Effect of murine anti-CXCL13 antibody on germinal center formation in C57BL/6 mice challenged with NP-KLH. Mice were treated with 30 mg/kg of MAb 5261-muIg antibody and corresponding mouse isotype control, on days −3, 0 (the day of the immunization), 4 and 7 (n = 9/group). (A) Total IgM and IgG1 anti-NP antibody-secreting cells were detected by ELISPOT on wells coated with NP14-BSA. (B) The frequencies of high affinity IgG1 anti-NP-secreting cells were determined by ELISPOT on wells coated with NP4-BSA. (C) Number of germinal centers (n = 9 mice/group). Follicles were hand counted. Number of PNA+ germinal centers in relation to total number of follicles per group was calculated using ImagePro software. (D) Mean germinal center area. Area of each PNA+ germinal center for each group was calculated using ImagePro software by PNA+ pixel area and then converted to μm. The numbers of GC analyzed were: 201 in Control group and 102 in MAb 5261-muIg-treated group. (E) Percentages of activated T cells (CD4+/CD62Llow/CD44+) in spleens and bone marrow. Statistical significance was evaluated by Student’s unpaired t-test. *P = 0.0125; **P = 0.0016; ****P < 0.0001; P = 0.2 and 0.71 for IgG1 and IgM portions of the graph, respectively (A).