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INDIVIDUAL RESEARCHER

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Current Research

Signaling pathways in macrophage activation Activation of macrophages to produce cytokines, reactive oxygen species and nitric oxide is important for host defense against many pathogens. This laboratory has emphasized signaling via receptors for bacterial lipopolysaccharide (LPS), Toll-like receptor 4, and the IgG antibody receptor, FcgammaR. With regard to cytokines, we have studied the LPS-stimulated secretion of the pro-inflammatory cytokine Interleukin (IL)-12 as well as the anti-inflammatory cytokine, IL-10. Studies with protein kinase C (PKC) inhibitors demonstrated that LPS-stimulated IL-10 secretion was reduced but surprisingly IL-12 secretion was augmented. Just the opposite was observed when PKC activation was enhanced by adding diacylglycerol or ligation of FcgammaR prior to LPS stimulation. Similarly, inhibition of the p42/44 mitogen activated protein kinase (MAPK) reduced IL-10 while augmenting IL-12 secretion. Thus, activation of PKC and p42/44 MAPK augments IL-10 and inhibits IL-12 secretion. We are currently using antisense to evaluate the role individual PKC isoforms in the control of these cytokines. With regard to the production of reactive oxygen species via the NADPH oxidase, we have found that activation of the oxidase by Fc?R ligation required PKC and p42/44 MAPK activation. Further studies demonstrated substantial differences between the signaling for the activation of the NADPH oxidase and induction of nitric oxide production. While PKC inhibitors blocked both bactericidal functions, p42/44 inhibitors blocked only the NADPH oxidase. In addition, FcgammaR ligation alone stimulated the NADPH oxidase but this stimuli only augmented nitric oxide production induced with LPS. Thus, activation of these macrophage functions are mediated by unique signaling pathways. This knowledge may allow each of these functions to be manipulated separately to evaluate their individual roles in the control and treatment of infections.

References

1. Fronhofer V, Lennartz MR, Loegering DJ. Role of PKC isoforms in the FcR-mediated inhibition of LPS-stimulated IL-12 secretion by macrophages. Journal of Leukocyte Biology, 79: 408-415, 2006.



2. Cheeseman, K, Kashiwagi K, Ueyama T, Flax L, Shirai Y, Loegering DJ, Saito N, Lennartz MR.Targeting of PKC-e during FcR-Dependen Phagocytosis Requires the C1B domain and PI-PLC. Molecular Biology of the Cell, 17:799-813, 2006.



3. Ao X, Rotundo RF, Loegering DJ, and Stenken JA, In Vivo Microdialysis Sampling of Cytokines Produced in Mice Given Bacterial Lipopolysaccharide, Journal of Microbiological Methods. 62: 327-336, 2005.



4. Loegering DJ, Lennartz MR: Signalling pathways for Fc receptor-stimuated tumor necrosis factor-secretion and respiratory burst in RAW 264.7 macrophages. Inflammation 28:23-31, 2004.