Enterovirus-A71 (EV-A71), a member of the genus Enterovirus
in the Picornaviridae
, is one of the most common causes of hand, foot, and mouth disease (HFMD) in younger children2,3
and occasionally causes large-scale epidemics worldwide, especially within the Asia-Pacific region. In addition, EV-A71 is consistently associated with severe complications of the neurological and pulmonary system that may result in permanent paralysis or even death, especially among younger children4
The underlying pathology of the immune system in response to EV-A71 infection is not fully understood, in part due to the lack of appropriate animal models that accurately recapitulate the human condition. This is because Homo sapiens
is the only natural host for EV-A71 infection5
. Inevitably, this hinders the development of promising vaccines and drugs. Understandably, EV-A71 is a public health concern and possesses significant socioeconomic burden6
Using Humanized Mice to Model HFMD Infection
One approach for modelling EV-A71 infection is the use of human immune system-engrafted mice
. In the present study, Ke et al. used human immune system-engrafted mice infected with a human isolate (non-mouse adapted) of EV-A71 strain 417
. They showed that EV-A71 infection was pathogenic and decreased the survival of humanized mice, but not of the corresponding non-humanized controls.
EV-A71-infected humanized mice
presented with diminished neurobehavioral functions, as well as histopathological signs of cellular inflammation and tissue damage of the brain stem and spinal cord that were accompanied by high viral loads within these respective organ systems. Severe forms of EV-A71-associated neurological complications were found in EV-A71-infected moribund mice, which are similar to those reported in patients, such as aseptic meningitis, brainstem and cerebellar encephalitis8
Together, these murine features phenocopy the clinical EV-AY1 syndrome and validate the in vivo
humanized mouse as a model for human HFMD infection.
How the Immune System Reacts to HFMD
Ke et al. also utilized this mouse model to investigate the role of the human immune system during EV-A71 infection, demonstrating activation of human T-cells as well as an infiltration of human immune cells into the murine brains and lungs. Specifically, the authors reported a significant upregulation of circulating activated human CD4+ and CD8+ cells between three to seven weeks post-infection that were accompanied by EV-A71-specific human T cell responses.
Furthermore, the authors uncovered increased secretion of proinflammatory cytokines in the EV-A71-infected humanized mice, such as human IFN-γ, IL-8 and IL-17A, and proposed a contribution to the exacerbation of disease pathogenesis.
Studying Immune Responses to Infectious Disease
Collectively, this article demonstrates the utility of humanized mouse model to investigate the pathogenesis of EV-A71 infection and delineate the accompanying human immune responses. This humanized murine model will provide a platform for the evaluation of anti-EV-A71 therapeutics, and further insights into the human immune responses to infectious diseases for translational research
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