Potential antigen‐presenting cells in normal extraocular muscles demonstrated with double immunoenzyme staining

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Abstract
Antigen‐presenting cells are of crucial importance for the initiation and regulation of regional immune responses. In a previous study, indirect morphological evidence that morphologically normal human orbital tissues contain HLA‐DR‐positive macrophages, which may represent antigen‐presenting cells, has ben obtained. In the present study, these cells were characterized in detail using double immunoenzyme staining techniques with monoclonal antibodies directed against several well‐characterized monocyte/macrophage markers and against HLA‐DR gene products. The orbital muscular tissues appear to contain numerous HLA‐DR, monocyte/macrophage marker double‐stained cells, which are considered to be potential antigen‐presenting cells. The cells are widely distributed in the connective tissue of all the orbital muscular tissues studied and consist of several subsets with different phenotypes. Furthermore, site‐specific differences were shown between recti muscles and the levator/Müller's muscles with respect to the distribution of HLA‐DR and one monocyte/macrophage marker (OKM5). Many of the orbital antigen‐presenting cells appear to be of the dendritic type and are considered to be of major importance in regulating local orbital immunity.