Mechanisms of coxsackievirus B5 mediated β‐cell death depend on the multiplicity of infection

Coxsackievirus infections may trigger and accelerate pancreatic β‐cell death, leading to type I diabetes. Unrestricted coxsackievirus B5 replication in cultured β‐cells inoculated with high multiplicity leads to rapid lytic cell death. Evidence from other virus‐host cell systems indicates that host cell responses to infection may depend on the multiplicity of infection (MOI). Thus, the aim of this study was to compare the mechanisms of β‐cell death during high versus low multiplicity of coxsackievirus B5 infection. Cultures of highly differentiated mouse insulinoma cells and primary adult human islets were infected with coxsackievirus B5 at multiplicities of >1,000 or <0.5 TCID 50 per cell. The results of nuclear morphology and viability stainings, TUNEL staining and electrophoretic DNA fragmentation analysis showed high multiplicity infection to predominantly induce necrosis and transient apoptosis. In low multiplicity culture, however, necrosis was only moderately induced and apoptosis increased steadily with time. This was best demonstrated by a tenfold higher apoptosis/necrosis ratio than after high multiplicity inoculation. Expression of γ‐glutamyl cysteine synthetase increased in both infective cultures but the level of intracellular glutathione permanently depleted only at high multiplicity and recovered fully at low multiplicity. Thus, apoptosis represents an important mechanism of β‐cell death after low multiplicity of coxsackievirus B5 infection. This process is associated with maintenance of a physiological intracellular glutathione profile differing dramatically from the high multiplicity infection during which necrosis dominates and intracellular thiol balance deteriorates. These data suggest that the pattern and mechanisms of coxsackievirus B5 infection induced β‐cell death depend on the MOI. J. Med. Virol. 72:586–596, 2004. © 2004 Wiley‐Liss, Inc.