Long-term systemic and mucosal SARS-CoV-2 IgA response and its association with persistent smell and taste disorders

Abstract

Introduction: Current approved COVID-19 vaccines, notably mRNA and adenoviral vectored technologies, still fail to fully protect against infection and transmission of various SARS-CoV-2 variants. The mucosal immunity at the upper respiratory tract represents the first line of defense against respiratory viruses such as SARS-CoV-2 and is thus critical to develop vaccine blocking human-to-human transmission.

Methods: We measured systemic and mucosal Immunoglobulin A (IgA) response in serum and saliva from 133 healthcare workers from Percy teaching military hospital following a mild infection (SARS-CoV-2 Wuhan strain, n=58) or not infected (n=75), and after SARS-CoV-2 vaccination (Vaxzevria®/Astrazeneca and/or Comirnaty®/Pfizer).

Results: While serum anti-SARS-CoV-2 Spike IgA response lasted up to 16 months post-infection, IgA response in saliva had mostly fallen to baseline level at 6 months post-infection. Vaccination could reactivate the mucosal response generated by prior infection, but failed to induce a significant mucosal IgA response by itself. Early post-COVID-19 serum anti-Spike-NTD IgA titer correlated with seroneutralization titers. Interestingly, its saliva counterpart positively correlated with persistent smell and taste disorders more than one year after mild COVID-19.

Discussion: As breakthrough infections have been correlated with IgA levels, other vaccine platforms inducing a better mucosal immunity are needed to control COVID-19 infection in the future. Our results encourage further studies to explore the prognosis potential of anti-Spike-NTD IgA in saliva at predicting persistent smell and taste disorders.

Keywords: IgA; SARS-CoV2 vaccine; Spike N-terminal domain; dysgeusia; dysosmia; mucosal immunity; smell; taste.

Figure 1

Serum anti-SARS-CoV-2 IgA kinetics and specificity up to 16 months after COVID-19 acute infection and without immunization. Serum anti-SARS-CoV2 IgA (UA/ml) were quantified on a MesoQuickPlex SQ120 using the V-PLEX COVID-19 Coronavirus Panel 2 IgA kit, from naive (COVID-, blue) and previously infected (COVID+, red) individuals at enrollment (V1, boxplots on the left), and its kinetic of decrease (mean slope in red) for symptomatic COVID-19+ individuals up to 16 months after the acute infection (timeline evolution of the signal on the right). (A) Serology IgA titers against the whole Spike. (B) Serology IgA titers against the Spike/RBD. (C) Serology IgA titers against the Spike/NTD. (D) Serology IgA titers against the Nucleocapsid. The red dashed line corresponded to the positivity threshold, determined by the quantitative variable maximizing both sensitivity and specificity (i.e. Youden index). Wilcoxon-rank sum test: *** p<0.001. Linear mixed models were used to calculate the mean slope between each visit (red line).

Figure 2

Serum anti-SARS-CoV-2 total Immunoglobulins (Ig) and seroneutralization titers at each visit and without immunization for previously infected individuals. (A) Titers of total Ig targeting the Spike/RBD and (B) the Nucleocapsid in serum from previously infected individuals are represented at enrollment (V1), 6 months (V2) and 12 months (V3) later. (C) Seroneutralization titers from previously infected individuals at V1, V2 and V3. The positivity thresholds are represented with a red dashed line. Linear regression slopes from (A, B) were significantly different from zero with p < 0.001.

Figure 3

Saliva anti-SARS-CoV-2 IgA kinetics and specificity up to 16 months after COVID-19 acute infection and without immunization. Saliva anti-SARS-CoV2 IgA (UA/ml) were quantified on a MesoQuickPlex SQ120 using the V-PLEX COVID-19 Coronavirus Panel 2 IgA kit, from naive (COVID-, blue) and previously infected (COVID+, red) individuals at enrollment (V1, boxplots on the left), and its kinetic of decrease (mean slope in red) for symptomatic infected individuals up to 16 months after the acute infection (timeline evolution of the signal on the right). (A) Salivary IgA titers against the whole Spike. (B) Salivary IgA titers against the Spike/RBD. (C) Salivary IgA titers against the Spike/NTD. (D) Salivary IgA titers against the Nucleocapsid. The red dashed line corresponded to the positivity threshold, determined by the quantitative variable maximizing both sensitivity and specificity (i.e. Youden index). Wilcoxon-rank sum test: ns, not significant, ** p<0.01, *** p<0.001. Linear mixed models were used to calculate the mean slope between each visit (red line).

Figure 4

Serum and saliva anti-Spike IgA titers against human coronaviruses. (A) Normalized log-10 transformed serology titers of anti-Spike IgA (log10 UA/ml) in saliva (left) and serum (right) from naive (COVID-, blue) and previously infected (COVID+, red) individuals measured by MSD technology at enrollment (V1). IgA specificity corresponds to the Spike proteins from human coronaviruses (hCoV) 229E, HKU1, NL63, OC43, SARS-CoV-1 and SARS-CoV-2. Kruskal-Wallis test: ns, not significant; * p<0.05; *** p<0.001. (B) Correlation matrices in saliva (left) and serum (right) at V1 showing significant positive correlations between alpha-coronaviruses (hCoV 229E and NL63), beta-coronaviruses (hCoV OC43, HKU1, SARS-CoV-1, SARS-CoV-2), as well as SARS-CoV-2 antigen specificity (N, Spike, Spike/RBD, Spike/NTD) in previously infected individuals. Only significant correlations (Spearman, p<0.05) are represented on the matrices. The color and size of the dots (scale next to the graph) indicate the degree of correlation (Spearman, rho) between the different parameters (small to large indicating low to high correlation).

Figure 5

Impact of the number of vaccine doses on serum anti-SARS-CoV-2 IgA titers in the presence (red) or absence (blue) of a previous COVID-19 infection. (A) Serology IgA titers against the whole Spike. (B) Serology IgA titers against the Spike/RBD. (C) Serology IgA titers against the Spike/NTD. (D) Serology IgA titers against the Nucleocapsid. Two-Way ANOVA tests with Tukey post’hoc test: ns, not significant; * p<0.05; ** p<0.001; *** p<0.001.

Figure 6

Impact of the number of vaccine doses on saliva anti-SARS-CoV-2 IgA titers in the presence (red) or absence (blue) of a previous COVID-19 infection. (A) Salivary IgA titers against the whole Spike. (B) Salivary IgA titers against the Spike/RBD. (C) Salivary IgA titers against the Spike/NTD. (D) Salivary IgA titers against the Nucleocapsid. Two-Way ANOVA tests with Tukey post’hoc test: ns, not significant; * p<0.05; ** p<0.001; *** p<0.001.

Figure 7

SARS-CoV-2 vaccination reactivated mucosal immunity in previously infected individuals. (A) Salivary anti-Spike IgA post-immunization (Visit 3) positively correlated with salivary anti-Spike IgA post-infection (Visit 1) in previously infected individuals (Pearson correlation, R² = 0.735, p<0.001). (B) After immunization, the correlation between saliva and serum anti-Spike IgA was well differentiated in naive (COVID-, blue) and previously infected (COVID+, red) individuals, underlining the reactivation of mucosal immunity in previously infected individuals only: COVID+ group (Adj R² = 0.44, slope = 0.45); COVID- group (Adj R² = 0.31, slope = 1), p<0.001.

Figure 8

Persistent taste and smell disorders more than one year after infection are associated with higher initial titers of anti-Spike NTD IgA. (A) Normalized log-10 transformed serology titers of anti-SARS-CoV-2 IgA (log10 UA/ml) in saliva (left) and serum (right) measured at visit 1 by MSD technology from individuals suffering from taste disorders persistent for less (brown, n=28) or more (orange, n=10) than one year. (B) Normalized log-10 transformed serology titers of anti-SARS-CoV-2 IgA (log10 UA/ml) in saliva (left) and serum (right) measured at visit 1 by MSD technology from individuals suffering from smell disorders persistent for less (brown, n=27) or more (orange, n=15) than one year. Antigen specificity corresponds to the Nucleocapsid (N), Spike (S), Spike-receptor binding domain (S_RBD) and Spike-N-terminal domain (S_NTD). Kruskal-Wallis test: ns, not significant; * p<0.05.