Interferon inducible GBPs restrict Burkholderia thailandensis motility induced cell-cell fusion.

Innate immunity responds to pathogens by producing alarm signals and activating pathways that make host cells inhospitable for pathogen replication. The intracellular bacterium Burkholderia thailandensis invades the cytosol, hijacks host actin, and induces cell fusion to spread to adjacent cells, forming multinucleated giant cells (MNGCs) which promote bacterial replication. We show that type I interferon (IFN) restricts macrophage MNGC formation during B. thailandensis infection. Guanylate-binding proteins (GBPs) expressed downstream of type I IFN were required to restrict MNGC formation through inhibition of bacterial Arp2/3-dependent actin motility during infection. GTPase activity and the CAAX prenylation domain were required for GBP2 recruitment to B. thailandensis, which restricted bacterial actin polymerization required for MNGC formation. Consistent with the effects in in vitro macrophages, Gbp2-/-, Gbp5-/-, GbpChr3-KO mice were more susceptible to intranasal infection with B. thailandensis than wildtype mice. Our findings reveal that IFN and GBPs play a critical role in restricting cell-cell fusion and bacteria-induced pathology during infection.

T lymphocyte regulation by mevalonate metabolism.

Whereas resting T cells, which have low metabolic requirements, use oxidative phosphorylation (OXPHOS) to maximize their generation of ATP, activated T cells, similar to tumor cells, shift metabolic activity to aerobic glycolysis, which also fuels mevalonate metabolism. Both sterol and nonsterol derivatives of mevalonate affect T cell function. The intracellular availability of sterols, which is dynamically regulated by different classes of transcription factors, represents a metabolic checkpoint that modulates T cell responses. The electron carrier ubiquinone, which is modified with an isoprenoid membrane anchor, plays a pivotal role in OXPHOS, which supports the proliferation of T cells. Isoprenylation also mediates the plasma membrane attachment of the Ras, Rho, and Rab guanosine triphosphatases, which are involved in T cell immunological synapse formation, migration, proliferation, and cytotoxic effector responses. Finally, multiple phosphorylated mevalonate derivatives can act as danger signals for innate-like γδ T cells, thus contributing to the immune surveillance of stress, pathogens, and tumors. We highlight the importance of the mevalonate pathway in the metabolic reprogramming of effector and regulatory T cells.

Zoledronic acid, an aminobisphosphonate, modulates differentiation and maturation of human dendritic cells.

Zoledronic acid (ZOL), an effective nitrogen-containing bisphosphonate against excessive bone loss, has been shown affecting the function of cells of both innate and acquired immunity. In this study, we tested the effect of ZOL on differentiation and maturation of human myeloid dendritic cells (DC). When ZOL (1.1 to 10 microM) was added to the culture of starting monocytes, but not to immature DC, the recovery rate of DC was markedly reduced in a concentration-dependent manner. The mature DC differentiated in the presence of ZOL had fewer and shorter cell projections. ZOL treatment affected DC differentiation and maturation in terms of lower expression of CD1a, CD11c, CD83, CD86, DC-SIGN, HLA-DR, and, in contrast, higher expression of CD80. IL-10 production by DC was inhibited by ZOL treatment whereas IL-12p70 secretion remained unchanged. Interestingly, ZOL augmented the allostimulatory activity of DC on naive CD4(++)CD45(+)RA(++) T cells in terms of their proliferation and interferon-gamma production. Addition of geranylgeraniol abrogated the effect of ZOL on DC differentiation and prenylation of Rap1A. It suggests that ZOL redirects DC differentiation toward a state of atypical maturation with allostimulatory function and this effect may go through prevention of Rap1A prenylation.

Nonpeptide antigens, presentation mechanisms, and immunological memory of human Vgamma2Vdelta2 T cells: discriminating friend from foe through the recognition of prenyl pyrophosphate antigens.

Human Vgamma2Vdelta2 T cells play important roles in mediating immunity against microbial pathogens and have potent anti-tumor activity. Vgamma2Vdelta2 T cells recognize the pyrophosphorylated isoprenoid intermediates (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), an intermediate in the foreign 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway, and isopentenyl pyrophosphate (IPP), an intermediate in the self-mevalonate pathway. Infection with bacteria and protozoa using the MEP pathway leads to the rapid expansion of Vgamma2Vdelta2 T cells to very high numbers through preferential recognition of HMBPP. Activated Vgamma2Vdelta2 T cells produce proinflammatory cytokines and chemokines, kill infected cells, secrete growth factors for epithelial cells, and present antigens to alphabeta T cells. Vgamma2Vdelta2 T cells can also recognize high levels of IPP in certain tumors and in cells treated with pharmacological agents, such as bisphosphonates and alkylamines, that block farnesyl pyrophosphate synthase. Activated Vgamma2Vdelta2 T cells are able to kill most tumor cells because of recognition by T-cell receptor and natural killer receptors. The ubiquitous nature of the antigens converts essentially all Vgamma2Vdelta2 T cells to memory cells at an early age. Thus, primary infections with HMBPP-producing bacteria are perceived by Vgamma2Vdelta2 T cells as a repeat infection. Extensive efforts are underway to harness these cells to treat a variety of cancers and to provide microbial immunity.

Direct tumor lysis by NK cells uses a Ras-independent mitogen-activated protein kinase signal pathway.

Destruction of tumor cells is a key function of lymphocytes, but the molecular processes driving it are unclear. Analysis of signal molecules indicated that mitogen-activated protein kinase (MAPK)/extracellular regulated kinase 2 critically controlled lytic function in human NK cells. We now have evidence to indicate that target ligation triggers a Ras-independent MAPK pathway that is required for lysis of the ligated tumor cell. Target engagement caused NK cells to rapidly activate MAPK within 5 min, and PD098059 effectively blocked both MAPK activation and tumoricidal function in NK cells. Target engagement also rapidly activated Ras, detected as active Ras-GTP bound to GST-Raf-RBD, a GST fusion protein linked to the Raf protein fragment containing the Ras-GTP binding domain. However, Ras inactivation by pharmacological disruption with the farnesyl transferase inhibitor, FTI-277, had no adverse effect on the ability of NK cells to lyse tumor cells or to express MAPK activation upon target conjugation. Notably, MAPK inactivation with PD098059, but not Ras inactivation with FTI-277, could interfere with perforin and granzyme B polarization within NK cells toward the contacted target cell. Using vaccinia delivery of N17 Ras into NK cells, we demonstrated that IL-2 activated a Ras-dependent MAPK pathway, while target ligation used a Ras-independent MAPK pathway to trigger lysis in NK cells.