Fig 2: Donors used for B cell sorting have Spike binding IgG, IgA and IgM, nAbs and SARS-CoV-2 Spike reactive IgG+ B cells(A) Kinetics of the antibody binding response (IgM, IgA, IgG against S and RBD) and neutralization activity against SARS-CoV-2 pseudovirus (PV) for donors P003, P008, and P054 in the acute and convalescent phase. ELISA data is reported as area under the curve (AUC, left y axis). Neutralization ID50 is shown on the right y axis. The asterisk indicates the time point from which mAbs were cloned for each donor. Experiments were performed in duplicate and repeated twice where plasma was available.(B) Fluorescent activated cell sorting (FACS) showing percentage of CD19+IgG+ B Cells binding to SARS-CoV-2 Spike. A healthy control PBMC sample collected prior to the COVID-19 pandemic was used to measure background binding to Spike. The full gating strategy can be found in Figure S1.

Fig 3: Distribution of total B lymphocytes (CD19+ and CD19+CD20+) in peripheral blood. CD19+ and CD19+CD20+ in the RRI group (n=30) (16.14±6, P=4.5×10-5 and 15.65±6, P=0.0001) and in the control group (n=10) (22.56±2 and 21.9±3). The results are presented as a percentage from lymphocytes (means ± SD). RRI, respiratory recurrent infection.

Fig 4: The seropositivity of anti-TRIM21 Ab is related to aberrant B cell differentiation in patients with SLE. (A) Percentages of CD19+ B cells in PBMCs and in resting B cells isolated by magnetic-activated cell sorting in SLE patients with anti-TRIM21 Ab, those without anti-TRIM21 Ab and healthy controls. (B) Flow cytometric analysis shows an increased rate of CD19+CD20-CD38+ plasmablasts at 24 h after stimulation with anti-IgM Ab, CD40L, and TLR7 ligand. The panels show the cells after gating with population positive to both CD19 and CD27. (C) Percentage of plasmablasts at 24 h after stimulation with anti-IgM Ab, CD40L, and/or TLR3/7 ligands in healthy controls (n = 5), SLE patients without anti-TRIM21 Ab seropositivity (n = 11) and those with anti-TRIM21 Ab seropositivity (n = 6). Values are shown as means ± SEM. Statistically significance data (*p < 0.05 and **p < 0.01) by Student's t-test, respectively.

Fig 5: Distribution of mature/naive B cells and memory B cells in peripheral blood. Mature/naive B cells and memory B cells in the RRI group (n=30) (76.8±10, P=0.027 and 23.2±10, P=0.027) and in the control group (n=10) (81.95±4 and 18.05±4). The results are presented as percentage from B cells (CD19+CD20+) (means ± SD). RRI, respiratory recurrent infection.