字幕表 動画を再生する 英語字幕をプリント Measles is one of the most contagious diseases known to man. In fact, if someone with measles coughs in an elevator, 90% of the people who use that elevator after will catch the disease. Unless of course you've been vaccinated. Then you'll be completely fine. This is the measles virus, it's been around for thousands of years and has been responsible for the deaths of millions of people. Now, on the surface, measles symptoms seem fairly innocuous. But the real damage, the damage that can lead to death, happens on a cellular level. Hi I'm Roberto Cattaneo. I'm a Doctor of Philosophy and Professor of Molecular Biology at the Mayo Clinic. I'm studying the measles virus since about 35 years. Measles uses the trachea as a trampoline. It is in the ideal position in the body to get expelled and to get aerosolized dispersed in the air in small particles very efficiently. When someone with measles coughs or sneezes, these droplets contain the measles virus, and because measles is a respiratory disease, all someone needs to do is breathe in that infected air in order to contract measles. Unless, of course, they've been vaccinated. When the measles virus reaches the lungs, it is met by a type of white blood cell called a macrophage. Usually, macrophages seek out and destroy dangerous pathogens like viruses. But the measles virus tricks the macrophage into not seeing it as a danger and instead, safely transports the virus into the body's lymph nodes. It's here that the virus begins to replicate and spread throughout the entire lymphatic system. Yea, I mean the macrophages thinks to have a system in which they basically get rid of the virus And measles can stay there. So not only it is invisible but it begins to make damage to these cells. The task of these cells is also to go out and fight infection, but instead of fighting infection, they go out with the virus and distribute it to the body. Now, as the virus starts to spread, it enters immune cells that express a protein named SLAM. These cells are “memory” immune cells, meaning that they remember other pathogens that previously infected the host. Measles attacks and kills these SLAM-expressing memory cells and once those memories of past infections are erased, the body will be in a much weaker position to fight off future infections This is why measles is so deadly. But even though the virus has tricked your immune system to helping it, that doesn't mean your immune system has given up. Well, at some point the immune system will notice and will secrete cytokines and attract other immune cells. So at some point the enemy will be identified and taken care of. But for the viruses in fact it is only necessary to get out of the host and find a new host. So it's in fact better not to kill the host. That's right, it's in the best interest of the virus not to kill you, that's some other diseases job. The job of the measles virus is to find a new host, which brings us to another protein the virus expresses: nectin4. And we discovered nectin4 as the epithelial receptor or host exit receptor for measles virus. As measles spreads throughout the body, it also enters cells that express the protein nectin4. This protein is expressed very preferentially in the trachea. And the more the virusit replicates in the trachea, the more cells it kills there. This dead cell build up actually causes the human host to cough or sneeze, helping spread it into a new human host, bringing us right back to where we started. Now, the good news is that once you get the measles, your body learns how to defeat it and you probably won't get it again. This is similar to how the vaccine works, but the difference is you're given a weaker dose, so you can become immune without getting sick or damaging your immune cells. So the vaccine causes the host to remain immune to measles we think for life long or almost life long time. And without measles, other diseases, the ones that actually do the killing, have gone down. Basically the number of hospitalization has been reduced considerably sometimes to about half for several different infectious diseases. So, if you haven't been vaccinated... Yea, the vaccine works beautifully. maybe think about it? Measles may be the enemy of the immune system, but researchers, including Dr Cattaneo, are working on ways to alter the measles virus so it kills cancer cells. For me, a reason to continue study measles is to make it into a friend, making an old enemy into a new friend by modifying it genetically.