Immunomorphologic studies of macrophages and MHC class II-positive dendritic cells in the iris and ciliary body of the rat, mouse, and human eye

Purpose. To establish the presence of distinct populations of macrophages and MHC class II (Ia)-positive dendritic cells (DC) in the iris and ciliary body of the rat, mouse, and human eye. Methods. Iris-ciliary body wholemounts from a variety of rat strains, balb/c mice, and human eyes were investigated by single and double immunohistochemistry, immunoelectron microscopy, and confocal microscopy to determine the phenotype, density, distribution, and location of macrophage and DC populations. Results. Dendritiform and pleiomorphic macrophages were distributed in a regular array within the rat iris and ciliary body stroma (600 to 700 cells/mm² or 7000 cells per iris). Ia⁺ DC were distributed in a similar regular network (400 cells/mm² or 5500 cells per iris) within the iris stroma and ciliary epithelium. In the rat, a strain-dependent variation in the numbers of DC was noted, F344 rats displaying highest numbers of DC (962 ± 398 cells/mm²) and WAG strain the lowest numbers (285 ± 218 cells/mm²). Double color immunoperoxidase staining using anti-Ia and anti-pan specific macrophage monoclonal antibodies revealed that macrophages and Ia⁺ DC are distinct populations with only 5% to 15% overlap. Single immunoperoxidase of mouse iris and ciliary body using anti-pan macrophage and anti-Ia antibodies produced findings identical to those in rat. Preliminary studies of human tissue using confocal microscopy of immunostained whole irides also revealed a regular array of macrophages and MHC class II (HLA-DR)⁺ dendritiform cells. Conclusions. The mammalian iris contains rich networks of dendritiform-pleiomorphic macrophages and MHC class II⁺ DC. These findings suggest that the DC in the tissues lining the anterior chamber represent a rich network of putative antigen presenting cells and are the most likely candidates for transmitting antigen-specific signals from the anterior chamber in vivo and in experimental models such as ACAID. These observations have wide implications for the understanding of the pathogenesis of anterior and posterior uveitis.