Help from an unexpected direction
Snake bite causes panic: the bite site swells and becomes numb, the victim begins to sweat, feels weak and unconscious, becomes nauseous and has a dangerously high blood pressure. Do the cells that cause allergic reactions help in the fight for survival?
The caecilian doesn't stand a chance. The teeth of the otter have burrowed deep into their skin, the poison has penetrated the elongated body of the earth-dwelling animal and is distributed with the bloodstream. Soon the reptile will be hypothermic. A little later it will have breathed its last and finally end up in the snake's stomach.
Most viper vipers are not fatal to humans, but a bite from Atractaspis engaddensis, native to Israel, can also kill humans. Their venom is a devastating mix of toxic substances - including safratoxins, which are toxic to the heart. There is no antidote.
So is there any hope for those bitten by A. engaddensis? But - it could be that the immune system intervenes to help. At least, that's what observations by Martin Metz's team led by Stanford University's Stephen Galli suggest.
The scientists were interested in the effects of snake venom on a specific type of immune cell: the mast cell. These cells, which are mainly found in connective tissue, contain messenger substances that they send out when they come into contact with foreign bodies. These trigger inflammatory reactions by attracting numerous other immune cells, causing swelling by expanding the vessels and constricting the bronchi. Mast cells are also the masterminds of allergic reactions and, if overactive, can cause life-threatening anaphylactic shock.
They are also suspected of being involved in the local tissue damage caused by snake bites and the distribution of snake venom throughout the body. On the other hand, they are also able to break down the vasoconstricting peptide endothelin-1, which is released during bacterial infections or sepsis. This is interesting because endothelin-1 closely resembles the most toxic component of A. engaddensis venom, sarafotoxin 6b.
Could the mast cells possibly also contribute to the detoxification of otter venom? Metz and his colleagues put it to the test. They injected different doses of sarafotoxin 6b into normal mice and those lacking mast cells due to a genetic modification. The deficient mutants without mast cells died from the poison within an hour. The normal rodents, on the other hand, activated their mast cells and thus survived a dose ten times higher than their modified counterparts. No wonder, because the researchers could hardly detect any sarafotoxin in their bodies one hour after the injection, but they found a lot of it in the mutants.
Mice with mast cells survived not only the single toxin, but also the un altered venom of peacocks and other snake species, such as the rattlesnake and copperhead, whose venom does not contain sarafotoxins. These immune cells of the rodents were also able to defuse bee venom. Specimens without the helpful cells, however, fell prey to all the toxins tested.
If human mast cells are similarly aggressive against snake venom, it might be possible to develop a remedy for the bite of A. engaddensis and possibly other snakes.