A junctional adhesion molecule (JAM) is a protein that is a member of the immunoglobulin superfamily,[1][2] and is expressed in a variety of different tissues, such as leukocytes, platelets, and epithelial and endothelial cells.

[6] Two JAM molecules contain N-terminal domains that react in a highly complementary fashion due to prolific ionic and hydrophobic interactions.

It commonly consists of Arg58-Val59-Glu60 located on the N-terminus and can dissociate into monomers based on the conditions of the solution it is exposed to.

[10] JAM-2 has also shown to act as a ligand for many immune cells, and plays a role in lymphocyte attraction to specific organs.

[10] JAM-3 functions similarly to JAM-2 as it is localized around the tight junctions of epithelial and endothelial cells, but has been shown to be unable to adhere to leukocytes in the manner that other JAMs can.

Vitronectin is a ligand for integrins αvβ3 and αvβ5, which exhibit selective cooperativity with bFGF and VEGF in the activation of the MAPK pathway.

[3] In the absence of JAM-1, these leukocytes cannot moderate β1 integrin endocytosis, and cannot be effectively expressed on the surface of the cell (which is essential for motility).

[8] Recent studies have also pointed to JAM-1 preserving structural integrity of tissues more so than regulating cell number.

JAMs play a significant role in many diverse physiological processes within the human body, including: Tight junctions serve to provide most of the function for the barrier that is present on epithelial cell surfaces.

Studies have shown that proteins found in tight junctions serve as intermediaries that moderate angiogenic signaling pathways.

Within the Sertoli cells of the male reproductive system, JAM-3 interacts with JAM-2 to influence the polarity of both round and elongated spermatids.