Granulocyte macrophage colony stimulating factor exerts dominant effects over macrophage colony stimulating factor during macrophage differentiation in vitro to induce an inflammatory phenotype

BACKGROUND

Macrophages (Mφ) can exist along a spectrum of phenotypes that include pro-inflammatory (M1) or anti-inflammatory (M2) immune cells. Mφ colony stimulating factor (M-CSF) and granulocyte Mφ colony stimulating factor (GM-CSF) are cytokines important in hematopoiesis, polarization and activation of Mφ.

METHODS AND RESULTS

To gain a greater understanding of the relationship between GM-CSF and M-CSF, we investigated an in vitro model of differentiation to determine if GM-CSF and M-CSF can antagonize each other, in terms of Mφ phenotype and functions. We determined that Mφ cultured in mixed M-CSF: GM-CSF ratios exhibit M1-like GM-CSF-treated macrophage phenotype when the ratios of the two cytokines are 1:1 in culture. Moreover, GM-CSF is dominant over M-CSF in influencing Mφ production of proinflammatory cytokines such as IL-6, TNFα, and IL-12p40, and the anti-inflammatory cytokine IL-10.

CONCLUSIONS

Our data established that GM-CSF is more dominant over M-CSF, triggering the Mφ to become pro-inflammatory cells. These findings provide insight into how GM-CSF can influence Mφ activation with implications in inflammatory diseases where the Mφ status can play a significant role in supporting the inflammatory conditions.

Genomic and transcriptomic characterization of delta SARS-CoV-2 infection in free-ranging white-tailed deer (Odocoileus virginianus)

White-tailed deer (WTD) are susceptible to SARS-CoV-2 and represent an important species for surveillance. Samples from WTD (n = 258) collected in November 2021 from Québec, Canada were analyzed for SARS-CoV-2 RNA. We employed viral genomics and host transcriptomics to further characterize infection and investigate host response. We detected Delta SARS-CoV-2 (B.1.617.2) in WTD from the Estrie region; sequences clustered with human sequences from October 2021 from Vermont, USA, which borders this region. Mutations in the S-gene and a deletion in ORF8 were detected. Host expression patterns in SARS-CoV-2 infected WTD were associated with the innate immune response, including signaling pathways related to anti-viral, pro- and anti-inflammatory signaling, and host damage. We found limited correlation between genes associated with innate immune response from human and WTD nasal samples, suggesting differences in responses to SARS-CoV-2 infection. Our findings provide preliminary insights into host response to SARS-CoV-2 infection in naturally infected WTD.

Corrigendum: M(IL-4) tissue macrophages support efficient interferon-gamma production in antigen-specific CD8+ T cells with reduced proliferative capacity

[This corrects the article DOI: 10.3389/fimmu.2017.01629.].

The Activated Macrophage - A Tough Fortress for Virus Invasion: How Viruses Strike Back

Macrophages (Mφ) are innate immune cells with a variety of functional phenotypes depending on the cytokine microenvironment they reside in. Mφ exhibit distinct activation patterns that are found within a wide array of activation states ranging from the originally discovered classical pro-inflammatory (M1) to the anti-inflammatory (M2) with their multi-facades. M1 cells are induced by IFNγ + LPS, while M2 are further subdivided into M2a (IL-4), M2b (Immune Complex) and M2c (IL-10) based on their inducing stimuli. Not surprisingly, Mφ activation influences the outcome of viral infections as they produce cytokines that in turn activate cells of the adaptive immune system. Generally, activated M1 cells tend to restrict viral replication, however, influenza and HIV exploit inflammation to support their replication. Moreover, M2a polarization inhibits HIV replication at the post-integration level, while HCMV encoded hrIL-10 suppresses inflammatory reactions by facilitating M2c formation. Additionally, viruses such as LCMV and Lassa Virus directly suppress Mφ activation leading to viral chronicity. Here we review how Mφ activation affects viral infection and the strategies by which viruses manipulate Mφ polarization to benefit their own fitness. An understanding of these mechanisms is important for the development of novel immunotherapies that can sway Mφ phenotype to inhibit viral replication.

Sustained IL-4 priming of macrophages enhances the inflammatory response to TLR7/8 ligand R848

Macrophages (Mϕ) are highly plastic, and can acquire a variety of functional phenotypes depending on the presence of different stimuli in their local environment. Mφ stimulated by interleukin (IL)-4 induce an alternative activation state and function as anti-inflammatory cells and promote tissue repair. However, there is overwhelming evidence that IL-4 can play a role in promoting inflammation. In asthma and allergic inflammation, IL-4 mediates proinflammatory responses that lead to tissue damage. Thus the effect of IL-4 on the outcome of the immune responses is greatly influenced by other cofactors and cytokines present in the microenvironment. R848 (resiquimod), a TLR7/8 agonist is a novel vaccine adjuvant, triggering a strong Th1-skewed response but its efficacy as a vaccine adjuvant shows variable results. It is not currently known whether the presence of IL-4 can dampen or enhance immunity in response to TLR7 agonists. In the present study, we sought to investigate the impact of IL-4-induced Mφ polarization on the outcome of R848 stimulation. The activation marker expression and production of cytokines were measured in murine spleen-derived Mφ. Protein expression levels of innate recognition molecules and transcription factors involved, including retinoic-acid inducible gene I, mitochondrial antiviral signaling protein, stimulator of interferon genes (STING), and IFN regulatory factors were evaluated in activated Mφ. These play a crucial role in the control of viral replication and optimal CD8+ T cell priming. We report that sustained priming with IL-4 alone promotes an antiviral response in Mφ, and enhances proinflammatory responses to R848 treatment. This highlights the need for better understanding of IL-4 proinflammatory functions and its potential use as a broad-acting antiviral in combination with R848 may be used in combination with other therapies to target the innate arm of immunity against emerging infections.

Lymphocytic choriomeningitis virus infection of dendritic cells interferes with TLR-induced IL-12/IL-23 cytokine production in an IL-10 independent manner

Dendritic cells produce IL-12 and IL-23 in response to viral and bacterial infection and these cytokines are responsible for successful pathogen clearance. How sequential viral and bacterial infections affect the production of IL-12 and IL-23 is currently not known. Our study demonstrates that in dendritic cells infected with Lymphocytic choriomeningitis virus (LCMV), TLR activation with bacterial PAMPs resulted in reduced IL-12 and IL-23 expression compared to non-infected cells. Furthermore, expression of other proinflammatory cytokines, TNF-α and IL-6, were not inhibited under these conditions. We discovered that TLR-induced phosphorylation of p38 was significantly inhibited in LCMV-infected cells. We detected enhanced expression of suppressor of cytokine signalling (SOCS)-3 and IL-10. Yet, neutralizing IL-10 did not restore IL-12/IL-23 expression. Taken together, these results show that virus infection interferes with the magnitude of TLR-mediated inflammatory responses by repressing specific cytokine expression.

On taking the STING out of immune activation

Nearly a decade ago, an endoplasmic reticulum (ER) adaptor protein called stimulator of interferon genes (STING) was found to be critical in the induction of type I IFN production in response to DNA virus infection. STING functions by sensing cytoplasmic DNA and activates key transcription factors, including IFN regulatory factor (IRF)-3 and IRF7, to initiate type I IFN expression. Type I IFNs are vital in immunity against viral infections and can influence cancer cell proliferation, migration, and apoptosis. Several studies have shown that STING activation results in potent antitumor activity by generating strong tumor-specific cytotoxic T-cell responses. Moreover, compared with wild-type, STING-knockout mice show greater susceptibility to viral infections. In this review, we discuss the importance of STING signaling during the induction of immune responses, especially those associated with type I IFN in viral infections and tumor immunity. Furthermore, we highlight recent data that unravel how the STING signaling pathway can be negatively regulated.

M(IL-4) Tissue Macrophages Support Efficient Interferon-Gamma Production in Antigen-Specific CD8+ T Cells with Reduced Proliferative Capacity

CD8⁺ cytotoxic T cell (CTL) responses are necessary for the lysis of virally infected cells and control of infection. CTLs are activated when their TCRs bind a major histocompatibility complex (MHC)-I/peptide complex on the surface of antigen presenting cells such as macrophages (MΦ). It is now apparent that MΦ display remarkable plasticity in response to environmental signals to polarize into classically activated M(LPS + IFN-γ) or alternatively activated M(IL-4). However, little is known about how MΦ activation status influences their antigen presentation function to CD8⁺ T cell in models of virus infection. Consequently, we tested how polarization of spleen-derived (Sp)-MΦ impacts direct presentation of viral antigens to influence effector and proliferative CD8⁺ T-cell responses. We show that M(IL-4) Sp-MΦ retain MHC-I surface expression and the ability to stimulate IFN-γ production by CTL following peptide stimulation and lymphocytic choriomeningitis virus infection to levels similar to M0 and M(LPS + IFN-γ) MΦ. However, memory CD8⁺ T cells cultured in the presence of M(IL-4) MΦ underwent significantly reduced proliferation and produced similar IFN-γ levels as coculturing with M0 or M(LPS + IFN-γ) cells. Thus, these results show a novel ability of polarized MΦ to regulate CD8⁺ T-cell proliferation and effector functions during virus infection.

Spleen-derived macrophages are readily polarized into classically activated (M1) or alternatively activated (M2) states

Bone marrow derived macrophages (BM-MΦ) that differentiate from precursor cells can be polarized into classically activated pro-inflammatory (M1) or alternatively activated (M2) states depending upon the cytokine microenvironment. We questioned whether tissue MΦ, such as spleen-derived MΦ (Sp-MΦ), have the ability to differentiate into M1 or M2 cells. We show in response to activation with IFN-gamma (IFN-γ) and lipopolysaccharide (LPS), that the Sp-MΦ readily acquired an M1 status indicated by up-regulation of iNOS mRNA, nitric oxide (NO) production, and the co-stimulatory molecule CD86. Conversely, Sp-MΦ exposed to IL-4 exhibited increased levels of mannose receptor (CD 206), arginase-1 (Arg)-1 mRNA expression, and significant urea production typical of M2 cells. At this stage of differentiation, the M2 Sp-MΦ were more efficient at phagocytosis of cell-associated antigens than their M1 counterparts. This polarization was not indefinite as the cells could revert back to their original state upon the removal of stimuli and exhibited flexibility to convert from M2 to M1. Remarkably, both M1 and M2 Sp-MΦ induced more CD4 expression on their cells surface after stimulation. We also demonstrate that adherent macrophages cultured for a short term in IL-4 enhances ARG-1 and YM-1 mRNA along with increasing urea producing capacity: traits indicative of an M2 phenotype. Moreover, in response to in vivo virus infection, the adherent macrophages obtained from spleens rapidly express iNOS. These results provide new evidence for the polarization capabilities of Sp-MΦ when exposed to pro-inflammatory or anti-inflammatory cytokines.