In 1845 a group of Dutchmen emigrated to South America and founded a colony in Suriname. Two weeks after their arrival 180 people died from typhoid fever. Two years later another 37 died of yellow fever. These two epidemics killed more than half of the Dutch emigrants in Suriname.
In 1979, more than 100 years later, blodbank doctors in the Netherlands began to unravel the mystery of these devastating epidemics. Was it arbitrary who survived the diseases? If not, what protected some people but not others? The doctors compared the 4th generation immigrants in Suriname and Dutch blood donors.
Most of the blood tests showed no difference between the Surinamese immigrants and the Dutch, but one test indicated that HLA-B7, which was found in many blood donors in the Netherlands, was almost gone in the descendants in Suriname. In contrast HLA-B35, which is rare in the Netherlands, was found in quite a few of the 4th generation Dutch in Suriname.
What is so special about HLA-B7 and HLA-B35? They belong to the HLA molecules , which are found on all cells of the body. These molecules act like noticeboards for the immune system, displaying protein fragments from both the body’s own cells and from any invading organisms.
When security guards make their rounds they scan barcodes at checkpoints to verify that everything is in order. Similarly, the immune system’s T cells verify that all is well by checking that the HLA molecules on cells do not contain anything new and unexpected. If the T cells detect something new in an HLA molecule the cells that are different are attacked and removed so they can’t pose a threat to the body’s health.
The various HLA molecules differ from one another in their capacity to bind specific protein fragments. Each of us only have a few different HLA molecules, inherited from our parents. This means that we each have different abilities to display pieces of different microbes to our T cells. Among the Dutch in Suriname those who had the HLA-B35 molecules instead of the HLA-B7 molecules were better able to display protein fragments from the two diseases that ravaged their colony. This helped them survive the two epidemics, and they lived to pass on the HLA-B35 molecule to future generations.
HLA molecules are obviously important to the immune system’s ability to detect the presence of microbes in the body. Even so, don’t get too worried: there are strikingly few examples of certain HLA molecules providing more or less effective protection against infections.
Blogpost by Anne Spurkland 25th November 2014
Translation edited by Alisa Dewan, 26th February 2015
Originally published in Norwegian 30/08/12