Sting allergy ‘may be protective’
Thursday 24th October 2013, 5:10PM BST.
Potentially deadly allergic reactions to bee stings may have evolved to protect us from nature’s venomous threats, research suggests.
Scientists found that an immune response to small amounts of bee venom helped mice resist a subsequent lethal dose.
A similar effect was seen when mice were exposed to venom from one of the world’s most poisonous snakes, the Russell’s viper.
The findings indicate that the reaction which can trigger life-threatening anaphylaxis may have evolved to provide protection against stings and bites from poisonous animals.
However, demonstrating that this is true in humans as well as mice may prove impossible because of the dangers involved.
In one of two studies, a US and German team injected mice with amounts of honeybee venom equivalent to one or two stings.
The animals developed a specific immune response which increased their resistance to lethal amounts of bee venom. Mice exposed to a low dose of Russell’s viper venom were protected in much the same way.
In both cases, the effect was due to immunoglobulin E (IgE) antibodies produced in response to a broad range of environmental triggers, many seemingly harmless.
IgE antibodies work in conjunction with immune cells called mast cells, which have been shown to detoxify components of snake venom.
The second study showed how a destructive enzyme in bee venom induces an immune response in mice. Affected animals acquired protection against near-lethal doses of the enzyme.
“Everyone who ever witnessed or even experienced an anaphylactic reaction to a bee or a wasp sting will wonder why evolution did not get rid of such a potentially deadly immune reaction,” said Dr Martin Metz, from the Charite Medical University in Berlin.
“We have now shown in mice that the development of IgE antibodies to honeybee venom and also to the venom from a poisonous snake can protect mice to some degree from the toxic effects of the venoms.”
Colleague Dr Philipp Starkl, from Stanford University in the US, said: “It was kind of a dogma that most IgE-related responses are detrimental. We and others speculated that there should be some very positive evolutionary pressure to keep these cells and these antibodies, because if they were just bad and deleterious, they would have been eliminated.”
Professor Stephen Galli, another Stanford scientist, said it remained a mystery why some people were susceptible to anaphylaxis.
“P erhaps only certain people, who for genetic or other reasons exhibit especially severe IgE-dependent reactions, are at risk for developing anaphylaxis when stung by bees,” he said. “This notion is supported by clinical observations showing that only a small fraction of people who have IgE antibodies against honeybee venom develop anaphylaxis upon being stung by a bee.”
Dr Ruslan Medzhitov, from Yale University School of Medicine in the US, who led the second team, said: “Our study adds to the argument that allergy evolved to protect us from noxious factors in the environment – it protects us by making us sneeze, cough, vomit, and itch, by inducing a runny nose and tears.
“All of these reactions are designed to expel something harmful from the body. They are unpleasant, but they protect by being unpleasant.”
Both studies are published in the Cell Press journal Immunity.
Prof Galli added: “Our findings support the hypothesis that this kind of venom-specific, IgE-associated, adaptive immune response developed, at least in evolutionary terms, to protect the host against potentially toxic amounts of venom, such as would happen if the animal encountered a whole nest of bees, or in the event of a snakebite.
“Anaphylaxis probably represents the extreme end of a spectrum of IgE-associated reactivity, which in some unfortunate individuals is either poorly regulated or excessively robust, so the reaction itself can become dangerous to them.”
He stressed it was not yet known whether IgE responses also protected humans from poisonous stings and bites, adding that it would be unthinkable to test lethal doses of venom on humans.
“We experience allergies in a much cleaner world, where we don’t have the same threats of venomous creatures and potentially toxic food that existed for much of our evolutionary history,” said Prof Galli. “And so we’re left with this residual type of reactivity that seems completely mysterious and pointless and harmful. This is the first evidence, that we know of, indicating that IgE-associated ‘allergic-type’ immune responses can actually reduce the toxicity of naturally occurring venoms.”