Figure 3. Loss of Ly108 reverses the SAP requirement in CD4⁺ T cells for T cell help to B cells.

(a-d) WT, Sh2d1a^−/−, or Slamf6^−/−Sh2d1a^−/− CD45.1⁺ SM TCR transgenic CD4⁺ T cells were transferred into Sh2d1a^−/− recipient mice subsequently infected with LCMV. Splenocytes were analyzed day 8 after infection. (a) Germinal center B cells (Fas^hiGL7^hi) and (b) plasma cells (CD138⁺IgD^lo) shown as % of total B cells (CD19⁺CD4⁻). (c) Tfh cells (CXCR5⁺) and (d) GC Tfh cells (CXCR5⁺PD1^hi) shown as a % of SM (CD45.1⁺CD4⁺B220⁻). (e-g) Slamf6^−/−Sh2d1a^−/− SM CD4⁺ T cells (CD45.1⁺) were transduced with Ly108-1, Ly108-2, SAP or GFP vector in vitro, transferred into Sh2d1a^−/− recipient mice, and mice were infected with LCMV. (e) Germinal center B cells (Fas^hiGL7^hi) are shown 8 days after infection, as a % of total B cells. (f) Plasma cell (CD19⁺ IgD^loCD138⁺) frequencies, as a % of total B cells. (g) MFI of Ly108 expression on Slamf6^−/−Sh2d1a^−/− SM CD4⁺ T cells transduced with empty vector (GFP) or Ly108 vector (Ly108-2), in comparison to endogenous Ly108 expression on WT SM cells. Data are representative of 4 (a-c,e) or 2 (d,f,g) independent experiments. N = 4 or more mice per group. * P < 0.05, ** P < 0.005, *** P < 0001. Error bars are SEM.