Toxoplasma gondiiInduces Granulocyte Colony-Stimulating Factor and Granulocyte-Macrophage Colony-Stimulating Factor Secretion by Human Fibroblasts: Implications for Neutrophil Apoptosis

Abstract

Human neutrophils are rescued from apoptosis following incubation with once-washed, fibroblast-derived Toxoplasma gondii tachyzoites. Both infected and uninfected neutrophils are rescued, implicating a soluble mediator. In this study we investigated the origin and identity of this soluble mediator. Neutrophils were incubated either with purified tachyzoites or with conditioned medium derived from T. gondii-infected human fibroblasts. Conditioned medium was found to be a potent stimulus that delayed neutrophil apoptosis up to 72 h, whereas purified and extensively washed tachyzoites had no effect. Delayed apoptosis correlated with up-regulation of the neutrophil antiapoptotic protein, Mcl-1, and the neutrophil interleukin 3 receptor ␣ subunit (IL-3R␣), suggesting a role for granulocyte-macrophage colony-stimulating factor (GM-CSF). GM-CSF and granulocyte colony-stimulating factor (G-CSF) were measurable in conditioned medium by enzymelinked immunosorbent assay. Neutralizing antibodies to GM-CSF and G-CSF were additive in abrogating delayed neutrophil apoptosis induced by conditioned medium. Inhibitors of Src family tyrosine kinases, G i proteins, phosphatidylinositol 3-kinase, p44 erk1 and p42 erk2 mitogen-activated protein kinases, and Jak2 kinases partially attenuated the effect of conditioned medium, consistent with a role for G-CSF and/or GM-CSF. Hence, delayed neutrophil apoptosis is mediated by GM-CSF and G-CSF secreted by T. gondii-infected human fibroblasts. This enhanced neutrophil survival may contribute to the robust proinflammatory response elicited in the T. gondii-infected host.

Infection withToxoplasma gondiiBradyzoites Has a Diminished Impact on Host Transcript Levels Relative to Tachyzoite Infection

“…The GM-CSF induction agrees with the work of others that found it to be significantly induced in tachyzoite-infected fibroblasts (9). This protein promotes granulocyte and macrophage differentiation and proliferation and would thus increase inflammation.…”

Dynamic changes in Mcl-1 expression regulate macrophage viability or commitment to apoptosis during bacterial clearance

“…Although altered Mcl-1 expression in cells during exposure to microorganisms has been described previously (16,27,44,48), the functional consequences of altered Mcl-1 expression in vivo during the host response to infection have not previously been demonstrated. We demonstrate that delaying the induction of apoptosis by overexpressing Mcl-1 in macrophages from Mcl-1 transgenic mice reduces AM apoptosis as well as the efficiency of bacterial clearance in a subclinical model of pneumococcal infection.…”

“…Furthermore, proteasome inhibition delays neutrophil apoptosis in association with decreased turnover of . Upregulation of Mcl-1 can delay apoptosis in neutrophils during Toxoplasma gondii infection, demonstrating its role in prolonging survival of phagocytes engaged in critical host defense functions (48). In view of the important role of neutrophils in successful resolution of pneumococcal pneumonia (49), it is likely that levels of Mcl-1 expression in neutrophils also contribute to the outcome of pneumococcal infection.…”

Viruses, bacteria and Hallmarks of Cancer. Self-sufficiency in growth signals.

“…Intracellular interleukin 6 mediates platelet-derived growth factorinduced proliferation of nontransformed cells [87] Staphylococcus Pore-forming Staphylococcus aureus alpha-toxin triggers epidermal growth factor receptor-dependent proliferation [88] EGFR Epidermal growth factor induces bladder cancer cell proliferation through activation of the androgen receptor [89] Toxoplasma Toxoplasma gondii induces granulocyte colony-stimulating factor and granulocytemacrophage colony-stimulating factor secretion [90] G-CSF, GM-CSF Effects of granulocyte-colonystimulating factor and granulocyte/macrophage-colonystimulating factor administration on T cell proliferation… [91] …”