Immunohistochemistry of frozen sections from several tissues. Note the intense staining of myeloid cells in bone marrow (BM) and the red pulp of the spleen (SPL), and in addition, the labeling of blood and lymphatic vessels clearly seen in lymphoid tissues (Peyer patches [PP], thymus and lymph node [LN] stained with an anti–VCAM-1 antibody, as described in “Materials and methods”). Slides were permanently mounted, and photographs were taken using a Nikon COOLPIX 995 digital camera (Nikon USA, Melville, NY) with an adapter that fits into the eyepiece of an Olympus BH-2 microscope (Olympus America, Melville, NY). A 10×/0.25 objective was used for all except the sections from thymus, for which a 20×/0.40 objective was used. These were transferred directly to the computer, and Photoshop 7.0 (Adobe Systems, San Jose, CA) was used to adjust brightness, contrast, and color balance.