Corticosteroids such as prednisone (cortisone) have widespread and powerful effects. They can influence complex processes such as carbohydrate, protein and lipid metabolism, electrolyte and water balance, functions of the cardiovascular system, the kidney, skeletal muscle, nervous system and immune system. They are messenger molecules, acting as the control point for protein synthesis. In this way, they can cause remarkably complex responses.

Corticosteroids are released from the adrenal cortex in the brain, in response to stimuli from somewhere in the body. The released corticosteroids reach target cells, and once inside, specific protein molecules bind the steroid (so-called steroid receptors). The protein-steroid complex goes into the nucleus where it binds to specific regulatory sequences of DNA. This controls the synthesis of sometimes several different proteins involved in a single response, i.e. the immune response. The key point is that lots of things happen in a coordinated fashion due to the presence of a steroid.

Prednisone supresses inflamation. Inflamation is a very complex process and involves many types of cells and many proteins, but prednisone can apparently supress all of this. It is used to control unwanted immune reactions such as allergic reactions (bad case of poison ivy, etc.) and serious autoimmune conditions (lupus, etc.). It is a wonder drug for people experiencing these problems. HOWEVER:

Short-term exposure is no problem, but long-term exposure causes numerous side effects such as early cataracts, bone density loss, facial swelling, weakness of the limbs, increased susceptibility to infection, ulcers, and several more equally unpleasant problems. Patients also can exhibit serious withdrawal symptoms if they come off of prednisone too quickly.

Interesting references for the MOTD prednisone include a review on late phase allergic inflammation responses, use of corticosteroids in allergic disease, use of corticoseteroids in asthma treatment, and side effects of long term use.