HLA class I and beta 2-microglobulin expression in frozen and formaldehyde-fixed paraffin sections of neuroblastoma tumors.

Ten solid neuroblastoma tumors were examined for beta 2-microglobulin (beta 2-m) and HLA-class I expression in an immunocytochemical assay. Blood vessel endothelium and a small population of cells (less than 6% of small round cells) were consistently stained in frozen sections of each tumor. No beta 2-m or HLA-class I reactivity was detected in the remainder (greater than 94%) of the small round cells in each tumor. The localization of most of the positive cells near stromal tissue and blood vessels suggests that most of these cells may be of non-tumor origin. The patients from which the tumors were taken varied in degree of disease involvement, yet no differences with respect to beta 2-m and HLA-class I expression were found among the tumors. A procedure for visualizing beta 2-m and HLA-class I molecules in formaldehyde-fixed, paraffin-embedded tissue is described. This confirmed the results in frozen sections. These findings extend previous reports of weak beta 2-m and HLA-class I levels in cells of neuronal origin. The clinical implications are discussed.