Characterization of 1D6 mAb and identification of BAFF-positive cells within GCs. (A) FACS analysis of BAFF expression using 1D6 mAb. BAFF transfectants and mock transfectants were stained with 1D6 mAb (solid lines) or isotype-matched control Ab (IgG1) (dashed lines) followed by FITC-conjugated Ab to mouse IgG1. (B) Cell lysates were prepared from BAFF transfectants and mock transfectants and subjected to immunoblotting analysis using 1D6 mAb or antihuman BAFF (TALL-1) polyclonal Ab. (C) Peripheral blood monocytes (CD14⁺ cells more than 98%) were activated by IFN-γ (1000 U/mL) and LPS (10 ng/mL) for 24 hours. After blocking with normal mouse serum plus control IgG1 mouse mAb, BAFF expression was evaluated by FACS analysis using 1D6 mAb. (D) BAFF-positive cells or FDCs (brown) localized in GCs, as determined by immunohistochemical staining of serial human lymph node sections with 1D6 mAb or CNA.42 mAb, respectively (magnification × 200). (Inset) High magnification (× 400). Nuclei were visualized by hematoxylin staining. Data shown are representative of 3 different experiments.