What is the pathophysiology of Wells syndrome (eosinophilic cellulitis)?

Updated: Mar 26, 2020
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Dirk M Elston, MD  more...
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At least some cases of Wells syndrome (eosinophilic cellulitis) may represent hypersensitivity to an arthropod bite or sting. An impressive response of peripheral lymphocytes to mosquito salivary gland extracts has been documented in some patients with Wells syndrome. [8] A dermal infiltrate of histiocytes, eosinophils, and eosinophilic granules occurs between collagen bundles, which forms the classic flame figures. The eosinophilic infiltrate is almost always restricted to the epidermis and the dermis, but it has also been found in the subcutaneous tissue and the underlying muscle. The location of the infiltrate is correlated with the different clinical features.

Th2-skewing immune dysregulation may be evident, as may a strong CD4+ T-cell proliferation in response to mosquito salivary gland extracts, probably reflecting a significant association between Wells syndrome and mosquito bites in some patients. [9] In one study, immunophenotyping of peripheral T cells revealed an increased proportion of CD3+ and CD4+ T cells. [10] These lymphocytes spontaneously release significant amounts of interleukin 5 (IL-5); this finding suggests that activated T cells may be involved in the pathogenesis of blood and tissue eosinophilia. The eosinophils then degranulate in the dermis, causing edema and inflammation. [11]

With immunofluorescent stains, eosinophil major basic protein is identified in the granules of the flame figures. On electron microscopy, the collagen fibers are intact; this finding suggests that an initial degeneration of collagen is not a factor in initiating the formation of flame figures.

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