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