Proliferation and apoptosis in primary gastric B-cell non-Hodgkin's lymphoma

To elucidate the role of cell turnover in primary gastric B-cell non-Hodgkin's lymphomas we studied tissue samples of 72 patients-26 small cell (25 MALT lymphomas) and 46 large cell (31 MALT lymphomas). Proliferation indices and apoptotic indices were measured by Mib-1 expression and terminal deoxynucleotidyltransferase (TdT)-mediated nick end labelling, respectively. Furthermore, expression of the apoptosis related gene-products bcl-2 and p53 was studied. Large cell lymphomas showed significantly higher proliferation indices (59.1% vs. 15.4%) and apoptotic indices (3.2% vs.0.7%) than small cell lymphomas. Proliferation and apoptotic indices were positively correlated (r = 0.371, P = 0.03). Expression of the bcl-2 protein was significantly higher in the small cell lymphomas. Furthermore, cases with a high bcl-2 expression showed both a significantly decreased proliferation (P < 0.0001) and apoptotic index (P = 0.0096) compared to bcl-2 negative cases. Expression of the mutant p53 protein was present in 8.0% of small cell and in 18.2% of large cell lymphomas. p53 positive cases showed significantly higher proliferation indices, but showed no correlation with apoptotic index. These data suggest that impaired apoptosis by bcl-2 may be more prominent than proliferation in the genesis of small cell lymphomas, whereas a high cell turnover characterizes large cell primary gastric lymphomas.