Allergic reactions ‘to protect us from venom’

Scientists have 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 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 suffered anaphylaxis.

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.