Neutrophil Functions and Autoimmune Arthritis in the Absence of p190RhoGAP: Generation and Analysis of a Novel Null Mutation in Mice

Abstract

β2 integrins of neutrophils play a critical role in innate immune defense, but they also participate in tissue destruction during autoimmune inflammation. p190RhoGAP (ArhGAP35), a regulator of Rho family small GTPases, is required for integrin signal transduction in fibroblasts. Prior studies have also suggested a role for p190RhoGAP in β2 integrin signaling in neutrophils. To directly test that possibility, we have generated a novel targeted mutation completely disrupting the p190RhoGAP-encoding gene in mice. p190RhoGAP deficiency led to perinatal lethality and defective neural development, precluding the analysis of neutrophil functions in adult p190RhoGAP−/− animals. This was overcome by transplantation of fetal liver cells from p190RhoGAP−/− fetuses into lethally irradiated wild-type recipients. Neutrophils from such p190RhoGAP−/− bone marrow chimeras developed normally and expressed normal levels of various cell surface receptors. Although p190RhoGAP−/− neutrophils showed moderate reduction of β2 integrin-mediated adherent activation, they showed mostly normal migration in β2 integrin-dependent in vitro and in vivo assays and normal β2 integrin-mediated killing of serum-opsonized Staphylococcus aureus and Escherichia coli. A neutrophil- and β2 integrin-dependent transgenic model of the effector phase of autoimmune arthritis also proceeded normally in p190RhoGAP−/− bone marrow chimeras. In contrast, all the above responses were completely blocked in CD18−/− neutrophils or CD18−/− bone marrow chimeras. These results suggest that p190RhoGAP likely does not play a major indispensable role in β2 integrin-mediated in vitro and in vivo neutrophil functions or the effector phase of experimental autoimmune arthritis.