These mice have a neo cassette disrupting exons 2-3 of the macrophage migration inhibitory factor (glycosylation-inhibiting factor) (MIf) gene, abolishing gene expression. MIF is a lymphokine involved in cell-mediated immunity, immunoregulation, and inflammation. It plays a role in the regulation of macrophage function. Mice that are homozygous null for the Mif gene are viable and fertile. No Mif gene product (mRNA or protein) is detected. While null mice exhibit signs of endotoxemia in response to intraperitoneally injected LPS (25 mg/kg), they are resistant to its lethal effects. Plasma levels of tumor necrosis factor alpha assayed after LPS administration is half that observed in wildtype mice. The Jackson Laboratory 2024, used with permission.