dsRNA formed as an intermediate during Coxsackievirus infection does not induce NO production in a β-cell line with or without addition of IFN-γ

Virus infection is one environmental factor that has been implicated as a precipitating event initiating β-cell damage during the development of type 1 diabetes. One aim of this study was to investigate how permissive an insulin-producing β-cell line, RINm5F, is to enterovirus (EV) infections. A second aim was to study if the viral replicative intermediate, double-stranded RNA (dsRNA), together with IFN-γ results in nitric oxide (NO) production. Monolayer cultures of RINm5F cells were not permissive to infection with seven different strains of EV. However, when the growth pattern of the β-cell line changed and the cells started to grow as free-floating RIN cell clusters (RCC), all EV strains replicated. Immunostaining for the Coxsackie-adenovirus-receptor (CAR) detected the protein on the free-floating RIN cell clusters, but not on the RINm5F cells cultured as a monolayer of β-cells. This shows that the CAR expression can change and/or the CAR protein can be redistributed on the cell surface as a consequence of altered growth pattern thus allowing viral replication in a previously non-permissive β-cell line. As expected, NO production was significantly increased (p < 0.05) by addition of synthetic dsRNA and IFN-γ to the RCC. In contrast, the dsRNA formed during virus infection with a Coxsackievirus B4 strain (E2) with or without addition of IFN-γ did not induce NO production in these cells. This indicates that synthetic dsRNA does not mimic a real viral infection in that respect, and suggests an NO-independent mechanism for virus-induced β-cell damage.