This strain is also called p55/p75-KO. The Tnfrsf1a and Tnfrsf1b double knockout mouse models were obtained by knocking out both exon 2-5 region of mouse Tnfrsf1a gene and exon2 of mouse Tnfrsf1b gene. Tnfrsf1a and Tnfrsf1b deletion (p55 and p75 deficiency) homozygous mice are viable and fertile, and these homozygous mice fail to bind TNF (tumor necrosis factor).