When a venomous snake bites its prey, a deadly cocktail of toxins rushes into the victim¿s body causing sweating or chills, nausea, blurred vision, convulsions, and ultimately, death. It has long been thought that the victim¿s immune system exacerbated the effects of the venom. Now, a new study shows that mast cells in the immune system of mice actually unleash proteins that break down some of the most toxic components of snake venom.
Found in all mammalian immune systems, mast cells were assumed to worsen snakebite symptoms because they respond to a variety of triggers in the body, including bacteria and parasites, by instigating tissue changes such as inflammation and blood vessel dilation. Although these reactions can be helpful, out of control mast cells sometimes overreact to certain chemical compounds, causing allergic reactions, asthma and anaphylaxis--the latter of which can be fatal in its most severe form, anaphylactic shock. Most animal venom triggers an immediate mast cell response, which scientists assumed was probably similarly harmful.
Researchers led by Stephen Galli and Martin Metz of the Stanford University School of Medicine, however, were encouraged by previous results that showed mast cells protect mice against the toxic protein endothelin-1, which is associated with conditions such as sepsis and high blood pressure. Because this protein closely resembles sarafotoxin, the most toxic substance in the venom of the Israeli mole viper, the researchers hypothesized that mast cells might offer some protection from this compound as well. Injecting the viper venom into mice with normally functioning immune systems and also into genetically altered mice that lack mast cells, they found that the normal mice could withstand 10 times the amount of venom. The researchers also tested the venoms of the western diamondback rattlesnake and the southern copperhead, along with the honeybee, and found that mast cells produce proteases that break down a different toxic component in each of them.
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The next step, according to the researchers, is to work with human mast cells to see if they exhibit the same protective effects. If so, the results of this study, published in the July 28 issue of Science, may someday lead to less species-specific snakebite treatments. The researchers also hope that other potentially positive mast cell effects will be investigated. ¿I don¿t think that evolution came up with the mast cell so that people could eat a peanut and suddenly die,¿ says study author Galli. ¿Hopefully this will help researchers think about other ways mast cells might be beneficial.¿
