Comparative study and effects of macrophage colony-stimulating factor (M-CSF) administration on NK1.1+ cells in mouse spleen and bone marrow

An Epstein-Barr virus encoded inhibitor of Colony Stimulating Factor-1 signaling is an important determinant for acute and persistent EBV infection

Acute Epstein-Barr virus (EBV) infection is the most common cause of Infectious Mononucleosis. Nearly all adult humans harbor life-long, persistent EBV infection which can lead to development of cancers including Hodgkin Lymphoma, Burkitt Lymphoma, nasopharyngeal carcinoma, gastric carcinoma, and lymphomas in immunosuppressed patients. BARF1 is an EBV replication-associated, secreted protein that blocks Colony Stimulating Factor 1 (CSF-1) signaling, an innate immunity pathway not targeted by any other virus species. To evaluate effects of BARF1 in acute and persistent infection, we mutated the BARF1 homologue in the EBV-related herpesvirus, or lymphocryptovirus (LCV), naturally infecting rhesus macaques to create a recombinant rhLCV incapable of blocking CSF-1 (ΔrhBARF1). Rhesus macaques orally challenged with ΔrhBARF1 had decreased viral load indicating that CSF-1 is important for acute virus infection. Surprisingly, ΔrhBARF1 was also associated with dramatically lower virus setpoints during persistent infection. Normal acute viral load and normal viral setpoints during persistent rhLCV infection could be restored by Simian/Human Immunodeficiency Virus-induced immunosuppression prior to oral inoculation with ΔrhBARF1 or infection of immunocompetent animals with a recombinant rhLCV where the rhBARF1 was repaired. These results indicate that BARF1 blockade of CSF-1 signaling is an important immune evasion strategy for efficient acute EBV infection and a significant determinant for virus setpoint during persistent EBV infection.

Epstein-Barr virus (EBV) is a herpesvirus that persistently infects nearly all humans by adulthood. Acute and persistent phases of EBV infection are associated with a variety of human diseases, including infectious mononucleosis and cancer. To investigate how EBV interacts with the host to successfully establish acute and persistent infection, we combined the power of the rhesus macaque animal model for EBV infection with genetic engineering of the EBV-related herpesvirus, or lymphocryptovirus (LCV), that naturally infects rhesus macaques. We created a recombinant rhLCV carrying a mutated EBV BARF1 homologue, a replication-associated viral protein that is secreted and blocks Colony Stimulating Factor-1 (CSF-1) signaling, a cytokine important for innate immunity. Oral inoculation of rhesus macaques showed that the virus' ability to block CSF-1 was important for achieving the normally high viral loads during acute infection, and surprisingly, was also needed to establish normal levels of virus infection, or viral setpoint, during persistent infection. These studies show that virus-mediated interruption of innate immunity is critical for both acute and persistent phases of EBV infection. Understanding how EBV successfully infects humans and how the natural history of EBV infection can be disrupted will aid in development of vaccines to prevent EBV-associated diseases.

Therapeutic applications of macrophage colony-stimulating factor-1 (CSF-1) and antagonists of CSF-1 receptor (CSF-1R) signaling

Macrophage-colony stimulating factor (CSF-1) signaling through its receptor (CSF-1R) promotes the differentiation of myeloid progenitors into heterogeneous populations of monocytes, macrophages, dendritic cells, and bone-resorbing osteoclasts. In the periphery, CSF-1 regulates the migration, proliferation, function, and survival of macrophages, which function at multiple levels within the innate and adaptive immune systems. Macrophage populations elicited by CSF-1 are associated with, and exacerbate, a broad spectrum of pathologies, including cancer, inflammation, and bone disease. Conversely, macrophages can also contribute to immunosuppression, disease resolution, and tissue repair. Recombinant CSF-1, antibodies against the ligand and the receptor, and specific inhibitors of CSF-1R kinase activity have been each been tested in a range of animal models and in some cases, in patients. This review examines the potential clinical uses of modulators of the CSF-1/CSF-1R system. We conclude that CSF-1 promotes a resident-type macrophage phenotype. As a treatment, CSF-1 has therapeutic potential in tissue repair. Conversely, inhibition of CSF-1R is unlikely to be effective in inflammatory disease but may have utility in cancer.

Production of interferon-gamma by myeloid cells--fact or fancy?

Myeloid cells are usually viewed as targets rather than producers of interferon (IFN)-gamma. However, since 1993 several studies have suggested that macrophages and dendritic cells can also secrete IFN-gamma in response to various stimuli, which led to the idea of autocrine myeloid-cell activation in innate immunity. Here, we review this concept in the light of recent findings that illustrate the necessity of specific cell markers, cell purity, sensitive single-cell cytokine detection methods, and of further insights into the developmental origin of myeloid and lymphoid cell lineages. We also discuss the possible function of intracellular IFN-gamma in macrophages and the evidence for a protective role of myeloid IFN-gamma in vivo.

Minute numbers of contaminant CD8+ T cells or CD11b+CD11c+ NK cells are the source of IFN-gamma in IL-12/IL-18-stimulated mouse macrophage populations

Macrophages were reported to be strong producers of interferon gamma (IFN-gamma) after stimulation by interleukin 12 (IL-12) plus IL-18, which gave rise to a novel concept of auto-crine macrophage activation. Here, we show that peritoneal exudate and bone marrow-derived mouse macrophages generated by conventional techniques contain small quantities of CD11b(+)CD11c(+)CD31(+)DX5(+)NK1.1(+) natural killer (NK) cells or CD3(+)CD8(+)TCRbeta(+) T cells, respectively. Intracellular cytokine staining, purification of macrophages by sorting, and the analysis of macrophages from alymphoid RAG2(-/-)gamma-chain(-/-) mice revealed that the high amount of IFN-gamma protein in the supernatants of unseparated IL-12/IL-18-stimulated macrophage populations originates exclusively from the contaminating lymphoid cells. Notably, IL-12/IL-18 still induced IFN-gamma mRNA in highly purified macrophages from wild-type mice and in macrophages from RAG2(-/-)gamma-chain(-/-) mice, whereas nuclear translocation of signal transducer and activator of transcription 4 (STAT4) and production of IFN-gamma protein were no longer detectable. These results question the concept of autocrine macrophage activation by secreted IFN-gamma, suggest differences in the expression of IFN-gamma mRNA and protein between macrophages and lymphoid cells, and illustrate that the limited purity of most myeloid cell populations (</= 98%) might lead to false conclusions.

Administration of macrophage colony-stimulating factor mobilized both CD11b+CD11c+ cells and NK1.1+ cells into peripheral blood

We attempted the phenotypic characterization of peripheral blood (PB) cells after daily administration of macrophage colony-stimulating factor (M-CSF) in mice. The number of CD11b+ cells was increased by M-CSF treatment (2- and 5-day injections). Notably, CD11bbrightCD11cdim, CD11b+CD11c+ and CD11b+CD80+ cells were significantly increased by 2-day treatment of M-CSF. On the other hand, the number of NK1.1+ cells was not changed by the 2-day treatment, but it was significantly increased by the 5-day treatment. However, the numbers of CD3+ and NK1.1+CD3+ cells were not changed by M-CSF treatment. Then, mononuclear cells (MNCs) were separated from the PB of mice treated with saline or M-CSF, and they were incubated with GM-CSF + IL-4 or IL-2. Compared with the saline-treated one (S-MNCs), the MNCs of M-CSF-treated mice (M-MNCs) showed strong proliferation by the GM-CSF + IL-4 stimulation. The MNCs could stimulate proliferation of allo-T cells in the mixed lymphocyte reaction (MLR), especially the M-MNCs showed strong reaction. On the other hand, the stimulation by IL-2 induced strong cell growth of MNCs. And M-CSF treatment enhanced this response. Furthermore, the M-MNCs (stimulated by IL-2 in vitro) exhibited greater cytotoxicity against Yac-1 cells than the S-MNCs. In conclusion, we found that administration of M-CSF mobilized CD11b+, CD11b+CD11c+, CD11b+CD80+, and NK1.1+cells into PB. And the injection of M-CSF facilitates the generation of dendritic and natural killer cells from PB cells in vitro. These results suggest that the mobilized cells may provide for application of immunotherapy.