Plasmid-mediated early killing of eucaryotic cells by Shigella flexneri as studied by infection of J774 macrophages

In Shigella flexneri a 220-kilobase plasmid encodes the ability to invade nonprofessional phagocytes by a mechanism similar to phagocytosis. In this report, the continuous macrophage cell line J774 was used to study the intracellular fate of both invasive and noninvasive strains. pWR100, the virulence plasmid of S. flexneri serotype 5, mediated very efficient and rapid killing of J774 macrophages, as measured by cellular detachment and uptake of trypan blue. For this to occur, the bacteria had to be within the cells, since the macrophages were protected by cytochalasin D. A battery of strains differing in their levels of Shiga toxin production showed that inhibition of protein synthesis by Shiga toxin, as measured by [35S]methionine incorporation into infected macrophages, was not required for early killing of cells. Damage to J774 macrophages rather correlated with the ability of invasive bacteria to rapidly and efficiently lyse the membrane of the phagocytic vacuole. The role of the release of bacteria within the cytosol for subsequent expression of cytotoxic activity is discussed, and mitochondria are proposed as a potential target for this activity.

Multiplication of Shigella flexneri within HeLa cells: lysis of the phagocytic vacuole and plasmid-mediated contact hemolysis

Virulent strains of Shigella flexneri invade HeLa cells with high efficiency. This crucial step in the pathogenic process is encoded by a 140-megadalton plasmid which induces phagocytosis of the bacteria by host cells. In this report we used pWR100, the virulence plasmid of S. flexneri serotype 5, and pHS4108, a 32-megadalton subclone of pWR100, to demonstrate that the plasmid is also responsible for rapid intracellular growth of the bacteria. The ability to replicate intracellularly was not correlated with induction of Shiga toxin. However, plasmid-mediated intracellular multiplication was strongly correlated with the ability of the bacteria to rapidly and efficiently lyse the phagocytic vacuole and replicate freely in the cytoplasm. Temperature-regulated plasmid-mediated contact hemolytic activity strongly correlated with both phagosomal membrane lysis and efficient intracellular multiplication. We propose this virulence plasmid-associated hemolysin to be an important factor in the invasion and proliferation of Shigella spp. in mammalian cells.

[Some comments on the biological properties of calcitonin: an eventual new therapeutic utilization (author's transl)]

The calcitonin-adrenal antagonism brings the authors to propose a new therapeutic use of calcitonin. That hormone could minimize the effects of externe stimulations and its use as sedative is proposed.