Dose-dependent pathogenicity and inflammatory imbalance in severely immunodeficient mice infected with mpox virus

The global spread of mpox continues to pose a threat to public health, with immunocompromised patients being at greater risk for severe disease. This study aimed to establish a lethal severe infection model using NPG (NOD.Cg-Prkdc^scid Il2rg^tm1/Vst) mice, a strain with profound immunodeficiency, to simulate severe mpox in immunocompromised patients and investigate disease progression, viral replication kinetics, tissue tropism, and immune responses. In our study, mice were inoculated with three doses of mpox virus (high: 2 × 10⁷, medium: 2 × 10⁶, low: 2 × 10⁵ TCID₅₀ [50% tissue culture infective dose]) or phosphate-buffered saline as a negative control. Body weight, clinical signs, and survival were monitored. Viral loads in plasma and tissues, histopathological changes, and inflammatory responses were evaluated to systematically characterize the pathogenicity of mpox virus in severely immunodeficient mice. The results showed that NPG mice were highly susceptible to mpox virus, showing a clear dose-dependent response. The high-dose group exhibited 100% lethality, and the medium-dose group had a 50% survival rate, whereas the low-dose and control groups survived throughout the study. Plasma and tissue viral loads, as well as histopathological severity, followed a dose-dependent pattern. Viremia remained persistently high, and animals that died at different time points exhibited uniformly high viral loads across multiple tissues. By day 10 postinfection, markedly elevated levels of pro-inflammatory cytokines were detected in plasma, whereas anti-inflammatory cytokines remained largely uninduced. We found that the infection of severely immunodeficient mice with mpox virus results in dose-dependent lethality, persistent high viral loads, and a pronounced pro-/anti-inflammatory imbalance. These findings provide important insights into the pathogenesis of mpox in immunocompromised populations and develop a practical animal model for evaluating therapeutic interventions.