Fig. 4: Analysis of the local T cells at the site of injury 3 days post-surgery in comparison to the bone marrow from untreated mice revealed significant differences in T-cell activation states.

d, f Introducing a fracture decreased CXCR3 presentation on the cell surface in CD4+ T cells and increased the expression of PD-1 accordingly. a Interestingly, CXCR3 expression on CD8+ T cells was highly regulated by the initial experience level, as in aged mice, CXCR3 expression on CD8+ T cells 3 days post-surgery was downregulated, which was not seen in immunoaged mice. c However, there was no significant increase in PD-1 surface expression on memory and effector CD8+ T cells, and less PD-1 expression on memory/effector T cells resulted in escape from immune regulation. b, e Introducing a fracture activated CD8+ memory T cells, as shown by increased levels of CD107a on the cell surface. CD8+ T cells showed a significantly higher activation state in immunoaged mice 3 days post-surgery than in the aged-only group. N = 4 per group; box-and-whisker plot with a line at the median; Welch’s t-test; black * = between immunological experience groups, gray * = between untreated and osteotomized groups.