Tertiary lymphoid organs and other cells in chronic inflammation
THE CONTEXT
Chronic inflammatory reactions may contain organized lymphoid structures, eosinophils, and persistent neutrophilic infiltrates.
Tertiary lymphoid organs
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Accumulated lymphocytes, antigen-presenting cells, and plasma cells can form clusters resembling lymph node follicles. These structures are called tertiary lymphoid organs.
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They occur in the synovium in longstanding rheumatoid arthritis, the thyroid in Hashimoto thyroiditis, and the microenvironment of some cancers.
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Their functional significance is not established.
Eosinophils
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Eosinophils are abundant in IgE-mediated immune reactions and parasitic infections.
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Their recruitment involves adhesion molecules similar to those used by neutrophils and specific chemokines, such as eotaxin, produced by leukocytes and epithelial cells.
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Eosinophil granules contain major basic protein, a highly cationic protein that is toxic to parasites and also injures epithelial cells. This explains their contribution to both parasite control and tissue damage in allergic reactions.
Neutrophils
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Although characteristic of acute inflammation, neutrophils may remain numerous in chronic inflammation because of persistent microbes or mediators produced by activated macrophages and T lymphocytes.
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A neutrophilic exudate may persist for months in chronic bacterial osteomyelitis.
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Neutrophils also contribute to chronic lung damage caused by smoking and other irritants.