David Vetter was born without a functioning immune system and spent his life in a bubble that protected him from germs. He died at age 12 in 1984. Scientists are using gene therapy to treat the disorder so that children can live normally. Science Source hide caption

itoggle caption Science Source

The genetic factors responsible for a cat's stripes might help researchers understand disease resistance in humans. kennymatic via Flickr hide caption

itoggle caption kennymatic via Flickr

Bacteroides species are some of the most common bacteria in the human gut. Enviornmental Health Perspectives hide caption

itoggle caption Enviornmental Health Perspectives

Even in the remote Faroe Islands, some children have high levels of perfluorinated compounds in their blood. The chemicals may interfere with the immune system. Stig Nygaard/Flickr hide caption

itoggle caption Stig Nygaard/Flickr

Dr. Ralph Steinman of Rockefeller University died Friday, three days before he was named a winner of the Nobel Prize in Physiology or Medicine for "his discovery of the dendritic cell and its role in adaptive immunity."

Mike Groll/AP hide caption

itoggle caption Mike Groll/AP