CD84 functions as a homophilic adhesion molecule and enhances IFN-gamma secretion: adhesion is mediated by Ig-like domain 1.
CD84 is a member of the CD2 subset of the Ig superfamily of cell surface molecules. Its cytoplasmic tail binds to Src homology 2 domain-containing protein 1A (signaling lymphocytic activation molecule-associated protein), a protein encoded by the X-linked lymphoproliferative disease gene. It is preferentially expressed on B lymphocytes, monocytes, and platelets. We show that it is also expressed on thymocytes and T cells. CD84 was positive on CD4-CD8- thymocytes, and its expression decreased with cell maturation. It is expressed on mature T cells preferentially on CD45RO+. To identify the CD84 ligand, we generated a soluble Ig fusion protein containing the human CD84 extracellular domains (CD84-Ig). Because receptor-ligand interactions occur between several members of this subfamily, we assayed CD84- Ig binding with all members of the CD2 family. CD84- Ig bound to CD84-transfected cells, whereas no binding was detected with cells expressing other CD2 subfamily receptors, showing that CD84 binds to itself. Anti-CD84 mAbs recognizing epitopes wholly within domain 1 of CD84 blocked the binding of the CD84- Ig fusion protein to CD84-transfected cells and platelets. Data from CD84 domain human/mouse chimeras further revealed that only the first extracellular domain of the molecule is involved in the ligand receptor recognition. The CD84-CD84 interaction was independent of its cytoplasmic tail. Finally, concurrent ligation of human CD84 with mAbs or CD84- Ig and CD3 enhanced IFN-gamma secretion in human lymphocytes. Thus, CD84 is its own ligand and acts as a costimulatory molecule.[1]References
- CD84 functions as a homophilic adhesion molecule and enhances IFN-gamma secretion: adhesion is mediated by Ig-like domain 1. Martin, M., Romero, X., de la Fuente, M.A., Tovar, V., Zapater, N., Esplugues, E., Pizcueta, P., Bosch, J., Engel, P. J. Immunol. (2001) [Pubmed]
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