In the current study, we explored the role of TNF cluster cytokines on the lipopolysaccharide (LPS)-mediated, synergistic increase in brain injury after hypoxic ischemic insult in postnatal day 7 mice. Pretreatment with moderate doses of LPS (0.3 g/g) resulted in particularly pronounced synergistic injury within 12 h. Systemic application of LPS alone resulted in a strong upregulation of inflammation-associated cytokines TNFα, LTΒ, interleukin (IL) 1Β, IL6, chemokines, such as CXCL1, and adhesion molecules E-Selectin, P-Selectin and intercellular adhesion molecule-1 (ICAM1), as well as a trend toward increased LTα levels in day 7 mouse forebrain. In addition, it was also associated with strong activation of brain blood vessel endothelia and local microglial cells. Here, deletion of the entire TNF gene cluster, removing TNFα, LTΒ and LTα completely abolished endotoxin-mediated increase in the volume of cerebral infarct. Interestingly, the same deletion also prevented endothelial and microglial activation following application of LPS alone, suggesting the involvement of these cell types in bringing about the LPS-mediated sensitization to neonatal brain injury. © 2011 USCAP, Inc All rights reserved.