Macrophages and MHC class II positive dendritiform cells in the iris and choroid of the pig

Macrophages and dendritic cells (DC) are considered to play an important role in the initiation and propagation of uveitis. Little is known about these cells in the normal pig uveal tract, despite the fact that the pig eye shares many similarities with the human eye and is considered as a suitable species to investigate the pathogenesis of human ocular disease. The aim of this study was to investigate the presence of immunocompetent cells in the uveal tract of the normal pig.

Iris and choroid wholemounts and cryostat sections were obtained from normal pig eyes. Single and double immunohistochemistry was performed by using anti-porcine leukocyte (CD45), anti-porcine macrophage (CD163, CD14), anti-porcine MHC class II (MCA1335), anti-human MHC class II (MCA379G), anti-porcine B lymphocyte (IgM), anti-porcine T lymphocyte (CD6) and anti-porcine granulocyte (MCA1219) monoclonal antibodies.

A rich network of dendritiform CD163 positive tissue macrophages was observed in normal pig iris and choroid wholemounts (368 + 84/mm(2), 402 + 97/mm(2), respectively). Approximately 50% of the CD163 positive tissue macrophages in the iris coexpressed MHC class II. Double immunostaining revealed that a small population of the MHC class II positive cells, did not express macrophage markers, and probably represent classical DCs. B lymphocytes and granulocytes were not detected in iris and choroid wholemounts. An occasional T cell could be observed per high power field in iris wholemounts but not in the choroid.

The present study reveals that the normal pig uveal tract contains a rich network of tissue macrophages and MHC class II positive dendritiform cells. At least three populations could be distinguished: MHC class II positive and negative tissue macrophages and MHC class II+ dendritiform cells lacking tissue macrophage markers.