Bacteria-killing proteins cover blood type blind spot

Emory University ^ | Feb 14, 2010 | Unknown

[decimon]

A set of proteins found in our intestines can recognize and kill bacteria that have human blood type molecules on their surfaces, scientists at Emory University School of Medicine have discovered.

The results were published online Feb. 14 and are scheduled to appear in the journal Nature Medicine.

Many immune cells have receptors that respond to molecules on the surfaces of bacteria, but these proteins are different because they recognize structures found on our own cells, says senior author Richard D. Cummings, PhD, professor and chair of the Department of Biochemistry. "It's like having a platoon in an army whose sole purpose is to track down enemy soldiers that are wearing the home country's uniforms."

Blood type comes from differences in sugar molecules attached to proteins on red blood cells. If incompatible blood types are mixed, the antibodies from one person will make red blood cells from the other person clump together, with devastating results in an emergency. But someone's immune system usually doesn't make antibodies to the sugar molecules on his or her own red blood cells. That creates a potential blind spot that bacteria could exploit.

For example, a strain of E. coli (O86) has molecules on its surface like those in humans with blood type B. People with blood type B are unable to produce antibodies against E. coli O86. Although O86 is known to infect birds, it's not a major danger like other types of E. coli, some of which can cause severe diarrhea.

Cummings and his colleagues wanted to know why more bacteria haven't adopted the tactics of E. coli O86 to get around the immune system. Searching for proteins that could bind to the sugar molecules characteristic of blood types A and B, graduate students Sean Stowell, PhD, and Connie Arthur identified proteins called galectin-4 and galectin-8.

"These proteins are separate from antibodies and other parts of the immune system," Cummings says. "They kill bacteria like E. coli O86 all by themselves within a couple of minutes."

When E. coli O86 is exposed to these proteins and viewed by electron microscopy, "it looks as if somebody is tearing away at their outer membranes," he adds.

However, galectins-4 and -8 did not kill human red blood cells expressing blood group antigens. High levels of lactose (milk sugar) can inhibit the lethal activity of these galactins, whereas sucrose (cane sugar) does not.

"This raises the question of whether there are dietary effects, as from milk sugars or other dietary polysaccharides, that might inhibit activity of these galectins on intestinal microbes and their proliferation and colonization," Cummings says.

Cummings notes the unique properties of galectins-4 and -8 may provide an explanation for why the human population has such a diversity of sugar molecules on blood cells. The diversity may ensure that some part of the population might be able to fend off a bacterial infection. For example, ABO blood type seems to affect susceptibility to Helicobacter pylori, a bacterium linked to ulcers.

Galectins were thought to have evolved long before "adaptive immunity," the part of vertebrates' immune systems that is responsible for producing a variety of antibodies. Galectins may have allowed the generation of a diverse group of blood type sugar molecules in human tissues as a safe set of molecules to evolve because immunity is backstopped by galectins, Cummings says.

Galectins-4 and-8 were also able to kill another variety of E. coli that display a sugar molecule found on many mammalian cells, although more protein was needed. That leads to a question Cummings and his colleagues are investigating now: What else do galectins recognize, and how does that constrain the kinds of bacteria that can live in our intestines? In addition, it may now be possible, given these results, to engineer molecular changes in these galectins to allow them to kill other types of pathogenic bacteria that display other types of sugar molecules on their surface. Such developments could lead to new types of antibiotics for pathogenic microbes.

###

The research was supported by the National Institute of General Medical Sciences of the National Institutes of Health and the Consortium for Functional Glycomics and also involved key contributions from Marcelo Dias-Baruffi, PhD, and colleagues at the Universidade de São Paolo in Ribeirão Preto, Brazil.

Reference: S.R. Stowell et al. Innate immune lectins kill bacteria expressing blood group antigen. Nat. Med. 16, page numbers (2010).

The Robert W. Woodruff Health Sciences Center of Emory University is an academic health science and service center focused on missions of teaching, research, health care and public service. Its components include the Emory University School of Medicine, Nell Hodgson Woodruff School of Nursing, and Rollins School of Public Health; Yerkes National Primate Research Center; Winship Cancer Institute of Emory University; and Emory Healthcare, the largest, most comprehensive health system in Georgia. Emory Healthcare includes: The Emory Clinic, Emory-Children's Center, Emory University Hospital, Emory University Hospital Midtown, Wesley Woods Center, and Emory University Orthopaedics & Spine Hospital. The Woodruff Health Sciences Center has $2.3 billion in operating expenses, 18,000 employees, 2,500 full-time and 1,500 affiliated faculty, 4,500 students and trainees, and a $5.7 billion economic impact on metro Atlanta.

Learn more about Emory's health sciences: http://emoryhealthblog.com - @emoryhealthsci (Twitter) - http://emoryhealthsciences.org

[decimon]

Ping.

This is just bouncing off of me today but it looks like it must be important.

[grey_whiskers]

Don't have dairy products with Mexican food (lest it E. coli contaminated?)

Cheers!

[Battle Axe]

For those of you uninitiated, Peter D’Adamo wrote a book about blood type diets.

Blood Type A (40% of USA) no dairy, no red meat, veg. fish ok
Blood Type O (50% of USA) no bread, no dairy, meat and fat ok
Blood Type B (9% of USA) no chicken, no corn
Blood Type AB(1% of USA) a varied diet ok

There are lots of other things you should avoid in each blood group. Type O very long lived, often found in jail, higher percentage dies in accidents.
Type B capable of stress and 2nd longest life, dies of stroke.
Type AB prone to autoimmune diseases
Type A dies early due to cancer and heart disease.

These are generalizations. I'm a B and I still eat some chicken.

[MHGinTN]

Interesting! Thanks for pointing to the book. Wonder if my local library can get a copy. I’ll have to put that on my list.

[SunkenCiv]

· join list or digest · view topics · view or post blog · bookmark · post a topic · subscribe ·
	Gods Graves Glyphs	Thanks decimon, wonder if there's a connection with milk-drinkers and non-. For example, ABO blood type seems to affect susceptibility to Helicobacter pylori, a bacterium linked to ulcers. I'm trying to find my own post here, quoting Matt Ridley's "Genome", on some examples of diseases which are either rare, or much more common (depending on the disease) in people with this or that blood type. Ah well. Ancient DNA Reveals Neandertals With Red Hair, Fair Complexions European Neanderthals had ginger hair and freckles [ and Type O blood ] To all -- please ping me to other topics which are appropriate for the GGG list. GGG managers are SunkenCiv, StayAt HomeMother, and Ernest_at_the_Beach
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[neverdem]

Innate immune lectins kill bacteria expressing blood group antigen

[martin_fierro]

A set of proteins found in our intestines can recognize and kill bacteria that have human blood type molecules on their surfaces

Turns out my sh*t knows its stuff!

[SunkenCiv]

GENOME
the autobiography of
a species in 23 chapters
by Matt Ridley
(from chap 9)

The different kind blood group you have determines your susceptibility to certain diseases. For example, people with A blood are less likely to get diarrhoea than people with B blood. People with O blood are more susceptible to getting diarrhoea than anybody else. People with AB blood are virtually immune to diarrhoea because of their resistance. Nobody really yet knows how AB genotype protects them from this disease. "Since people with the O blood are the most susceptible to the disease, shouldn't they die out according to natural selection?' you are probably asking. That is true but there are a couple of things that keep the O group alive and one of them is malaria. People with O blood are more resistant to malaria than other groups. Another thing is that the O group is less likely to get certain cancers. These benefits cancel out the negative effect that the O blood group has on the diarrhoea disease so, this balance has kept the group from disappearing.

[SunkenCiv]