Interestingly, Cad−/− mice have no overt phenotype; mice lacking DNAse II, the enzyme that degrades the chromatin of engulfed cells in macrophages, die because of constitutive production of interferon β [25], and Dnase2−/− Ifnar1−/− double mutant mice (that survive excessive interferon β production because they lack the receptor) develop chronic polyarthritis [26]. The gene discussed is IFNAR1; the disease is polyarticular arthritis.