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Tardigrades are polyextremophiles; scientists have reported their existence in hot springs, on top of the Himalayas, under layers of solid ice and in ocean sediments. Many species can be found in a milder environment like lakes, ponds and meadows, while others can be found in stone walls and roofs. Tardigrades are most common in moist environments, but can stay active wherever they can retain at least some moisture.
Tardigrades are one of the few groups of species that are capable of reversibly suspending their metabolism and going into a state of cryptobiosis. Several species regularly survive in a dehydrated state for nearly ten years. Depending on the environment they may enter this state via anhydrobiosis, cryobiosis, osmobiosis or anoxybiosis. While in this state their metabolism lowers to less than 0.01% of normal and their water content can drop to 1% of normal. Their ability to remain desiccated for such a long period is largely dependent on the high levels of the non-reducing sugar, trehalose, which protects their membranes. In this cryptobiotic state the tardigrade is known as a tun.
Tardigrades have been known to withstand the following extremes while in this state:
Temperature – tardigrades can survive being heated for a few minutes to 151 °C (424 K), or being chilled for days at -200 °C (73 K), or for a few minutes at -272 °C (~1 degree above absolute zero).
Pressure – they can withstand the extremely low pressure of a vacuum and also very high pressures, more than 1,200 times atmospheric pressure. Tardigrades can survive the vacuum of open space and solar radiation combined for at least 10 days. They can also withstand pressure of 6,000 atmospheres, which is nearly six times the pressure of water in the deepest ocean trench.
Dehydration – tardigrades have been shown to survive nearly 10 years in a dry state. When encountered by extremely low temperatures, their body composition goes from 85% water to only 3%. As water expands upon freezing, dehydration ensures the tardigrades do not get ripped apart by the freezing ice (as waterless tissues cannot freeze).
Radiation – tardigrades can withstand median lethal doses of 5,000 Gy (of gamma-rays) and 6,200 Gy (of heavy ions) in hydrated animals (5 to 10 Gy could be fatal to a human). The only explanation thus far for this ability is that their lowered water state provides fewer reactants for the ionizing radiation. In September 2007, a space launch (Foton-M3) showed that tardigrades can survive the extreme environment of outer space for 10 days. After being rehydrated back on Earth, over 68% of the subjects protected from high-energy UV radiation survived and many of these produced viable embryos, and a handful survived full exposure to solar radiation.
Originally posted by uva3021
reply to post by LikeDuhObviously
Lets put it this way, there is a growing cohort of people found to be immune to the HIV virus. And its just a happy accident.
As HIV accumulates in the blood, specific immune cells that target viruses - called CD8 - begin to over-produce a receptor molecule called Programmed Death-1. As this PD-1 builds up on the surface of the CD8 cells, the immune cells became weaker and produced fewer virus-killing chemicals, such as cytokines.