Group B coxsackieviruses (CVBs) have a well-established association with type 1 diabetes but the mechanism of depletion of beta-cell mass following infection has not yet been defined. In this report we show that the major difference in pathogenesis between the E2 diabetogenic strain of CVB4 and the prototypic JVB strain in SJL mice is not in tropism for islet cells but in the degree of damage inflicted on the exocrine pancreas and the resulting capacity for regeneration of both acinar and islet tissue by the host. Both strains replicated to a high titre in acinar tissue up to day 3 post-infection (p.i.), while the islets of Langerhans were largely spared. However, the pancreas in the JVB-infected animals then regenerated and many small islets were seen throughout the tissue by day 10 p.i. In contrast, the acinar tissue in E2-infected mice became increasingly necrotic until all that remained by day 21 p.i. were large islets containing varying numbers of dead cells, caught up in strands of connective tissue. Surviving beta cells were found to synthesize little insulin, although islet amyloid polypeptide was detected and glucagon synthesis in alpha cells appeared normal or enhanced. Our results suggest that the key to CVB-E2-induced damage lies in the exocrine tissue and prevention of islet neogenesis rather than from direct effects on existing islets.

The mechanism of induction of apoptosis by double-stranded RNA (dsRNA) is not fully characterized. The dsRNA is normally present in extremely low quantities in cells, but following infection with RNA viruses, large quantities of the dsRNA viral replicative intermediate may be produced triggering the antiviral response as well as cell death. In this report, transfection of polyinosinic-polycytidylic acid [poly(I:C)] into NIT 1 cells has been used as a model of intracellular dsRNA-induced beta-cell apoptosis. At 18 h post transfection, 45% of the cells were apoptotic as indicated by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) staining, and this was accompanied by an increase in nuclear factor kappaB (NF-kappaB) p50/p65 nuclear translocation and cleavage of caspases 3 and 8. The NF-kappaB inhibitor peptide, SN50, significantly reduced caspase-3 activity and the percentage of TUNEL-positive cells, substantiating a role for NF-kappaB in inducing intracellular dsRNA-mediated apoptosis. Concomitantly, RNA-dependent protein kinase activity was observed at 3 h post transfection along with phosphorylation and degradation of inhibitory kappaB-alpha. Expression of TRAIL (TNF-related apoptosis-inducing ligand), Fas, IL-15, and caspase-12 mRNAs was up-regulated in the presence of poly(I:C) but not when SN50 was also added. In contrast, there was no change detected in Fas, Fas-associated death domain, Bcl-2, Bcl-xl, Bax, p53, or XIAP(X-linked inhibitor of apoptosis protein) expression up to 12 h after poly(I:C) transfection. In addition, caspase-12 was cleaved, and phosphorylation of eukaryotic initiation factor 2alpha occurred, suggesting that an endoplasmic reticulum stress pathway was involved in addition to NF-kappaB induction of an extrinsic pathway, possibly mediated by TNF-related apoptosis-inducing ligand.