Immunohistochemical analysis of MARCO expression in vivo. Frozen sections (7 μm) of spleens from mice kept in pathogen-free (A) or in conventional (B) animal house conditions were double stained with anti-CD11c (green) for DC identification and anti-MARCO ED31 (red) mAbs. Stained sections were analyzed by confocal microscopy. MARCO and CD11c double-positive cells (yellow) were present in spleens only of animals maintained in conventional animal house conditions (B). Original magnification, × 400.