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.

Differential TLR7-mediated cytokine expression by R848 in M-CSF- versus GM-CSF-derived macrophages after LCMV infection.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) play an important role in macrophage (MФ) development by influencing their differentiation and polarization. Our goal was to explore the difference between M-CSF- and GM-CSF-derived bone marrow MФ responsiveness to TLR7-mediated signalling pathways that influence cytokine production early after infection in a model of acute virus infection. To do so, we examined cytokine production and TLR7-mediated signalling at 1 h post-lymphocytic choriomeningitis virus (LCMV) Armstrong (ARM) infection. We found that R848-induced cytokine expression was enhanced in these cells, with GM-CSF cells exhibiting higher proinflammatory cytokine expression and M-CSF cells exhibiting higher anti-inflammatory cytokine expression. However, R848-mediated signalling molecule activation was diminished in LCMV-infected M-CSF and GM-CSF macrophages. Interestingly, we observed that TLR7 expression was maintained during LCMV infection of M-CSF and GM-CSF cells. Moreover, TLR7 expression was significantly higher in M-CSF cells compared to GM-CSF cells. Taken together, our data demonstrate that although LCMV restrains early TLR7-mediated signalling, it primes differentiated MФ to enhance expression of their respective cytokine profiles and maintains levels of TLR7 expression early after infection.

Granulocyte/Macrophage Colony-Stimulating Factor-Derived Macrophages Exhibit Distinctive Early Immune Response to Lymphocytic Choriomeningitis Virus Infection.

Granulocyte/macrophage colony-stimulating factor (GM-CSF) and macrophage CSF (M-CSF) modulate differentiation and immune functions of macrophages (MΦ). Our aim was to evaluate how different MΦ differentiation conditions influence the MΦ response to virus infection. To address this, we differentiated bone marrow-derived MΦ in either GM-CSF or M-CSF and measured the cytokine responses to two different strains of lymphocytic choriomeningitis virus (LCMV) (clone 13; Cl13 or Armstrong; ARM). GM-CSF MΦ infected with either LCMV-ARM or -Cl13 produced more IL-6 than M-CSF MΦ, whereas M-CSF MΦ generated more IL-10 than GM-CSF MΦ. Interestingly, in M-CSF MΦ, LCMV-ARM induced more IL-10 production than Cl13. However, we could not detect any IL-12p70 or IL-23 after infection from either cell types. We also observed that GM-CSF MΦ was more efficient than M-CSF MΦ in supporting antigen-specific CD8+ T cell proliferation. Taken together, our data demonstrate that GM-CSF and M-CSF MΦ differ in how they respond to viral infection by their production of different cytokines, and their support for CD8+ T cell proliferation.

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.