TLR-4 Agonist Induces IFN-γ Production Selectively in Proinflammatory Human M1 Macrophages through the PI3K-mTOR– and JNK-MAPK–Activated p70S6K Pathway

Abstract

IFN-γ, a proinflammatory cytokine produced primarily by T cells and NK cells, activates macrophages and engages mechanisms to control pathogens. Although there is evidence of IFN-γ production by murine macrophages, IFN-γ production by normal human macrophages and their subsets remains unknown. Herein, we show that human M1 macrophages generated by IFN-γ and IL-12– and IL-18–stimulated monocyte-derived macrophages (M0) produce significant levels of IFN-γ. Further stimulation of IL-12/IL-18–primed macrophages or M1 macrophages with agonists for TLR-2, TLR-3, or TLR-4 significantly enhanced IFN-γ production in contrast to the similarly stimulated M0, M2a, M2b, and M2c macrophages. Similarly, M1 macrophages generated from COVID-19–infected patients’ macrophages produced IFN-γ that was enhanced following LPS stimulation. The inhibition of M1 differentiation by Jak inhibitors reversed LPS-induced IFN-γ production, suggesting that differentiation with IFN-γ plays a key role in IFN-γ induction. We subsequently investigated the signaling pathway(s) responsible for TLR-4–induced IFN-γ production in M1 macrophages. Our results show that TLR-4–induced IFN-γ production is regulated by the ribosomal protein S6 kinase (p70S6K) through the activation of PI3K, the mammalian target of rapamycin complex 1/2 (mTORC1/2), and the JNK MAPK pathways. These results suggest that M1-derived IFN-γ may play a key role in inflammation that may be augmented following bacterial/viral infections. Moreover, blocking the mTORC1/2, PI3K, and JNK MAPKs in macrophages may be of potential translational significance in preventing macrophage-mediated inflammatory diseases.

The evolution of powerful yet perilous immune systems

“…Multicellular organisms face an additional obstacle because their defenses arise from a multitude of cells, each of which has both limited information and limited agency [ 4 , 57 , 58 ], but which together form the powerful, perilous collective. TLR signaling and induced cytokine secretion, for example, occur at a cellular scale [e.g., TLR-2, -3, or -4 agonists induce interferon (IFN)-γ production by human M1-like inflammatory macrophages in vitro [ 59 ]], but affect fitness at the organismal scale (e.g., strong IFN-γ responsiveness is essential for controlling chronic pulmonary aspergillosis and extending the life of human patients [ 60 ]). Similarly, sensitive cellular detection of LPS by a wide array of host species [ 61 ] may translate into disastrously potent cytokine responses and life-threatening septic shock at the organismal scale (e.g., in C57BL/6 mice injected with LPS [ 62 ]).…”

A virulence factor as a therapeutic: the probiotic Enterococcus faecium SF68 arginine deiminase inhibits innate immune signaling pathways

“… 81 More recently, innate immune signaling through TLR4, the LPS receptor, has also been found to involve mTORC1/2 and the JNK and MAPK pathways. 82 We suggest that all of the observations from both this study and prior in vitro and in vivo studies can be explained by ADI-dependent depletion of arginine pools and inactivation of mTORC1 of host cells, with the possible qualification that it would likely be a localized effect in vivo, i.e . affecting intestinal epithelia and gut-associated immune cell populations, rather than systemic effects.…”

Exploring Pro-Inflammatory Immunological Mediators: Unraveling the Mechanisms of Neuroinflammation in Lysosomal Storage Diseases

“…The activation of mTOR (mechanistic target of rapamycin), LAT (linker for activation of T cells), PI3K (phosphoinositide 3-kinase), AKT (protein kinase B), JNK (c-Jun N-terminal kinases), RIP3K (receptor-interacting protein kinase 3), ERK (extracellular signal-regulated kinase), and p38-MAPK (p38 mitogen-activated protein kinases) signaling causes the massive production of IFN-α, IFN-β, IFN-γ, IL1 α, IL1 β, TNF α, IL6, IL12, IL17, and C5a [ 325 , 326 , 327 , 328 , 329 , 330 , 331 , 332 , 333 , 334 , 335 , 336 , 337 ]. Studies have demonstrated the involvement of several of the signaling cascades in lysosomal storage diseases, particularly in the context of disease pathogenesis and potential therapeutic targets.…”