Cracking Microbial Code

On Tomorrow’s Table, Pamela Ronald shares a breakthrough in the study of bacterial communication. Although bacteria have been known to use a limited chemical vocabulary, for the first time they have been observed to use a protein as a signalling mechanism. Ronald writes, “Ax21 is a small protein. It is made inside the bacterial cell, processed to generate a shorter signal and then secreted outside the bacterium.” In the species studied, perception of Ax21 caused nearly 500 genes—ten percent of the bacterium’s genome—to change expression. Thus galvanized, individual bacteria assemble into “elaborate protective bunkers” called biofilms, producing “a virulent arsenal including ‘effectors’ that are shot directly into the host to disrupt host defenses.” As Ronald says, “this process transforms the bacteria from a benign organism to a fierce invader.” While the bacterium in question infects a rice plant, Ax21 and similar proteins may play the same role in other pathogens—including those that infect animals and humans. But we multicellular types are not defenseless: Ronald and her team have shown, for the first time, that a host’s immune receptors can overhear the microbial call-to-arms and prepare for war. 2011 Nobel Laureate Bruce Beutler also discusses Ronald’s work as it relates to his own, beginning at 40:45 in his Nobel Lecture of Dec. 7.

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Billions of B-Cells

On We Beasties, Kevin Bonham tells us all his thoughts on GoD—the Generation of Diversity that enables B-cells “to make antibodies that recognize almost any chemical structure that has ever existed or will ever exist.” By recombining three essential pieces of an antibody (with 100, 30, and 6 variants respectively), using enzymes to slice up DNA and stitch it back together, and owing to a little extra variation from our parents and a dash of random nucleotides, B-cells can fabricate about 10 billion different antibodies to intercept viruses, bacteria, and other intruders. On ERV, Abbie tells us that the same antibody can come in five different forms, or isotypes, that fill functional niches in a total immune response. Abbie writes, “Because your immune system is mindless […] this ends up generating a lot of waste, like many evolved systems.” But “it also means youve got a lot of bases covered when you are exposed to a new pathogen.”

All About Antibodies

i-486b8126c029ffcb3dfb6a0ae70bda35-bodybuzz.jpgERV familiarizes us with the different “layers” of the immune system, including intrinsic, innate, and adaptive immunity. The last layer makes specific antibodies to recognize pathogens, but in the case of HIV, capable antibodies aren’t enough to stave off the progression of disease. ERV writes, “HIV-1 evolves to escape these antibodies…and your body can’t catch up.” The high mutability of HIV-1 makes for a very plastic envelope, meaning the virus continually shifts shape and evades the watchful eye of the immune system. In another post, ERV explains that antibodies make diseases like Dengue fever more deadly, as “non-neutralizing antibodies attached to viruses cause them to ‘stick’ to cells they normally couldn’t infect.” This phenomenon leads ERV to warn “anything but a ‘perfect’ vaccine could cause more severe disease after exposure.” On Neurotopia, Scicurious tells how inventive researchers made a “cocaine vaccine,” allowing antibodies to bind to chemical agents and keep them from passing into the brain. And on Effect Measure, Revere considers the possibility “abortive rabies” in the case of a girl who had antibodies for the deadly virus but no trace of infection.

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