Immunohistochemical detection of nucleolar protein p120 in paraffin-embedded tissues.

The monoclonal antibody FB-2 recognizes the antigen p120-kDa protein (p120), associated with the nucleolar matrix. p120 has originally been reported as expressed and detectable in malignant and non-neoplastic proliferating cells, but not in most normal resting tissues and benign tumours. In the present study, a reliable immunostaining method was used to detect p120 on formalin-fixed, paraffin wax-embedded tissue, testing it on 148 samples from different neoplastic and non-neoplastic tissues from different organs (breast, colon, lung, prostate, bladder, lymph nodes, skin, tongue and liver). The immunostaining was performed after the application of a specific antigen-unmasking protocol based on six consecutive cycles of microwave oven heating. Under these retrieval conditions, p120 antigen was clearly detectable, not only in hyperplastic and malignant cells, but also in stromal and normal non-proliferating cells of all the tissues evaluated. Our results show that the nucleolar protein p120 can be detected by routine immunohistochemistry in formalin-fixed, paraffin-embedded tissue and is expressed in all nucleated cells under any biological condition.