TOLERANCE TO LIPOPOLYSACCHARIDE IN HUMAN BLOOD MONOCYTES

When monocytes are stimulated with Lipopolysaccharide (LPS), they effi ciently produce cytokines like tumor necrosis factor (TNF). Upon secon dary stimulation, this response is only minimal, and there is little T NF: mRNA transcription, mRNA accumulation, and protein production. Stu dies with the monocytic cell line Mono Mac 6 have shown that in such t olerant cells the CD14 LPS receptor is still present, and the transcri ption factor NF-kB is still efficiently mobilized. This NF-kB complex has, however, a different composition, that does not transactivate TNF promoter reportergene constructs. We now show that similar mechanisms apply to primary blood monocytes. After primary stimulation these cel ls also produce high levels of TNF and then develop tolerance in that upon secondary challenge little TNF is produced. CD14 cell surface exp ression is unchanged or even increased in tolerant cells and NF-kB mob ilization does still occur. The complex mobilized in such tolerant mon ocytes is, however, composed mainly of high mobility binding proteins. This indicates that p50 homodimers predominate in NF-kB complex of to lerant blood monocytes, similar to what has been reported for Mono Mac 6 cells. The data add to the notion that p50 binding to the cognate - kB DNA motif in the TNF promoter may be responsible for the unresponsi veness in LTS tolerance.