CR2 and systemic lupus erythematosus: Indeed, data generated using mice deficient in the Cr2 gene (encoding both mouse CR1 and CR2 through alternative splicing; Cr2−/− (Kurtz et al., 1990; Molina et al., 1990)), appeared to confirm that both these proteins were important in the development of auto-antibodies in lupus susceptible mice (Wu et al., 2002).