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PECAM1, also known as CD31 (platelet endothelial cell adhesion molecule 1), is one of the most abundant proteins at the endothelial cell-cell border and a foundational marker used to identify blood vessels in both research and pathology. Although it was cloned and characterized decades ago, the past decade of work has recast PECAM1 from a simple adhesion "glue" into a sophisticated signaling and mechanosensing receptor that coordinates the dialogue between blood, immune cells, and the vessel wall. Expressed not only on endothelial cells but also on platelets, monocytes, neutrophils, and a subset of T cells, PECAM1 sits at the interface where circulating elements meet the endothelium — a position that lets it govern barrier integrity, leukocyte exit, and vascular remodeling. This review surveys its structure, its roles in transmigration and mechanotransduction, its functions beyond the junction in platelets and the brain, and its emerging value as a biomarker and therapeutic node.
PECAM1 is a ~130 kDa type I transmembrane glycoprotein belonging to the immunoglobulin superfamily. Its extracellular region contains six immunoglobulin-like domains, of which the membrane-distal D1 and D2 domains mediate the homophilic, PECAM1-PECAM1 binding that underlies both endothelial cell-cell adhesion and leukocyte-endothelial engagement. The intracellular tail lacks kinase activity but carries immunoreceptor tyrosine-based inhibitory motif (ITIM)-like sequences that, upon phosphorylation, recruit phosphatases such as SHP-2 and transmit modulatory signals. This arrangement means PECAM1 is both an adhesion receptor and a signaling hub. Its expression is remarkably broad across the vasculature: it is concentrated at intercellular junctions of continuous endothelium, present on circulating platelets and leukocytes, and detectable on certain T-cell populations. That distribution is why PECAM1 has become a canonical endothelial identifier in immunohistochemistry and why its biology spans vascular, immune, and hemostatic systems.
Figure 1. Overall structure of PECAM-1 IgL1-2 trans-homophilic dimer.
(Source: Hu M, et al. 2016)
The best-characterized function of PECAM1 is its role in the final step of leukocyte exit from the bloodstream — transendothelial migration, or diapedesis. For years the model was straightforward: PECAM1 on the leukocyte's leading pseudopod engages endothelial PECAM1 at the intercellular border, allowing the cell to slip through the junction. High-resolution live imaging has refined this picture considerably. Work published in 2023 showed that the physical traction a leukocyte exerts on endothelial PECAM1 is sensed through a mechanotransduction complex that includes vascular endothelial growth factor receptor 2 (VEGFR2); endothelial PECAM1 thus acts as a force sensor that converts mechanical tension into a permissive signal for diapedesis. Strikingly, this process required VEGFR2 and phosphorylation of its Y1175 residue but not VEGF ligand or VEGFR2 kinase activity, revealing a ligand-independent scaffolding role. Endothelial-specific deletion of VEGFR2 cut neutrophil extravasation by more than 75% across multiple inflammatory models, establishing the PECAM1-VEGFR2 axis as a discrete, druggable node for selective anti-inflammatory therapy.
Viewed through the lens of mechanotransduction, PECAM1 is less a static anchor and more a tension-gated switch. When a leukocyte pushes against the endothelial border, PECAM1 transmits that force into the cell, where it reorganizes the actin cytoskeleton and licenses junction opening. This explains why PECAM1 engagement reinforces barrier stability under baseline flow yet becomes a gateway during inflammation: the same receptor that "zips" cells together also reports when a cell is trying to leave. The intracellular tail's ITIM-like motifs help convert engagement into phosphatase recruitment, tempering pro-adhesive and pro-survival signals — a built-in brake that balances adhesion with quiescence. Recent structural work dissecting the PECAM1 homophilic binding interface at atomic resolution has clarified how the D1/D2 dimer docks onto a partner molecule and why point perturbations at the interface alter endothelial barrier function, providing a concrete structural basis for the receptor's dual adhesive and signaling lives.
Figure 2. The leukocyte adhesion cascade.
(Source: Shihata WA, et al. 2016)
Beyond the junction, PECAM1 is expressed on platelets and circulating leukocytes, where it participates in thrombosis, wound healing, and developmental vascular patterning. During embryogenesis PECAM1 appears early on angioblasts and persists on all endothelial cells of developing and adult vessels, marking it as one of the most reliable endothelial identifiers in basic research and diagnostic pathology. In platelets, PECAM1 engagement modulates aggregation and granule release, linking endothelial integrity to hemostatic control. Loss-of-function studies reveal that PECAM1 is not strictly required for blood vessel formation but fine-tunes it: without PECAM1, endothelial cell survival, migration, and the organization of the intermediate filament cytoskeleton are perturbed, producing subtle but measurable defects in vascular maturation. These non-junctional functions matter clinically because they connect endothelial adhesion to broader cardiovascular phenotypes, including how vessels respond to injury and remodel after ischemia.
An especially active frontier is PECAM1 at the blood-brain barrier. Brain endothelial cells and perivascular immune cells both express CD31, and a 2023 review argued that endothelial, leukocyte, and soluble forms of CD31 together regulate transendothelial migration, increase BBB permeability, and drive neuroinflammation. The authors proposed that CD31 and its dynamic phosphorylation in brain endothelia contribute to Alzheimer's disease pathogenesis, particularly in ApoE4 carriers — the major genetic risk factor — where peripheral low-grade inflammation may enter the CNS through a "leaky" CD31-gated interface. CD31-mediated pathways modulate Src family kinases, selected G proteins, and β-catenin, which in turn affect cell-cell attachment, activation, permeability, and ultimately neuronal injury. This reframes PECAM1 as a gatekeeper at the brain's border, a conceptually attractive target for neurodegenerative and neuroinflammatory conditions.
Cleavage of surface PECAM1 releases a soluble form (sCD31) into the circulation, and the source of that fragment matters. Full-length, transmembraneless sCD31 is produced mainly by endothelial cells and reflects endothelial turnover, whereas truncated shed forms arise from activated platelets and leukocytes during inflammation and thrombosis. A 2025 study showed that leukocyte-shed soluble CD31 can unmask coronary disease even in individuals judged low-risk by classical factors, and that source-specific soluble CD31 signatures track vulnerable plaques. This is significant because generic assays that cannot distinguish the forms may miss the signal — a reminder that the biology of the molecule, not just its presence, carries diagnostic value. As a vascular biomarker, sCD31 sits at the intersection of endothelial health, thrombo-inflammation, and atherosclerotic risk.
The clinical relevance of PECAM1 keeps widening. In atherosclerosis, CD31 biology is implicated in both plaque stability and the thrombo-inflammatory state of the vessel wall; source-resolved soluble CD31 adds a layer of risk stratification beyond traditional inflammatory markers. In acute lung injury and acute respiratory distress syndrome, where alveolar-capillary barrier breakdown and excessive neutrophil migration are central, PECAM1's dual role in permeability and transmigration makes it a plausible contributor and target. Blocking PECAM1 has been shown to reduce neutrophil recruitment and tissue injury across several inflammatory models, and PECAM1-deficient mice show attenuated leukocyte infiltration and foreign-body inflammation with reduced angiogenesis. These findings reframe endothelial junctions as active participants in, not mere victims of, disease.
Manipulating PECAM1 offers several angles. Disrupting the PECAM1-VEGFR2 mechanotransduction axis could blunt leukocyte extravasation with greater selectivity than broad immunosuppressants, potentially benefiting autoimmune, atherosclerotic, and ischemia-inflammation conditions. Stabilizing endothelial PECAM1 homophilic engagement might reinforce barrier function in sepsis, ischemia-reperfusion, and inflammatory injury. For oncology, the opposite logic applies: since PECAM1 supports tumor angiogenesis and vessel formation, tempering its adhesive or survival signals could starve pathological neovessels. The chief hurdle is context dependence — the same receptor that must be sealed in sepsis must be opened to heal a wound — so biomarkers that report PECAM1 state in real time will be essential to time and target these interventions. Source-specific soluble CD31 assays are a first step in that direction.
References
| Target | Cat. No. | Product Name | Size | Species | Application | Detection Sample | |
| PECAM1 | DEIA-BJ2240 | Rat Pecam1(Platelet endothelial cell adhesion molecule) ELISA Kit | 96T | Rat | Quantitative | Serum, plasma, tissue homogenates, other biological fluids | Inquiry |
| DEIA235 | Human Platelet/Endothelial Cell Adhesion Molecule, PECAM1 ELISA Kit | 5 plates | Human | Quantitative | Plasma, tissue homogenates and other biological fluids. | Inquiry | |
| DEIA9556 | Human PECAM1 ELISA Kit | 96T | Human | Quantitative | Serum, plasma, buffered solutions, cell culture medium | Inquiry | |
| CKERS-PECAM1-231H | Human Platelet/Endothelial Cell Adhesion Molecule, PECAM1 ELISA Kit | 5 plates | Quantitative | Inquiry |
| Target | Cat. No. | Product Name | Expression System | Tag/Conjugate | Application | |
| PECAM1 | DAG-P0329 | Human PECAM1 peptide | N/A | Unconjugated | ELISA | Inquiry |
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