Identifying common immunological mechanisms in fibrosis: an immunophenotypic analysis of the capsular response to silicone

Abstract

Silicone is implanted widely in aesthetic and reconstructive surgery. The resultant immune response is poorly understood but implicated in two divergent capsular pathologies: fibrosis (capsular contracture, CC) and lymphomagenesis (breast-implant associated anaplastic anaplastic large cell lymphoma, BIA-ALCL). In this doctoral thesis, I have sought to characterise the immune response to silicone using an in vivo mouse model of capsular fibrosis. The primary hypothesis is that smooth and textured silicone surfaces elicit differing cellular, transcriptomic and proteomic immune responses that are pathologically significant. A model of capsular fibrosis was developed by implanting smooth and textured silicone breast implant shells in the dorsum of irradiated and unirradiated immune-competent C57BL/6J-WT mice. Implant capsules were excised at serial post-operative time points prior to morphometric, flow cytometry, immunohistochemical and immunofluorescent characterisation. RNA-seq and total proteomic analysis were undertaken to delineate transcriptomic and proteomic differences across in vivo samples according to surface. Median capsular thicknesses increased between early and late time-points with collagen laid down within the first 2 weeks (w) post-implantation then remaining static. Immunohistochemistry demonstrated early CD45+ (pan-leukocyte) and F4/80+ (macrophage) capsular infiltration that subsequently declined. Immunofluorescence was confirmatory. Further evidence for the immunogenicity of smooth implant capsules was provided by flow cytometry where statistically significant increases in T- (CD3+, CD4+ and CD8+), dendritic and NK cells were seen at 4 w as well as greater macrophage responses. RNA-seq found adipogenesis, oxidative phosphorylation, fatty and bile acid metabolism hallmark pathways to be upregulated in textured compared to smooth implants at 12 w post-implantation. Gene analysis found smooth implants to discordantly express myogenic and fibrotic pathways at 12 w with downregulation of cell cycle processes. Chemokine analysis found IL6 and IL10 to be elevated in all capsules at 1 w and 12 w post-implantation. Proteomic analysis demonstrated correlation between proteomic and RNA-seq datasets with fat metabolism proteins elevated in textured relative to smooth implant capsules but less clarity evident for immune-related proteins. In conclusion, smooth and textured implant surfaces elicited differing but temporally dynamic immune responses. Immunogenicity of smooth implants capsules was matched with a transcriptomic propensity for fibrosis but not proliferation. Textured implant capsules upregulated lipid metabolism divergently as compared to smooth implants and we postulate that this has modulatory implications for immune cells. Further work is necessary to correlate findings of the in vivo experiments against pathological human capsular tissue derived form our translational study of Breast-implant Associated anapLastic large cell lymphoma and Capsular contracture (BASILICA).