Background: Human amnion epithelial cells (hAECs) can be isolated from widely available fetal membranes and have pluripotency traits akin to embryonic stem cells. They are non-teratogenic and have immunomodulatory properties. In animal models of lung disease, hAECs mitigate injury by modulating inflammation without significant engraftment. Moreover, administration of hAECs following injury reduces the number of infiltrating macrophages at the site of injury suggesting that hAECs may mediate repair by modulating macrophage response.

Aims: To understand the effects of hAECs on macrophage polarization and behaviour.

Hypothesis: hAECs mediate repair by shifting the phenotype of macrophages from a pro-inflammatory M1 towards the reparative M2 phenotype. 

Methods: We used a bleomycin mouse model of lung injury to assess interactions between hAECs and macrophages. Four million hAECs were administered intraperitoneally into C57BL/6 mice 24 hours following bleomycin challenge. Using flow cytometry and quantitative PCR analyses, we measured the expressions of M1 and M2 macrophage specific markers. Using in vitro co-culture, we determined the effects of soluble factors from hAECs on macrophage phenotype and behaviour. 

Results: hAEC treatment reduced the number of infiltrating macrophages into lungs, which were predominantly M2 (**p<0.01). Additionally, expression of M2 specific genes, Arg-1 and Ym-1, were increased (**p<0.01, ***p<0.001 respectively). Soluble factors secreted by hAECs induced an M2 phenotype in bone marrow-derived macrophages primed to an M1 phenotype with LPS (*p<0.05). This accompanied a decrease in the macrophages’ migratory ability towards MIP-2 and an increase in phagocytic ability (**p<0.01, *p<0.05 respectively). Culturing macrophages in hAEC conditioned medium did not affect survival/proliferation. 

Conclusion: This study provides evidences that hAECs can directly affect macrophage behaviour towards a pro-reparative state, which may contribute to hAEC mediated repair.