Early biochemical events during macrophage activation.

The roles of cyclic AMP-dependent protein kinase (cA-PK) and ornithine decarboxylase (ODC) in the induction of macrophage (M(phi)) activation have been studied. The relationship of early changes in these biochemical parameters to changes in RNA and DNA synthesis has been evaluated. Three M(phi) systems, adherent peptone-elicited peritoneal exudate cells (PEC) from C3H-HeN mice and two murine M(phi) tumor cell lines, have been utilized in these studies. The M(phi) tumor cell lines were the J774.1 representing an activated M(phi) and the PU5-1.8 representing a M(phi) of the monocyte types. The activating agents utilized in this research included BCG cell wall material (BCGcw), lipopolysaccharides from E. Coli (LPS) and the synthetic adjuvant, N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP). Additional studies assessed the effects of prostaglandins of the E series (PGE), cyclic AMP analogs (8 Bromo-cAMP, 8-BrcAMP) and a phosphodiesterase inhibitor (methyl-isobutyl-xanthine, MIX) on the induction of ODC in macrophages. BCGcw, MDP and LPS promoted a dose dependent increase in ODC activity that reached a maximum within 4 hours in each M(phi) system. Two lines of evidence suggest a role for cAMP in the induction of ODC. BCGcw and PGE were able to activate cA-PK within 2 hours in all three M(phi) systems. The increase in cA-PK activity preceeded the maximum in ODC activity observed in each M(phi) system. In addition, ODC activity was induced or enhanced in the macrophage cell line by PGE, 8-BrcAMP and MIX agents known to increase intracellular cAMP. The early increases in cA-PK and ODC in response to BCGcw are associated temporally with an increase in RNA synthesis in all three systems. Increases in protein synthesis are also evident in response to BCGcw in each system. The changes observed in cA-PK activity, ODC activity, RNA synthesis and protein synthesis in response to an activating agent are believed to be associated with an induction of protein synthetic events which are involved in M(phi) activation. Two observations supported the concept that M(phi) activation includes a change in specific cell functions and protein synthetic events. First, BCGcw and other immunoactivators decrease cell proliferation and DNA synthesis in J774.1 and PU5-1.8 cells. Second, PEC undergo similar biochemical changes and can be stimulated to increase production of a specific protein, such as arginase. In fact, all of the M(phi) systems studied are known to respond to activating agents by increasing protein synthesis. In summary, these results indicate that an activation of cA-PK and induction of ODC are early biochemical markers of the activation process in M(phi). A role for cAMP in some critical step(s) involved in the activation process is inferred by these results.