allergy sufferers rejoice. Two new studies suggest that your sneezing and wheezing may actually protect you. The researchers report that mice that develop an allergic reaction to the venom in bee stings are more likely to survive potentially lethal doses of the same poison later. The results show that allergy can be beneficial and reveal some of the molecular machinery at work, but experts say that the implications for humans are still unclear.
In humans and other mammals, the immune system pushes unknown and potentially harmful substances such as viruses or toxins, in one of two ways. Said reaction "type 1" responds to viruses, bacteria and other microbes by destroying them, while reaction "type 2" uses an array of symptoms, including sneezing, coughing and diarrhea to expel allergens in the body.
Because type 2 response and the antibody it produces immunoglobulin E (IgE), were associated with resistance to worm infections, many scientists believe that they have evolved to protect against parasites (contrary to germs), but that they have no purpose of modern protection. In the developed world without parasite, they are rampant in response to benign substances such as pollen or peanuts with boring or, in the case of anaphylactic shock (an extreme allergic reaction that can cause severe swelling and difficulty breathing) the consequences of the life threatening. Or the prevailing theory goes.
But pathologist Stephen Galli of the School of Medicine of Stanford University in Palo Alto, California, the type of thinking 2 replies had gotten a bad reputation. To explore the effects and unravel the benefits-potential type 2 reactions, he and his colleagues exposed mice to a common allergen: bee venom. They administered a dose of venom about the same as found in one or two bee stings in both mouse strains: type 1 strain response and subject to subject like response deformation 2. Two control groups of same strains received no injection.
Regardless of their predisposition to type 1 or 2 reactions, both groups of mice "bitten" showed a response type 2, the rise of production of specific IgE antibodies to the venom. Then, three weeks later, the researchers gave all the mice a potentially lethal dose of venom and waited to see what would happen.
"It was a response to an allergist would not expect," said Galli. "The second time, the mice were protected."
Eighty-six percent of type 1-prone mice that had had an allergic reaction survived the dose, against only 7% of the mice that were not allergic. Among mice prone 2 standard, 80% of allergic mice survived, while only 28% of non-allergic mice did. Scientists have seen a similar protective effect when they repeated the experiment using snake venom, which contains some of the same allergens present in bee venom.
The antibodies protected mice even when the rodents were not produced. Injecting mice with deficient IgE-specific IgE rich blood serum the poison was sufficient to confer protection, said Galli. And repeat the experiment in mice lacking IgE or the ability to respond showed no protective effect.
The results suggest that type 2 responses may have evolved to protect against venoms as well as parasites and they still serve that function, reports the team today in the journal immunity .
defense mechanism could help humans survive in the difficult conditions in which we evolved, said Galli. "We spent a lot of time meeting with insects and venomous reptiles, and it is likely that this defense mechanism has made this possible."
In a separate study also published today in Immunity immunologist Ruslan Medzhitov of medical school and his colleagues at Yale University confirm that mice with type 2 previous response to bee venom have greater resistance to potentially lethal doses of the substance and later the mice lacking IgE miss this protective effect. in addition, the team found the venom ingredient that triggers the allergy an enzyme called PLA2 as cell membranes and damage is found in snake venoms, spiders, and many other creatures. the researchers worked at each stage of the chain of events that led to the reaction type 2. the immune system sends a wave of chemical messengers called cytokines to repair damage PLA2 and activates the type 2 response, Medzhitov said.
"As far as I know, this is the first direct evidence that IgE-mediated responses may be protective and beneficial," said Medzhitov. "It is like the feeling of pain. It is very unpleasant, but very important for our protection"
"They are very convincing, excellent education," said immunogeneticist Kathleen Barnes of Johns Hopkins University in Baltimore, Maryland, who was not involved in either study, "but we must be cautious in applying these results in humans." human type 2 responses are a number of mysteries, they say it. it is unclear, for example, that people with severe type 2 responses, which are prone to allergies, enjoy a greater resistance to poisons than the rest of us, or why type 2 response can cause life-threatening symptoms in some people. the studies provide important new information, but leave these questions unanswered, she said.
Fred Finkelman immunologist at the University of Cincinnati College of Medicine in the Ohio agrees. "Together, these studies complement our understanding of the evolution of the allergic response," he said. "But what is the beginning of the story at the end of it."
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