Semaphorin 7A on keratinocytes induces interleukin-8 production by monocytes

Background: Semaphorin 7A (Sema7A) expressed on activated T cells stimulates cytokine production in monocytes through its receptor, alpha 1 beta 1 integrin. Objective: To study the significance of Sema7A expressed on keratinocytes in skin inflammation where interaction between keratinocytes and beta 1-integrin expressing inflammatory cells, such as monocytes, takes place. Methods: The regulation of Sema7A expression on keratinocytes by various cytokines was studied by flow cytometry and immunoblot. beta 1-integrin expressing human monocyte cell line, THP-1 cells, were co-cultured with paraformaldehyde-fixed normal human epidermal keratinocytes (NHK) and IL-8 production by THP-1 cells was studied. The significance of beta 1-integrin or Sema7A within this cell interaction was examined by the experiments using beta 1-integrin blocking antibody or Sema7A siRNA. Results: IFN-gamma and TNF-alpha slightly increased Sema7A expression, while IL-4 decreased it. Among cytokines tested, TGF-beta 1 most strikingly increased the Sema7A expression on NHK. When NHK was stimulated by TGF-beta 1, paraformaldehyde-fixed, and co-cultured with THP-1 cells, IL-8 production by THP-1 cells was increased compared to THP-1 cells only. When THP-1 cells were pretreated with beta 1-integrin blocking antibody, this increase in IL-8 production by THP-1 cells was inhibited. Likewise, when NHK were pretreated with Sema7A siRNA before fixation and co-cultured with THP-1 cells, increase in IL-8 production by THP-1 cells was inhibited. Conclusion: Our results suggest that Sema7A on keratinocytes and beta 1-integrin on monocytes contribute to monocyte activation by keratinocytes within skin inflammation, such as psoriasis or wound. (C) 2011 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.