Inflammation that has a slow onset and persists for weeks or more is classified as being chronic. The symptoms are not as severe as with acute inflammation, but the condition is insidious and persistent. Chronic inflammation may follow on from acute inflammation or exist by itself. An acute inflammation will become chronic if the immune system is unable to rid the body of the offending foreign agent or if the agent is constantly able to re-enter the body. In the case of persistent infections, such as tuberculosis,

and auto immune diseases chronic fatigue will arise without the person first going through the acute inflammation stage.

The main cells involved in chronic infection are macrophages and lymphocytes. Because both these cells have a single nuclei, they are known as mononuclear cells. With the aid of chemical mediators such as lymphokines, macrophages do an excellent job of engulfing and neutralizing or killing foreign antigens. Lymphocytes are the predominant cell in chronic inflammation. There are two types, labeled T and B. T-lymphocytes are produced in the thymus gland. They ensure cell based immunity from infection. B-lymphocytes originate in the bone marrow and ensure humoral (bodily fluid) immunity. The activation of B-lymphocytes produces plasma cells, which manufacture and secrete antibodies to fight specific types of antigens.

Macrophages and lymphocytes are interdependent in that the activation of one stimulates the actions of the other.

Certain chronic infections cells known as eosinophils accumulate. Within their cytoplasm are bright red granules. These granules contain a substance called ‘major basic protein’ which has the ability to destroy certain antigens.

In cases of chronic inflammation involving foreign particulate matter, such as splinters, macrophages cells can fuse together to form multinucleated giant cells. Tuberculosis may also cause macrophage cells to unite in this manner.

A key feature of chronic inflammation is collagen production. If too much collagen is formed, this can lead to the condition known as fibrosis. Connective tissue cells known as fibroblasts enter the area of tissue injury and then go to work to produce collagen which is necessary to replace the tissue lost during long term inflammation. The dilated blood vessels which are characteristic of acute inflammation are not evident in cases of chronic inflammation.

The two major complications associated with chronic infection are fibrosis leading to scarring and persistence. The overabundance of collagen production over time can lead to scarring that can cause permanent distortion of the tissue, interfering with it’s function. Chronic inflammation can be continually stimulated by substances with low antigenic properties or by auto-immunity.