Expression of type XV collagen in HEVs in vivo and its rapid down-regulation in cultured HEVECs. (A) In situ hybridization analysis (original magnification, × 40) of type XV collagen mRNA in human tonsils reveals an expression pattern similar to that of DARC. Cryosections were hybridized with type XV collagen or DARC sense and antisense riboprobes. (B) In situ hybridization (original magnification, × 40) with type XV collagen antisense riboprobe (left) followed by immunostaining with the HEV-specific mAb MECA-79 (right) demonstrates expression of type XV collagen mRNA in MECA-79–positive HEVs. (C) Semiquantitative RT-PCR analysis of type XV collagen down-regulation in cultured HEVECs after 48 hours ex vivo (D2 HEVECs) compared with freshly isolated HEVECs (D0 HEVECs). Amplification of GAPDH mRNA was used as an internal control. (D) Comparison of type XV collagen mRNA levels in D0 HEVECs, D2 HEVECs, and D0-HUVECs by real-time quantitative RT-PCR. β-actin mRNA was used as a standard. Standard deviations are shown; N.D. indicates not detected.