Two days ago, I cut my finger while slicing apples. This required urgent fingertip bandaging so there wasn’t too much mess while I finished the apples. But the cut was not dangerous or life-threatening in any way. It’s because I was born that way. When I don’t tend to get sick with the flu either, it’s because I’ve become like that.
Immunologists divide the immune system into innate and adaptive. We take the innate for granted. We consider it obvious that a cut in the finger will heal itself in about 4-5 days. The innate immune system, which includes things like the macrophages, is so effective that it’s only very recently that scientists have begun to gain detailed insight into how it works. The innate immune system is largely the same in all people.
The adaptive immune system, on the other hand, is tailored to me and to the environment I have lived in. This part of the immune system includes T and B cells. It is the adaptive immune system that prevents me from getting the flu, chickenpox, measles, and many other infectious diseases that I have had earlier in life or that I have been vaccinated against. When doctors try to understand why we get sick from infections, or why someone suffer from chronic inflammatory diseases, it has traditionally been the adaptive immune system that has been in focus. This is probably why we have the most knowledge about how this part of the immune system works.
For long, immunologists thought of the innate and the adaptive immune systems as two separate entities that had little to do with each other. Now we know there is a lot of cross-talk and even tight connections between the two parts of the immune system. To use my finger as an example:
When I cut my finger, bacteria will immediately enter the wound. The injury itself, as well as the bacteria, will trigger an inflammatory response. The bacteria will be engulfed by macrophages, which also summon other parts of the innate immune system to the site of injury. In most cases, this is enough to remove the bacteria and repair the damage. If the bacteria are too numerous or they are particularly aggressive, the innate immune system needs help from the adaptive immune system. Antigen-presenting cells from the innate immune system will stimulate T-helper cells so that an immune response adapted to the specific microbe is initiated. This is why a bacterial infection following a cut in the finger will almost always be contained at the site of injury and will heal within a few days.
Blog post by Anne Spurkland, written 25.10.12. Last updated and translated to English on 20th January 2024
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