PROTEIN-KINASE-C REGULATES MACROPHAGE TUMOR-NECROSIS-FACTOR SECRETION- DIRECT PROTEIN-KINASE-C ACTIVATION RESTORES TUMOR-NECROSIS-FACTOR PRODUCTION IN ENDOTOXIN TOLERANCE

Background. Macrophages pretreated in vitro with endotoxin (LPSp) secr ete less tumor necrosis factor (TNF) in response to a second LPS activ ating (LPSa) stimulus. Protein kinase C (PKC) is required for TNF secr etion in a macrophage stimulated with LPSa. In these experiments we ex amined the role of PKC in TNF signal transduction in naive and toleran t macrophages. Methods. Murine macrophages were cultured +/- LPSp for 24 hours. Cultures were washed and treated for 1 hour with PKC inhibit ors or phorbol myristate acetate (PMA), a direct PKC activator. Cells were then stimulated with a range of LPSa for 6 hours, and TNF was det ermined by bioassay. Results. LPSa-stimulated TNF secretion by nontole rant macrophages was inhibited by LPSp in the absence of PAS. PKC inhi bitors decreased TNF naive macrophages and exaggerated inhibition in t olerant cells. Depletion of PKC by 24 hours of PMA decreased TNF produ ction by both naive and tolerant macrophages. PKC activation with PMA 1 hour before LPSa augmented TNF secretion in naive cells and reversed TNF inhibition of tolerant cells. Conclusions. Direct PKC activation with PMA restored TNF secretion in LPS-tolerant macrophages. Endotoxin tolerance may alter the LPSa signal transduction pathway between the LPS receptor and PKC activation.