Mycobacterium tuberculosis may escape helper T cell recognition by infecting human fibroblasts
Introduction
The intracellular pathogen Mycobacterium tuberculosis (Mtb) causes tuberculosis (TB) and is able to infect antigen presenting cells (APCs), including macrophages and dendritic cells (DCs) [1]. In these cells, Mtb survives in modified phagosomes and uses multiple mechanisms to evade both innate and adaptive host immunity, including inhibition of phagosome maturation, resistance to innate microbicidal mechanisms and cytokine-mediated host defenses, as well as inhibition of antigen presentation [2], [3]. Since TB is mainly transmitted via airborne droplets from people with active respiratory disease to susceptible individuals, Mtb most commonly affects the lungs. Thus, it is generally accepted that the first cell types confronting Mtb during primary infection are alveolar macrophages and type II pneumocytes [4], [5]. However, this microorganism can enter a variety of other cell types in vitro, as shown by several authors following the early observations by Shepard, [6] who demonstrated that Mtb can enter monolayers of HeLa, monkey kidney and human amnion cells [6], [7]. More recently, Mtb has been shown to infect lung epithelial and endothelial cells [8], [9], [10], [11] as well as adipocytes [12] and fibroblasts [13], [14], in addition to professional APCs, such as monocytes and DCs, even if the capacity of Mtb to replicate within these different cell types may vary significantly [15], [16]. The capacity of Mtb to infect cells different from macrophages has also been proven by ex vivo experiments showing Mtb or its DNA in different cell types in both TB patients and subjects with latent TB infection (LTBI), corroborating the significance of in vitro experiments [12], [17]. In particular, Mtb was shown to persist intracellularly in lung tissue without histological evidence of tuberculous lesions and Mtb DNA was shown to be situated not only in macrophages but also in other non-professional APCs [17]. The capacity of Mtb to infect and replicate within different cell types may be dependent on both the capacity of cells to internalize and host Mtb and/or to the strength of the immune response, which may force Mtb to colonize alternative cell types possibly in relation to the TB stage. This is relevant since internalization in non-professional APCs may represent an important pathogenic feature of mycobacterial infection. In these cells major histocompatibility complex (MHC) class I expression is constitutive but class II is not expressed in normal conditions, although it may be induced by interferon (IFN)-γ release [18]. Non-professional APCs are not capable of priming antigen specific T cells, but they can present antigen to memory CD4+ T cells in inflammatory microenvironments where they are induced to express MHC class II molecules by locally released IFN-γ. The capacity of mycobacteria to infect, survive and interfere with antigen processing and presentation in these cells is far from being elucidated [19]. Moreover the role of non-professional APCs in TB is intriguing in the light of their possible contribution in maintaining the infection latent and possibly representing the mycobacterial reservoir in LTBI [17]. In this paper we investigated whether the known capacity of Mtb to interfere with MHC class II expression and the consequent impairment of antigen presentation could be observed in non professional APCs such as fibroblasts. In fact, fibroblasts are recruited [20] and proliferate into TB lesions where they are involved in tissue remodeling and granuloma formation, thus representing possible target for Mtb infection.
Section snippets
Ethics statement
This study has been approved by the Istituto Superiore di Sanità review board and written informed consent has been obtained by the healthy volunteers who participated to the study.
Bacterial cultures
Mtb H37Rv (ATCC 27294) and Bacillus Calmette-Guérin (BCG), (ATCC 27291) were grown with gentle agitation (80 r.p.m.) in Middlebrook 7H9 broth (Difco Laboratories, Detroit, MI) supplemented with 0.05% Tween 80 (Sigma Chemical Company, St. Louis, MO) and 10% Middlebrook ADC enrichment (Becton Dickinson, Mountain View,
Mycobacteria infect human fibroblasts
The human fibroblasts cell line MRC-5 and RNFib were infected with Mtb or BCG at MOI of 3:1 or 10:1 respectively. After 2 days of incubation cells were fixed and stained by Kinyoun method and microscopically observed to evaluate the cell-mycobacteria interactions. Fig. 1 reports Kinyoun staining of MRC-5 fibroblasts cultures after BCG (Fig. 1A) or Mtb (Fig. 1B) infection. Mycobacteria are associated to fibroblasts and only rare mycobacterial cells are found in the intercellular spaces. In
Discussion
In this work we confirm that in vitro Mtb infects human fibroblasts. Infection seems not to be related to the virulence of Mtb, since also the vaccine strain BCG is endowed with the same capacity to infect and grow within fibroblasts. These observations are in line with previous published data demonstrating the capacity of Mtb, as well as attenuated or non-pathogenic mycobacteria such as M. smegmatis, to infect non-phagocytic cells [8], [9], [10], [11] by macropinocytosis through lamellipodia
Acknowledgments
This work was partially supported by the 7th EC Framework Programme Project “NEWTBVac” Grant #241745.
References (39)
- et al.
Internalization of a non-pathogenic mycobacteria by macropinocytosis in human alveolar epithelial A549 cells
Microb Pathog
(2008) - et al.
Comparison of the ability of Mycobacterium avium, M. smegmatis, and M. tuberculosis to invade and replicate within HEp-2 epithelial cells
Tuberc Lung Dis
(1995) - et al.
Persistence of DNA from Mycobacterium tuberculosis in superficially normal lung tissue during latent infection
Lancet
(2000) - et al.
Invariant chain modulates HLA class II protein recycling and peptide presentation in nonprofessional antigen presenting cells
Cell Immunol
(2007) - et al.
Mycobacterial manipulation of the host cell
FEMS Microbiol Rev
(2005) - et al.
A dangerous liaison between two major killers: Mycobacterium tuberculosis and HIV target dendritic cells through DC-SIGN
J Exp Med
(2003) - et al.
High content phenotypic cell-based visual screen identifies Mycobacterium tuberculosis acyltrehalose-containing glycolipids involved in phagosome remodeling
PLoS Pathog
(2010) - et al.
Regulation of antigen presentation by Mycobacterium tuberculosis: a role for Toll-like receptors
Nat Rev Microbiol
(2010) - et al.
Type II alveolar cells play roles in macrophage-mediated host innate resistance to pulmonary mycobacterial infections by producing proinflammatory cytokines
J Infect Dis
(2002) Use of HeLa cells infected with tubercle bacilli for the study of antituberculous drugs
J Bacteriol
(1957)
A study of the growth in HeLa cells of tubercle bacilli from human sputum
Am Rev Tuberc
The efficiency of the translocation of Mycobacterium tuberculosis across a bilayer of epithelial and endothelial cells as a model of the alveolar wall is a consequence of transport within mononuclear phagocytes and invasion of alveolar epithelial cells
Infect Immun
Mycobacterium tuberculosis invades and replicates within type II alveolar cells
Infect Immun
Comparison of in vitro models for the study of Mycobacterium tuberculosis invasion and intracellular replication
Infect Immun
Is adipose tissue a place for Mycobacterium tuberculosis persistence?
PLoS One
Interactions of attenuated Mycobacterium tuberculosis phoP mutant with human macrophages
PLoS One
Differential growth characteristics and streptomycin susceptibility of virulent and avirulent Mycobacterium tuberculosis strains in a novel fibroblast-mycobacterium microcolony assay
Infect Immun
Constrained intracellular survival of Mycobacterium tuberculosis in human dendritic cells
J Immunol
Mycobacterium tuberculosis infects dendritic cells with high frequency and impairs their function in vivo
J Immunol
Cited by (18)
Single-cell transcriptomics reveals cell type diversity of human prostate
2022, Journal of Genetics and GenomicsCitation Excerpt :Fibrocytes (precursors of fibroblasts) have a potent antigen-presenting function in T cells (Chesney et al., 1997). Fibroblasts were reported to present heat-killed Mycobacterium tuberculosis (Mtb) (Mariotti et al., 2013). In human lungs, fibroblasts present bacterial antigens to lung T-helper (Th) cells (Hutton et al., 2017).
Human tuberculosis and Mycobacterium tuberculosis complex: A review on genetic diversity, pathogenesis and omics approaches in host biomarkers discovery
2021, Microbiological ResearchCitation Excerpt :Fibroblasts also express MHC class II molecule in antigen presentation to CD4 + T cells upon activation by IFN-γ. It is shown that fibroblasts infected with M. tuberculosis has loss the antigen presentation capability to T cells, indicating that M. tuberculosis can evade from T-helper immune cell surveillance by infecting fibroblast (Mariotti et al., 2013). Different studies reported that the microenvironment of the granuloma (low pH, hypoxia, high concentrations of carbon monoxide (CO) and nitric oxide (NO) and absence of carbon and nutrients) promotes the expressions of M. tuberculosis genes that are critical in dormancy induction (Ahmad, 2011).
Primary mouse lung fibroblasts help macrophages to tackle Mycobacterium tuberculosis more efficiently and differentiate into myofibroblasts up on bacterial stimulation
2016, TuberculosisCitation Excerpt :Possible infection of fibroblasts in the host by Mtb has been hinted by the detection of Mtb DNA in these cells on lung sections [15]. Mtb invasion and replication inside human lung fibroblast cell line was subsequently shown [16,17]. Fibroblasts are present in almost all organs, providing scaffolding support through the synthesis and remodelling of extracellular matrix.
Exploring the Potential of Exosomes as Biomarkers in Tuberculosis and Other Diseases
2024, International Journal of Molecular SciencesMycobacterium tuberculosis programs mesenchymal stem cells to establish dormancy and persistence
2020, Journal of Clinical InvestigationAnatomic and cellular niches for mycobacterium tuberculosis in latent tuberculosis infection
2019, Journal of Infectious Diseases