Expression of the HNK-1 carbohydrate epitope in human retina and retinoblastoma. An immunohistochemical study with the anti-Leu-7 monoclonal antibody.

Fifty formalin-fixed and paraffin-embedded retinoblastoma specimens and five normal human eyes were studied with the monoclonal anti-Leu-7 antibody, directed against the HNK-1 carbohydrate epitope that is shared by human natural killer cells and many neuronal, glial and neuroectodermal cells. The laboratory method was a sensitive immunohistochemical staining procedure, and neuroectodermal tumours that usually express this epitope were used as positive controls. In the human retina, Müller cell membranes were positively stained, but additional staining of neuronal cells was not excluded at the light microscopical level. A positive cytoplasmic reaction was also seen in ciliary and retinal pigment epithelial cells. All but one intraocular retinoblastomata studied contained cells staining positively for the HNK-1 epitope, but these cells were probably not neoplastic. Although positive reaction has previously been reported in three retinoblastomata, the present results suggest that positive cells are derived from entrapped and infiltrated retina. Staining of adjacent sections against leukocyte common antigen suggested that the positively staining cells were not natural killer cells.