In vivo biotinylation of the bloodstream-accessible tissue compartment in a syngeneic mouse model of B-cell lymphoma. (A) Healthy and lymphoma-bearing mice were subjected to the terminal perfusion with a reactive ester derivative of biotin, leading to the covalent modification of proteins accessible from the bloodstream. Tumors and corresponding normal organs were excised and homogenized for the preparation of total protein extracts. Biotin-tagged proteins were enriched on streptavidin Sepharose, on-resin digested with trypsin, resulting peptides were separated by nanocapillary reverse-phase HPLC, and submitted to the comparative proteomic analysis. (B) Streptavidin-based detection of biotinylated structures (green) in perfused lymphoma tissues harvested from liver, lymph nodes, and spleen, in relation to vascular endothelium (CD31, red). Scale bars represent 50 μm.