Chronic Inflammation

Definition:  Chronic inflammation can be defined as a prolonged inflammatory process (weeks or months) where an active inflammation, tissue destruction and attempts at repair are proceeding simultaneously. 

Causes of chronic inflammation:

1.  Persistent infections  

-  Certain microorganisms associated with intracellular infection such as tuberculosis,

leprosy, certain fungi etc characteristically cause chronic inflammation. 

-  These organisms are of low toxicity and evoke delayed hypersensitivity reactions.

2.  Prolonged exposure to non-degradable but partially toxic substances either endogenous lipid components which result in atherosclerosis or exogenous substances such as silica, asbestos.

3.  Progression from acute inflammation: Acute inflammation almost always progresses to chronic inflammation following:

  a. Persistent suppuration as a result of uncollapsed abscess cavities, foreign body materials (dirt, cloth, wool, etc), sequesterum in osteomylitis, or a sinus/fistula from chronic abscesses.

 4.  Autoimmunity. Autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosis are chronic inflammations from the outset.

Morphology:

Cells of chronic inflammation:

-   Monocytes and Macrophages  are the prima Dona (primary cells) in chronic inflammation. Macrophages arise from the common precursor cells in the bone marrow, which give rise to blood monocytes. These cells are then diffusely scattered in various parts of the body, in the liver (Kupffer cells), spleen, lymph nodes (sinus histiocytes), lungs (alviolar macrophages), bone marrow, brain (microglia), skin  (Langerhan’s cells), etc…. These cells constitute the mononuclear- phagocytic system.

-  Macrophages are scavenger cells of the body. 

Other cells in chronic inflammation: 

 1.  T-Lymphocytes are primarily involved in cellular immunity with lymphokine production, and they are the key regulator and effector cells of the immune system. 

2.  B-lymphocytes and Plasma cells produce antibody directed either against persistent antigen in the inflammatory site or against altered tissue components. 

3.  Mast cells and eosinophils appear predominantly in response to parasitic infestations & allergic reactions.

  Though neutrophils are hallmarks of acute inflammatory reactions, large numbers of neutrophils may be seen in some forms of chronic inflammation, notably chronic osteomylitis, actinomycosis, & choric lung diseases induced by smoking and other stimuli.

Thus, the overall differentiation points between acute and chronic inflammations include:

References

Bezabeh ,M. ; Tesfaye,A.; Ergicho, B.; Erke, M.; Mengistu, S. and Bedane,A.; Desta, A.(2004). General Pathology. Jimma University, Gondar University Haramaya University, Dedub University.