hAPRIL.01A and hAPRIL.03A decrease thymus-independent type II antibody responses in APRIL transgenic mice without affecting the splenic B-cell compartment. Mice (5 per group) were immunized with NP-Ficoll at day 0 and treated with the indicated proteins for 1 month from the start of injection. Anti–NP-specific antibody titres (IgM-IgG-IgA) were measured by ELISA at the indicated time points. (A) Anti-NP antibody titres in APRIL-Tg and WT littermates treated with PBS. (B) Effect of hAPRIL.01A and hAPRIL.03A on anti-NP antibody titers in APRIL-Tg mice. (C) Effect of TACI-Fc on anti-NP antibody titres in APRIL Tg mice. Please note: Some of the control lines are shown in multiple figures. The TACI-Fc and antibody inhibition were performed within one experiment, but are shown in separate graphs for clarity. Y-axis represents OD measured in the ELISA and therefore represents a relative measure of NP-specific antibodies. (D) Representative FACS profiles (and relative histograms) to show the percentage of T (CD3 positive) and B (B220 positive) lymphocytes in the spleen of APRIL Tg mice treated with the indicated proteins. (E) Splenocytes from the same mice were also screened for different B-cell subsets: M indicates mature; MZ, marginal zone; T2, transitional 2; and T1, transitional 1 B cells. Percentages of mature B cells are plotted on the histogram. ***P < .001, **P < .01, 1-way ANOVA.