Macrophages play an important role in the pathogenesis of chronic colitis. However, it remains unknown how macrophages residing in the colonic lamina propria are regulated. We characterized colonic lamina proprial CD11b-positive cells (CLPMφ). CLPMφ of wild-type mice, but not IL-10-deficient mice, displayed hyporesponsiveness to TLR stimulation in terms of cytokine production and costimulatory molecule expression. We compared CLPMφ gene expression profiles of wild-type mice with IL-10-deficient mice, and identified genes that are selectively expressed in wild-type CLPMφ. These genes included nuclear IκB proteins such as Bcl-3 and IκBNS. Because Bcl-3 has been shown to specifically inhibit LPS-induced TNF-α production, we analyzed the role of IκBNS in macrophages. Lentiviral introduction of IκBNS resulted in impaired LPS-induced IL-6 production, but not TNF-α production in the murine macrophage cell line RAW264. 7. IκBNS expression led to constitutive and intense DNA binding of NF-κB p50/p50 homodimers. IκBNS was recruited to the IL-6 promoter, but not to the TNF-α promoter, together with p50. Furthermore, small interference RNA-mediated reduction in IκBNS expression in RAW264. 7 cells resulted in increased LPS-induced production of IL-6, but not TNF-α. Thus, IκBNS selectively suppresses LPS-induced IL-6 production in macrophages. This study established that nuclear IκB proteins differentially regulate LPS-induced inflammatory cytokine production in macrophages.