M1 and M2 macrophage recruitment during tendon regeneration induced by amniotic epithelial cell allotransplantation in ovine

Recently, we have demonstrated that ovine amniotic epithelial cells (oAECs) allotransplanted into experimentally induced tendon lesions are able to stimulate tissue regeneration also by reducing leukocyte infiltration. Amongst leukocytes, macrophages (My) M1 and M2 phenotype cells are known to mediate inflammatory and repairing processes, respectively. In this research it was investigated if, during tendon regeneration induced by AEC5 allotransplantation, M1M phi and M2M phi phenotype cells are recruited and differently distributed within the lesion site. Ovine AECs treated and untreated (Ctr) tendons were explanted at 7, 14, and 28 days and tissue microarchitecture was analyzed together with the distribution and quantification of leukocytes (CD45 positive), M phi (CD68 pan positive), and M1M phi (CD86, and IL12b) and M2M phi (CD206, YM1 and 1L10) phenotype related markers. In oAEC transplanted tendons CD45 and CD68 positive cells were always reduced in the lesion site. At day 14, oAEC treated tendons began to recover their microarchitecture, contextually a reduction of M1M phi markers, mainly distributed close to oAECs, and an increase of M2M phi markers was evidenced. CD206 positive cells were distributed near the regenerating areas. At day 28 oAECs treated tendons acquired a healthy-like structure with a reduction of M2M phi. Differently, Ctr tendons maintained a disorganized morphology throughout the experimental time and constantly showed high values of M1M phi markers. These findings indicate that M2M phi recruitment could be correlated to tendon regeneration induced by oAECs allotransplantation. Moreover, these results demonstrate oAECs immunomodulatory role also in vivo and support novel insights into their allogeneic use underlying the resolution of tendon fibrosis.