Immunofluorescent histology of LNs and spleens from hu-mice. Tissue sections were stained with Abs against mCD45 (green) and hCD45 (blue) (left panels), or hCD3 (red) and hCD20 (blue) (right panels). Representative sections of a human spleen (top panel), of spleens from hu-mice of categories I, II, IV and V (as described in Fig. 2A), and of LN tissue from a hu-mouse of category IV are shown. Sections shown are 10X magnifications and are representative of at least two samples from a minimum of 3 mice per category, with the exception of category II (high B cell numbers) that represents only one sample. The human spleen section is representative of more than 8 sections from two individuals.