ABSTRACT
Tuberculosis is characterized by a tight interplay between Mycobacterium tuberculosis (M. tb) and host cells within granulomas. These cellular aggregates restrain M. tb spreading but do not kill all bacilli, which persist for years. A more detailed investigation of the interaction between M. tb and granuloma cells is needed to improve our understanding of this persistence and to explain the physiopathology of tuberculosis. In the present study, a recently developed in vitro human model of tuberculous granulomas has been used to analyse the modulation of granuloma cell differentiation by M. tb, in comparison to poorly virulent mycobacteria, which do not persist. It is reported that whilst all mycobacteria species induce granuloma formation, only M. tb triggers the differentiation of granuloma macrophages into very large multinucleated giant cells (MGCs) that are unable to mediate any bacterial uptake. This loss of function is not due to cell quiescence, as MGCs still display NADPH oxidase activity, but it correlates with decreased expression of phagocytosis receptors. This phenomenon is specific for the virulent species of M. tuberculosis complex, as poorly virulent species only induce the formation of small multinucleated cells (MCs) with conserved mycobacterial uptake ability, which never reach the MGC differentiation stage. The phenotype of MGCs thus strongly resembles mature dendritic cells with a loss of microbial uptake ability, despite conserved antigen presentation. In M. tb-induced granulomas, MGCs thus seem to be devoted to the destruction of bacilli that have been ingested in previous differentiation stages, ie in macrophages and MCs.
Subject(s)
Giant Cells, Langhans/microbiology , Giant Cells/microbiology , Granuloma, Giant Cell/microbiology , Mycobacterium tuberculosis/physiology , Tuberculosis/transmission , Antigen-Presenting Cells/pathology , Axilla , BCG Vaccine , Flow Cytometry , Giant Cells/enzymology , Giant Cells/ultrastructure , Giant Cells, Langhans/enzymology , Giant Cells, Langhans/ultrastructure , Granuloma, Giant Cell/pathology , Humans , Immunohistochemistry/methods , Lymph Nodes/microbiology , Microscopy, Confocal , NADP/metabolism , Phagocytosis , Species Specificity , Staining and Labeling , Tuberculosis/pathology , VirulenceABSTRACT
Poxviruses are among the largest and most complex viruses known. Vaccinia virus, the prototype of the family Poxviridae, has been studied much more than myxoma virus. The aim of this work was to have a better knowledge about myxoma virus morphogenesis. The characterization of the main stages of MV morphogenesis was achieved by ultrastructural and immunological analysis. Specific antibodies were raised against M022L and M071L, two envelope proteins of extracellular enveloped virus and intracellular mature virus, respectively. The main stages of assembly were similar to those seen with other poxviruses, and the duration of the whole replication cycle was estimated to be around 16 h, longer than what was described for vaccinia virus. Morphological changes of infected cells were associated with the development of long cellular projections and enlarged microvilli. Intracellular enveloped viruses are associated with the cytoskeleton to move through the cell. Unlike earlier studies, as many cell-associated enveloped viruses as intracellular enveloped viruses were observed in relation with specialized microvilli, although these structures were rarely noticed. Finally, an unusual spreading process was observed, which uses cytoplasmic corridors.
