Lipid-specific IgMs induce antiviral responses in the CNS: implications for progressive multifocal leukoencephalopathy in multiple sclerosis

Progressive multi-focal leukoencephalopathy (PML) is a potentially fatal encephalitis caused by JC polyomavirus (JCV). PML principally affects people with a compromised immune system, such as patients with multiple sclerosis (MS) receiving treatment with natalizumab. However, intrathecal synthesis of lipid-reactive IgM in MS patients is associated with a markedly lower incidence of natalizumab-associated PML compared to those without this antibody repertoire. Here we demonstrate that a subset of lipid-reactive human and murine IgMs induce a functional anti-viral response that inhibits replication of encephalitic Alpha and Orthobunyaviruses in multi-cellular central nervous system cultures. These lipid-specific IgMs trigger microglia to produce IFN-β in a cGAS-STING-dependent manner, which induces an IFN-α/β-receptor 1-dependent antiviral response in glia and neurons. These data identify lipid-reactive IgM as a mediator of anti-viral activity in the nervous system and provide a rational explanation why intrathecal synthesis of lipid-reactive IgM correlates with a reduced incidence of iatrogenic PML in MS

The atypical chemokine receptor ACKR2 suppresses Th17 responses to protein autoantigens

Chemokine-directed leukocyte migration is a critical component of all innate and adaptive immune responses. The atypical chemokine receptor ACKR2 is expressed by lymphatic endothelial cells and scavenges pro-inflammatory CC chemokines to indirectly subdue leukocyte migration. This contributes to the resolution of acute inflammatory responses <i>in vivo</i>. ACKR2 is also universally expressed by innate-like B cells, suppressing their responsiveness to the non-ACKR2 ligand CXCL13, and controlling their distribution <i>in vivo</i>. The role of ACKR2 in autoimmunity remains relatively unexplored, although <i>Ackr2</i> deficiency reportedly lessens the clinical symptoms of experimental autoimmune encephalomyelitis induced by immunization with encephalogenic peptide (MOG<sub>35–55</sub>). This was attributed to poor T-cell priming stemming from the defective departure of dendritic cells from the site of immunization. However, we report here that <i>Ackr2</i>-deficient mice, on two separate genetic backgrounds, are not less susceptible to autoimmunity induced by immunization, and in some cases develop enhanced clinical symptoms. Moreover, ACKR2 deficiency does not suppress T-cell priming in response to encephalogenic peptide (MOG<sub>35–55</sub>), and responses to protein antigen (collagen or MOG<sub>1–125</sub>) are characterized by elevated interleukin-17 production. Interestingly, after immunization with protein, but not peptide, antigen, <i>Ackr2</i> deficiency was also associated with an increase in lymph node B cells expressing granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine that enhances T helper type 17 (Th17) cell development and survival. Thus, <i>Ackr2</i> deficiency does not suppress autoreactive T-cell priming and autoimmune pathology, but can enhance T-cell polarization toward Th17 cells and increase the abundance of GM-CSF<sup>+</sup> B cells in lymph nodes draining the site of immunization

Illustrations of a focal spinal cord lesion of MOG induced EAE in the DA rat.

<p>LFB staining shows a focal demyelinated lesion in the dorsal funiculus with myelin loss (A–B). ED-1 immunostaining highlights the presence of macrophages/microglia cells within the lesion (C). MBP immunohistochemistry illustrates the loss of myelin and the presence of myelin-laden macrophages (close up in insert) is indicative of recent myelin phagocytosis (D).</p

Distribution of GFP labeled SC after delivery in the cisterna magna and the spinal cord.

<p>GFP-SC (green) are detected both in the cerebellar parenchyma (A, B) and meninges (C) 7 days (A–C) after cisterna magna delivery as well as 21 days after in the proximal spinal cord (D). GFP-SCs grafted in the spinal cord parenchyma (E, F) are concentrated around blood vessels, some migrate away from the graft toward a lesion (L) identified by MOG immunostaining through white matter (E, arrows). (F) Same field illustrating GFP-SCs, inset is a higher magnification.</p

Interaction of GFP-SCs with myelin and astrocytes after delivery in the cisterna magna or the spinal cord parenchyma.

<p>Combined detection of MOG, GFAP and GFP on cryostat sections showed that GFP-SCs grafted in the cisterna magna (A, D) or the spinal cord (B,C, E, F) are found in demyelinated lesions (delineated by dashed lines) detected by MOG immunostaining (red) both after 7 days (B) and 21 days (A, C) after delivery. GFAP+ astrocytes (blue) interact with GFP-labeled SCs in the cisterna magna (D) and the spinal cord (E, F); 7 days (E) or 21 days (F) after spinal cord graft or 21 days after cisterna magna graft (D).</p

Average scores, maximal scores, cumulative scores (calculated from day 25 to day 45) and mortality rate in non-operated, CT and SCs grafted animals.

*<p>: is significantly different from control and non-operated animals, p<0.05.</p

EAE score evolution after GFP-SC graft in the spinal cord.

<p>The graph depicts the clinical scores of EAE animals grafted with GFP-SC (white circles, 7 animals) and medium injected animal (black squares, 5 animals). Surgeries were performed 2 days after the first clinical signs (occurring 12 days after the induction of the disease). A difference between the two groups is observed from day 25 and is significant (Mann-Whitney rank test; p<0.05) around 30 days after the first clinical signs.</p

One route of SC migration: the blood vessels.

<p>SC grafted in the spinal cord parenchyma are often localized in white matter around blood vessels (asterisks), evidenced with anti-laminin antibody (blue). While at 7 days SC are present close to the blood vessel wall (A), at 21 days they are embedded in the perivascular space but remote from the vascular wall (B).</p

Comparison of the remyelination potential of GFP-SCs grafted in the cisterna magna or the spinal cord.

<p>Twenty one days after SC delivery in the cisterma magna (A) or the spinal cord (B–F), exogenous remyelination was assessed using an anti-P0 antibody (red). P0 positivity colocalized with GFP-SCs (C, confocal microscopy), more frequently after spinal cord graft than cisterna magna delivery. C is a higher magnification of B and corresponds to the lesion detected on an adjacent section and illustrated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042667#pone-0042667-g005" target="_blank">Fig 5C</a>. GFP-SCs produce P0+ myelin (red D, E) that surrounds neurofilament (NF) + axons (blue D, F). Inserts are higher magnifications of dashed boxes.</p