Proliferation and apoptosis in malignant and normal cells in B cell non-Hodgkin's lymphomas

We have examined apoptosis and proliferation in lymph node cell suspensions from patients with B-cell non-Hodgkin's lymphoma using flow cytometry. A m ethod was developed which allowed estimation of the fractions of apoptotic cells and cells in the S-phase of the cell cycle simultaneously with tumour -characteristic light chain expression. Analysis of the tumour S-phase frac tion and the tumour apoptotic fraction in lymph node cell suspensions from 95 B-cell non-Hodgkin's lymphoma (NHL) patients revealed a non-normal distr ibution for both parameters. The median fraction of apoptotic tumour cells was 1.1% (25 percentiles 0.5%, 2.7%). In the same samples, the median fract ion of apoptotic normal cells was higher than for the tumour cells (1.9%; 2 5 percentiles 0.7%, 4.0%; P = 0.03). The median fraction of tumour cells in S-phase was 1.4% (25 percentiles 0.8%, 4.8%), the median fraction of norma l cells in S-phase was significantly lower than for the tumour cells (1.0%; 25 percentiles 0.6%, 1.9%; P = 0.004). When the number of cases was plotte d against the logarithm of the S-phase fraction of the tumour cells, a dist ribution with two Gaussian peaks was needed to fit the data. One peak was c entred around an S-phase fraction of 0.9%; the other was centred around 7%. These peaks were separated by a valley at approximately 3%, indicating tha t the S-phase fraction in NHL can be classified as 'low' (< 3%) or 'high' ( > 3%), independent of the median S-phase fraction. The apoptotic fractions were log-normally distributed. The median apoptotic fraction was higher (1. 5%) in the 'high' S-phase group than in the 'low' S-phase group (0.8%; P = 0.02). However, there was no significant correlation between the two parame ters (P > 0.05).