The motheaten mouse has long served as a paradigm for complex autoimmune and inflammatory disease. Null mutations in Ptpn6, which encodes the nonreceptor protein-tyrosine phosphatase Shp1, cause the motheaten phenotype. However, Shp1 regulates multiple signaling pathways in different hematopoietic cell types, so the cellular and molecular mechanism of autoimmunity and inflammation in the motheaten mouse has remained unclear. By using floxed Ptpn6 mice, we dissected the contribution of innate immune cells to the motheaten phenotype. Ptpn6 deletion in neutrophils resulted in cutaneous inflammation, but not autoimmunity, providing an animal model of human neutrophilic dermatoses. By contrast, dendritic cell deletion caused severe autoimmunity, without inflammation. Genetic and biochemical analysis showed that inflammation was caused by enhanced neutrophil integrin signaling through Src-family and Syk kinases, whereas autoimmunity resulted from exaggerated MyD88-dependent signaling in dendritic cells. Our data demonstrate that disruption of distinct Shp1-regulated pathways in different cell types combine to cause motheaten disease.