Immunohistochemical characterization of dendritic cells and macrophages in the aqueous outflow pathways of the rat eye

Abstract

Immunohistochemical studies were performed to determine the distribution, phenotype and ontogeny of macrophages and dendritic cells (DCs) in the aqueous humour outflow pathways of the rat eye. Optimal fixation and indirect immunoperoxidase techniques were employed in conjunction with a panel of mAbs on tangential frozen sections of ocular tissues from a total of 37 Wistar Furth rats aged 12–13 days ( n = 8), 3 weeks ( n = 12), 7 weeks ( n = 5) and 15 weeks ( n = 12). The density of immunopositive cells was scored qualitatively. A moderate to low density of Ia + cells with a dendritic morphology were observed in the trabecular meshwork. DCs were also identified in the suprachoroidal space and in the connective tissues of nerves and vessels piercing the sclera, i.e. in association with non-conventional aqueous outflow pathways. The phenotypical and morphological characteristics of these cells would indicate that they may potentially act as antigen presenting cells (APCs). Non-dendritic pleomorphic cells with a macrophage phenotype were also identified in the trabecular meshwork, and bipolar or elongated cells with a macrophage phenotype were a noticeable feature in the perivascular region of collector channels and the limbal episcleral veins. Some macrophage and DC-like cells were observed in intimate association with limbal mast cells. Theories on the mechanisms of Anterior Chamber Associated Immune Deviation (ACAID) have assumed APCs are largely absent from the tissues lining the anterior chamber. Our findings of a low but moderate density of putative APCs in the conventional and non-conventional aqueous humour outflow pathways are discussed in relation to the various theories of ACAID.