TB is a pretty simple one. If you've had/been exposed to TB, your body mounts a very strong, concerted response to it. One of the routes to battle TB is that it produces antibodies, including ones to a TB protein called tuberculin (a surface protein on the bacterium). Now, one of the neat things about the immune system is, it has a memory. It keeps cells around that produce antibodies to stuff you've been exposed to.. not at full strength, but its still there. That way, your body is primed to keep that infection from coming back. Works for that most part with a wide range of diseases. It's also one of the major premises of vaccination/immunity (you get vaccinated against, say... measels... your body will keep produce low levels of antibodies against measels to ensure you don't get measels when exposed (again or for the first time)). This was actually first documented, I believe, during the bubonic plague in which people who had the plague and recovered were then enlisted to treated/interact with plague bearers, since it was noticed you didn't get the plague again. (side note, I'm tired and could be mixing plague and smallpox, but go with me on this =).
So anyhow, like I said, your body has a memory of TB, and its one of it's major immune-response-inducing proteins, tuberculin. When they do the skin test, they introduce a small amount of tuberculin under the skin. Your body, if it's see that before, will go hog wild on it and you'll get localized inflammation (swelling, redness, yada yada). People who haven't might have a little nonspecific reaction, but it ain't no big thing. People who have get big inflamed reactions around the injection point.
You'll always test positive for TB now (unless you become incredibly immune compromised.. have a bone marrow transplant and chemo, etc...).
Ciao, C.Sc. |
