Inactivated Influenza A H1N1pdm [A/California/07/09]

The global incidence of type 1 diabetes (T1D) is rapidly increasing, suggesting that environmental factors play an important role in its etiology. Several studies have implicated viral infections as a possible cause of T1D, including enteroviruses such as coxsackievirus B, measles, congenital rubella, mumps, cytomegalovirus, and influenza B. A report from a large Norwegian cohort showed an increased risk of T1D after infection with H1N1pdm. Here, researchers show that human H1N1 A/California/2009-derived viruses infect human islets in vitro, inducing a proinflammatory response accompanied by a substantial increase in CXCL9 and CXCL10 release. In vivo, infected mice displayed a marked susceptibility to the virus, with localization also found in extrapulmonary organs, including the pancreas. Infection was able to induce mild changes in blood glucose in C57B6 mice after chemical injury of the islets, but did not modulate autoimmune damage to islets in NOD mice. Studies have shown that influenza H1N1pdm strains are able to infect and replicate in mammalian pancreatic cells in vitro and in vivo but do not cause any functional impairments consistent with diabetes.

Here, the susceptibility of primary mouse islet cells and the MIN6 insulinoma cell line to infection with the mouse-adapted H1N1 pdm was investigated. Receptor detection using lectin staining for both cell sources revealed a high abundance of α-2,6 sialic acid-linked sialic acid molecules and α-2,3 linked residues (Figure 1A). In situ hybridization clearly demonstrated the presence of viral RNA within cells 4 days after viral infection (Figure 1B). Colocalization between viral and insulin RNA in dispersed mouse islet cells indicated that primary mouse β cells were susceptible to infection. Visual inspection of infected cells by light microscopy, cell recovery, and live/dead assays revealed no obvious cytopathic effects at any time post-infection (days 0 to 4; Figure 1C). Two groups of mice (nine per group) were infected with 10⁶ TCID₅₀/50 μL of mouse-adapted H1N1pdm virus by IN (light anesthesia) and IP routes, respectively. A third group of mice (IPin) of 6 mice were inoculated with inactivated mouse-adapted H1N1pdm virus by IP route to assess the absence of viral replication (Figure 1D). Three to five days later, RNA for the viral M gene was detected by (r)RT-PCR in the lungs and pancreas of 9 of 9 mice and 3 of 9 mice infected by IN route, respectively. In addition, 8 of 9 mice infected by IP route were positive for the viral M gene in both pancreas and lung.

Figure 1. Susceptibility of mouse to H1N1 pdm mouse-adapted virus. (Capua I, et al., 2018)