Diversity of Human Immune System Multigene Families and its Implication in the Genetic Background of Rheumatic Diseases

Naoyuki      Tsuchiya; Chieko      Kyogoku; Risa      Miyashita; Kimiko      Kuroki

Abstract

A large number of molecules in the immune system are encoded by multigene families. These genes are rich in pairs of activating and inhibitory receptors that share the same ligands, thereby playing a crucial role in immunoregulation. Furthermore, multigene families tend to be highly polymorphic. Thus, multigene families are strong candidates for containing genes that enhance susceptibility to immune system-related diseases. Here, we review studies from our group, as well as other investigators, on three multigene families that belong to the immunoglobulin (Ig) - like receptor superfamily: Fcγ receptor (FCGR), killer cell Ig-like receptor (KIR) and leukocyte Ig-like receptor (LILR) families. FCGR genes have been implicated in susceptibility to systemic lupus erythematosus (SLE). In FCGR2B encoding an inhibitory receptor expressed in B cells, monocytes and dendritic cells, a polymorphism within the transmembrane region, Ile232Thr, was identified and found to be associated with susceptibility to SLE in three Asian populations. Functional analyses revealed that SLE-associated FcγRIIb-232Thr was less efficient in entering the membrane lipid raft, and exhibited reduced inhibitory potential against B cell receptor signaling. Although the frequency of this polymorphism was low in Caucasians, another polymorphism within the promoter region was reported to be associated with SLE. KIR/HLA combinations have been shown to be associated with various autoimmune and infectious diseases. Recently, LILR families have also been found to be highly polymorphic, and association with several diseases has been identified. These results emphasize the role of multigene families in the diversity of human immune response and susceptibility to diseases.

Keywords: Fcg receptor (FCGR), killer cell Ig-like receptor (KIR), leukocyte Ig-like receptor (LILR), polymorphism, systemic lupus erythematosus, rheumatoid arthritis, susceptibility

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