Fig. 4: B cells initiate CD4⁺ T cell responses against HBsAg.

a–d OT-II T cells, labeled with Violet tracer where indicated, were transferred into WT or μMT mice, followed by pHBV1.3/OVA323-339 HDI. Spleens, draining LNs (dLNs), and livers were harvested for FACS analysis from days 2 to 4.5 post-HDI. a Representative histogram and geoMFI data of CD69 expression at day 2 (n = 3). b Representative Violet tracer dilution and proliferation index at day 3.5 (spleen and dLN: n = 5; liver: n = 4). c Representative FACS plots and percentages of CXCR5⁺Bcl6^hi OT-II T cells at day 3.5 (n = 5). d Representative FACS plots and percentages of T-bet⁺GzmB^hi OT-II T cells at day 4.5 (n = 6). e, f Representative FACS plots and percentages of endogenous CD25⁺OX40⁺ (e, n = 7) and T-bet⁺GzmB^hi (f, n = 6) CD4⁺ T cells in the spleens, dLNs, and livers from μMT versus WT mice at day 5 post-pHBV1.3 HDI. g Representative Violet tracer dilution and proliferation index of transferred OT-II T cells in spleens, dLNs, and livers from μMT mice reconstituted with MHC-II KO versus WT B cells at day 3.5 post-pHBV1.3/OVA323-339 HDI (n = 3). h, i Circulating HBsAg levels (h, n = 4) and intrahepatic HBsAg levels (i, n = 15 view fields from 5 mice) in WT and μMT mice, with serum collected at the indicated time point and liver tissues on day 14 after pHBV1.3 HDI. Scale bars, 50 μm. At least two independent experiments were performed. Horizontal lines in (a–g, i) represent median values. Error bars in (h) show mean ± SD. Statistical significance was calculated using two-tailed Student’s t-tests (a–g, i) and two-way ANOVA (h). Significance levels are indicated as follows: *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. Source data and exact p-values are provided in the Source Data file.