Galectins Seek And Destroy Camouflaged Bacteria, Without The Help Of Other Immune Responses
Some bacteria try to trick our body's defenses by camouflaging themselves with the same carbohydrate coatings most of our own cells have. But scientists have discovered that our immune systems have the last laugh, because they produce a family of proteins that can recognize and kill these camouflaged bacteria.
These proteins, called galectins, can recognize a large number of disease-producing bacteria by their carbohydrate coatings, and can be engineered to be used as antibiotics to kill bacteria and treat infections. The research, conducted by scientists at the Emory University School of Medicine will be published in Nature Chemical Biology.
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The discovery was made by observing 300 different intestinal bacterial glycans (carbohydrates found on the surfaces of cells) in a microarray. The microarray helps present multiple glycans on a single slide, and helps screen for naturally occurring glycans in the human body. "Many microbes cover themselves with glycans that somewhat resemble our own cells," said Dr. Richard D. Cummings, professor and chair of the Department of Biochemistry at the university. "That limits how well the immune system can use antibodies to respond to those microbes."
To prevent an auto-immune attack, our bodies don't usually make antibodies that fight molecules found on our own cells. Yet, this hole in defense can be exploited by bacteria that resemble our own cells. Galectins prevent this by directly recognizing microbial invaders.
This research builds on earlier discoveries describing galectins that recognize and kill bacteria that express the human blood group B antigen on their surface.
In comparison to antibodies, galectins don't need other immune responses to help kill bacteria. The researchers identified several varieties of bacteria, including Pseudomonas aeruginosa and Providencia alcalifaciens, which can be killed by galectins. The bacterial strains that carried the target glycan were effectively destroyed by the galectins.
"These studies have opened the way to understanding the ways in which adaptive or antibody-based factors work together with innate or galectin-based factors to give us immunity against a broad range of microbes," Cummings said in the release.
In addition, the microarray technology provides tools to study glycan-binding antibodies and
galectins in varying populations. "These studies use tiny amounts of blood - just a few drops - and show how glycan microarrays could supersede previous technology," he says. "Using these tools, investigators could identify developmental- and age-specific differences in anti-microbial glycan antibodies in humans, which may predict susceptibility to disease."
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