Targeted Mutation of TNF Receptor I Rescues the RelA-Deficient Mouse and Reveals a Critical Role for NF-κB in Leukocyte Recruitment

Abstract

NF-κB binding sites are present in the promoter regions of many acute phase and inflammatory response genes, suggesting that NF-κB plays an important role in the initiation of innate immune responses. However, targeted mutations of the various NF-κB family members have yet to identify members responsible for this critical role. RelA-deficient mice die on embryonic day 15 from TNF-α-induced liver degeneration. To investigate the importance of RelA in innate immunity, we genetically suppressed this embryonic lethality by breeding the RelA deficiency onto a TNFR type 1 (TNFR1)-deficient background. TNFR1/RelA-deficient mice were born healthy, but were susceptible to bacterial infections and bacteremia and died within a few weeks after birth. Hemopoiesis was intact in TNFR1/RelA-deficient newborns, but neutrophil emigration to alveoli during LPS-induced pneumonia was severely reduced relative to that in wild-type or TNFR1-deficient mice. In contrast, radiation chimeras reconstituted with RelA or TNFR1/RelA-deficient hemopoietic cells were healthy and demonstrated no defect in neutrophil emigration during LPS-induced pneumonia. Analysis of RNA harvested from the lungs of mice 4 h after LPS insufflation revealed that the induction of several genes important for neutrophil recruitment to the lung was significantly reduced in TNFR1/RelA-deficient mice relative to that in wild-type or TNFR1-deficient mice. These results suggest that TNFR1-independent activation of RelA is essential in cells of nonhemopoietic origin during the initiation of an innate immune response.

NF-κB and the immune response

“…Thus, rela À/À /tnfr1 À/À double knockout mice have increased susceptibility to bacterial infection (Alcamo et al, 2001). Likewise, B cells from p50 À/À mice do not respond efficiently to LPS, emphasizing the importance of p50-containing complexes, that is, p50/RelA, p50/ p50/BCL-3 and p50/c-Rel, in TLR signaling .…”

“…NF-kB regulates the expression of adhesion molecules, both on leukocytes and endothelial cells, which allow the extravasation of leukocytes from the circulation to the site of infection (Eck et al, 1993). Indeed, RelA-deficient mice display a severe defect in the recruitment of circulating leukocytes to sites of inflammation (Alcamo et al, 2001).…”

Crosstalk via the NF-κB signaling system

“…Initially, the embryonic lethality of rela -/-mice due to massive hepatocyte apoptosis (Beg et al, 1995) revealed a novel function of RelA:p50 as an anti-apoptotic regulator but presented obstacles for genetically assessing RelA's function in the immune system. When the lethality was rescued upon combined inactivation of the gene encoding TNFR1, the resulting rela -/-tnfr1 -/-mice showed an increased susceptibility to bacterial infection and succumbed to neonatal death (Alcamo et al, 2001). Radiation chimeras that were reconstituted with RelA/ TNFR1 deficient hematopoietic cells, also indicated a role for RelA in mounting immune responses.…”

NF‐κB as a potential molecular target for cancer therapy

“…Moreover, embryonic lethality observed in RelA-/-mice also occurs in mice deficient in IKKβ or IKKγ [82,122]. The insult leading to liver apoptosis was shown to be TNF-α signaling in the developing liver, as crossing RelA-/-mice with either TNFα-/-or TNFR-/-mice rescued this liver phenotype [1,32]. Although TNF-α activates caspases responsible for the initiation and execution of apoptosis, the concurrent activation of NF-κB abrogates TNF-α's pro-apoptotic activity, because NF-κB also targets genes coding for inhibitors of caspase activation and apoptosis.…”