Summary.The pattern and the sequence of tumour necrosis factor-a (TNFa) induced cell death in the acute T-lymphoblastic leukaemic cell line CCRF-CEM and its vinblastineresistant subline CEM/VLB 100 have been studied. Previously, we found that the CEM/VLB 100 cell line was more sensitive to TNFa-induced killing than its parental CCRF-CEM cell line. TNFa-induced cell death showed an apoptotic pattern, as detected by agarose electrophoresis, flow cytometry and transmission electron microscopy (TEM). TEM images revealed that autophagy and condensed mitochondria occurred earlier than nuclear fragmentation. The specific inhibitor of autophagy, 3-methyladenine (3MA), inhibited the formation of autophagosomes. TNFa-induced DNA fragmentation and cytolysis were completely inhibited by 10 mM 3MA. Inhibition of the fusion of lysosomes with autophagosomes by asparagine did not block TNFa-induced apoptosis. In addition, amino acid and protein deprivation enhanced TNFa-induced autophagy but not apoptosis. We propose that the early stages of autophagy are required for, but do not necessarily result in, TNFa-induced apoptosis.

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SUMMARYThe ribonucleoprotein (RNP) of avian infectious bronchitis virus (IBV) was examined by electron microscopy after shadowing with carbon/platinum. Linear RNP strands up to 6.7/zm in length, from three IBV strains, were sensitive to both pancreatic RNase and to proteases. These strands were obtained from spontaneously disrupted complete particles but not from disrupted incomplete particles that lacked RNP. They were also released from Nonidet P40-disrupted particles and could be isolated on sucrose density gradients at a density of 1.27 g/ml. In some cases, helical RNP complexes associated with virus particles were observed that were similar to RNPs of human coronavirus strain 229E and mouse hepatitis virus strain 3.