(A) OT-II T:B cell conjugation assays were conducted using CD4+ T cells transiently transfected with DNA constructs expressing either GFP, GFP-SAP, GFP-SAP(R78A), or GFP-SAP(R55L), n=6, mean ± SEM frequency of CD4+CD19+ conjugates in total GFP+CD4+ events, **p<0.005 (See Figure S2 for western blot and representative FACS plot). (B) CD11c+ splenic DCs, splenic B cells and LPS-activated B cells were assessed for SLAM, Ly108, and CD84 expression (n=3). (C–D) Day 9 post-NP-OVA in alum immunization, (C) B cells or (D) Tfh (CD4+CD44+CXCR5hiPD-1hi) and non-Tfh (CD4+CD44+CXCR5loPD-1lo) cells were evaluated for Ly108 and CD84 expression (n=2, 2–5 mice/genotype).