The Brain Reacting to COVID-19: Analysis of the Cerebrospinal Fluid and Serum Proteome, Transcriptome and Inflammatory Proteins

Patients with COVID-19 can have a variety of neurological symptoms, but the pathomechanism of CNS involvement in COVD-19 remains unclear. While routine cerebrospinal fluid (CSF) analyses in patients with neurological manifestations of COVID-19 generally show no or only mild inflammation, more detailed data on inflammatory mediators in the CSF of patients with COVID-19 are scarce. Here, we used mass spectrometry to study the proteome, Enzym-linkend immunoassays, semiquantitative cytokine arrays, autoantibody screening, and RNA profiling to study the neuroinflammation. We study the inflammatory response in paired CSF and serum samples of patients with COVID-19 (n=38). Patients with herpes simplex virus encephalitis (HSVE, n=10) and patients with non-inflammatory, non-neurodegenerative neurological diseases (n=28) served as controls. Proteomics on single protein level and subsequent pathway analysis showed similar yet strongly attenuated inflammatory changes in the CSF of COVID-19 patients compared to HSVE patients. CSF/serum indices of interleukin-6, interleukin-16 and CXCL10 together point at an origin from these inflammatory proteins from outside the central nervous system. When stratifying COVID-19 patients into those with and without bacterial superinfection as indicated by elevated procalcitonin levels, inflammatory markers were significantly higher in those with concomitant bacterial superinfection. RNA sequencing in the CSF revealed 101 linear RNAs comprising messenger RNAs, micro RNAs and t-RNA fragments being significantly differentially expressed in COVID-19 than in HSVE or controls. Our findings may explain the absence of signs of intrathecal inflammation upon routine CSF testing despite the presence of SARS-CoV2 infection-associated neurological symptoms. The relevance of blood-derived mediators of inflammation in the CSF for neurological post-COVID-19 symptoms deserves further investigation.