | TIB 202 | Human acute monocytic leukemia cell line |
| RPMI-1640 | Hyclone | SH30096.01 | For maintaining THP-1 cells |
| Phorbol 12-myristate 13-acetate | Sigma-Aldrich | P 8139 | Caution: Hazardous |
| YPD | BD-Difco | 242710 | For growing Candida glabrata cells |
| Formaldehyde | Sigma-Aldrich | F8775 | For fixation of C. glabrata-infected THP-1 macrophages |
| Phosphate buffered saline (PBS) | Buffer (137 mM NaCl, 10 mM Phosphate, 2.7 mM KCl, pH 7.4) for washes | ||
| Saline-sodium citrate (SSC) | Buffer (3 M NaCl, 0.3 M sodium citrate for 20x concentration) for washes | ||
| Prehybridization buffer | Buffer (50% formamide, 5x Denhardt’s solution, 5x SSC, 1% SDS) for hybridization | ||
| VECTASHIELD mounting medium | Vector Labs | H-1200 | For mounting slides for confocal microscopy |
| 32P-labeled α-dCTP | JONAKI-BARC | LCP-102 | For radiolabeling of signature tags |
| 100 mm tissue culture dishes | Corning | 430167 | To culture THP-1 cells |
| 24-well tissue culture plate | Corning | 3527 | To perform C. glabrata infection studies in THP-1 macrophages |
| 4-chamber tissue culture-treated glass slide | BD Falcon | REF354104 | To image C. glabrata-infected THP-1 macrophages |
| Hemocytometer | Rohem India | For enumeration of cells | |
| Table top microcentrifuge | Beckman Coulter | Microfuge 18 | For spinning down cells in microtubes |
| Table top centrifuge | Remi | R-8C | For spinning down cells in 15 ml tubes |
| Spectrophotometer | Amersham Biosciences | Ultraspec 10 | To monitor absorbance of yeast cells |
| Plate incubator | Labtech | Refrigerated | To grow C. glabrata cells |
| Shaker incubator | New Brunswick | Innova 43 | To grow C. glabrata cells |
| Water jacketed CO2 incubator | Thermo Electron Corporation | Forma series 2 | To culture THP-1 cells |
| Confocal microscope | Carl Ziess | Ziess LSM 510 meta | To observe C. glabrata-infected THP-1 macrophages |
| Compound microscope | Olympus | CKX 41 | To observe C. glabrata and THP-1 macrophages |
| PCR machine | BioRad | DNA Engine | To amplify unique tags from input and output genomic DNA |
| Hybridization oven | Labnet | Problot 12S | For hybridization |
| PhosphorImager | Fujifilm | FLA-9000 | For scanning hybridized membranes |
| Thermomixer | Eppendorf | Thermomixer Comfort | For denaturation of radiolabeled signature tags |
| Gel documentation unit | Alphainnontech | Alphaimager | To visualize ethidium bromide-stained DNA in agarose gels |
References
- Pfaller, M. A., Diekema, D. J. Epidemiology of Invasive Candidiasis: a Persistent Public Health Problem. Clin. Microbiol. Rev. 20 (1), 133-163 (2007).
- Pfaller, M. A., Diekema, D. J., et al. Results from the ARTEMIS DISK global antifungal surveillance study. J. Clin. Microbiol. 48 (4), 1366-1377 (1997).
- Chakrabarti, A., Chatterjee, S. S., Shivaprakash, M. R. Overview of opportunistic fungal infections in India. Jpn. J. Med. Mycol. 49 (3), 165-172 (2008).
- Kaur, R., Domergue, R., Zupancic, M. L., Cormack, B. P. A yeast by any other name: Candida glabrata and its interaction with the host. Curr. Opin. Microbiol. 8 (4), 378-384 (2005).
- Silva, S., Negri, M., Henriques, M., Oliveira, R., Williams, D. W., Azeredo, J. Candida glabrata, Candida parapsilosis and Candida tropicalis: biology, epidemiology, pathogenicity and antifungal resistance. FEMS Microbiol. Rev. 36 (2), 288-305 (2012).
- Kaur, R., Ma, B., Cormack, B. P. A family of glycosylphosphatidylinositol-linked aspartyl proteases is required for virulence of Candida glabrata. Proc. Natl. Acad. Sci. U.S.A. 104 (18), 7628-7633 (2007).
- Seider, K., Brunke, S., et al. The facultative intracellular pathogen Candida glabrata subverts macrophage cytokine production and phagolysosome maturation. J. Immunol. 187 (6), 3072-3086 (2011).
- Rai, M. N., Balusu, S., Gorityala, N., Dandu, L., Kaur, R. Functional genomic analysis of Candida glabrata-macrophage interaction. PLoS Pathog. 8 (8), e1002863 (2012).
- Roetzer, A., Gratz, N., Kovarik, P., Schüller, C. Autophagy supports Candida glabrata survival during phagocytosis. Cell Microbiol. 12 (2), 199-216 (2010).
- Theus, S. A., Cave, M. D., Eisenach, K. D. Activated THP-1 Cells: an attractive model for the assessment of intracellular growth rates of Mycobacterium tuberculosis isolates. Infect. Immun. 72 (2), 1169-1173 (2004).
- Murayama, T., Ohara, Y., et al. Human Cytomegalovirus induces Interleukin-8 production by a human monocytic cell line, THP-1, through acting concurrently on AP-1- and NF-kB-binding sites of the Interleukin-8 gene. J. Virol. 71 (7), 5692-5695 (1997).
- Gross, O., Poeck, H., et al. Syk kinase signalling couples to the Nlrp3 inflammasome for anti-fungal host defence. Nature. 459, 433-436 (2009).
- Auwerx, J. The human leukemia cell line, THP-1: a multifacetted model for the study of monocyte-macrophage differentiation. Experientia. 47 (1), 22-31 (1991).
- Tsuchiya, S., Kobayashi, Y., et al. Induction of maturation in cultured human monocytic leukemia cells by a phorbol diester. Cancer Res. 42 (4), 1530-1536 (1982).
- Castaño, I., Kaur, R., et al. Tn7-based genome-wide random insertional mutagenesis of Candida glabrata. Genome Res. 13 (5), 905-915 (2003).
