MDM2 EXPRESSION IN LYMPHOID-CELLS AND REACTIVE AND NEOPLASTIC LYMPHOID-TISSUE - COMPARATIVE-STUDY WITH P53 EXPRESSION

MDM2 and p53 immunohistochemical protein expression was analysed in ly mphocytes and in reactive and neoplastic lymphoid tissue. Phytohaemagg lutinin (PHA)-stimulated lymphocytes displayed MDM2 and p53 co-express ion. In 8 of 8 tonsils, 24 of 24 Hodgkin's disease (HD), and 10 of 24 high-grade non-Hodgkin's lymphoma (HG-NHL) specimens, MDM2 paralleled p53 nuclear expression in non-tumour and tumour cells. The number of p ositive cells was greater and the staining intensity was stronger for p53 than for MDM2. In another nine of the 24 HG-NHL cases studied, dis sociated expression was observed, with high p53 expression and very lo w or absent MDM2 expression. In five cases, both MDM2 and p53 were neg ative. The eight low-grade NHL (LG-NHL) cases were also MDM2- and p53- negative. MDM2 and p53 expression in PHA-activated lymphocytes and rea ctive lymphoid tissue is probably an expression of opposing biological signals regulating cell proliferation. Parallel MDM2 and p53 expressi on in all HD and in 10 out of 24 HG/NHL cases may indicate that this g rowth suppressive pathway is maintained in those cases. However, disso ciated MDM2/p53 expression (nine cases) and the absence of expression of both proteins (five cases) may represent examples of deregulation o f this growth control pathway. These findings are in agreement with pr evious in vitro studies in cell lines regarding the role of MDM2/p53 i nteraction in the regulation of growth control and extend this observa tion to normal lymphocytes and reactive lymphoid tissue, suggesting a possible role for MDM2 deregulation in lymphomagenesis.