Rapid down-regulation of the chemokine receptor DARC ex vivo. (A) Double immunofluorescence staining of human tonsil sections with anti-DARC (green) and anti–MECA-79 (red) antibodies reveals coexpression of DARC and MECA-79 antigens in HEVs in situ. (B) Double immunofluorescence staining with anti-DARC (green) and anti–MECA-79 (red) antibodies of stromal cell suspensions obtained from human tonsils and cultured for 24 hours outside the lymphoid tissue microenvironment. DARC protein is expressed at the surface of MECA-79–positive HEVECs within 24 hours of culture. Original magnification, × 20 (A) and × 100 (B). (C) FACS analysis with anti-DARC and anti–MECA-79 antibodies of tonsillar stromal cell suspensions after 24 hours or 48 hours ex vivo. The MECA-79–positive HEVEC population is positive for DARC within 24 hours of culture but becomes negative for DARC after 48 hours.