Defective regulation of CXCR2 facilitates neutrophil release from bone marrow causing spontaneous inflammation in severely NF-κB-deficient mice

NF-κB is a major regulator of innate and adaptive immunity. Neutrophilic granulocytes (neutrophils) constitutively express RelA/ p65 (Rela), c-Rel (Crel), and p50 (Nfκb1) but not p52 (Nfκb2) subunits. In this paper, we describe Crel^-/-Nfκb1^-/-Rela ^+/- mice that have the most severe genetic neutrophil NF-κB deficiency compatible with life, Rela^-/- mice being embryonic lethal. Crel^-/- Nfκb1^-/-Rela^+/- mice developed spontaneous dermal and intestinal inflammation associated with chronic neutrophilia, elevated CXCL1, and G-CSF. The bone marrow contained fewer nucleated cells and was enriched in myeloid progenitor cells. Neutrophilia was preserved when Crel^-/-Nfκb1^-/-Rela^+/- bone marrow was transferred into wild-type mice, but mixed bone marrow chimeras receiving wild-type and Crel^-/-Nfkb1^-/-Rela^+/- bone marrow showed normal circulating neutrophil numbers, excluding an intrinsic proliferation advantage. In mixed bone marrow chimeras, Crel ^-/-Nfκb1^-/-Rela^+/- neutrophils were preferentially mobilized from the bone marrow in response to CXCL1 injection, LPS-induced lung inflammation, and thioglycollate-induced peritonitis. Crel ^-/-Nfκb1^-/-Rela^+/- neutrophils expressed higher levels of the CXCL1 receptor CXCR2 both under resting and stimulated conditions and failed to downregulate CXCR2 during inflammation. Treatment with an anti-CXCR2 Ab abolished preferential mobilization of Crel ^-/-Nfκb1^-/-Rela^+/- neutrophils in peritonitis in mixed chimeric mice and neutrophilia in Crel^-/- Nfκb1^-/-Rela^+/- mice. We conclude that severe NF-κB deficiency facilitates neutrophil mobilization, which causes elevated numbers of preactivated neutrophils in blood and tissues, leading to spontaneous inflammation. These neutrophil effects may limit the usefulness of global NF-κB inhibitors for the treatment of inflammatory diseases.