The impact of SFRs on T cell–dependent humoral immunity can be masked by high doses of antigen and involves multiple SFRs. (A–G) Mice were immunized as in Fig. 2 B, except that either a higher (100 µg) or a lower (1 µg) dose of NP-OVA was used. The protocol is shown in A. For the higher dose (100 µg), production of anti-NP IgG1 (B), GC B cell numbers (C), numbers of NP-specific GC B cells (D), and Bcl-2 expression in GC B cells (E) are represented. For the lower dose (1 µg), production of anti-NP IgG1 is depicted (F). A table of the ratio of NP-IgG1 in SFR KO mice compared with WT mice is shown in (G). The data for the 10 µg dose are from Fig. 2 C. (H–K) The indicated mice were immunized as detailed for Fig. 2 B, except that various doses of NP-OVA were used. The protocol is shown in H. For SLAMF1,5,6 tKO compared with WT mice, NP-specific IgM and IgG1 were measured and depicted in I–K (I, 10 µg NP-OVA; J, 100 µg NP-OVA; K, 1 µg NP-OVA). (L) Table showing the ratio of NP-IgG1 in tKO mice compared with WT mice. For B, WT, n = 10; SFR KO, n = 14. For C and D, WT, n = 8; and SFR KO, n = 6. For E, WT, n = 4; SFR KO, n = 4; For F, WT, n = 9; and SFR KO, n = 10. For I, WT, n = 6; and SLAMF1,5,6 tKO, n = 8. For J, WT, n = 9; and SLAMF1,5,6 tKO, n = 7. For K, WT, n = 9; and SLAMF1,5,6 tKO, n = 7. Data are from one experiment (B, E, F, J, and K) or two experiments (C, D, and I). Each symbol represents one mouse. *, P < 0.05; **, P < 0.01 (two-tailed Student’s t test). Data are shown as mean ± SEM. D, day; ns, not significant.