Differentiation of monocytes to macrophages primes cells for lipopolysaccharide stimulation via accumulation of cytoplasmic nuclear factor kappa B

During infection, circulating blood monocytes migrate from the vasculature to the extravascular compartments where they mature into tissue macrophages . The maturation process prepares the cell to actively participate in the i nflammatory and the immune responses, and many transcription factors have b een found to be involved. Here we report on a novel role for nuclear factor kappa B (NF-kappa B) in this process. Its accumulation in the cytoplasm of differentiated macrophages is responsible for the enhanced ability of the cell to respond to lipopolysaccharide (LPS) stimulation, as determined by t umor necrosis factor alpha (TNF-alpha) secretion. Differentiation of the hu man monocytic cell line THP-1 into macrophage-like cells was induced by exp osure of the cells to phorbol myristate acetate. DNA-bindable NF-kappa B wa s not detected in the cytoplasm of undifferentiated THP-1 cells but accumul ated in the cytoplasm of the cells following differentiation. No TNF-alpha was detected in the media of resting differentiated and nondifferentiated T HP-1 cells. Stimulation with LPS of differentiated cells induced the produc tion of higher levels of TNF-alpha than stimulation of nondifferentiated ce lls. This hyperresponsiveness to LPS was found in the mRNA and secreted TNF -alpha levels. Furthermore, stimulation with LPS induced the translocation of NF-kappa B from the cytoplasm into the nucleus. This translocation proce ss was more rapid in the differentiated cells than in the nondifferentiated cells, and the resultant accumulated levels of NF-kappa B in the nucleus w ere higher. The DNA-bindable NF-kappa B was identified as a heterodimer of p65 and p50. The results suggest that NF-kappa B accumulation in the cytopl asm during maturation of monocytes to macrophages primes the cells for enha nced responsiveness to LPS and results in the rapid secretion of inflammato ry mediators, such as TNF-alpha, by mature macrophages following LPS challe nge.