Toxoplasma gondii induces granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor secretion by human fibroblasts: implications for neutrophil apoptosis.
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 alpha subunit (IL-3Ralpha), 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 enzyme-linked 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.
Channon
Jacqueline Y
JY
Department of Microbiology, Dartmouth Medical School, Lebanon, New Hampshire 03756, USA. jacqueline.channon@dartmouth.edu.
Miselis
Kristin A
KA
Minns
Laurie A
LA
Dutta
Chaitali
C
Kasper
Lloyd H
LH
D000818:Animals; D017209:Apoptosis; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D005347:Fibroblasts / Q000378:metabolism / Q000469:parasitology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology; D016179:Granulocyte Colony-Stimulating Factor / Q000096:biosynthesis*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000096:biosynthesis*; D006801:Humans; D018664:Interleukin-12 / Q000096:biosynthesis; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D009504:Neutrophils / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D016185:Receptors, Interleukin-3 / Q000096:biosynthesis; D014122:Toxoplasma / Q000502:physiology*
D017077:Culture Media, Conditioned; D016185:Receptors, Interleukin-3; D016179:Granulocyte Colony-Stimulating Factor; D018664:Interleukin-12; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D019869:Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go