Human amnion epithelial cells (hAECs) modulate immunological responses to mediate repair of lung injury

Amnion cells derived from either amniotic fluid or the membrane under specific culturing conditions can differentiate into cells from the ectoderm, endoderm and mesoderm lineage. Their plasticity and self-renewal capabilities are grounds towards their use as treatment in various animal models of injury. Human amnion epithelial cells (hAECs) in particular, have been shown to mitigate injury and accelerate repair in neonatal and adult mouse models of lung injury. These early studies suggest that hAECs manipulate repair through integration and differentiation into lung cells. However, more recent studies have cast doubt on in vivo differentiation as a primary mechanism of repair. Instead, amelioration of lung injury may be associated with initial communication between hAECs and host inflammatory response during injury. I hypothesised that hAECs mediate repair of lung injury by modulation phenotype, behaviour and function of macrophages, T cells and neutrophils. My first study investigated the role of macrophage phenotype and function in hAEC-mediated resolution of lung injury. I demonstrated that hAEC transplantation significantly reduces bleomycin-induced pulmonary fibrosis and macrophage infiltrate into the site of injury. I also showed for the first time that hAECs polarise macrophages from an inflammatory M1 towards and antiinflammatory M2 phenotype in vivo. Additionally, through a series of in vitro studies, I showed that these effects were reflective of direct hAEC and macrophage interaction. There was evidence, which showed that hAECs inhibited macrophage chemotaxis and promoted phagocytosis. The conclusions drawn from this study suggest that, hAECs reduced inflammation by inhibiting macrophage infiltration towards the site of injury subsequently accelerating repair by increasing M2 macrophage polarization and function. Next, I explored the importance of T regulatory cells in hAEC-mediated resolution of lung injury by using lymphocyte deficient Rag 1-/- mice. These mice are known for their inability to produce mature T cells. I showed that hAECs require Tregs to fully elicit their reparative effects in bleomycin-induced lung injury. Administration of hAECs and Tregs not only reduced fibrosis in these mice, but significantly decreased inflammation. Using flow cytometric, molecular and histological methodologies accumulated from my previous study, I was able to confirm that hAECs and Tregs interact directly, and macrophage polarisation is dependent on this event. By investigating the response of hAEC administration in lymphocyte deficient Rag 1-/- mice, I was able to determine the importance between Tregs and hAECs in mitigating lung injury. Finally, with the aim of elucidating the cause for these immunomodulatory characteristics, I investigated key factors, which may be involved in these processes. Using wildtype mice, I fully delineated the immunomodulatory changes happening in vivo. I looked at immune cell population changes at the onset and at peak of inflammation and found significant alteration in neutrophil, macrophage and T cell numbers following hAEC transplantation. Next I identified ii a key immunomodulatory factor Lipoxin A4 (LXA4), which may be involved in hAEC-mediated repair of injury. I found changes in LXA4 levels and its ligand FPR2 in bronchoalveolar lavage fluid and lungs of mice treated with hAECs respectively. Through in vitro studies using neutralising antibodies, I will further elucidate the importance of LXA4 in hAEC-mediated immunomodulation. In this current study, to gain further insights into the mechanisms by which hAECs may affect tissue repair, we set out to ask whether hAECs could directly alter neutrophil, macrophage and T cell phenotype and function. Further delineating immunological events following hAEC administration represents an important step in translating this research to the clinic.