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Background: Within the past 10 years, immune mechanisms associated with acute ischemic stroke (AIS) have been brought into focus, but data on B cell activation and intrathecal Ig production is still scarce. In this study, we determined the prevalence of an elevated IgG index, positive oligoclonal bands (OCBs) and chemokine C-X-C motif ligand 13 (CXCL13) levels in the cerebrospinal fluid (CSF) as markers of intrathecal IgG synthesis and B cell activation in patients with AIS., Methods: In a retrospective study we analyzed the cerebrospinal fluid (CSF) from 212 patients with AIS from December 2013 to May 2018 assessing intrathecal Ig synthesis, OCBs and CXCL13 concentrations., Results: Overall, 5.7% (12/212) of AIS patients showed an intrathecal IgG synthesis, 0.5% (1/212) with isolated elevated IgG index, 5.2% (7/136) isolated positive OCBs and 2.9% (4/136) both elevated IgG index and positive OCBs. CXCL13 levels were elevated in 3.6% (3/83) of the patients. Approximately one third of these patients had simultaneously chronic inflammatory CNS disease (multiple sclerosis, neuromyelitis optica spectrum disorder, neurosarcoidosis). There was no significant association between CSF findings and stroke characteristics including vascular territory, localization, volume, etiology, acute treatment, or blood-brain barrier dysfunction. Intrathecal IgG synthesis was more common in patients with prior stroke. Longitudinal CSF analysis did not reveal any newly-occurring, but instead mostly persistent or even disappearing intrathecal IgG synthesis after AIS., Conclusions: We found no evidence of a relevant B cell recruitment and intrathecal IgG synthesis in patients with AIS. In fact, the occurrence of intrathecal IgG synthesis was associated with concurrent chronic inflammatory CNS disease or previous stroke. Consequently, in patients with first-ever AIS and intrathecal IgG synthesis, physicians should search for concomitant inflammatory CNS disease., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Laichinger et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The Vi capsular polysaccharide (CPS) of Salmonella enterica serovar Typhi, the cause of human typhoid, is important for infectivity and virulence. The Vi biosynthetic machinery is encoded within the viaB locus composed of 10 genes involved in regulation of expression (tviA), polymer synthesis (tviB-tviE), and cell surface localization of the CPS (vexA-vexE). We cloned the viaB locus from S. Typhi and transposon insertion mutants of individual viaB genes were characterized in Escherichia coli DH5α. Phenotype analysis of viaB mutants revealed that tviB, tviC, tviD and tviE are involved in Vi polymer synthesis. Furthermore, expression of tviB-tviE in E. coli DH5α directed the synthesis of cytoplasmic Vi antigen. Mutants of the ABC transporter genes vexBC and the polysaccharide copolymerase gene vexD accumulated the Vi polymer within the cytoplasm and productivity in these mutants was greatly reduced. In contrast, de novo synthesis of Vi polymer in the export deficient vexA mutant was comparable to wild-type cells, with drastic effects on cell stability. VexE mutant cells exported the Vi, but the CPS was not retained at the cell surface. The secreted polymer of a vexE mutant had different physical characteristics compared to the wild-type Vi.