Expression of SIRPβ2 in lymph nodes and thymus. (A) SIRPβ2 is mainly expressed in the paracortical area (PC) of lymph nodes with only sparse positive cells in the mantle and in the germinal center (GC) of B-cell follicles. (B-C) Two-color immunofluorescence of lymph nodes with mAbs anti-SIRPβ2 (B) (green) and anti-CD3 (red) (C). The large majority of lymph node SIRPβ2⁺ cells, including those found in the germinal center, coexpress CD3. (D) Two-color immunofluorescence of a lymph node shows diffuse expression of SIRPβ2 in lymphocytes of the T-cell area (green), clustered around scattered CD11c⁺ DCs (red). Cell-cell interactions between SIRPβ2⁺ lymphocytes and CD11c⁺ DCs appear as yellow dots (arrowheads and insert). HEV indicates high endothelial venule. (E) SIRPβ2⁺ lymphocytes are numerous in the thymic medulla (M) and scattered in the cortex (C). SIRPβ2 was detected by indirect immunoperoxidase technique and counterstaining with Meyer hematoxylin (A,E). Scale bars are 200 μm (A-C,E) and 100 μm (D). Magnification is 100 × (A-C,E) and 200 × (D).