New research offers supportive evidence for the hygiene hypothesis—that reduced exposure to microbes during childhood increases susceptibility to certain diseases by failing to promote the natural development of the immune system.
Using mouse models of irritable bowel disease and allergic asthma, a team led by scientists at Brigham and Women's Hospital and Harvard Medical School, in Boston, discovered that germ-free mice raised in sterile conditions had more invariant natural killer T (iNKT) cells accumulate in their colon and lungs, resulting in increased inflammation, compared with mice lacking only specific pathogens raised in nonsterile conditions (Olszak T et al. Science. doi:10.1126/science.1219328 [published online March 22, 2012]). Invariant NKT cells secrete proinflammatory molecules in response to foreign antigens and are thought to have a role in ulcerative colitis and asthma in humans.
Hampton T. Early Microbe Exposure. JAMA. 2012;307(17):1790. doi:10.1001/jama.2012.3995