Fig 2: SARS-CoV-2-specific IgG, IgA, and IgA1 levels decrease in saliva three months after BNT162b2 vaccinationSARS-CoV-2-specific antibody responses were measured in the saliva of vaccinated naïve (n = 59) and SARS-CoV-2-Exp (n = 17) subjects at different time points: at the time of the first (T0) and the 2nd dose vaccine dose (T1) (indicated with an arrow), at 7–10 days (T2) and 3 months (T3) after the 2nd dose. Saliva was tested for IgG and IgA to full-length spike and its receptor-binding domain (RBD) and for anti-spike IgA1 and IgA2. The titers of antigen-specific Ig were normalized by dividing the values of SARS-CoV-2-specific Ig by total IgA or total IgG concentrations of each sample. The normalization was applied only to values higher than LoD. The adjusted values are expressed in AU. The box plots show the interquartile range, the horizontal lines show the median values, and the whiskers indicate the minimum-to-maximum range. Each dot corresponds to an individual subject. Log scale on y axis (except for IgA2). P-values were determined using the Friedman test with the Dunnett's multiple comparison test.

Fig 3: Peripheral plasmablasts switch to IgA2 in COVID-19 patients with prolonged stay in ICU.a Binding of IgG, IgM, IgA1, and IgA2 antibodies to SARS-Cov-2-S protein expressed on the surface of transfected 293T cells. Data represent ?MFI, which was calculated as following: MFI of transfected cells, incubated with sera and stained with respective anti-hIg, minus MFI of untransfected cells, incubated with sera and stained with respective anti-hIg. Dotted line indicates a ?MFI of 1500. b Percentage of isotype-positive cells among sequenced CD27high CD38high B cells determined by single-cell BCR sequencing. Donors were grouped as “HC” for healthy controls (three donors), “1st week” for patients within 7 days after ICU admission (six donors) and “Late” for patients who have been admitted to the ICU for more than a week at the time of analysis (eight donors). Lines indicate measurements from the same patient at different time points. Two-sided Mann–Whitney U test. c UMAP representation of immunoglobulin isotype expression. Percentages refer to the total number of sequenced cells per donor. For IgG1 and IgA2 of COVID-19 patients the absolute number of cells is shown. Arrows represent the time (5–31 days and see Supplementary Table 1) patients had spent in the ICU at the time of analysis (upper) and the shift in cytokine milieu to allow switching to IgG1/IgA1/IgA2 (left). d Concentration of total IgA in the serum of COVID-19 patients at both early (less than a week) and late time points after ICU admission as determined by ELISA. Lines indicate measurements from the same patient at different time points. Two-sided Wilcoxon exact test.

Fig 4: SARS-CoV-2-specific IgG, IgA, and IgA1 levels decrease in plasma three months after BNT162b2 vaccinationSARS-CoV-2-specific antibody responses were measured in the plasma of vaccinated naïve (n = 44) and SARS-CoV-2-Exp (n = 12) subjects at different time points: at the time of the first (T0) and the 2nd dose vaccine dose (T1) (indicated with an arrow), at 7–10 days (T2) and 3 months (T3) after the 2nd dose. Plasma was tested for IgG and IgA to full-length spike and its receptor-binding domain (RBD) and for anti-spike IgA1 and IgA2. The titers of antigen-specific Ig are expressed in IU/ml, except for IgA2 that are expressed in AU (see Materials and Methods). LoD is indicated by a dotted line: LoD (spike IgG) = 12, LoD (RBD IgG) = 13.8, LoD (spike IgA) = 54.22, LoD (RBD IgA) = 54.08, LoD (IgA1) = 74.64; LoD (IgA2) = 0.009. The box plots show the interquartile range, the horizontal lines show the median values, and the whiskers indicate the minimum-to-maximum range. Each dot corresponds to an individual subject. Log scale on y axis (except for IgA2). P-values were determined using the Friedman test with the Dunnett's multiple comparison test.

Fig 5: Release of SARS-CoV-2-specific IgA1 and IgA2 antibodies in plasma and saliva after BNT162b2 vaccination and in COVID-19 patients IgA1 and IgA2 subtypes specific for spike protein were measured in plasma and saliva at different time point (T0,T1, T2) of vaccinated naïve (plasma: n = 64; saliva: n = 63 (IgA1), n = 55 (IgA2)) or SARS-CoV-2-Exp (plasma: n = 21; saliva: n = 18) subjects. Subjects received the first vaccine dose at day 0 (T0), and the 2nd dose at day 21 (T1) (indicated with an arrow). T2 corresponds to 7–10 days after the 2nd dose. For plasma samples, the titers of antigen-specific IgA1 and IgA2 are expressed in IU/ml and AU, respectively (see Methods). LoD is indicated by a dotted line: LoD (IgA1) = 74.64; LoD (IgA2) = 0.009. For saliva samples, the titers of antigen-specific Ig were normalized by dividing the values of SARS-CoV-2-specific Ig by total IgA concentration of each sample. The normalization was applied only to values higher than LoD. The adjusted values are expressed in AU.IgA1 and IgA2 subtypes specific for spike protein were measured in plasma and saliva of vaccinated naïve and SARS-CoV-2-Exp subjects 7–10 days after second dose (T2), and the antibody response was compared to that obtained in COVID-19 patients (plasma: n = 28; saliva: n = 26) and in nonvaccinated subjects (n = 19, Control). Data information: The box plots show the interquartile range, the horizontal lines show the median values, and the whiskers indicate the minimum-to-maximum range. Each dot corresponds to an individual subject. Log scale on y axis (only for IgA1). P-values were determined using the Friedman test with the Dunnett's multiple comparison test (A) or the Kruskal–Wallis test with the Dunn's multiple comparison test (B). Source data are available online for this figure.