Lipopolysaccharide (LPS) and zymosan-resistant mutant isolated from a macrophage-like cell line, WEHI-3, with a defective response to LPS under serum-free conditions

A LPS-resistant mutant, W3SF-1, was isolated from a murine macrophage-like cell line, WEHI-3. The W3SF-1 mutant did not produce a significant amount o f nitric oxide (NO) or TNF-alpha even with high concentrations of LPS in th e presence or absence of FCS, whereas the parental WEHI-3 cells produced th em in response to LPS. The parental cells expressed a significant level of TNF-alpha mRNA after LPS stimulation, whereas the mutant cells did not. Thi s defective response of the mutant cells to LPS was neither dependent on th e concentration or chemical structure of LPS, nor on the time of LPS treatm ent. The mutant cells also showed a defective response to zymosan, suggesti ng that the defect in the mutant cells is common to LPS and zymosan in the signal transduction pathways. The parental and mutant cells showed similar levels of Mac1, F4/80 and CD14, suggesting that these surface markers of ma crophages are not linked directly to the defective responses of the mutant to LPS. The treatment of mutant cells with IFN-gamma did not restore the de fect of NO or TNF-alpha production on LPS treatment. Binding experiments wi th I-125-labelled LPS showed a similar binding affinity for LPS in the pare ntal and the mutant cells. These results suggest that the defect in the W3S F-1 mutant cells may not reside in the LPS binding but rather in the early step of signal transduction pathways in the cells after LPS binding.