Fig 2: Resistant Mice Exhibit Increased T:B Cell Interactions and B Cell FunctionalityResistant and susceptible mice were infected with P. yoelii pRBCs.(A) Representative contour plots and flow cytometry gating of splenocytes at day 9 p.i. to identify T and B cell conjugates.(B) Total number of T and B cell conjugates (CD3+CD4+CD19+B220+ doublets) per spleen on the indicated day p.i. Data (means ± SEs) are from 2 independent experiments (n = 8 mice per time point, day 9, n = 4) were analyzed by unpaired t test.(C) Representative contour plots (gated on B220+CD19+ cells) on day 14 p.i. to identify GC B cells (GL7+CD95+).(D) Representative histograms to identify BCL-6+ GC B cells.(E) Percentage of BCL-6+ GC B cells per spleen at days 8 and 14 p.i. Data (means ± SEs) from 3 independent experiments (n = 8 mice per time point) were analyzed by unpaired t test.(F) Representative flow cytometry graphs identifying CD73+ GC B cells from spleens at day 21 p.i.(G) Percentage of CD73+ GC B cells per spleen.(H) Total number of CD73+ GC B cells per spleen.(I) Mean fluorescence intensity (MFI) of CD73 on GC B cells.(J) Representative contour plots for CD19+IgD-CD138-CD38hi memory B cells (MBCs).(K) Total number of MBCs per spleen on the indicated day p.i. Data (means ± SEs) from 2 independent experiments (n = 10 mice per time point) were analyzed by unpaired t test.(G–I) Data (means ± SEs) from 2 independent experiments (n = 10 mice per time point) were analyzed by unpaired t tests.*p < 0.05, **p = 0.01, ***p = 0.001, and ****p = 0.0001.

Fig 3: Tac Mice Have Sustained Splenic GC Architecture Compared to CR Mice during P. yoelii InfectionMice from Tac and CR were infected with P. yoelii pRBCs. Spleens from Tac and CR mice were removed at days 0, 7, 9, and 11 p.i., frozen, sectioned, and mounted on slides. Tissue sections were stained for anti-B220 (green), anti-CD3 (red), and anti-GL7 (gray), and analyzed through confocal microscopy.(A–C) Representative spleen sections of Tac and CR mice on the indicated day (A). Stitched mosaic image of Tac spleen D11 (B) and CR spleen D11 p.i. (C).(D–F) Total B220+ (D), (E) CD3+, and (F) GL7+ cells per spleens of infected mice at days 0, 7, 9, and 11. Data (means ± SEs) are cumulative results from 2–3 independent experiments per time point and were analyzed by 2-way ANOVA; multiple comparisons were analyzed with Tukey’s post hoc multiple comparisons test; *p < 0.05, and ***p < 0.001.

Fig 4: Gut Microbiota Composition Affects Expansion of GC B Cells and Titers of Parasite-Specific AntibodiesGerm-free mice were colonized with cecal contents from Tac (resistant) (GF-Tac; n = 7) or CR (susceptible) (GF-CR; n = 5) mice. Colonized GF mice and control Tac and CR mice (n = 5 each) were infected with P. yoelii.(A) Percentage of parasitemia following P. yoelii infection.(B) Area under the curve (AUC) analysis of parasitemia curves.(C–F) Spleens were removed at day 19 and total numbers of antigen-specific CD4 cells (CD4+CD49+CD11a+), T follicular helper cells (Tfh) (CD4+CD44+CXCR5+PD1+), plasmablasts (CD19+B220+IgD-CD138+), and GC B cells (CD19+CD95+GL7+) were determined. Data (means ± SDs) were analyzed by unpaired t tests. *p < 0.05, **p = 0.01, ***p = 0.001, and ****p = 0.0001.(G–K) Sera was collected from P. yoelii-naive mice or the indicated mice at day 13 post-P. yoelii infection and reacted against MSP119-coated plates to detect antibodies by ELISA.(L) Sera from Tac, GF+Tac, CR, and GF+CR mice was collected at days 0, 7, 13, and 19 p.i., diluted at 1:200, and reacted against P. yoelii whole-parasite lysate-coated plates. Anti-IgG antibody was used to detect P. yoelii-specific IgG. Data were acquired from a single experiment and were analyzed by 2-way ANOVA. a = GF+Tac versus CR, b = GF+Tac versus GF+CR, c = Tac versus GF+CR, and d = Tac versus CR.*p < 0.05, **p = 0.01, ***p = 0.001, and ****p = 0.0001.