B cells going viral in the CNS: Dynamics, complexities, and functions of B cells responding to viral encephalitis

CD6 Regulates CD4 T Follicular Helper Cell Differentiation and Humoral Immunity During Murine Coronavirus Infection

During activation the T cell transmembrane receptor CD6 becomes incorporated into the T cell immunological synapse where it can exert both co-stimulatory and co-inhibitory functions. Given the ability of CD6 to carry out opposing functions, this study sought to determine how CD6 regulates early T cell activation in response to viral infection. Infection of CD6 deficient mice with a neurotropic murine coronavirus resulted in greater activation and expansion of CD4 T cells in the draining lymph nodes. Further analysis demonstrated that there was also preferential differentiation of CD4 T cells into T follicular helper cells, resulting in accelerated germinal center responses and emergence of high affinity virus specific antibodies. Given that CD6 conversely supports CD4 T cell activation in many autoimmune models, we probed potential mechanisms of CD6 mediated suppression of CD4 T cell activation during viral infection. Analysis of CD6 binding proteins revealed that infection induced upregulation of Ubash3a, a negative regulator of T cell receptor signaling, was hindered in CD6 deficient lymph nodes. Consistent with greater T cell activation and reduced UBASH3a activity, the T cell receptor signal strength was intensified in CD6 deficient CD4 T cells. These results reveal a novel immunoregulatory role for CD6 in limiting CD4 T cell activation and deterring CD4 T follicular helper cell differentiation, thereby attenuating antiviral humoral immunity.

Elevated levels of β2-microglobulin in cerebrospinal fluid in adult patients with viral encephalitis/meningitis

BACKGROUND

Increased cerebrospinal fluid (CSF) β2-microglobulin (β2-MG) values are attributed to immune activation, lymphoid cell turnover and release of tissue destruction in the central nervous system (CNS). We investigated plasma and CSF β2-MG levels in adult patients with viral encephalitis/meningitis and their correlations with clinical parameters.

METHOD

CSF samples from 26 patients with viral encephalitis/meningitis were collected. Moreover, 24 CSF samples from patients with non-inflammatory neurological disorders (NIND) as controls were collected. Plasma samples from 22 enrolled patients and 20 healthy individuals were collected. The β2-MG levels were measured by immunoturbidimetry on an automatic biochemical analyzer. Clinical data were extracted from an electronic patient documentation system.

RESULT

CSF levels of β2-MG, adenosine deaminase (ADA), white blood cell (WBC), lactate dehydrogenase (LDH), protein and lactate were significantly increased in patients with viral encephalitis/meningitis respectively (p < 0.001, p < 0.001, p < 0.001, p = 0.001, p < 0.001, p = 0.013). In contrast, no statistically significant difference was found in plasma levels of β2-MG. Furthermore, CSF levels of β2-MG were weakly correlated with WBC (r = 0.426, p = 0.030), lymphocyte percentage (r = 0.599, p = 0.018), ADA (r = 0.545, p = 0.004) and LDH (r = 0.414, p = 0.036), but not with lactate (r = 0.381, p = 0.055), protein (r = 0.179, p = 0.381) and plasma levels of β2-MG (r = -0.156, p = 0.537) in viral encephalitis/meningitis patients.

CONCLUSION

CSF β2-MG may be a potential inflammatory marker for viral encephalitis/meningitis in adult patients diagnosed with viral encephalitis/meningitis.

Ablation of microglia following infection of the central nervous system with a neurotropic murine coronavirus infection leads to increased demyelination and impaired remyelination

Intracranial inoculation of susceptible mice with a glial-tropic strain of mouse hepatitis virus (JHMV), a murine coronavirus, results in an acute encephalomyelitis followed by viral persistence in white matter tracts accompanied by chronic neuroinflammation and demyelination. Microglia are the resident immune cell of the central nervous system (CNS) and are considered important in regulating events associated with neuroinflammation as well as influencing both white matter damage and remyelination. To better understand mechanisms by which microglia contribute to these immune-mediated events, JHMV-infected mice with established demyelination were treated with the small molecular inhibitor of colony stimulating factor 1 receptor (CSF1R), PLX5622, to deplete microglia. Treatment with PLX5622 did not affect viral replication within the CNS yet the severity of demyelination was increased and remyelination impaired compared to control mice. Gene expression analysis revealed that targeting microglia resulted in altered expression of genes associated with immune cell activation and phagocytosis of myelin debris. These findings indicate that microglia are not critical in viral surveillance in persistently JHMV-infected mice yet restrict white matter damage and remyelination, in part, by influencing phagocytosis of myelin debris.