Page 48 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Inflammatory Lesions
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6.2 Macrophagic Inflammation
VetBooks.ir General information

• Macrophages are large mononuclear cells involved in the innate cell-mediated immunity.
They originate from circulating monocytes, which migrate into tissues through the
endothelium.
• Macrophages are commonly seen in established or chronic inflammatory processes.
Cytological features
• Macrophagic inflammation is diagnosed when the sample contains a vast predominance of
macrophages and is also known as granulomatous.
• Macrophagic inflammation may be associated with other inflammatory cells, including
neutrophils, lymphocytes and plasma cells. When admixed with neutrophils, the inflamma-
tion is referred to as pyogranulomatous.
• Other cell types, including epithelioid macrophages, multinucleated giant cells and reactive
fibroblasts, may also be present.
• Epithelioid macrophages: mononuclear cells, often arranged in cohesive groups, with
large amounts of uniformly basophilic cytoplasm, overall resembling epithelial cells.
• Multinucleated giant cells: result of the fusion of multiple epithelioid macrophages.
They have a large cytoplasm and contain multiple small nuclei arranged either haphaz-
ardly (foreign-body-type giant cells) or peripherally (Langhans-type giant cells).
• Macrophages often display phagocytosis. In haemorrhagic events, they may contain red blood
cells (erythrophagocytosis), haemosiderin (haemosiderophages) and/or haematoidin crystals.
They can also engulf cellular debris, leucocytes (leucophagia) and/or infectious agents.
• Specific types of macrophagic inflammation (e.g. panniculitis, foreign body/injection reaction)
will be discussed in specific chapters.

Causes
• Selected infectious agents (e.g. Mycobacterium spp., Leishmania spp., fungi, feline infectious
peritonitis (FIP) infection).
• Endogenous or exogenous foreign body reaction.
• Chronic irritation.