In 1901, Karl Landsteiner, a Viennese physician, discovered that humans had four different blood types called A, B, AB and O. For the next 100 years, nobody knew why humans have these four different types. However, researchers in England recently dug up the bodies of people who had died from the 1665 London plague, and made the startling discovery that most of the people who died had type B blood, showing that far fewer people had type B blood than before the plague. Scientist now have to explain why people with Type B blood were more likely to die from plaque. We know that the plague was caused by infection with a bacteria called Yersinia pestis that came from bites by fleas that had picked up the germ by first biting infected rats.
When a germ gets into your system, you make a protein called an antibody that attaches to it and kills it. Your body is not supposed to ever make antibodies against itself. Your immunity recognizes a germ by the sugar surfaces on cell membranes. Type B surface membrane on red cells is the same as the surface membrane of certain bacteria. Yersinia pestis is a bacteria that you can still get today from bites from infected fleas. So, if you are type B, you cannot make antibodies against type B surface of cells, because you would attack yourself and destroy all your red blood cells. So, when yersinia gets into your bloodstream, your immunity does not kill it, so it causes horrible blisters and swollen lymph nodes and you can go into shock and die. 12,000 citizens of London died from yersinia in one week in 1665.
Don’t think that you are safe just because you do not have type B blood and, therefore, are not likely to die from an intestinal bacteria such as Yersinia. People in blood group A, are at much higher risk for heart attacks than those in other groups because their blood is far more likely to clot. They have higher blood levels of factor VIII, which helps blood clot, and clots are the terminal factor that blocks arteries to cause a heart attack.
There are more than 300 known variations in blood types. For example, you are also classified as to whether the surface of your red blood cells contain a Duffy surface. Almost no one in Africa has the Duffy red blood cell type. The Duffy surface protein is a key that opens cells to let the cause of malaria in. So, if you are bitten by a mosquito that is infected with malaria and you have the Duffy blood type, Plasmodium viva, the bacteria that cause malaria will enter your cells just as if they belong there and you will die. So, if you lived in Africa, where malaria is epidemic, you would die. Over time, in Africa, people who had Duffy proteins died from malaria. Almost all Caucasians have the Duffy proteins on the surface of their red cells because their ancestors were not exposed to malaria.
Your red blood cells may have another surface protein called Lewis blood type. People with the Lewis blood type are at extremely high risk for stomach ulcers. The Lewis blood type is the surface protein on Helicobacter pylori, which causes more than 90 percent of stomach and intestinal ulcers. If you have the Lewis surface protein on your red blood cells, you cannot make antibodies against the Lewis surface protein. Helicobacter has the same surface protein as the Lewis red cell type. So Helicobacter punches holes in your stomach, while your immune system stands by and does nothing, because Helicobacter bacteria look just like your own cells with the Lewis surface to your immune system. See People with Type O Blood Get More Stomach Ulcers