Rapid Recruitment of Neutrophils Containing Prestored IL-12 During Microbial Infection

Abstract

Neutrophils are well known to rapidly migrate to foci of infection, where they exert microbicidal functions. We sought to determine whether neutrophils responding to in vivo infection with the protozoan pathogen Toxoplasma gondii were capable of IL-12 production as suggested by recent in vitro studies. Intraperitoneal infection induced a neutrophil influx by 4 h, accompanied by ex vivo IL-12 p40 and p70 release. Approximately 85% of the neutrophils displayed intracellular stores of IL-12, as determined by flow cytometry and confocal fluorescence microscopy. Neutrophils from IFN-γ knockout mice also expressed IL-12, ruling out an IFN-γ-priming requirement. Neither infected nor uninfected peritoneal macrophages displayed intracellular IL-12, but these cells were strongly IL-10+. Infection per se was unnecessary for IL-12 production because peritoneal and peripheral blood neutrophils from uninfected animals contained IL-12+ populations. Expression of the granulocyte maturation marker Gr-1 (Ly-6G) was correlated with IL-12 production. Mice depleted of their granulocytes by mAb administration at the time of infection had decreased serum levels of IL-12 p40. These results suggest a model in which neutrophils with prestored IL-12 are rapidly mobilized to an infection site where they are triggered by the parasite to release cytokine. Our findings place neutrophils prominently in the cascade of early events leading to IL-12-dependent immunity to T. gondii.

Toxoplasma gondiiTachyzoites Inhibit Proinflammatory Cytokine Induction in Infected Macrophages by Preventing Nuclear Translocation of the Transcription Factor NF-κB

“…In parallel, our laboratory has found that both human and mouse neutrophils serve as an early IL-12 source during parasite infection (33)(34)(35). In the course of our studies on mouse responses to infection, we found that i.p.…”

“…tachyzoite inoculation induced a rapid influx of IL-12-positive PMN. However, we were surprised to find that in the same population neither infected nor noninfected M displayed detectable IL-12 (33). We now formally show that tachyzoites invade host M without inducing IL-12 or TNF-␣ and without inducing nuclear translocation of NF-B p65, a major transcriptional activator of inflammatory cytokine genes.…”

“…with tachyzoites do not express detectable IL-12 p40 (33). To examine the general capacity of M to produce and secrete IL-12 and TNF-␣, thioglycolate-elicited peritoneal M (PM) and several macrophage cell lines were subjected to tachyzoite infection with RH strain tachyzoites (2 h) or to stimulation with LPS (30 min).…”

IL-12 Suppression During Experimental Endotoxin Tolerance: Dendritic Cell Loss and Macrophage Hyporesponsiveness

“…It is possible, e.g., that IFN-␣␤ is important mechanistically in the induction of tolerance in peritoneal macrophages, but that serum cytokines derive largely from splenic DCs (hepatic macrophages, intravascular neutrophils; Ref. 62) that have no such dependence on IFN-␣␤. Second, there may be extensive redundancy in mechanism; single-knockout mice may be insufficient.…”

Expression of dendritic cell markers on cultured neutrophils and its modulation by anti-apoptotic and pro-apoptotic compounds

“…CD80 and CD86 are involved in the Th1 and Th2 responses, respectively (Kuchroo et al, 1995). It was reported that neutrophils promote the Th1 responses in experimental models of infection with Legionella pneumophillia or Toxoplasma gondii (Bliss et al, 2000;Tateda et al, 2001). However, it is still unclear if T cells can interact with neutrophils that express MHC and co-stimulatory molecules.…”