All transmembrane FcRLs contain ITIMs and/or ITAMs in their intracytoplasmic domain
All transmembrane FcRLs contain ITIMs and/or ITAMs in their intracytoplasmic domain. Immunoreceptor tyrosine-based inhibition motifs, Innate immunity, Lymphoid cells, Myeloid cells, Negative regulation, Positive regulation == From Fc Receptors to Fc Receptor-Like Molecules == The concept of receptors for the Fc portion of immunoglobulins arose in the 1960s to explain cell-mediated biological activities of antibodies. Opsonins indeed enabled antigen to enter phagocytic cells (Berken and Benacerraf, 1966); cytophilic antibodies sensitized tissues that released histamine upon antigen challenge (Bloch, 1967); distinct classes of antibodies differentially regulated secondary antibody responses (Henry and Jerne, 1968). These biological effects requiring the Fc portion of antibodies, the name Fc receptor (FcR) was coined (Paraskevas Baloxavir marboxil et al., 1972). FcRs for various antibody classes were identified as binding sites on a variety of cells (Vaughan and Boyden, 1964;Kulczycki and Baloxavir marboxil Metzger, 1974;Unkeless et al., 1988). FcRs were characterized functionally and biochemically (Holowka et al., 1980;Ernst et al., 1993;Pfefferkorn and Yeaman, 1994). Murine and human cDNAs encoding FcRs were cloned, sequenced, and expressed by transfection (Ravetch and Kinet, 1991); corresponding genes were located on chromosomes and their exon/intron organization was elucidated (Qiu et al., 1990). The extracellular domains of FcRs were recognized as members of the immunoglobulin superfamily (IgSF) (Williams and Barclay, 1988); amino acid sequences enabling them to interact with antibodies, extracellularly (Hulett and Hogarth, 1994), and to signal, intracellularly (Daron, 1997), were dissected; the 3D-structure of their extracellular domains in complex with immunoglobulin Fc portions was solved (Garman et al., 1998;Maxwell et al., 1999). Finally, a collection of genetically modified FcR knock out (KO), knock in (KI), and transgenic mice was generated that enabled FcR functions to be delineatedin vivo(Smith et al., 2012). FcRs thus appeared as a family of functionally, structurally, and genetically related molecules that play major roles in antibody-dependent processes in physiology, in pathology, and, with the advent of passive immunotherapy, in therapeutics. Genes encoding FcR-related molecules were unexpectedly discovered, clustered with humanFCRgenes (according to the usual Rabbit polyclonal to ZNF540 typographic convention, protein names are in roman type, whereas gene names are in italics; names of human genes are in upper case, whereas names of murine genes are in lower case), in the early 1990s (Imboden et al., 1989;Seaman et al., 1991). Similar genes were found in the same clusters as mousefcrgenes (Figure 1). A whole family of putative Fc receptor-like molecules (FcRLs the abbreviation FcRL is used instead of FCRL for consistency with FcR) thus emerged (Davis et al., 2001;Hatzivassiliou et al., 2001), whose existence was progressively confirmed (Li et al.,2014). As FcRLs originated from genetic studies, much less is known of their biological functions, compared to FcRs. A syntenic chromosomal linkage, a similar genetic organization, a common membership Baloxavir marboxil of the IgSF suggest that FcRLs may be functionally related to FcRs. Supporting this assumption, both FcRs and FcRLs possess immunoreceptor tyrosine-based activation motifs (ITAMs), like B cell and T cell receptors (BCR and TCR) for antigen (Reth, 1989), and/or immunoreceptor tyrosine-based inhibition motifs (ITIMs), like inhibitory receptors expressed by natural killer (NK) cells (Vivier and Daron, 1997). FcRs and FcRLs therefore belong to the immunoreceptor family. Differences in their structure, ligands, and pattern of expression, however, indicate that FcRs and FcRLs play distinct, complementary roles. == Figure 1. == Human and murine Fc receptor (FcR) and Fc receptor-like molecule (FcRL) genes. Organization of the genes encoding FcRs (red) and FcRLs (blue) in humans and mice, on their respective chromosomes (Chr.) (Davis.