Confocal microscopy of IL-12/IL-12Rβ1 colocalization in B cells. Untreated and 24-hour IFN-γ-activated primary B cells were treated with recombinant IL-12 for 15 minutes at 4 or 37°C, before intracellular staining with anti-IL-12 and anti-IL-12Rβ1. Confocal microscopic analysis of serial 1-μm optical sections was performed from the cell surface to the cell interior. Superimposed IL-12 (red) and IL-12Rβ1 (green) staining patterns are shown. Yellow staining indicates IL-12 and IL-12Rβ1 colocalization (original magnification, × 63). The projection image of the different optical sections is shown. Microscopy confocal analysis of 3 individual serial sections from the surface to the interior of one cell is also shown (5-fold magnification of projection image). (A) Control without IL-12. (B-C) Non-preactivated (B) and 24-hour IFN-γ-preactivated (C) primary B cells were treated with recombinant IL-12 at 37°C. (D) Non-preactivated cells were treated with recombinant IL-12 at 4°C. Isotype controls were used, as described in “Materials and methods,” for each of the 4 experimental conditions.