Patients surviving a septic episode exhibit persistent immune impairment and increased mortality due to enhanced vulnerability to infections. In the present study, using the cecal ligation and puncture (CLP) model of polymicrobial sepsis, we addressed the hypothesis that altered vagus nerve activity contributes to immune impairment in sepsis survivors. CLP-surviving mice exhibited less TNFα in serum following administration of LPS, a surrogate for an infectious challenge, than control-operated (control) mice. To evaluate the role of the vagus nerve in the diminished response to LPS, mice were subjected to bilateral subdiaphragmatic vagotomy at 2 weeks post-CLP. CLP-surviving vagotomized mice exhibited increased serum and tissue TNFα levels in response to LPS-challenge compared to CLP-surviving, non-vagotomized mice. Moreover, vagus nerve stimulation in control mice diminished the LPS-induced TNFα responses while having no effect in CLP mice, suggesting constitutive activation of vagus nerve signaling in CLP-survivors. The percentage of splenic CD4+ ChAT-EGFP+ T cells that relay vagus signals to macrophages was increased in CLP-survivors compared to control mice, and vagotomy in CLP-survivors resulted in a reduced percentage of ChAT-EGFP+ cells. Moreover, CD4 knockout CLP-surviving mice exhibited an enhanced LPS-induced TNFα response compared to wild-type mice, supporting a functional role for CD4+ ChAT+ T cells in mediating inhibition of LPS-induced TNFα responses in CLP-survivors. Blockade of the cholinergic anti-inflammatory pathway with methyllcaconitine, an α7 nicotinic acetylcholine receptor antagonist, restored LPS-induced TNFα responses in CLP-survivors. Our study demonstrates that the vagus nerve is constitutively active in CLP-survivors and contributes to the immune impairment.

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The fetal brain is constantly exposed to maternal IgG before the formation of an effective blood-brain barrier (BBB). Here, we studied the consequences of fetal brain exposure to an antibody to the astrocytic protein aquaporin-4 (AQP4-IgG) in mice. AQP4-IgG was cloned from a patient with neuromyelitis optica spectrum disorder (NMOSD), an autoimmune disease that can affect women of childbearing age. We found that embryonic radial glia cells in neocortex express AQP4. These cells are critical for blood vessel and BBB formation through modulation of the WNT signaling pathway. Male fetuses exposed to AQP4-IgG had abnormal cortical vasculature and lower expression of WNT signaling molecules Wnt 5a and Wnt 7a. Positron emission tomography of adult male mice exposed in utero to AQP4-IgG revealed increased blood flow and BBB leakiness in the entorhinal cortex. Adult male mice exposed in utero to AQP4-IgG had abnormal cortical vessels, fewer dendritic spines in pyramidal and stellate neurons, and more S100β + astrocytes in the entorhinal cortex. Behaviorally, they showed impairments in the object-place memory task. Neural recordings indicated that their grid cell system, within the medial entorhinal cortex, did not map the local environment appropriately. Collectively, these data implicate in utero binding of AQP4-IgG to radial glia cells as a mechanism for alterations of the developing male brain and adds NMOSD to the conditions in which maternal IgG may cause persistent brain dysfunction in offspring.

Sepsis survivors show impaired responsiveness to antigen (Ag), which is linked to increased susceptibility to infection. Using the cecal ligation and puncture (CLP) model of sepsis, we showed that CLP surviving mice have a reduced antibody response to the T-dependent Ag, NP-CGG, compared to mice that underwent a sham procedure, but an intact response to the T-independent Ag, NP-Ficoll. CLP mice have reduced TNFα levels due to sustained vagus nerve activity. We hypothesized that reduced TNFα production might lead to disruption in follicular dendritic cell (FDC) function and impaired germinal center (GC) responses. FDCs play a key role in GC responses and TNFα is critical for FDC clustering and maturation. Immunofluorescence staining in spleens showed a reduced number of FDC clusters and reduced binding of immune complexes on FDCs in CLP mice compared to sham mice. NP-specific GC B cells sorted from CLP mice immunized with NP-CGG exhibit reduced TNFα, AICDA, and BCL6 mRNA expression compared to sham mice. To confirm the role of the vagus nerve in impaired FDC clusters, CLP mice were subjected to bilateral subdiaphragmatic vagotomy 2 weeks post-CLP. These mice exhibit increased anti-NP IgG levels in response to immunization with NP-CGG compared to non-vagotomized CLP mice. FDC are radioresistant cells; therefore, we lethally irradiated sham and CLP mice and reconstituted them with bone marrow cells from naive mice that never experienced sepsis. CLP mice still show an impaired Ag-specific response confirming involvement of FDCs and vagus nerve signals. In summary, our data suggest that altered vagus nerve activity, low TNFα, and disruption in FDC function contributes to reduced Ag-specific humoral responses in sepsis survivors.