Mice were euthanized by CO 2 inhalation. Tissues were collected and fixed in 4% paraformaldehyde overnight. Immunohistochemical staining was performed on 5 mm thick sections prepared from formalin fixed, paraffin-embedded blocks. Sections were deparaffinized in xylene and rehydrated in a graded alcohol series. Slides were quenched in 3% hydrogen peroxide, steamed for antigen retrieval in DIVA/citrate buffer (pH 6. media. Blood smears on positive charged glass slides (Surgipath, Richmond, IL), fixed in methanol for 15 sec and stained as above. Mouse anti-human IgG1 (eBioscience, San Diego, CA) was used as an isotype control.