Pyrin levels in human monocytes and monocyte-derived macrophages regulate IL-1beta processing and release
Seshadri, S.; Duncan, M.D.; Hart, J.M.; Gavrilin, M.A.; Wewers, M.D.
Journal of Immunology 179(2): 1274-1281
2007
ISSN/ISBN: 0022-1767 PMID: 17617620 Document Number: 605663
Macrophages and their precursors, monocytes, are key cells involved in the innate immune response. Although both monocytes and macrophages produce caspase-1, the key enzyme responsible for pro-IL-1 beta processing; macrophages are limited in their ability to activate the enzyme and release functional IL-1 beta. In this context, because mutations in the pyrin gene (MEFV) cause the inflammatory disorder familial Mediterranean fever, pyrin is believed to regulate IL-1 beta processing. To determine whether variations in pyrin expression explain the difference between monocytes and macrophages in IL-1 beta processing and release, pyrin was studied in human monocytes and monocyte-derived macrophages. Although monocytes express pyrin mRNA and protein, which is readily inducible by endotoxin, monocyte-derived macrophages express significantly less pyrin mRNA and protein. Pyrin levels directly correlated with IL-IA processing in monocytes and macrophages; therefore, we asked whether pyrin might promote IL-1 beta processing and release. HEK293 cells were transfected with pyrin, caspase-1, apoptotic speck protein with a caspase recruitment domain, and IL-1 beta. Pyrin induced IL-1 beta processing and release in a dose-dependent manner. Conversely, pyrin small interference RNA suppressed pro-IL-1 beta processing in both THP-1 cells and fresh human monocytes. In summary, both pyrin expression and IL-1 beta processing and release are diminished upon the maturation of monocytes to macrophages. When pyrin is ectopically expressed or silenced, IL-1 beta processing and release parallels the level of pyrin. In conclusion, in the context of endotoxin-induced activation of mononuclear phagocytes, pyrin augments IL-1 beta processing and release.