Neuro-axonal injury in COVID-19: the role of systemic inflammation and SARS-CoV-2 specific immune response

Abstract

Background: In coronavirus disease-2019 (COVID-19) patients, there is increasing evidence of neuronal injury by the means of elevated serum neurofilament light chain (sNfL) levels. However, the role of systemic inflammation and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific immune response with regard to neuronal injury has not yet been investigated.

Methods: In a prospective cohort study, we recruited patients with mild-moderate (n = 39) and severe (n = 14) COVID-19 and measured sNfL levels, cytokine concentrations, SARS-CoV-2-specific antibodies including neutralizing antibody titers, and cell-mediated immune responses at enrollment and at 28(±7) days. We explored the association of neuro-axonal injury as by the means of sNfL measurements with disease severity, cytokine levels, and virus-specific immune responses.

Results: sNfL levels, as an indicator for neuronal injury, were higher at enrollment and increased during follow-up in severely ill patients, whereas during mild-moderate COVID-19, sNfL levels remained unchanged. Severe COVID-19 was associated with increased concentrations of cytokines assessed [interleukin (IL)-6, IL-8, interleukin-1 beta (IL-1β), and tumor necrosis factor-alpha (TNF-α)], higher anti-spike IgG and anti-nucleocapsid IgG concentrations, and increased neutralizing antibody titers compared with mild-moderate disease. Patients with more severe disease had higher counts of defined SARS-CoV-2-specific T cells. Increases in sNfL concentrations from baseline to day 28(±7) positively correlated with anti-spike protein IgG antibody levels and with titers of neutralizing antibodies.

Conclusion: Severe COVID-19 is associated with increased serum concentration of cytokines and subsequent neuronal injury as reflected by increased levels of sNfL. Patients with more severe disease developed higher neutralizing antibody titers and higher counts of SARS-CoV-2-specific T cells during the course of COVID-19 disease. Mounting a pronounced virus-specific humoral and cell-mediated immune response upon SARS-CoV-2 infection did not protect from neuro-axonal damage as by the means of sNfL levels.

Keywords: SARS-CoV-2; cytokines; immune response; neurofilament light chain protein; neurologic damage.

Figure 1.

Serum cytokine and SARS-CoV-2-specific antibody concentrations in relation to COVID-19 severity. (a) Serum IL-6, IL-8, IL-1β, and TNF-α serum concentration at baseline and day 28(±7) in patients with severe (red) and mild–moderate (blue) COVID-19. (b) Anti-spike (S1/S2), neutralizing antibody, and anti-nucleocapsid antibody concentration at baseline and day 28(±7) in patients with severe (red) and mild–moderate (blue) COVID-19. Black horizontal bars indicate median values. Whiskers indicate interquartile ranges. COVID-19, coronavirus disease-2019; IL-6, interleukin-6; IL-8, interleukin-8; IL-1β, interleukin-1β; TNF-α, tumor necrosis factor-alpha.

Figure 2.

Cell-mediated immunity in relation to COVID-19 severity. (a) SFUs per 250,000 PBMCs upon stimulation with the SNMO peptide pool at baseline and day 28(±7) in patients with severe (red) and mild–moderate (blue) COVID-19. (b) SFUs per 250,000 PBMCs upon stimulation with the S2N peptide pool at baseline and day 28(±7) in patients with severe (red) and mild–moderate (blue) COVID-19. Black horizontal bars indicate median values. Whiskers indicate interquartile ranges. COVID-19, coronavirus disease-2019; IFN-γ, interferon-gamma; IL-2, interleukin-2; PBMCs, peripheral blood mononuclear cells; SFUs, spot forming units; SNMO, spike protein, nucleocapsid protein, membrane protein, open reading frame proteins; S2N, spike-2 protein, nucleocapsid protein.

Figure 3.

Serum neurofilament light chain concentrations (log10 transformed) in relation to COVID-19 severity (unadjusted analysis). COVID-19, coronavirus disease-2019.

Figure 4.

Unadjusted (black) and adjusted (red) associations between antibodies at day 28(±7) and changes in sNfL levels. (a) Changes in sNfL levels (log10 fold-change; cube-root transformed differences) in correlation to anti-spike IgG antibody concentration at day 28(±7). (b) Changes in sNfL levels (log10 fold-change; cube-root transformed differences) in correlation to neutralizing antibody titers at day 28(±7). (c) Changes in sNfL levels (log10 fold-change; cube-root transformed differences) in correlation to anti-nucleocapsid IgG antibody concentration at day 28(±7). Dashed black line: regression line of the unadjusted linear regression model. Gray shade area: 95% confidence interval of the unadjusted linear regression model. Red solid line: regression line of the adjusted linear regression model. Red shade area: 95% confidence interval of the adjusted linear regression model. AU/ml, arbitrary units per milliliter; S/C, specimen/calibrator ratio; ΔsNfL, difference in serum neurofilament concentration at day 28(±7) to baseline; sNfL, serum neurofilament light chain. ^aRegression coefficient per 100 AU/ml.