Fig 1: Expression of IL-21 in pancreatic islets through an insulin promoter transgenic construct leads to increased cellularity of lymphoid organs and altered expression of B-cell maturation markers in IL-21Tg mice. A: Murine IL-21 was cloned into the transgenic construct under the control of the human insulin promoter and HBS (hepatitis B virus) terminator sequences. B: IL-21 mRNA levels were measured in pancreatic tissue from IL-21Tg and littermate controls by quantitative RT-PCR. C: Immunohistochemical staining for paraffin embedded pancreatic tissue with an IL-21–specific polyclonal antibody (left panel Tg-, right panel Tg+, a representative islet is marked with an arrow). Original magnification: ×20. Total cell numbers in spleen (D) and pancreatic draining lymph nodes (E) (*P < 0.05) and IgD vs. IgM staining (F) of B220+ cells (top panels) and frequencies of mature (IgM+ IgD+) and marginal zone/transitional (IgM+ IgD-) B-cells are shown. CD23 vs. CD21 staining of IgM+ cells (bottom panels) and mean fluorescence intensity for each marker is shown on the relevant axis (n = 4 for all experiments shown). (A high-quality digital representation of this figure is available in the online issue.)