Supplementary Material for: Macrophages and Fibroblasts Differentially Contribute to Tattoo Stability

<b><i>Background:</i></b> Little information is available about the complexity and function of skin cells contributing to the high stability of tattoos. It has been shown that dermal macrophages play an important role in the storage and maintenance of pigment particles. By contrast, the impact of dermal fibroblasts, forming the connective tissue of the skin, on the stability of the tattoo is not known. <b><i>Method:</i></b> In this study, we compared the cell number and the particle load in dermal macrophages versus dermal fibroblasts, isolated from tail skin of tattooed mice. <b><i>Results:</i></b> Microscopic analysis revealed that both cell populations contained the tattoo particles, although in largely different amounts. A small number of macrophages with high side scatter intensity contained a large quantity of pigment particles, whereas a high number of dermal fibroblasts harbored only a few pigment particles. Using the CD64^dtr mouse model that allows for selective, diphtheria toxin-mediated depletion of macrophages, we have previously shown that macrophages hold the tattoo in place by capture-release and recapture cycles. In the tattooed skin of macrophage-depleted mice, the content of pigment particles in fibroblasts did not change; however, the total number of fibroblasts carrying particles increased. <b><i>Conclusion:</i></b> The present study demonstrates that dermal macrophages and fibroblasts contribute in different ways to the tattoo stability and further improves our knowledge on tattoo persistence.

<b><i>背景：</i></b> 目前关于构成纹身高稳定性的皮肤细胞的复杂性与功能，相关研究信息仍较为匮乏。已有研究证实，真皮巨噬细胞（dermal macrophages）在色素颗粒的储存与维持过程中发挥着重要作用。与之相对，构成皮肤结缔组织的真皮成纤维细胞（dermal fibroblasts）对纹身稳定性的影响尚不明晰。<b><i>方法：</i></b> 本研究对取自纹身小鼠尾部皮肤的真皮巨噬细胞与真皮成纤维细胞，分别进行细胞数量及颗粒负载量的对比分析。<b><i>结果：</i></b> 显微镜观测显示，两类细胞群均含有纹身色素颗粒，但含量差异显著。少量具有高侧向散射强度的巨噬细胞内含大量色素颗粒；而大量真皮成纤维细胞仅携带少量色素颗粒。此前我们借助CD64^dtr小鼠模型——该模型可通过白喉毒素选择性耗竭巨噬细胞——证实巨噬细胞通过捕获-释放-再捕获循环将纹身色素固定于皮肤内。在巨噬细胞被耗竭的纹身小鼠皮肤中，成纤维细胞内的色素颗粒含量未发生变化，但携带颗粒的成纤维细胞总数有所增加。<b><i>结论：</i></b> 本研究证明，真皮巨噬细胞与真皮成纤维细胞通过不同机制参与纹身稳定性的维持，进一步深化了我们对纹身持久性的认知。