Invasion of Vero cells and induction of apoptosis in macrophages by pathogenic Leptospira interrogans are correlated with virulence

Abstract

Interactions of virulent Leptospira interrogans serovar icterohaemorrhagiae strain Verdun with Vero cells (African green monkey kidney fibroblasts) and a monocyte-macrophage-like cell line (J774A.1) were assayed by a double-fluorescence immunolabelling method. Infectivity profiles were investigated according to (i) the duration of contact between leptospires and eukaryotic cells and (ii) the number of in vitro passages after primary isolation from lethally infected guinea pigs. Comparative experiments were conducted with the corresponding high-passage avirulent variant and the saprophytic leptospire Leptospira biflexa Patoc I. In Vero cells, virulent leptospires were quickly internalized from 20 min postinfection, whereas avirulent and saprophytic strains remained extracellularly located. In addition, the virulent strain demonstrated an ability to actively invade the monocyte-macrophage-like J774A.1 cells during the early stages of contact and to induce programmed cell death, as shown by the detection of oligonucleosomes in a quantitative sandwich enzyme immunoassay. In both cellular systems, subsequent in vitro subcultures demonstrated a progressive decrease of the invasiveness, pointing out the necessity of using primocultures of Leptospira for virulence studies. Invasiveness of virulent leptospires was significantly inhibited with monodansylcadaverine, indicating that internalization was dependent on receptor-mediated endocytosis. Invasion of epithelial cells and induction of apoptosis in macrophages may be related to the pathogenicity of Leptospira, and both could contribute to its ability to survive in the host and to escape from the immune response.

p53 signalling controls cell cycle arrest and caspase-independent apoptosis in macrophages infected with pathogenicLeptospiraspecies

“…Mononuclear macrophages and neutrophils have been shown to phagocytose leptospires, but only the former can kill the phagocytosed intracellular leptospires (Wang et al, 1984;Davis et al, 2009), indicating that mononuclear macrophages are much more important than neutrophils in defence mechanisms against leptospiral infection. However, Merien et al first reported that Leptospira interrogans, a common species of pathogenic Leptospira, could cause macrophage apoptosis (Merien et al, 1997). Our previous studies demonstrated that L. interrogans serovar Lai strain Lai induced apoptosis of human and mouse macrophages through both the caspase-8/3-dependent and caspase-independent mitochondrion-related apoptosis inducing factor (AIF) and/or endonuclease G (EndoG) pathways, but the classifical mitochondrion-related cytochrome c (Cyt c)-caspase-9/3 pathway was not involved in apoptosis (Jin et al, 2009;Li et al, 2010).…”

Destruction of the hepatocyte junction by intercellular invasion of Leptospira causes jaundice in a hamster model of Weil's disease

“…Leptospires have a characteristic spiral shape and corkscrew motion, and these features are considered to relate with its pathogenicity for host tissue invasion (Barocchi et al 2002). Penetration of cells such as human umbilical vein endothelial cells, Madin-Darby canine kidney cells, Vero cells and macrophage by leptospires were reported in in vitro studies (Barocchi et al 2002;Merien et al 1997, Thomas & Higbie 1990. Therefore, we carefully investigated whether leptospires localized in hepatocytes using SEM.…”

Responses of Human Endothelial Cells to Pathogenic and Non-Pathogenic Leptospira Species

“…Although little is known about how Leptospira species establish infection in their hosts, adhesion to the host cell surface and extracellular matrix (ECM) by pathogens is often the first critical step in the initiation of infection. Several groups have investigated the adhesion of Leptospira interrogans to endothelial, fibroblast, kidney epithelial, and monocyte-macrophage cell lines cultured in vitro [3][4][5][6][7][8][9]. It is likely that pathogenic leptospires can attach to several different types of mammalian receptors to establish the infection.…”