Gonorrhea and immune evasion
Lots of bacteria try to colonize our mucosal surfaces – that’s airways (step throat, tuberculosis), gut (E. coli, Salmonella), aural cavity (ear infections), and urogenital tract (UTI’s, chlamydia). These regions of our bodies are exposed to the outside world, so they’re easy to access, and are usually pretty accommodating places for bugs to grow (warm, moist and enclosed).
Because of this, the immune system is ready with a host of mechanisms to keep harmful bugs off and out. I’ve mentioned some of these mechanisms before, but another one I failed to mention is exfoliation – the deliberate shedding of the top layers of cells in an effort to disrupt the bacteria from attaching. It’s kind of like turning the top 2 inches of ice to water on this guy:
But, as with most immune strategies, some pathogens have learned to evade them, and a new paper in Science describes a really devious form of this evasion by the bacterium that causes gonorrhea:
Neisseria gonorrhoeae, a Gram-negative microorganism, causes one of the most common sexually transmitted diseases worldwide. Even though these bacteria can induce the exfoliation of host cells upon contact, they are able to establish themselves on virtually every mucosal surface of the human body.
They found that certain strains of N. gonorrhoeae were able to bind a receptor on epithelial cells, which tricks them into expressing a molecule called CD105. This molecule then tells all the neighboring cells to activate another cell-surface protein (called an integrin) that makes cells stick to each other, preventing them from getting shed, and allowing the bacterium to stay attached. It would be as if that climber’s axe caused all the surrounding ice to get colder, preventing the ice from melting and throwing him off. When they knocked out the receptor, or CD105, or blocked the integrin activation, the bacterium was far less able to establish an infection, which the authors say may lead to therapeutic interventions. But then, most researchers say their stuff has therapeutic implications, and any treatments based on this research (which is in a mouse model) are probably a long way off.
Still, it’s another cool example of pathogens subverting the immune system, and even turning our own bodies against us to do it.
[PS – This is my first contribution to the Research Blogging network. Please give me feedback – I’d love to know what you think]
Muenzner P, Bachmann V, Zimmermann W, Hentschel J, & Hauck CR (2010). Human-restricted bacterial pathogens block shedding of epithelial cells by stimulating integrin activation. Science (New York, N.Y.), 329 (5996), 1197-201 PMID: 20813953