LPS stimulation of TNF-receptor deficient macrophages: a differential rolefor TNF-alpha autocrine signaling in the induction of cytokine and nitric oxide production

To evaluate the role of autocrine TNF-alpha signaling in macrophage activat ion immortalized macrophages from normal mice (B6/J2) and from mice contain ing gene targeted disruptions of the type 1 and type 2 TNF-receptor genes ( TRN) were stimulated under CD14-dependent or serum-free conditions. Althoug h the B6/J2 and TRN clones mounted similar nitric oxide responses to LPS in the presence of serum, the TRN macrophages responded poorly when stimulate d with LPS under serum free conditions. LPS stimulation of TRN and B6/J2 un der serum-free conditions resulted in equivalent levels of IL-1 beta, TNF-a lpha, and iNOS gene expression. However, Western blot analysis revealed tha t iNOS protein production by TRN was 2-fold lower than that produced by B6/ J2. These results indicate that autocrine TNF-alpha stimulation contributes to the signaling pathways initiated by ligation of LPS receptors in the ab sence of LBP and is involved in iNOS post-transcriptional regulation.