Immunohistochemical evidence for the expression of proliferating cell nuclear antigen (PCNA) by non-proliferating hepatocytes adjacent to metastatic tumours and in inflammatory conditions

The possibility that proliferating cell nuclear antigen (PCNA) is expressed by non‐proliferating liver cells was investigated. Liver biopsies from 107 patients were investigated, which included histologically normal liver, metastatic tumour, and inflammatory lesions. PCNA was detected using immunohistochemical staining with the monoclonal antibody PC10. This was compared with the proportion of proliferating cells as assessed by immunostaining for the Ki‐67 antigen using the monoclonal antibody MIB 1. Most cases of histologically normal liver showed few PC10‐positive cells. PCNA‐positive hepatocytes far outnumbered those positive with MIB 1 in specimens showing metastatic tumour or an inflammatory cell infiltrate. There was no relation between the degree of PCNA overexpression and the type of tumour present or the nature of the inflammatory lesion. Other cell types, including the biliary epithelium, did not show this large difference between the proportions of PC10‐ and MIB 1‐positive cells. It is concluded that non‐proliferating hepatocytes increase their levels of PCNA in a wide variety of pathological conditions. This may be mediated by cytokines released by tumour cells or inflammatory cells.