Figure 3.

Ddb1 is intrinsically required for expansion of T_FH cells but not for their differentiation per se. (A) Schematic diagram of SMARTA T-cell mix transfer experiments. Donor SMARTA CD4⁺ T cells from Ddb1-TaKO SMARTA mice (CD45.1⁺) and WT SMARTA mice (CD45.1⁺ CD45.2⁺) were mixed in a 1:1 ratio, and cells were adoptively transferred into WT mice (CD45.2⁺), follow by LCMV Armstrong infection. (B) Flow cytometry of CD4⁺ T cells in the spleen of mice generated in (A), assessed at days 2, 3, and 8 after LCMV Armstrong infection. Numbers adjacent to outlined areas indicate percentage of donor SMARTA CD4⁺ T cells. (C) Frequency (among CD4⁺ T cells) and total cell number of donor SMARTA CD4⁺ T cells in the spleen of mice in (A) (n = 6). (D) Flow cytometry of donor WT or Ddb1-TaKO SMARTA CD4⁺ T cells in the spleen of mice in (A) at day 8 after LCMV Armstrong infection. Numbers adjacent to outlined areas indicate percentage of CXCR5⁺ SLAM^lo T_FH cells (top) or CXCR5⁺ PD1⁺ GC T_FH cells (middle) or CXCR5⁺ Bcl-6⁺ GC T_FH cells (bottom). (E) Frequency (among donor SMARTA CD4⁺ T cells) and total cell number of T_FH cells and GC T_FH cells in donor WT or Ddb1-TaKO SMARTA CD4⁺ T cells at day 8 after LCMV Armstrong infection (n = 6). Each symbol represents an individual mouse, small horizontal lines indicate the mean ( ± s.d.). ns, not significant; **P < 0.01; ***P < 0.001; ****P < 0.0001 (Student’s unpaired t-test). Data are representative of three independent experiments (error bars, s.d.).