Immune cell diversity and regenerative markers reveal interactions among macrophages, rodlet cells, and stem cells in the kidney of Poecilia sphenops.

The kidneys of molly fish (Poecilia sphenops) exhibit complex immune and cellular activities, which are crucial for maintaining renal function and responding to environmental stressors. This study aimed to investigate the histological and immunohistochemical characteristics of immune cells, autophagy, and stem cell activity within the renal tissues of molly fish. Histological analysis revealed the presence of immune cells, including macrophages and granular leukocytes, concentrated around the renal corpuscles (RC) and renal tubules (RT). Additionally, numerous lymphocytes were observed surrounding the RC, and a notable presence of rodlet cells with a thick capsule and rodlet-like inclusions was detected around the RT. Immunohistochemical staining confirmed macrophage activity through CD68 and Iba1 expression, while APG5, an autophagy marker, was observed in macrophages, rodlet cells, and podocytes, indicating active autophagic processes. Polymorphic granulocytes expressed iNOS-2. Inflammatory markers IL-1β and NF-κB were highly expressed in rodlet cells and macrophages, respectively, suggesting their role in immune modulation. The expression of S100 protein in rodlet cells and acetylcholine in macrophages further highlights their specialized functions in immune regulation. Additionally, renal stem cells were identified by expressing Nrf2 and Sox9, indicating a potential role in tissue repair and regeneration. These findings provide critical insights into the kidney's dual function in immunity and regeneration, contributing to a better understanding of fish renal physiology and potential applications in environmental monitoring and aquaculture health management.