FIGURE 1.

Frequencies of CD27^–, CD21^– B cells and plasmablasts are elevated in acute COVID-19 and malaria compared with the healthy donors (HDs). (A) Representative FACS plots showing the frequency of transitional B cells (left panel) and the distribution of mature B cell subsets defined by CD21/CD27 (right panel) in HDs, COVID-19, and malaria patients. The panels are gated on CD19⁺, CD20⁺ cells, in the right panel transitional cells have been excluded (see Supplemental Fig. S3 for the detailed gating strategy). (B) Comparison of B cell subset distribution in HDs, COVID-19, and malaria patients. The pie charts show the mean frequency of transitional B cells (defined as CD24⁺, CD38⁺), naïve (CD21⁺, CD27^–), CD21+ memory (CD21⁺, CD27⁺), CD21^–, CD27⁺ memory(CD21^–, CD27⁺) and atypical memory (CD21^–, CD27^–) populations in HDs, COVID-19, and malaria patients. (C) Representative FACS plots showing the frequency of plasmablasts (CD19⁺, CD27⁺, CD38⁺) in HDs, COVID-19, and malaria patients (see Supplemental Fig. S4 for the detailed gating strategy). (D) Frequency of plasmablasts in HDs and COVID-19 and malaria patients. (E and F) Comparison of the frequencies of atypical memory B cells (E) and plasmablasts (F) between mild, moderate, and severe COVID-19 patients. Data are shown as mean ± sd, where *, **, ***, and **** indicate P values <0.05, <0.01, <0.001, and <0.0001