Immunostaining of normal hematopoietic tissue and appendix for the T- and B-cell-associated transmembrane adaptor proteins. LAT, LIME, and TRIM: These molecules are all expressed in T-cell areas in tonsil (note unstained high endothelial venules, arrow) but are absent from both mantle zone (MZ) B cells and germinal center (GC) cells in B-cell secondary lymphoid follicles (the staining for LAT and LIME seen in GCs represents T cells). Plasma cells underlying the tonsil epithelium express LIME but not LAT or TRIM. LAT, LIME, and TRIM are also all expressed both in medullary (M) thymocytes surrounding Hassall corpuscles (HC) and in immature T cells in cortical (C) lobules. Tissue sections of the appendix show that intraepithelial T lymphocytes are positive for LAT and TRIM but negative for LIME. NTAL: B cells in the germinal centers (GC) and mantle zones (MZ) of secondary lymphoid follicles express NTAL, and this molecule is also found in plasma cells and monocytoid B cells (in a lymph node affected by toxoplasmosis). The thymus, in contrast, shows only scattered NTAL⁺ cells in the medulla (M) surrounding a Hassall corpuscle (HC) and no labeling in the thymic cortex (C). PAG: This molecule is absent from mantle zone (MZ) B cells but is found on germinal center (GC) B cells and monocytoid B cells. It is also expressed more weakly in T cells in tonsil and the thymic medulla. The immature T cells in the thymic cortex (C) are even more weakly labeled. SIT: This molecule is weakly expressed in the tonsil in GC B cells and in T cells (seen at higher magnification in the adjacent image). SIT is strongly expressed by plasma cells (arrow in the low-power view of the tonsil) and in immature T cells in the thymic cortex. (All staining performed on paraffin sections by the immunoperoxidase technique. Images were acquired using a Nikon Eclipse E800 microscope [Nikon, Tokyo, Japan] and a Zeiss Axiocam digital camera [Zeiss, Oberkochen, Germany], using a 10×/0.45 Plan Apo or a 20×/0.75, 40×/0.95, or 60×/1.4 Plan Fluor objective lens [Zeiss] Axiovision 3 image acquisition software [Zeiss] and Adobe Photoshop 7 image processing and manipulation software (Adobe, San Jose, CA) were also used.)