Expression of hBAFF and hBAFFR. (A) Relative levels of hTNFSF13B mRNA in indicated human leukocyte subsets isolated from human PBMCs and hu-mice. hu-mice were generated by transplanting human umbilical cord HSCs into BRGS animals. Data were normalized relative to human naive T cells and are representative of 2 independent experiments. (B) hBAFF concentration in sera of BRGS intact mice (N = 5), humans (N = 5), and either BRGS hu-mice (N = 19) on the left or hBAFFKI-BRGS hu-mice (N = 8) on the right graph. The y-axes are on a different scale in the 2 graphs. Each symbol represents an individual mouse. Arithmetic mean ± standard error of the mean (SEM) are indicated for each group. Data were combined from 4 independent experiments. (C) BAFFR geometric mean fluorescence intensity (MFI) on CD20⁺ B cells from the following tissue of BRG(S) hu-mice: bone marrow (BM; N = 12), spleen (SP; N = 18), and lymph nodes (LN; N = 10). CD20⁻ cells (N = 18) were included as a reference negative control. Bars indicate mean ± SEM. Data were combined from 3 independent experiments. (D) Relative levels of mBAFF (left) and hBAFF (right) in sera of heterozygous (M/H) and homozygous (H/H) hBAFFKI (BALB/c) mice and littermate control wild-type (M/M) mice as measured by ELISA. Data of each graph were combined from 3 independent experiments with 2 mice per group for mBAFF ELISA and 1 to 2 mice per group for hBAFF ELISA, per experiment. The y-axis shows optical density (O.D.; 405 nm) values that were normalized relative to the average values obtained with M/M sera for mBAFF or with H/H sera for hBAFF in each experiment. *P < .05; **P < .01; ***P < .001; ****P < .0001. B, B cell; PMN, polymorphonuclear leukocyte; T, T cell.