Background: Human amnion epithelial cells (hAECs) have protective and reparative effects when administered immediately after and following established lung injury independent of functional differentiation. We hypothesized that hAECs exerted their reparative effects via immunomodulation, specifically by polarizing macrophages from proinflammatory M1 to proreparative M2 phenotypes, and by inducing the maturation of naïve T cells into regulatory T cells (Tregs).
Methods: To determine in vivo effects of hAECs on macrophages and Tregs during lung injury, we administered 0.3U bleomycin sulfate intranasally into in 8-week old C57Bl6J mice. One day later we administered 4 million hAECs or saline intraperitoneally. Animals were culled 3, 5, 7 or 14 days following bleomycin challenge (n=5 per group). To determine direct effects, we co-cultured hAECs and macrophages or naïve T cells from FoxP3-GFP mice.
Results: Macrophage infiltration in the lung was 8-fold lower in hAEC treated animals by day 7 (p<0.01). There was a shift in macrophage phenotype from M1 to M2 as determined by FACS profiling and qPCR. hAECs also significantly reduced hAEC migration towards MIP-2 in vitro (p<0.01) while concurrently polarizing macrophages from M1 to M2. Further, we determined that hAEC administration doubled Treg numbers in the lungs (p<0.01). This expansion in Treg numbers may be a direct effect as we observed that hAEC co-culture induced FoxP3 expression in naïve T cells.
Conclusions: The protective and reparative properties of hAECs are at least in part due to their ability to interact with macrophages and T cells for resolution of inflammation and fibrosis.