
A very interesting study was published in the April 9, 2010 issue of Science.1 In this study, Matam Vijay-Kumar and colleagues experimented with mice, trying to find out how their immune systems interacted with their body weight. Scientists have known for a while that obesity and the immune system are related, but most scientists have thought that obesity causes immune system disorders.2 That might, indeed, be true. However, this study shows that, most likely, immune system disorders can also cause obesity!
Mice (and most vertebrates, including people) have two levels of immunity: innate immunity and adaptive immunity. Innate immunity refers to the mechanisms in the body that protect against general threats. Adaptive immunity refers to the mechanisms in the body that protect against specific threats. So the mechanisms in the body that fight against all bacterial infections are a part of the body’s innate immunity, but when the immune system is attacking a specific species of bacterium, the adaptive immune system is at work.
Matam Vijay-Kumar and colleagues investigated a very specific part of the innate immune system and its effects on obesity in mice. The results were quite surprising.