Guest guest Posted March 21, 2006 Report Share Posted March 21, 2006 oops sorry! Sharon beat me to it! doris > > UC Study With Mice Links Thimerosal With Immune System Dysfunction > > From a UC announcement. > > Note: Thimerosal is a form of mercury widely used as a > preservative in pediatric vaccines. Mercury, particularly > the organic form of mercury such as thimerosal, is known for > its harmful effect on the nerve systems. Some studies linked > thimerosal with autism while some others disproved any link. > Autism or not, thimerosal is toxic and causes damage to > the nerve system. The only thing uncertain is whether such > damage would manifest itself clinically. > > > A team of cell biologists, toxicologists and molecular bioscientists > at the University of California, , has published a study connecting > thimerosal with disruptions in antigen-presenting cells known as dendritic > cells obtained from mice. > The study provides the first evidence that dendritic cells show > unprecedented sensitivity to thimerosal, resulting in fundamental changes in > the immune system's ability to respond to external factors. > The study was published online today and will be available in the July > print edition of Environmental Health Perspectives, the peer-reviewed > scientific publication of the National Institute of Environmental Health > Sciences. > " This is the first time that thimerosal has been shown to selectively > alter the normal functions of dendritic cells, " said Isaac Pessah, a > toxicologist with the UC School of Veterinary Medicine, director of > the Children's Center for Environmental Health and Disease Prevention and > senior author of the study. " Dendritic cells play pivotal roles in > overcoming viral and bacterial invaders by coordinating the immune system's > overall combat response. " One dendritic cell can activate as many as 300 > T-cells white blood cells that help find and kill external agents that > attack the immune system making them the most effective immune system > activators. > The study shows how intricate connections between calcium channels in > dendritic cells change when exposed to thimerosal. " The slightest > fluctuation in how calcium channels `communicate' can alter the growth, > maturation and activation of dendritic cells, " explained Pessah. " Thimerosal > dramatically alters how two key calcium channels, code-named RyR1 and IP3R1, > found in dendritic cells function as a team by `garbling' the normal > signaling system between them. " > When thimerosal at a concentration as low as 20 parts per billion > alters the fidelity of normal calcium signals, dendritic cells show abnormal > secretion of IL-6 cytokine a potent chemical signal that initiates > inflammatory responses. Higher concentrations 200 parts per billion > causes programmed death of dendritic cells, preventing them from maturing > and doing their primary job of activating T-cells. > Without proper feedback to guide its response, a normal dendritic cell > can quickly become " a rogue, producing misinformation that could activate > aberrant and harmful immune responses, " Pessah explained. > " Even one rogue dendritic cell can activate many inappropriate immune > responses. " > The research team conducted the study on cells cultured from a strain > of mouse not particularly susceptible to immune dysregulation. Using > fluorescent stains and powerful microscopes to study both immature and > mature dendritic cells from bone marrow cultured under normal physiological > conditions, the researchers discovered that extremely small levels of > thimerosal interfere significantly with calcium channel function after just > a few minutes of exposure. They also observed that immature dendritic cells > are particularly sensitive to thimerosal. > Thimerosal is a cheap and effective mercury-based preservative. Its > potential effects on embryonic neuron development led to its removal from > many pediatric vaccines, however it is still used in influenza, diphtheria > and tetanus vaccines, blood products and many over-the-counter > pharmaceuticals. The concentrations of thimerosal used by the UC > researchers were comparable to those attained in childhood vaccinations > containing the preservative. > Researchers and parents have previously proposed links between > childhood vaccines and autism, a neurodevelopmental disorder that affects > language skills and social interactions. In addition to being a direct > neurotoxicant, the UC study indicates that thimerosal may also be an > immunotoxicant, leaving the immune system vulnerable to microbes and other > external influences. > " Our findings do not directly implicate thimerosal as a single > causative agent for triggering neurodevelopmental disorders such as autism, " > Pessah said. " There is growing evidence that autism is several disorders > that we now refer to as just one. There is also growing evidence that some > children with autism have unique immune cell composition and responses to > antigens. The results of our work provide a framework to test the hypothesis > that the genetic background of some individuals may render them especially > susceptible to thimerosal. " > Other experts also advise drawing no final conclusions regarding > thimerosal and autism based on these outcomes. > " These findings should be interpreted cautiously. Although they > suggest that thimerosal may affect dendritic cell function, the > pathophysiological consequences of thimerosal remain unclear, " said A. > Schwartz, a physician and director of the National Institute of > Environmental Health Sciences. > Since cell functions can differ across organisms, Pessah will next > study dendritic cells isolated from the blood of children with and without > autism to confirm if the intercellular changes are the same in humans. The > initial mouse study was funded by the National Institute of Environmental > Health Sciences and the UC M.I.N.D. Institute. > Joining Pessah on the scientific team were molecular bioscientists > R. Goth, Ruth A. Chu and Gennady Cherednichenko and pathologist > P. Gregg. > A copy of " Uncoupling of ATP-mediated Calcium Signaling and > Dysregulated IL-6 Secretion in Dendritic Cells by Nanomolar Thimerosal " can > be downloaded at http://www.ehponline.org/docs/2006/8881/abstract.html. > Quote Link to comment Share on other sites More sharing options...
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