p53, Rb and bcl-2 expression during the cell cycle: a study in phytohaemagglutinin stimulated lymphocytes and microwave irradiated lymphoid tissue sections.

AIMS To determine the expression of p53, Rb, and bcl-2 during the cell cycle in stimulated peripheral blood lymphocytes (PBLs) and microwave heated reactive lymphoid tissue sections. METHODS The expression of p53, Rb and bcl-2 proteins in paraffin wax embedded tonsil tissue sections was detected by immunohistochemistry using an (APAAP) technique following microwave irradiation. Flow cytometric analysis as performed on phytohaemagglutinin (PHA) stimulated PBLs, with simultaneous S fraction determination. RESULTS Expression of p53 protein was detected in reactive tonsil germinal centre cells, in some suprabasal cells in the surface and cryptic epithelium, and in some endothelial cells. Analysis of p53 in PHA stimulated PBLs revealed expression of p53 by non-tumoral activated lymphocytes. Rb protein expression was increased in PHA stimulated PBLs and was usually detected in most germinal centre B cells, in isolated paracortical cells, in a fraction of endothelial cells, and in most epithelial suprabasal cells. Expression of bcl-2 in stimulated lymphocytes was inversely correlated with proliferation. This confirms findings in reactive tonsil tissue samples, where proliferating cells located in the germinal centres and paracortical area are mostly bcl-2 negative. CONCLUSIONS Expression of these three oncogenic and tumour suppressor proteins varies during the cell cycle in non-tumoral cells. Consequently, tumoral growth fraction must be taken into account when analysing dysregulation of these three genes in lymphomas and other tumours. The p53 protein may be detected in benign conditions, as its expression is not synonymous with malignancy or mutation of the p53 gene.