Expression of the enteroviral capsid protein VP1 in the islet cells of patients with type 1 diabetes is associated with induction of protein kinase R and downregulation of Mcl-1

Abstract

Aims/hypothesis Immunohistochemical staining reveals that the enteroviral capsid protein VP1 is present at higher frequency in the insulin-containing islets of patients with recent-onset type 1 diabetes than in controls. This is consistent with epidemiological evidence suggesting that enteroviral infection may contribute to the autoimmune response in type 1 diabetes. However, immunostaining of VP1 is not definitive since the antibody widely used to detect the protein (Clone 5D8/1) might also cross-react with additional proteins under some conditions. Therefore, we sought to verify that VP1 immunopositivity correlates with additional markers of viral infection. Methods Antigen immunoreactivity was examined in formalin-fixed, paraffin-embedded, pancreases from two different collections of type 1 diabetes and control cases: a historical collection from the UK and the nPOD (network of Pancreatic Organ donors with Diabetes) cohort from the USA.Results VP1 immunoreactivity was present in ∼20% of insulin-containing islets of both cohorts under stringent conditions but was absent from insulin-deficient islets. The presence of VP1 was restricted to beta cells but only a minority of these contained the antigen. The innate viral sensor, protein kinase R (PKR) was upregulated selectively in beta cells that were immunopositive for VP1. The antiapoptotic protein myeloid cell leukaemia sequence-1 (Mcl-1) was abundant in beta cells that were immunonegative for VP1 but Mcl-1 was depleted in cells containing VP1. Conclusions/interpretation The presence of immunoreactive VP1 within beta cells in type 1 diabetes is associated with a cellular phenotype consistent with the activation of antiviral response pathways and enhanced sensitivity to apoptosis. However, definitive studies confirming whether viral infections are causal to beta cell loss in human diabetes are still awaited.

Is Type 1 Diabetes “Going Viral”?

“…If so, it would be consistent with emerging data showing that low-level, persistent enteroviral infections can be detected in the peripheral blood of other recently diagnosed patients (8). Importantly, when IFN signature and low-level infection are considered together with evidence that a low-level, noncytolytic, persistent enteroviral infection of b-cells occurs in pancreata from cohorts in Italy (9), the U.K. (10,11), and the U.S. (network of pancreatic organ donors, nPOD) (11), one can envision a scenario where a primary acute viral infection leads to a secondary long-term persistent pancreatic infection that could ultimately drive the development of disease.…”

Interferon-α mediates human beta cell HLA class I overexpression, endoplasmic reticulum stress and apoptosis, three hallmarks of early human type 1 diabetes

“…Upon exposure to 'danger signals' (e.g. viral infection or other exogenous or endogenous mediators that remain to be determined; [10,36,42,43]), production and release of type I IFNs (IFNα/β) is triggered in beta cells and neighbour cells, exerting both autocrine and paracrine effects. IFNα binds to the IFNAR1 and activates the type I IFN pathway, in which the TYK2-STAT2-IRF9 axis plays a critical role.…”

Evaluation of the fidelity of immunolabelling obtained with clone 5D8/1, a monoclonal antibody directed against the enteroviral capsid protein, VP1, in human pancreas

“…A number of viruses have been implicated, but the majority view suggests that one or more enteroviruses are the most likely candidates [1,2]. However, this evidence remains largely circumstantial and relies on a body of epidemiological data supported by immunohistochemical studies conducted with pathological specimens recovered from patients diagnosed with type 1 diabetes [1,[3][4][5]. These have revealed that a minority of islet cells of individuals with recentonset disease (and some with longer-duration illness) display evidence of enteroviral antigen expression [3][4][5].…”