Apoptosis and expression of caspases 3, 6 and 8 in malignant non-Hodgkin'slymphomas

In this study we investigated the immunohistochemical expression of caspase s 3, 6 and 8 in 85 malignant non-Hodgkin's lymphomas and in 4 hyperplastic lymph nodes. The extent of apoptosis and the immunohistochemical expression of bcl-2 and bar was also studied. Caspase 3 immunoreactivity was seen in 84/85 (99%), caspase 6 in 46/85 (54%), and caspase 8 in 66/85 (78%) lymphom as. The immunoreactivity for caspase 3 was diffuse cytoplasmic while antibo dies to caspase 6 and 8 showed granular and fragmented, sometimes also nucl ear immunopositivity. High-grade non-Hodgkin's lymphomas expressed strong c aspase 6 and 8 immunoreactivity significantly more often than low-grade lym phomas (p=0.016 and p=0.0002, respectively). Strong caspase 3 immunoreactiv ity was also seen more often in high-grade lymphomas, but the association d id not reach statistical significance (p=0.14). There was a strong associat ion between the expression of caspase 3 and 6 (p=0.032), caspase 3 and 8 (p =0.042), and especially between caspase 6 and 8 (p=<0.00001). There was a s ignificant difference in the apoptotic index between low-grade (0.59+/-0.44 %) and high-grade lymphomas (1.96+/-1.92%) (p<0.001). Strong bcl-2 expressi on was seen in 35/80 (44%) and strong bar expression in 20/80 (25%) lymphom as. No significant association was found between the expression of bcl-2 or bar and the expression of the caspases. According to the results the expre ssion of caspases 6 and 8 is upregulated in high-grade compared with low-gr ade lymphomas and probably contributes to the execution of apoptosis in the m. A similar tendency could also be seen with caspase 3. The expression of the three caspases is significantly associated, suggesting that it is mutua lly regulated. Finally, the results suggest that the expression of bcl-2 or bar does not influence the expression of caspases 3, 6 and 8 in malignant lymphomas to a significant degree.