Effects of the pig renal epithelial cell line LLC-PK1 and its conditioned medium on the phenotype of porcine microglia in vitro

Microglia are dispersed throughout the central nervous system. Under physiological circumstances they display a ‘ramified’ resting phenotype. In different neuropathologies microglia reversibly transform into the activated form, an amoeboid phagocyte with a broad spectrum of immune effector functions. In this study, a coculture of porcine microglia and the pig renal epithelial cell line LLC-PK1 was used to investigate microglial cell biology. The morphology of the cocultures was elucidated as well as the functionality of the microglia cells by proliferation, superoxide and phagocytosis assays. Our results demonstrate that direct intercellular contact between the two cell types was necessary for microglia to acquire a ramified morphology. Moreover, the conditioned medium of the renal cells promoted proliferation of microglia, inhibited giant cell formation and stimulated microglia to retain their capability to generate superoxide and to perform phagocytosis. In conclusion, we have constructed a cell culture system showing differentiation of microglia in vitro and keeping them in optimal conditions.