The Secretome of Bullous Pemphigoid <scp>IgG</scp> ‐Treated Keratinocytes Induces a Pro‐Inflammatory Eosinophil Response

Bullous pemphigoid (BP) is an autoimmune blistering disease whereby the cutaneous antigens BP180 and BP230 are targeted by autoantibodies. Skin lesions in BP are characterized by an abundance of eosinophils. We recently demonstrated that the treatment of keratinocytes with antibodies from patients with BP induces a robust inflammatory response with release of numerous cytokines, chemokines, complement factors, and proteases. We thus questioned whether this keratinocyte inflammatory response was capable of directly inducing an inflammatory response in eosinophils. We therefore treated human eosinophils with conditioned media from keratinocytes treated with IgG from patients with BP (BP-IgG), or healthy controls (control-IgG) with or without supplemental IL-5. Flow cytometry revealed upregulation of CD107a/CD107b, markers of degranulation, on eosinophils treated with supernatants from BP-IgG relative to control-IgG treated keratinocytes. A decrease in CCR3 and CD101 was also identified. Functional activity of eosinophils was confirmed by performing a multiplex immunoassay on eosinophil supernatants. This revealed significant upregulation IL-6, IL-8, LIF, TGFα, MCP-4, MMP-9, and MMP-10. Supplemental IL-5 did not appear to significantly influence these responses. Our data demonstrate that the inflammatory activation of keratinocytes by BP-IgG affects eosinophils, driving phenotypic changes consistent with degranulation, as well as a pro-inflammatory and proteolytic response.