Localization of DNA and RNA in Eosinophil Secretory Granules

Abstract

Background: Although the accepted paradigm is that the proteins stored in eosinophil crystalloid granules are translated from messenger RNA transcribed in the cell nucleus, recent ultrastructural evidence suggests that protein synthesis may also take place within eosinophilic granules. Methods: We used 2 different methods to detect the presence of DNA and RNA in eosinophil secretory granules. Using bromodeoxyuridine, a thymidine analogue, and bromouridine, a uracil analogue, we labeled the DNA and RNA in eosinophils in vivo in rabbits. Immunoelectron microscopy to localize these molecules was performed on ultrathin sections of blood and bone marrow eosinophils using monoclonal anti-bromodeoxyuridine antibody with IgG as a control. The immunogold grain density was measured in each subcellular compartment within the eosinophils and analyzed using image analysis software. A combination of DNA/CD63 immunofluorescence staining and a fluorescently labeled molecular probe that stains RNA was used to examine the presence of DNA and RNA in the secretory granules of human blood eosinophils. Results: The mean density of bromodeoxyuridine-labeled DNA and bromouridine-labeled RNA immunogold grains in the secretory granules of blood and bone marrow eosinophils were significantly higher (p < 0.0005) than cytoplasmic or background staining. We also demonstrated the existence of DNA and RNA in the CD63-positive secretory granules of human peripheral blood eosinophils by means of immunofluorescent staining and a fluorescently labeled molecular probe. Conclusions: These results provide evidence that eosinophil granules are the site of DNA and RNA synthesis and suggest the potential for a new role(s) for eosinophil-secretory granules.

Human Eosinophil Leukocytes Express Protein Disulfide Isomerase in Secretory Granules and Vesicles

“…In addition, PDI was localized within secretory granules from human eosinophils. Evidence indicative of protein synthesis within secretory granules (Behzad et al 2010;Dvorak 2005;Wan et al 2007) and even lipid bodies (Dvorak 2005) in cells from the immune system, including human eosinophils (Behzad et al 2010;Wan et al 2007) supports the view that PDI might be involved in the proper folding and in the formation and reshuffling of the disulfide bridges of the proteins synthesized within these organelles.…”

Functions of tissue-resident eosinophils

“…What are the pathways that lead to eosinophil granules being populated with stores of cytokine proteins; how are cytokines processed to be stored within granules; and might cytokines even be synthesized locally within granules given that RNA has been detected within granules 147,148 ?…”

Neutrophil extracellular trap-associated RNA and LL37 enable self-amplifying inflammation in psoriasis

“…NaRNA could thus represent as an additional immunostimulatory component within NETs, which has not been appreciated so far. Interestingly, eosinophils were reported to pre-store RNA within their granules 47 , but with unknown significance. It can be assumed that RNA storage in granules is a general feature of granulocytes, in line with what we observed here (cf.…”