Figure 5. Macrophages from old mice have intrinsic differences that make them less antiinflammatory.

Congeneic BM chimeras were generated by injecting BM harvested from young or old C57BL/6 mice into lethally irradiated young or old mice (A). MMs sorted from O→Y expressed decreased M2 markers compared to Y→Y suggesting that the age-dependent loss of anti-inflammatory phenotype is intrinsic to the macrophage (B). Although not statistically significant, mice transplanted with old BM (O→Y and O→O) had a trend towards increased expression of iNOS (C). Bone marrow derived macrophages (BMDMs) prepared from old mice and treated with IL-4 and IL-13 to polarize to M2 activation state (M₂) exhibited reduced expression of M2 markers particularly CD206 and TGFβ (D). IFNγ-treated BMDMs (M₁) from young and old mice did not demonstrate significant differences in expression of proinflammatory M1 markers (E). When incubated with CD4⁺ T cells activated with anti-CD3 and anti-CD28 and labeled with CSFE, IL-4/IL-13-treated BMDMs from old mice demonstrated reduced suppression of lymphocyte proliferation (higher percent of CSFE-negative CD4⁺ cells) compared to those from young (F). For (D) and (E) RNA expression was normalized to untreated (M₀) macrophages from young mice. *p<.05 by one-way ANOVA with Bonferroni’s multiple comparisons test and t-test, **p<.01 by t-test. n≥5 for chimeric mouse groups.