Macrophages surround the sebaceous glands both in the healthy and the inflamed pilosebaceous unit; however, the reason for this phenomenon and the possible role of sebocytes in it has not yet been investigated. By performing immunohistochemistry on healthy biopsies, we could demonstrate that macrophages in the close proximity of sebaceous glands are exclusively alternatively activated (CD163 + /FXIII-A + /CD206 + /CD209 +). To investigate if sebocytes contribute to the differentiation, polarization and function of macrophages, human peripheral blood monocytes were differentiated and activated in the presence of either supernatant from the human SZ95 sebocyte cell line, or major sebum lipid components such as oleic-, linoleic-, palmitic-, stearic-acids and squalene. Our results showed that with the secretion of CXCL8, sebocytes could exert a chemoattractant effect towards monocytes, while sebocytes derived lipids promoted monocyte differentiation into alternatively activated macrophages as marked by the up-regulation of CD206, CD209 and FXIII-A. Moreover, detection of the produced IL-1b, IL-6 and TNFa protein levels by Propionibacterium acnes activated macrophages revealed a selective inflammatory effect for the various sebum lipids. Our results altogether suggest a role for sebaceous glands in initiating and modulating innate immune responses via their proteins and lipids that are of possible pathologic and therapeutic relevance.
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