Contents © 2004-2011 Massachusetts
General Hospital



Inflammation has been known to humankind for thousands of years, ever since ancient peoples described its hallmark symptoms — redness, pain and swelling. Centuries later, researchers have discovered several of the cellular and molecular events that underlie these symptoms, but much more remains to be understood. In particular, scientists know very little about body-wide, "systemic" inflammation that afflicts patients who have suffered a major traumatic injury.

The Inflammation and the Host Response to Injury research program is mapping out the steps involved in the immune system's response to injury. Identifying these molecular events and the genetic factors that drive them will help doctors predict the recovery outcomes of severely injured patients.

Your body uses inflammation to protect itself from an infection or an injury, and to instruct tissues to begin healing. Inflammation works primarily through your immune system.


Systemic Inflammation

The biology of traumatic injury involves a large-scale inflammatory reaction. Tissue damage recruits white blood cells traveling through blood to the scene of the injury. The immune system activates various types of immune cells during this process. If this process is not choreographed properly, major problems including the failure of multiple organs can occur.

The severe tissue damage that occurs with a crush injury, massive bleeding, or a serious burn causes physical and chemical changes to skin and/or underlying organs. Cell components and blood vessels physically break apart. Small pieces of tissue are thrust into the bloodstream and can become lodged, preventing the delivery of oxygen to the body's vital organs.

All of our blood is routed through our lungs to become enriched with the oxygen we breathe. Because the lungs receive the entire blood supply, this organ system is often the first to shut down after massive trauma. Hordes of inflammatory molecules and gatekeeper molecules called receptors that sense the ongoing inflammatory overload pass through the lungs, causing it to malfunction. Soon thereafter, other organ systems such as the brain, heart and kidneys fail.

In addition to major injury, many health problems have been linked to an overactive, uncontained inflammatory response. Chronic inflammation, which lasts for weeks, months, or longer, can cause lasting damage to many body tissues. For example, chronic inflammation can lead to Crohn's disease, a disorder involving severe abdominal pain and intestinal problems. Like Crohn's, other diseases such as multiple sclerosis, autoimmune disease, arthritis, and even some forms of cancer, are the consequence of unchecked, ongoing inflammation.


Acute Inflammation

You have probably heard of acute inflammation. In contrast to long-lived (chronic) inflammation, so-called acute inflammation usually lasts only a few days. In most cases it remains localized to a specific area of the body and is relatively easy to treat with medicines and proper care and rest of the affected area. During acute local inflammation, the response remains specific to a particular region of the body (for example, tennis elbow or a mosquito bite). An acute inflammatory reaction can be very painful due to the compression of nerves by swollen tissue, as well as from the release of chemical messengers that activate nerve cells in the wounded area to communicate to your brain that the injury hurts. During an acute inflammatory reaction, migration of fluids helps to recruit immune cells and natural tissue remodeling ingredients that play a role in healing. Some of these substances stimulate blood clotting to halt bleeding, and other molecules gently pry open the tissue so it can begin to sew itself back together and close up the wounded area.

Occasionally, an acute inflammatory reaction is severe and becomes systemic. Examples of this might be major trauma, a severe and overwhelming infection that spreads outside of a local area, or a very strong allergic reaction. In each of these cases, there is a major acute response that is mediated by the immune system.

Stage 1 Stage 2 Stage 3 Stage 4 Stage 5
The Stages of Acute Inflammation
Click on each illustration for a larger view and caption