Low relative expression of PECAM-1 mRNA within nonresolving human thrombi. The figure shows real-time PCR analysis of CTEPH thrombi (n = 6) and nonresolving DVT thrombi (n = 3) compared with pulmonary artery (n = 4). Chronic nonresolving thrombi are characterized by significant downregulation of PECAM-1 mRNA (normalized to 18S ribosomal RNA). PA, pulmonary artery.