Regulation of signal transduction by the Fc gamma receptor family members and their involvement in autoimmunity.

Recent studies on the nature and mode of action of inhibitory receptors and their intracellular phosphatase effector enzymes have identified a new area of research in the etiology of autoimmune diseases. Myeloid cells play a critical role in autoimmunity through their IgG receptors. A number of recent findings reveal that such cells express inhibitory receptors, including the elusive CD32/Fc gamma RIIB isoform, and express inhibitory phosphatases like SHP-1 and SHIP. Animals lacking the effector phosphatases exhibit a pronounced autoimmune and/or pro-inflammatory phenotype. Animals deficient in the expression of the inhibitory receptors often display a much less severe phenotype, likely due to the fact that hematopoietic cells have numerous and probably redundant inhibitory receptors. Genetic deficiencies in the limited number of effector molecules (SHP-1 and SHIP) lead to more dramatic effects on hematopoietic cells and level of inflammation in such animals. These recent findings in animal models open the intriguing possibility that the human homologues of genes encoding the inhibitory receptors like Fc gamma RIIB or effector phosphatases like SHIP might contribute to autoimmune diseases. However, while identification of genes involved in autoimmunity will greatly aid in diagnosis of human autoimmune disease, it is necessary to understand the biochemical mechanisms of action of the numerous inhibitory receptors and phosphatases in the hematopoietic system. Such information will permit the rational design of more efficient and effective treatments for patients. Additional experiments directed at the role and mechanism(s) of action of the inhibitory phosphatases SHP-1 and SHIP will uncover new candidates for diagnosis and treatment of autoimmune diseases.