Site-dependent distribution of macrophages in normal human extraocular muscles

Clinical data indicate that extraocular muscles have different susceptibilities for some orbital immune disorders depending on their anatomic location. The resident immunocompetent cells may be important mediators in the local pathogenesis of such disorders so the distribution of these cells was studied in extraocular muscles obtained from normal human donors. For comparison skeletal muscles were studied.

The cell distributions were analyzed quantitatively in cryostat cross-sections subjected to a two-step immunoperoxidase method using monoclonal antibodies against T cells, B cells, macrophages and several other markers for cell differentiation or activation. The macrophage distribution was analyzed in more detail using on-line semiautomatic image analysis equipment (VIDAS, Kontron, Elektronik GmbH, Eching, Germany).

Extraocular muscles contain numerous macrophages, fewer human leukocyte antigenD-related (HLA-DR) positive cells and T cells, whereas B cells are absent. The numeric density of all cell types, and macrophages in particular, is much higher in extraocular muscles than in skeletal muscles. In extraocular muscles the majority of T cells are positive for the CD8 antigen (suppressor/cytotoxic), in skeletal muscle CD4 positive T cells (helper) predominate.

Extraocular muscles contain many more CD8-positive cells and macrophages per square millimeter than skeletal muscles. Of all the cell types studied, only the macrophage distribution differs significantly among the normal extraocular muscles: the medial and inferior recti muscles contain about twice as many macrophages as the lateral rectus and superior oblique muscles. Their mean sizes (area) or shape distributions however, appear to be similar.