The complex role of Fcγ receptors in the pathology of arthritis

Autoantibodies of the IgG class and the immune complexes they form are central players in the pathology of rheumatoid arthritis (RA). Receptors for the Fc part of IgG, Fc gamma R constitute one of the main effector mechanisms through which IgG immune complexes exert their action. The different members of the Fc gamma R family exhibit extensive structural homology leading to redundancy in ligand specificity and signal transduction. Moreover, the initiation of effector mechanisms by IgG immune complexes can also be mediated by the complement system. This strong redundancy and high degree of complexity hampers a direct in vivo analysis of antibody effector pathways. Over the last decade, mice deficient for different combinations of Fc gamma R have been generated by gene targeting. These knockout mice provide excellent tools to define the specific contribution of the different Fc gamma R to IgG effector pathways in well-established in vivo mouse models for arthritis. This review will discuss the results of the studies that analyze the role of the different members of the Fc gamma R family in murine arthritis models and their implications for our understanding of the human disease.