Figure 4. Evidence of age- and TBI-induced immune senescence in the resident microglia population.

A representative histogram is shown for the forward scatter intensity of microglia after TBI (A). MI quantification of this histogram revealed a significant effect of both age and injury, as well as a statistical interaction. A representative histogram is shown for the side scatter intensity of microglia (B). To the right, MI quantification demonstrated a significant effect of both age and injury, as well as a statistical interaction. A representative histogram illustrates the relative intensity of microglial autofluorescence in the FITC channel (C). MFI quantification of this data is shown. A representative histogram shows the relative intensity of microglial autofluorescence in the PE channel (D) and MFI quantification is shown to the right. A representative histogram depicts the relative expression level of phosphorylated (Ser139) H2AX in microglia populations (E). MFI quantification of p-H2AX-positive microglia reveals a significant group effect of both age and injury. A representative histogram shows the relative expression level of BCL-2 in microglia, and the MFI quantification of BCL-2-positive microglia is shown (F). For scatter data, N=7 sham and N=12 TBI/group. For all other experiments, N=3 sham and N=6 TBI/group. Statistical comparisons between groups were determined by two-way ANOVA analysis with Tukey’s multiple comparisons test. Significant group effects of age, injury, and interaction between age and injury are shown in each box. Error bars show mean SEM. Abbreviation: FMO fluorescence minus one, FITC fluorescein isothiocyanate, PE phycoerythrin, SSC side scatter, FSC forward scatter, H2AX histone 2a X, BCL-2 B cell lymphoma 2, MI mean intensity, MFI mean fluorescence intensity, TBI traumatic brain injury, n.s. not significant, SEM standard error of mean. *p<0.05, **p<0.01, and ***p<0.001