Adhesion Molecule Pecam-1/CD31 is Expressed on Defined Subsets of Murine Lak Cells

Platelet-Endothelial Cell Adhesion Molecule (PECAM-1/CD31) is a member of the immunoglobulin gene superfamily 1. It consists of six extracellular C2-like immunoglobulin domains and reveals extensive homology with Carcino-Embryonic Antigen (CEA) and Intracellular Cell Adhesion Molecule-1 (ICAM-1)1. It is a type I transmembrane protein, carrying an 118aa cytoplasmic tail. PECAM-1 /CD31 is present not only on platelets and endothelia but also on monocytes, granulocytes and lymphocytes, predominantly of the naive phenotype1–7. It stabilizes cell-cell contacts between endothelial cells, activates high affinity states of in-tegrins on lymphocytes 3,7 ,and participates in the sequential adhesive events leading to arrest and extravasation of blood-borne cells into tissues 5. Here, we describe the distribution of PECAM-1/CD31 on different subsets of murine LAK cells using the monoclonal antibody EA-3. LAK cells, a heterogeneous mixture of IL-2 activated T- and NK-like cells, have been shown to reduce the number of metastases8–10 and to infiltrate into sites of lesions of established metastases 11, 12. On LAK cells, PECAM-1/CD31 has been shown to participate in the activation of high-affinity states of the integrin LFA-1 13. It is therefore conceivable that CD31+ LAK cells have advantages in infiltrating tumorous tissues.