LOW BCL-2 EXPRESSION AND INCREASED SPONTANEOUS APOPTOSIS IN T-LYMPHOCYTES FROM NEWLY-DIAGNOSED IDDM PATIENTS

The bcl-2 gene product has been shown to regulate apoptotic cell death, and its dysregulation has been shown to induce several abnormalities in the immune system. No data exist regarding bcl-2 expression in autoimmune diseases, such as human insulin-dependent diabetes mellitus (IDDM). We investigated bcl-2 protein expression by testing T lymphocytes from 15 newly-diagnosed (< 3 weeks) IDDM patients in comparison to 10 age-matched control subjects. The expression of bcl-2 on CD3(+) lymphocyte subsets was investigated after membrane permeabilization by two- or three-colour immunofluorescence, When the percentage and mean fluorescence intensity (MFI) of bcl-2(+)/CD3(+) cells from normal individuals and patients were compared, we found that bcl-2 expression within the CD3(+) and CD4(+) CD45R0(+) T-cell populations was reduced significantly in IDDM patients (46.8+/-15.4 vs 79.6+/-11.7; 25.7+/-3.8 vs 47.15+/-5.7, respectively; p < 0.001). To establish whether low bcl-2 expression in T cells from newly-diagnosed patients reflects their susceptibility to death by an apoptotic process, we also evaluated DNA staining with propidium iodide in CD3(+) lymphocyte suspension after a (24-72 h) culture period (spontaneous apoptosis). We found that IDDM patients have higher levels of spontaneous apoptosis (mean+/-SEM: 24 h = 4.6+/-0.8; 48 h = 9.9+/-1; 72 h = 12.8+/-1.1) than control subjects (24 h = 1.8+/-0.4; 48 h = 4.6+/-0.4; 72 h = 5.7+/-0.3; p < 0.02-0.001). Our study suggests that recent onset IDDM is characterised by reduced bcl-2 expression, which in turn may be associated with the increased spontaneous apoptosis we observed.