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OP0226 Human Mast Cells Engulf and Store Exogenous IL-17A
  1. T. Noordenbos1,2,
  2. J.E. Paramarta1,
  3. I.C. Blijdorp1,2,
  4. L.J. van Mens1,
  5. J. Stap3,
  6. R.A. Hoebe3,
  7. E. Mul4,
  8. N.G. Yeremenko1,2,
  9. D.L. Baeten1,2
  1. 1Amsterdam Rheumatology and immunology center
  2. 2Laboratory of experimental immunology
  3. 3Department of cell biology and histology
  4. 4Sanquin Research and Landsteiner Laboratory, Academic medical center, University of Amsterdam, Amsterdam, Netherlands


Background IL-17A plays an important role in rheumatic diseases, like rheumatoid arthritis and spondyloarthritis. Direct analysis of inflamed synovial tissue revealed an abundant presence of IL-17A-positive mast cells.

Objectives As mast cells are not known to produce IL-17A in mice, we aimed to investigate the mechanism of IL-17A expression by human mast cells.

Methods IL-17A, IL-17F and RORC mRNA and protein expression was assessed ex vivo and after PMA/ionomycine stimulation in primary human mast cells sorted from tonsils. Internalization of exogenous IL-17A was assessed by Western blot, imagestream, live imaging and confocal microscopy.

Results Immunohistochemistry and western blot analysis confirmed the presence of IL-17A protein in primary human mast cells. In contrast to T cells, however, mast cells did not express RORC protein, the exclusive transcriptional factor controlling IL-17A expression. Accordingly, IL17A, IL17F, and RORC gene expression was readily detectable in sorted T lymphocytes but not in mast cells, even after ex vivo stimulation. Given the discrepancy between the presence of IL-17A protein and absence of its transcriptional machinery, we investigated the uptake of GFP-fused or 6xhistidin-tagged recombinant IL-17A. Imagestream and Western blot indicated that both primary mast cells and the LAD2 mast cell line engulf and store exogenous IL-17A. Live imaging and confocal microscopy revealed that internalized IL-17A is stored in endocytic vesicles and that this uptake can be blocked by inhibiting receptor-mediated endocytosis.

Conclusions Human mast cells do not produce IL-17A but engulf and store exogenous IL-17A from the inflamed milieu. Molecular pathways of IL-17A uptake and eventually release are under investigation.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.2566

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