Abnormal regulation of the cytoskeletal regulator Rho typifies macrophages of the major murine models of spontaneous autoimmunity.

Macrophages (mphi) from prediseased mice of all the major murine models of spontaneous autoimmunity have an identical defect in cytokine expression that is triggered by serum and/or apoptotic cells. We show here that mphi from prediseased mice of the same models of spontaneous autoimmunity share a serum-dependent defect in the activity of Rho, a cytoplasmic G protein and cytoskeletal regulator. Affected strains include those developing lupus (BXSB, LG, MRL/l+, MRL/lpr, NZBWF1) and autoimmune diabetes (nonobese diabetic). No similar defect in Rho activity occurred in seven control strains. In the presence of serum, Rho activity in mphi from all autoimmune-prone strains was reduced to less than 10% of that in control mice. In contrast, under serum-free conditions, Rho activity was completely normal in autoimmune-prone mphi. The activities of Ras, another cytoplasmic G protein, and Rac and Cdc42, two additional G protein regulators of the cytoskeleton, were regulated normally in autoimmune-prone strains. Serum-dependent dysregulation of Rho was associated with multiple abnormalities, including increased adhesion to various surfaces, a more spread dendritic morphology, and an altered actin cytoskeletal organization. Our results suggest that mphi from multiple, genetically diverse, autoimmune-prone strains share a mutation or allelic difference affecting signal transduction within a specific Rho-regulatory pathway.