PCs and T cells interact in vitro and in vivo. Tonsillar PCs and T cells were purified and cultured in vitro. Immunofluorescence was used to assess interactions between PCs, T cells, and CD11c⁺ DCs in secondary lymphoid tissue. (A) Numbers of PCs recovered at 24 hours (□) and 48 hours (▩) after culture of PCs either alone (PC), with B cells (BC), or with T cells (TC), either alone, with isotype control Abs (hIg, gIg, or mIg) or with anti–IL-2, –IL-4, –IL-6, –IL-10, or –IL-21 or CD154 Abs. Results are representative of 2 independent experiments. (B) Percentage of live PCs recovered at 24 hours (□) and 48 hours (▩). (C) Numbers of PCs recovered at 24 hours after culture in the presence of transwells either alone (PC), with T cells (PC + TC) or with T cells separated by transwell. Results of 2 independent experiments shown. (D) The distribution of CD11c⁺ DCs relative to PCs and T cells. Expression of human CD138 (green), CD11c (blue), and CD3 (red) in tonsil, lymph node, and tonsil graft at 4 weeks after surgery. Staining is representative of 3 samples of each tissue, scale bar represents 50 μm. (E) The distance (in μm) of 100 (CD138⁺) PCs to the nearest CD3⁺, CD11c⁺ or CD138⁺ cells was measured in sections of tonsil, LN, and tonsil graft. Mean and SEM are shown. Staining is representative of 4 samples of each tissue type, and scale bar represents 50 μm.