title: Infection of human THP-1 cells with dormant Mycobacterium tuberculosis.
abstract: Dormant, non-replicating Mycobacterium tuberculosis H37Rv strain cultured in hypoxic conditions was used to infect THP-1 cells. CFUs counting, Kinyoun staining and electron microscopy showed that dormant bacilli infected THP-1 cells at a rate similar to replicating M. tuberculosis, but failed to grow during the first 6 days of infection. The absence of growth was specific to the intracellular compartment, as demonstrated by efficient growth in liquid medium. Quantification of β-actin mRNA recovered from infected cells showed that, in contrast with log-phase bacteria, infection with dormant bacilli determined a reduced THP-1 cell death. Gene expression of intracellular non-replicating bacteria showed a pattern typical of a dormant state. Intracellular dormant bacteria induced the activation of genes associated to a proinflammatory response in THP-1 cells. Though, higher levels of TNFα, IL-1β and IL-8 mRNAs compared to aerobic H37Rv infected cells were not paralleled by increased cytokine accumulation in the supernatants. Moreover, dormant bacilli induced a higher expression of inducible cox-2 gene, accompanied by increased PGE2 secretion. Overall, our data describe a new model of in vitro infection using dormant M. tuberculosis that could provide the basis for understanding how non-replicating bacilli survive intracellularly and influence the maintenance of the hypoxic granuloma.
authors.affiliation: Dipartimento di Malattie Infettive, Parassitarie e Immunomediate, Istituto Superiore di Sanità, Viale Regina Elena, 299, 00161 Rome, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Iona
authors.forename: Manuela
authors.initials: M
authors.lastname: Pardini
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Gagliardi
authors.forename: Marisa
authors.initials: M
authors.lastname: Colone
authors.forename: Anna Rita
authors.initials: AR
authors.lastname: Stringaro
authors.forename: Raffaela
authors.initials: R
authors.lastname: Teloni
authors.forename: Lara
authors.initials: L
authors.lastname: Brunori
authors.forename: Roberto
authors.initials: R
authors.lastname: Nisini
authors.forename: Lanfranco
authors.initials: L
authors.lastname: Fattorini
authors.forename: Federico
authors.initials: F
authors.lastname: Giannoni
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000502:physiology; D015169:Colony Count, Microbial; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism; D005798:Genes, Bacterial; D054884:Host-Pathogen Interactions; D006801:Humans; D042541:Intracellular Space / Q000276:immunology / Q000382:microbiology; D008264:Macrophages / Q000166:cytology / Q000276:immunology* / Q000382:microbiology*; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000254:growth & development* / Q000276:immunology / Q000378:metabolism; D014376:Tuberculosis / Q000276:immunology / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins; D016207:Cytokines; D015232:Dinoprostone