Fc receptors and their role in immune regulation and autoimmunity.

The activation threshold of cells in the immune system is often tuned by cell surface molecules. The Fc receptors expressed on various hematopoietic cells constitute critical elements for activating or downmodulating immune responses and combines humoral and cell-mediated immunity. Thus, Fc receptors are the intelligent sensors of the immune status in the individual. However, impaired regulation by Fc receptors will lead to unresponsiveness or hyperreactivity to foreign as well as self-antigens. Murine models for autoimmune disease indicate the indispensable roles of the inhibitory Fc receptor in the suppression of such disorders, whereas activating-type FcRs are crucial for the onset and exacerbation of the disease. The development of many autoimmune diseases in humans may be caused by impairment of the human Fc receptor regulatory system. This review is aimed at providing a current overview of the mechanism of Fc receptor-based immune regulation and the possible scenario of how autoimmune disease might result from their dysfunction.