Extracellular sombrero vesicles are hallmarks of eosinophilic cytolytic degranulation in tissue sites of human diseases

Eosinophils are a type of white blood cell that plays a crucial role in the immune system’s response to infections and allergic reactions. In recent years, researchers have discovered a unique structure within eosinophils called eosinophil sombrero vesicles (EoSVs), which are involved in transporting immune mediators. However, their significance in eosinophil-associated diseases (EADs) has remained unclear. A recent study by researchers at the Federal University of Juiz de Fora, Brazil sheds light on the role of EoSVs in EADs by investigating their numbers, structure, and distribution in different tissue biopsies.

Graphical Abstract

The study utilized advanced microscopy techniques, including transmission electron microscopy (TEM) and electron tomography, to analyze EoSVs in biopsy tissues from five prototypic EADs: eosinophilic chronic rhinosinusitis/nasal sinuses, ulcerative colitis/intestines, hypereosinophilic syndrome/skin, dermatitis/skin, and schistosomiasis/rectum. The researchers also compared the morphology of extracellular EoSVs with those isolated from peripheral blood eosinophils.

The findings revealed several important insights into the role of EoSVs in EADs:

  1. Eosinophil cytolysis, the release of cellular contents, including intact EoSVs and granules, is a consistent event in all EADs.
  2. EoSVs remain intact even after complete disintegration of cell organelles, indicating their resilience.
  3. The population and structure of EoSVs remain unchanged in the extracellular matrix, suggesting their stability in tissue environments.
  4. Free EoSVs closely associate with extracellular granules and externalized chromatin during eosinophil ETosis, a form of cell death.
  5. EoSVs were observed on the surface of other cells, such as plasma cells, indicating their potential role in propagating eosinophil immune responses post-cell death.

The study provides valuable insights into the role of EoSVs in EADs, highlighting their involvement in eosinophil cytolysis and immune responses in inflamed tissues. The findings suggest that EoSVs may serve as important mediators of eosinophil-driven inflammation and tissue damage in diseases characterized by eosinophilic infiltration. Further research into the mechanisms underlying EoSV formation and function could lead to new therapeutic strategies for EADs and other immune-related disorders.

Neves VH, Palazzi C, Malta KK, Bonjour K, Kneip F, Dias FF, Neves JS, Weller PF, Melo RCN. (2024) Extracellular Sombrero Vesicles are Hallmarks of Eosinophilic Cytolytic Degranulation in Tissue Sites of Human Diseases. J Leukoc Biol [Epub ahead of print]. [article]

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