Human CD84/SLAMF5 Fluorescein-conjugated Antibody

The CD2 family receptors are type I transmembrane glycosylated proteins belonging to the immunoglobulin (Ig) superfamily. They are characterized by an extracellular region containing an N-terminal variable (V) Ig domain lacking disulfide bonds and a truncated Ig constant 2 (C2) domain with two disulfide bonds (1). CD84, also known as Ly-9B, is a member of the CD150/SLAM (signaling lymphocyte activation molecule) subfamily of the CD2 family and is designated SLAMF5 (2). The SLAM family, comprising at least nine members, is defined by the presence of at least two immunoreceptor tyrosine-based switch motifs (ITSM) in the intracellular region. The ITSM motifs interact with the SH2 (Src homology 2) domain of cytoplasmic adaptor molecules SAP (SLAM-associated protein) and EAT-2 (EWS/FliI-activated transcript 2) to transduce SLAM family receptor-mediated signals (2). SLAM family receptors are thought to mediate cell adhesion in the immune synapse between T cells and antigen-presenting cells to modulate immune responses. Human CD84 cDNA encodes a 328 amino acid residue (aa) precursor protein with a 21 aa signal peptide and a 199 aa extracelllular domain (3). It is expressed on B and T cells, monocytes, granulocytes, committed hematopoietic progenitor cells, and platelets (3, 4). CD84 is self-associating. The homotypic CD84-CD84 interaction requires only the first N-terminal Ig V domain (4). In T cells, CD84 has been found to act as a co-stimulatory molecule, enhancing anti-CD3 induced IFN-gamma production in lymphocytes and increasing anti-CD3 induced proliferation in PHA T cells blasts (4, 5). In B cells, CD84 is differentially expressed, with the CD84^hi B cells representing a subset of memory B cells (6). While ligation of CD84 in the memory B cells leads to the recruitment of SAP and EAT-2, the exact role CD84 has in memory B cell function remains to be determined. Human and mouse CD84 share approximately 57% aa sequence identity.