Murine cytomegalovirus infection in mice results in an acute inflammatory reaction in peripheral nerves

Memory inflation: Beyond the acute phase of viral infection

Memory inflation is confirmed as the most commonly dysregulation of host immunity with antigen-independent manner in mammals after viral infection. By generating large numbers of effector/memory and terminal differentiated effector memory CD8+ T cells with diminished naïve subsets, memory inflation is believed to play critical roles in connecting the viral infection and the onset of multiple diseases. Here, we reviewed the current understanding of memory inflated CD8+ T cells in their distinct phenotypic features that different from exhausted subsets; the intrinsic and extrinsic roles in regulating the formation of memory inflation; and the key proteins in maintaining the expansion and proliferation of inflationary populations. More importantly, based on the evidences from both clinic and animal models, we summarized the potential mechanisms of memory inflation to trigger autoimmune neuropathies, such as Guillain-Barré syndrome and multiple sclerosis; the correlations of memory inflation between tumorigenesis and resistance of tumour immunotherapies; as well as the effects of memory inflation to facilitate vascular disease progression. To sum up, better understanding of memory inflation could provide us an opportunity to beyond the acute phase of viral infection, and shed a light on the long-term influences of CD8+ T cell heterogeneity in dampen host immune homeostasis.

Construction of a mouse model of Posner-Schlossman syndrome by anterior chamber infection with cytomegalovirus

Accumulated clinical evidence has shown that Posner-Schlossman syndrome (PSS) is most likely the result of recurrent human cytomegalovirus (HCMV) infection in the anterior chamber (AC). Establishing an animal model is necessary to investigate the pathogenesis of PSS. In this study, we constructed a mouse model of (PSS) by injecting murine cytomegalovirus (MCMV) into the AC of BALB/c mice. Twenty-five BALB/c mice were divided into 5 groups. Smith strain MCMV expressing enhanced green fluorescent protein (EGFP) was passaged with mouse embryonic fibroblast (MEF). Right eyes in the 4 experiment groups received AC injection of 1 μL of virus solution with concentrations of 10³,10⁴,10⁵,10⁶ pfu/mL respectively, and the control group received only PBS. PSS-like signs (mutton-fat keratic precipitates (KP), pupil dilation, IOP elevation and corneal edema) were recorded 0-28 days post-injection (DPI). Sections of eyeballs from another 9 mice harvested on 0,10 and 28 DPI were examined to locate KP and the fluorescence signal of the virus. Reversible PSS-like signs except KP were observed in 20% and 60% mice of 10⁴ and 10⁵ groups while no PSS-like signs in the control and 10³ group; 80% in the 10⁶ group with partially unreversible signs till 28DPI. Much More fluorescent signals of virus in the iris and KP were found on 10DPI than 28 DPI, while no fluorescent signals and KP on 0DPI. The extent of PSS-like signs (pupil dilation, IOP elevation and corneal edema) was virus concentration-dependent (Spearman correlation coefficient, r = 0.830, = 0.475, = 0.662, p < 0.0001, <0.05, <0.001, respectively, n = 25). Success rate of PSS model (mice with PSS-like signs) was also virus concentration-dependent (Chi-square trend test, χ² = 6.828, df = 1, p < 0.01, n = 25). Our results indicate that AC injection of 1 μL MEF passaged MCMV (Smith strain) of 10⁴-10⁶ pfu/mL in BALB/c mice can be used to construct a mouse model of PSS. MCMV can infect iris tissue and replicate in it and then establish latency. This might account for the recurrent and self-limited nature of PSS.

CX3CR1 But Not CCR2 Expression Is Required for the Development of Autoimmune Peripheral Neuropathy in Mice

One hallmark of Guillain-Barre syndrome (GBS), a prototypic autoimmune peripheral neuropathy (APN) is infiltration of leukocytes (macrophages and T cells) into peripheral nerves, where chemokines and their receptors play major roles. In this study, we aimed to understand the potential contribution of chemokine receptors CCR2 and CX3CR1 in APN by using a well-established mouse model, B7.2 transgenic (L31) mice, which possesses a predisposed inflammatory background. We crossbred respectively CCR2KO and CX3CR1KO mice with L31 mice. The disease was initiated by partial ligation on one of the sciatic nerves. APN pathology and neurological function were evaluated on the other non-ligated sciatic nerve/limb. Our results revealed that L31/CX3CR1KO but not L31/CCR2KO mice were resistant to APN. CX3CR1 is needed for maintaining circulating monocyte and CD8⁺ T cell survival. While migration of a significant number of activated CD8⁺ T cells to peripheral nerves is essential in autoimmune response in nerve, recruitment of monocytes into PNS seems optional. Disease onset is independent of CCR2 mediated blood-derived macrophage recruitment, which can be replaced by compensatory proliferation of resident macrophages in peripheral nerve. CX3CR1 could also contribute to APN via its critical involvement in maintaining nerve macrophage phagocytic ability. We conclude that blockade of CX3CR1 signaling may represent an interesting anti-inflammatory strategy to improve therapeutic management for GBS patients.

Inhibition of TLR4 signaling protects mice from sensory and motor dysfunction in an animal model of autoimmune peripheral neuropathy

BACKGROUND

While the etiology remains elusive, macrophages and T cells in peripheral nerves are considered as effector cells mediating autoimmune peripheral neuropathy (APN), such as Guillain-Barre syndrome. By recognizing both pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) signals, TLRs play a central role in the initiation of both innate and adaptive immune responses. In this study, we aimed to understand the involvement of TLR4 in the pathogenesis of APN and explore the potential of TLR4 as a drug target for therapeutic use.

METHODS

APN was induced by a partial ligation on one of the sciatic nerves in B7.2 (L31) transgenic mice which possess a predisposed inflammatory background. APN pathology and neurological function were evaluated on the other non-injured sciatic nerve.

RESULTS

TLR4 and its endogenous ligand HMGB1 were highly expressed in L31 mice, in circulating immune cells and in peripheral nerves. Enhanced TLR4 signaling was blocked with TAK 242, a selective TLR4 inhibitor, before and after disease onset. Intraperitoneal administration of TAK 242 not only inhibited monocyte, macrophage and CD8⁺ T cell activation, but also reduced the release of pro-inflammatory cytokines. TAK 242 protected mice from severe myelin and axonal loss, resulting in a remarkable improvement in mouse motor and sensory functions. TAK 242 was effective in alleviating the disease in both preventive and reversal paradigms.

CONCLUSION

The study identified the critical contribution of TLR4-mediated macrophage activation in disease course and provided strong evidence to support TLR4 as a useful drug target for treating inflammatory autoimmune neuropathy.

High-salt diet decreases mechanical thresholds in mice that is mediated by a CCR2-dependent mechanism

Background

Though it is well-known that a high-salt diet (HSD) is associated with many chronic diseases, the effects of long-term high-salt intake on physiological functions and homeostasis remain elusive. In this study, we investigated whether and how an HSD affects mouse nociceptive thresholds, and myeloid cell trafficking and activation.

Methods

Healthy C57BL/6 male and female mice were fed an HSD (containing 4% NaCl in chow and 1% NaCl in water) from the time of weaning for 3 to 4 months. Circulating monocytes, nerve macrophages, spinal microglia, and associated inflammatory responses were scrutinized using flow cytometry, immunohistochemistry, and quantitative real-time polymerase chain reaction (qPCR) approaches. Mouse pain sensitivity to mechanical stimuli was monitored with von Frey tests along the experimental duration.

Results

Mice on an HSD have reduced mechanical thresholds. They feel more pain than those on a normal diet (ND), e.g., regular laboratory chow (0.3% NaCl in chow). An HSD induced not only a remarkable expansion of circulating monocytes, CCR2⁺Ly6C^hi inflammatory monocytes in particular, but also an accumulation of CD11b⁺F4/80⁺ macrophages in the peripheral nerves and an activation of Iba-1⁺ spinal microglia. Replacing an HSD with a ND was unable to reverse the HSD-induced mechanical hypersensitivity or rescue the altered immune responses. However, treating HSD-fed mice with a chemokine receptor CCR2 antagonist effectively normalized the pain thresholds and immune cell profile in the periphery and spinal cord. An HSD failed to alter pain thresholds and myeloid cell activation in CCR2-deficient mice. Spinal microglial activation is required for HSD-induced mechanical hypersensitivity in male, but not in female mice.

Conclusion

Overall, this study provides evidence that an HSD has a long-term impact on physiological function. CCR2-mediated cellular response, including myeloid cell trafficking and associated inflammation, plays pivotal roles in salt-dietary modulation of pain sensitivity.