Retinal S antigen and retinoblastoma. A monoclonal antibody histopathologic study.

Using monoclonal antibody MAbA9-C6, which defines an epitope of retinal S antigen retained in fixed-tissue sections, we investigated S-antigen immunoreactivity in human fetal eyes from different gestational periods and 19 cases of retinoblastoma. S-antigen immunoreactivity was first observed in the outermost portion of the neuroblastic cell layer in the retina of a human fetus at 18 weeks' gestation, a stage preceding photoreceptor differentiation, and at all later stages examined thereafter. All adult eyes containing normal photoreceptors bound MAbA9-C6. In retinoblastomas, several different patterns of S-antigen immunoreactivity were recognized. In seven cases, S-antigen immunoreactivity appeared to be associated with normal photoreceptor elements incorporated into the growing tumor. S-antigen immunoreactivity was associated with fleurettes within the retinoblastoma in three cases and Flexner-Wintersteiner rosettes in seven cases. In 11 cases, S-antigen immunoreactivity was associated with isolated tumor cells. Our results show that S antigen may be a useful marker in the study of the embryologic development of the human retina and antigenic expression and modulation in retinoblastomas.