Genetic and immunological contributors to virus-induced paralysis

Abstract

Infection by a single virus can evoke diverse immune responses, resulting in different neurological outcomes, depending on the host's genetic background. To study heterogenous viral response, we use Theiler's Murine Encephalomyelitis Virus (TMEV) to model virally induced neurological phenotypes and immune responses in Collaborative Cross (CC) mice. The CC resource consists of genetically distinct and reproducible mouse lines, thus providing a population model with genetic heterogeneity similar to humans. We examined different CC strains for the effect of chronic stage TMEV-induced immune responses on neurological outcomes throughout 90 days post infection (dpi), with a particular focus on limb paralysis, by measuring serum levels of 23 different cytokines and chemokines. Each CC strain demonstrated a unique set of immune responses, regardless of presence or absence of TMEV RNA. Using stepwise regression, significant associations were identified between IL-1α, RANTES, and paralysis frequency scores. To better understand these interactions, we evaluated multiple aspects of the different CC genetic backgrounds, including haplotypes of genomic regions previously linked with TMEV pathogenesis and viral clearance or persistence, individual cytokine levels, and TMEV-relevant gene expression. These results demonstrate how loci previously associated with TMEV outcomes provide incomplete information regarding TMEV-induced paralysis in the CC strains. Overall, these findings provide insight into the complex roles of immune response in the pathogenesis of virus-associated neurological diseases influenced by host genetic background.

Serum Cytokines Predict Neurological Damage in Genetically Diverse Mouse Models

“…We focused on five CC strains we had found to represent maximum phenotypic divergence (e.g., mild to severe disease) based on their phenotypic responses to TMEV during the chronic phase of infection, described in detail [25,38,39,47]. In the current study, TMEV significantly induced various clinical symptoms such as a decreased righting response, hunching, and limb paralysis in those strains most severely affected by TMEV, allowing for strain categorization based on acute phenotypes.…”

“…Mice from each strain were then randomly sorted into exposure groups-PBS-injected or TMEV-infected (Table 1). Mice at four weeks of age were anesthetized by isoflurane inhalation (MWI, Meridian, ID, USA) and inoculated into the right mid-parietal cortex at a depth of ~1.5 mm with 20 µL of 1 × Phosphate Buffer Solution (PBS) (PBS-injected/control mice), or with 5.0 × 10 4 plaque-forming units (PFU) of BeAn strain of TMEV (TMEV-injected/infected mice) (American Type Culture Collection [ATCC] VR 995, Manassas, VA, USA), as previously used in [25,[37][38][39][40]. Mice were housed separately by exposure groups.…”

“…Limb clasping was evaluated and scored as previously described [38,45]; righting reflex scores were determined by how long each mouse took to right itself from a prone position, as described [38]. Clinical signs of limb weakness and paralysis were observed and scored on a scale of 0-4, with a score of 0 given to mice having normal stride and no signs of weakness, and a score of 4 representing the total loss of limb mobility characterized by lack of grip function and flaccid limb extension [25].…”

“…The stepwise regression procedure involves a forward selection mechanism that starts with the intercept-only model and proceeds according to the optimal stopping criterion to choose the final model. Following [25,46], inclusion and exclusion of variables were controlled by alpha to enter and alpha to leave parameters, in which both were set to 0.05. Additional details about these statistical analyses are available in Supplementary Statistical Methods.…”

“…Theiler's murine encephalomyelitis virus (TMEV) is a naturally occurring neurotropic, single-stranded RNA murine virus, often used to model human neurological damage associated with viral infections, e.g., epilepsy and MS [20,21]. While studies in inbred 2 of 22 mouse models have established different pathologies after TMEV infection, including seizures and demyelinating disease [22,23], a consistent finding is the variability of immune responses detected among infected models [24,25].…”