BugsFeed: 7 bad ass organisms that can survive intracellularly in immune cells

1. Mycobacterium tuberculosis - Stops fusion!

Phagolysosome fusion
Mycobacterium tuberculosis utilizes macrophages for its replication! (It uses the usual killer to expand it's army :O ) How does tuberculosis bacilli survive in macrophages? M. tuberculosis has evolved a number of very effective survival strategies - It inhibits phagosome-lysosome fusion and inhibits phagosome acidification ensuring it's survival inside the macrophage.

2. Brucella - Has chains, like Bruce Lee.

Brucella, Bruce Lee?
Brucella has a LPS O-chain. It ensures the Brucella containing vacuole (BCV) avoids fusion with lysosomes, prevents the deposition of complement at the bacterial surface and forms stable large clusters with MHC-II named macrodomians in the cell surface, interfering with MHC-II presentation of peptides to specific CD4+ T cells. Woah.

3. Listeria - It gets internalized in a vacuole and then runs away.

The pore-forming protein listeriolysin O mediates escape from host vacuoles. Once in the cytosol, the L. monocytogenes mediates efficient actin-based motility, thereby propelling the bacteria into neighboring cells. The cytosol is a favorable environment for listeria's growth.

4. Mycobacterium leprae - Cholesterol and TACO!

Mycobacterium leprae is able to induce lipid droplet formation in infected macrophages. Cholesterol mediates the recruitment of TACO from the plasma membrane to the phagosome. TACO, also termed as coronin-1A (CORO1A), is a coat protein that prevents phagosome-lysosome fusion and thus degradation of mycobacteria in lysosomes. The entering of mycobacteria at cholesterol-rich domains of the plasma membrane and their subsequent uptake in TACO-coated phagosomes promotes intracellular survival.

5. Coxiella brunetti - The indestrucible

This hardy, obligate intracellular pathogen has evolved to not only survive, but to thrive, in the harshest of intracellular compartments: the phagolysosome. Following internalization, the nascent Coxiella phagosome ultimately develops into a large and spacious parasitophorous vacuole (PV) that acquires lysosomal characteristics such as acidic pH, acid hydrolases and cationic peptides, defences designed to rid the host of intruders.

6. Salmonella - TTSS

Salmonella have a specialized secretion system, termed the type III secretion system (TTSS), as well as proteins secreted by this system, are encoded in Salmonella pathogenicity island 1 (SPI1). TTSS are used by bacterial pathogens to inhibit their phagocytosis, induce eukaryotic cell death, and alter the host cell cytoskeleton. Salmonella species have at least one other TTSS encoded on SPI2 that appears to be involved in intracellular survival.

7. Human Immunodeficiency Virus - Tries to not attract attention

After infecting cells, HIV survives. Ever wondered why?
It's because the HIV protein, Nef plays a role in downregulating the expression of various proteins needed for recognition by potentially dangerous CD8 T cells. Nef lowers the surface expression of CD4, and several haplotypes of MHC-I by redirecting their transport from the trans-Golgi network. Another gene, Tat, appears to upregulate the expression of Bcl-2 during the early phase of cellular infection, increasing the likelihood that it will receive survival signals.

Many viruses can survive intracellularly, but I've included specifically HIV in this list because it survives in immune cells and it is an important virus to know.

1. Survival mechanisms of pathogenic Mycobacterium tuberculosis H37Rv.
2. Identified Virulence Factors of Brucella : Intracellular survival
3. The cell biology of Listeria monocytogenes infection the intersection of bacterial pathogenesis and cell-mediated immunity
4. Lipid Droplets and Mycobacterium leprae Infection
5. Lounging in a lysosome: the intracellular lifestyle of Coxiella burnetii.
6. How Intracellular Bacteria Survive: Surface Modifications That Promote Resistance to Host Innate Immune Responses
7. Evasion of the Immune System by HIV

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