Rhodopsin and retinoblastoma. A monoclonal antibody histopathologic study.

Rhodopsin was identified in formaldehyde-fixed, paraffin-embedded human fetal retina, and in five retinoblastomas using monoclonal antibody (MAb) MAb-E. The binding pattern corresponding to rhodopsin immunoreactivity was then compared with S-antigen using another monoclonal antibody, MAbA9-C6. Rhodopsin and S-antigen were first observed in the 18-week-old human fetal eye, at a stage preceding photoreceptor differentiation. In adult eyes containing normal photoreceptor cells, rhodopsin immunoreactivity was restricted to the rod outer segments, whereas S-antigen immunoreactivity was localized to the entire photoreceptor cell. In retinoblastomas both monoclonal antibodies bound to the same area of the tumor; however, different and distinct staining patterns associated with each monoclonal antibody were recognized. In four cases, an intense well-circumscribed "halo" pattern, characteristic of cell-surface binding, was associated with rhodopsin, whereas the binding pattern associated with S-antigen was intense, well localized, and cytoplasmic in all cases. Our results show that some well-differentiated retinoblastomas express both rhodopsin and S-antigen, and as such express proteins that participate in the initial events in the phototransduction of vision.