It was noted, however, that the SLE phenotype found in the first described Dnase1 KO mice of mixed 129xBL/6J F2 genetic background depended on additional pre-disposing genes and/or environmental factors, since it does not occur in pure 129 or C57BL/6J mice under specific pathogen-free conditions [31, 32]. This evidence concerns the gene DNASE1 and systemic lupus erythematosus.