Combinatorial effects of interleukin 10 and interleukin 4 determine the progression of hepatic inflammation following murine enteric parasitic infection.

UNLABELLED: Mice lacking the immunoregulatory cytokine interleukin 10 (IL-10) develop necrotizing hepatitis after infection with Trichinella spiralis, and inflammation is dependent on the migration of intestinally activated CD4(+) T cells into the liver. Hepatic production of IL-4 is elevated in these mice, and we hypothesized that it plays a role in the development of hepatic pathology. Wild-type (WT), IL-10 knockout (KO), IL-4 KO, and IL-10/IL-4 KO mice were orally infected, and disease progression was followed by histological examination, alanine aminotransferase assays, and flow cytometric analysis of hepatocellular content. Both IL-10 KO and IL-10/IL-4 KO mice experienced hepatocellular injury, but only IL-10 KO mice advanced to a necrotic phase. Hepatic CD4(+) T cells were the major source of IL-4, and IL-10 regulated the number of intestinally-derived CD4(+)IL-4(+) cells. Sequestration of activated neutrophils in the liver required IL-4, and neutrophil depletion prevented progression to overt necrosis. Adoptive transfer of intestinal WT CD4(+) T cells inhibited neutrophil accumulation and inflammation, but their regulatory effects did not require IL-10 signaling. CONCLUSION: The absence of IL-10 led to hepatocyte injury during infection, but IL-4 was necessary for the development of neutrophil-dependent necrosis. These studies provide new insight into the combinatorial role of these cytokines and their targets in the generation and progression of hepatic inflammation.

Eosinophil deficiency compromises parasite survival in chronic nematode infection.

Immune responses elicited by parasitic worms share many features with those of chronic allergy. Eosinophils contribute to the inflammation that occurs in both types of disease, and helminths can be damaged or killed by toxic products released by eosinophils in vitro. Such observations inform the widely held view that eosinophils protect the host against parasitic worms. The mouse is a natural host for Trichinella spiralis, a worm that establishes chronic infection in skeletal muscle. We tested the influence of eosinophils on T. spiralis infection in two mouse strains in which the eosinophil lineage is ablated. Eosinophils were prominent in infiltrates surrounding infected muscle cells of wild-type mice; however, in the absence of eosinophils T. spiralis muscle larvae died in large numbers. Parasite death correlated with enhanced IFN-gamma and decreased IL-4 production. Larval survival improved when mice were treated with inhibitors of inducible NO synthase, implicating the NO pathway in parasite clearance. Thus, the long-standing paradigm of eosinophil toxicity in nematode infection requires reevaluation, as our results suggest that eosinophils may influence the immune response in a manner that would sustain chronic infection and insure worm survival in the host population. Such a mechanism may be deployed by other parasitic worms that depend upon chronic infection for survival.

Coordinated control of immunity to muscle stage Trichinella spiralis by IL-10, regulatory T cells, and TGF-beta.

We previously demonstrated that IL-10 is critical in the control of acute inflammation during development of Trichinella spiralis in the muscle. In this study, we use gene-targeted knockout mice, adoptive transfer of specific T cell populations, and in vivo Ab treatments to determine the mechanisms by which inflammation is controlled and effector T cell responses are moderated during muscle infection. We report that CD4(+)CD25(-) effector T cells, rather than CD4(+)CD25(+) regulatory T cells, suppress inflammation by an IL-10-dependent mechanism that limits IFN-gamma production and local inducible NO synthase induction. Conversely, we show that depletion of regulatory T cells during infection results in exaggerated Th2 responses. Finally, we provide evidence that, in the absence of IL-10, TGF-beta participates in control of local inflammation in infected muscle and promotes parasite survival.

IL-10 regulates movement of intestinally derived CD4+ T cells to the liver.

Diseases that affect the intestine may have hepatic manifestations, but the mechanisms involved in establishing hepatic disease secondarily remain poorly understood. We previously reported that IL-10 knockout (KO) mice developed severe necrotizing hepatitis following oral infection with Trichinella spiralis. In this study, we used this model of intestinal inflammation to further examine the role of IL-10 in regulating hepatic injury. Hepatic damage was induced by migrating newborn larvae. By delivering the parasite directly into the portal vein, we demonstrated that an ongoing intestinal immune response was necessary for the development of hepatitis. Intestinally derived CD4+ cells increased in the livers of IL-10 KO mice, and Ab-mediated blockade of MAdCAM-1 inhibited the accumulation of CD4+alpha(4)beta(7)+ cells in the liver. Moreover, adoptive transfer of intestinally primed CD4+ T cells from IL-10 KO mice caused hepatitis in infected immunodeficient animals. Conversely, transfer of wild-type donor cells reduced the severity of hepatic inflammation in IL-10 KO recipients, demonstrating regulatory activity. Our results revealed that IL-10 prevented migration of intestinal T cells to the liver and inhibited the development of hepatitis.

IL-10 prevents liver necrosis during murine infection with Trichinella spiralis.

Infection with Trichinella spiralis rarely leads to significant morbidity. In this study, we show that IL-10 knockout mice infected with this parasite develop extensive areas of coagulative necrosis in the liver, and newborn larvae are required for lesion formation. Histopathological examination revealed that the hepatic inflammatory infiltrate was mixed but dominated by eosinophils. Accordingly, infected IL-10 knockout mice displayed a marked eosinophilia. IL-10 was expressed during infection in mesenteric lymph node populations and liver tissue. Analysis of cytokine profiles revealed a codominant expression of type 1 and 2 mediators that was enhanced in the absence of IL-10. Additionally, CD11c(+) MHC class II(+) cells were increased in mesenteric lymph nodes of IL-10 knockout mice, suggesting a possible link between IL-10 and dendritic cell trafficking. Nevertheless, there were no significant differences in mortality or parasite burdens between the strains of mice, indicating that IL-10 is necessary to control the host's inflammatory response but does not impact establishment of the parasite. Expression of IL-10 appears to be an adaptation used by the liver to protect itself from damage caused by migrating newborn larvae.

Use of recombinant tissue-plasminogen activator in a dog with chylothorax secondary to catheter-associated thrombosis of the cranial vena cava.

A 4-year-old, castrated male Maltese developed cranial vena caval thrombosis and chylothorax following central venous catheterization for treatment of postoperative sepsis. Vena caval thrombolysis was attempted using recombinant human tissue-plasminogen activator (t-PA). Thrombolytic therapy led to an acute reduction in the size of the caval thrombus and was followed by prompt resolution of the chylothorax. Hemorrhage at the entry sites of a jugular catheter and esophagostomy tube placed at the time of treatment was a dose-limiting complication of t-PA therapy in this dog.

Cross-talk in the innate immune system: neutrophils instruct recruitment and activation of dendritic cells during microbial infection.

Type I inflammatory cytokines are essential for immunity to many microbial pathogens, including Toxoplasma gondii. Dendritic cells (DC) are key to initiating type 1 immunity, but neutrophils are also a source of chemokines and cytokines involved in Th1 response ignition. We found that T. gondii triggered neutrophil synthesis of CC chemokine ligand (CCL)3, CCL4, CCL5, and CCL20, chemokines that were strongly chemotactic for immature DC. Moreover, supernatants obtained from parasite-stimulated polymorphonuclear leukocytes induced DC IL-12(p40) and TNF-alpha production. Parasite-triggered neutrophils also released factors that induced DC CD40 and CD86 up-regulation, and this response was dependent upon parasite-triggered neutrophil TNF-alpha production. In vivo evidence that polymorphonuclear leukocytes exert an important influence on DC activation was obtained by examining splenic DC cytokine production following infection of neutrophil-depleted mice. These animals displayed severely curtailed splenic DC IL-12 and TNF-alpha production, as revealed by ex vivo flow cytometric analysis and in vitro culture assay. Our results reveal a previously unrecognized regulatory role for neutrophils in DC function during microbial infection, and suggest that cross-talk between these cell populations is an important component of the innate immune response to infection.

Interleukin-10 limits local and body cavity inflammation during infection with muscle-stage Trichinella spiralis.

The aim of this study was to characterize cellular responses to muscle-stage Trichinella spiralis. From its intracellular habitat in muscle, T. spiralis secretes potent glycoprotein antigens that elicit a strong systemic host immune response. Despite the magnitude and prolonged nature of this response, nurse cells are rarely destroyed by infiltrating cells. We tested the hypothesis that the anti-inflammatory cytokine interleukin-10 (IL-10) moderates cellular responses to muscle-stage parasites. Trichinella larvae colonize the diaphragm in large numbers, prompting us to evaluate regional responses in body cavities in addition to local responses in muscle. Mice deficient in IL-10 demonstrated an exaggerated inflammatory response around nurse cells and in the pleural cavity. The effect of IL-10 was most evident 20 days following muscle infection. The increased intensity of the response in IL-10-deficient mice did not affect parasite establishment or survival. Between 20 and 50 days postinfection, the inflammatory response was diminished in both wild-type and IL-10-deficient mice. Muscle infection also elicited an antibody response, characterized initially by mixed isotypes directed at somatic larval antigens and changing to an immunoglobulin G1-dominated response directed at tyvelose-bearing excreted or secreted antigens. We conclude that IL-10 limits local and regional inflammation during the early stages of muscle infection but that chronic inflammation is controlled by an IL-10-independent mechanism that is coincident with a Th2 response.