October 25, 2013
Bee Sting Study Suggests That Allergic Reactions Could Be Defense Mechanisms
[ Watch the Video: The Evolution Of An Allergy ]
redOrbit Staff & Wire Reports - Your Universe Online
Writing in Wednesday’s edition of the journal Immunity, scientists from the Stanford University School of Medicine and their colleagues describe how they injected mice with a small dose of bee venom, discovering that later the rodents were able to resist a much larger dose of the toxin.
“Innate immune responses occur in subjects exposed to a foreign substance, such as a pathogen or a toxic material like venom, for the first time,” officials from the California-based institution said in a statement. “Immune cells called mast cells, which reside in most of the body's tissues, are poised to unleash signals that turn on defense responses when a pathogen or toxin intrudes.”
They claim it is the first experimental evidence to suggest that the same immune response associated with allergic reactions could also have evolved in order to help protect an animal from poisons. Previous research conducted by the same scientists found that these mast cells produce enzymes capable of detoxifying snake venom, and that they can also enhance an individual’s natural resistance to bee venom.
Prior immunization is not required for these types of innate immune responses, nor is the development of specific antibodies. In contrast, during an adaptive immune response, the immune system creates antibodies that can recognize the toxin or pathogen that is invading the animal’s system. Adaptive immunity is typically a faster, more specified and more effective form of defense than innate immunity, the research team explained.
“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,” said Ruslan Medzhitov of Yale University School of Medicine, one of the researchers involved in the study. “All of these reactions are designed to expel something harmful from the body. They are unpleasant, but they protect by being unpleasant.”
“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,” added Martin Metz of Charité-Universitätsmedizin 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.”
IgE antibodies, which are a type of immunoglobulin made by the body which are involved in allergic reactions, bind to the surface of mast cells and cause them to initiate an adaptive immune response when exposed to toxins, co-lead author and postdoctoral researcher Thomas Marichal said.
Despite assumptions that most IgE-related responses are negative in nature, the research team speculated that they might be positive in some situations because otherwise, they would have been eliminated through evolution. Marichal’s team hypothesized that IgE could be essential for protection against lethal stings, and that allergic reactions were “an extreme, and maladaptive, example of this type of defense.”
In order to test their hypothesis, the scientists began by injecting mice with a low dose of venom equal to just one or two bee stings. The mice began to develop more venom-specific immune cells, as well as higher IgE antibody levels, in comparison to rodents that had been injected with just a salt solution.
Three weeks later, both groups of mice were injected with a potentially fatal dose of venom equal to five bee stings. According to the researchers, the mice that had been immunized experienced less hypothermia and were three times more likely to survive than the control group. They were also less likely to experience the anaphylaxis characteristic of severe allergic reactions, the study authors said.
“To determine whether IgE antibodies were required for this protection, the team tested mice with three types of mutations: mice without IgE, mice without functional IgE receptors on their mast cells, and mice without mast cells,” Stanford said. “In all three groups of mutant mice, pre-immunization with a low dose of bee venom did not confer protection against a lethal dose, suggesting that the protection depends on IgE signaling and mast cell activation.”