p50 (NF-kappa B1) is upregulated in LPS tolerant P388D1 murine macrophages.

Cells of the murine macrophage cell line P388D1 express cell surface CD14 and respond to LPS (lipopolysaccharide) stimulation with the production of TNF (tumor necrosis factor). When the cells are stimulated with LPS a second time then little TNF is produced, i.e. the cells are tolerant. Flow cytometry analysis demonstrates that this tolerance is not due to a downregulation of the CD14 cell surface receptor. Analysis of proteins binding to the -516 NF-kappa B motif of the murine TNF promoter reveals that constitutive p50p50 and LPS stimulation lead to mobilization of a heterodimer consisting of p65/c-rel. In tolerant cells less of the p65/c-rel heterodimer is mobilized but there is a strong upregulation of p50p50. These data show that tolerance to LPS in murine macrophages may involve a predominance of p50 homodimers.