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J. Cell Biol.,
Volume 142, Number 1, July 13, 1998 117-127





* Istituto di Ricerche Farmacologiche Mario Negri, 20157 Milano, Italy; Tight junctions are the most apical components of endothelial and epithelial intercellular cleft. In
the endothelium these structures play an important role
in the control of paracellular permeability to circulating
cells and solutes. The only known integral membrane
protein localized at sites of membrane-membrane interaction of tight junctions is occludin, which is linked inside the cells to a complex network of cytoskeletal and
signaling proteins. We report here the identification of a
novel protein (junctional adhesion molecule [JAM]) that
is selectively concentrated at intercellular junctions of
endothelial and epithelial cells of different origins. Confocal and immunoelectron microscopy shows that JAM
codistributes with tight junction components at the apical region of the intercellular cleft. A cDNA clone encoding JAM defines a novel immunoglobulin gene
superfamily member that consists of two V-type Ig
domains. An mAb directed to JAM (BV11) was found
to inhibit spontaneous and chemokine-induced monocyte transmigration through an endothelial cell monolayer in vitro. Systemic treatment of mice with BV11 mAb blocked monocyte infiltration upon chemokine administration in subcutaneous air pouches. Thus, JAM is
a new component of endothelial and epithelial junctions
that play a role in regulating monocyte transmigration.
Institute of Molecular Medicine, University of Oxford,
John Radcliffe Hospital, Headington, Oxford, OX3 9DU, United Kingdom; § Dipartimento di Farmacologia, Universita degli
Studi di Milano, and DIBIT, Milano, Italy 20129; and
Universita' degli Studi La Sapienza, Dipartimento di Medicina
Sperimentale e Patologia, 00161 Roma, Italy
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