Figure 10: Immunosuppressive cell types are enriched in aged human skin.

(a) Representative IHC staining for CD33 in human skin grouped by age. Scale bar, 100 μm. (b) Quantification of CD33 IHC staining in human skin grouped by age. * indicates P value <0.05 by Wald test. Data are presented as mean CD33⁺ cells per × 20 FOV+s.e.m. Data represents four donors per age group, multiple images (5–27) per donor were used for quantification. (c) Representative human IHC staining for CD15 grouped by age. Scale bar, 100 or 10 μm for zoomed inset image. * indicates location of zoomed image. (d) Quantification of CD15 IHC staining in human skin grouped by age. * indicates P value <0.05 by Wald test. Data are presented as mean CD15⁺ cells per × 20 FOV+s.e.m. Graph is of four donors per age group, multiple images (2–15) per donor were used for quantification. (e) Representative human IHC staining for CD14 grouped by age. Scale bar, 100 μm. (f) Quantification of CD14 IHC staining in human skin grouped by age. * indicates P value<0.05 by Wald test. Data are presented as mean CD14⁺ cells per × 20 FOV+s.e.m. Graph is of four donors per age group, multiple images (5–22) per donor were used for quantification. (g) Model for SASP-driven immunosuppression resulting in age-related tumour development. Senescent stromal cells accumulate in a mosaic fashion in aged stromal compartments in the absence of tumours. Through the SASP, senescent fibroblasts are sufficient to drive increases in inflammation that is characterized by enrichment of MDSCs. These MDSCs suppress anti-tumour CD8⁺ T-cell (CTL) responses and promote incipient tumour outgrowth. FOV, field of view.