IKBKB and periventricular leukomalacia: To determine the relevance of NF-κB inhibition in myeloid cells mainly microglia in PVL pathology, we crossed mice with conditional mutant of IKKb (IKKbf/f), which have exon 3 of the ikbkb (IKKb) gene flanked by loxP sites to a strain expressing cre recombinase driven by the promoter for the gene c-fms, which encodes colony stimulating factor receptor 1 (CSF-1R).