Macrophage migration inhibitory factor plays a critical role in mediating protection against the helminth parasite Taenia crassiceps

Modifications of serum and cellular parameters in trotters after a race. Macrophage migration inhibitory activity reduction and serum beta-glucan elevation

Trotters are exposed to a chronic prolonged stress, such as daily training and frequent races during their active lifespans. There is evidence that trotters undergo very often lethal lung infections after a race, and therefore, is likely that modifications of certain physiologic cellular parameters could account for the increased susceptibility to microbial diseases. Here, we demonstrate that in 7 trotters after a race either serum values (e.g., glycaemia, triglycerides, transaminases, gamma-glutamyltransferase, cholinesterase, amylase, alkaline phosphatase, total proteins, serum albumin, sodium, blood urea nitrogen, lactic dehydrogenase, creatine phosphokinase, and creatinine) or hematological parameters (red blood cell count, hemoglobin, lymphocyte and monocyte count) were increased. At the same time, in the same animals after a race, macrophage migration inhibitory factor activity was depressed, thus indicating an impaired T-lymphocyte response. Finally, increased levels of circulating beta-glucans in some horses, after a race, may suggest a reduced clearance of fungal cell wall components. Taken together, these findings indicate a condition of multiple organ dysfunction, such as the liver, the kidney, the pancreas, and skeletal muscles, as well as a reduced cell-mediated immune response in trotters, after a race.

Reactive oxygen species and 12/15-lipoxygenase contribute to the antiproliferative capacity of alternatively activated myeloid cells elicited during helminth infection

Understanding the role of CD11b(+)GR-1(+) myeloid suppressor cells in the immune suppression and immunoregulation associated with a variety of diseases may provide therapeutic opportunities. In this article, we show, in a model of helminth infection, that CD11b(+)GR-1(+) myeloid suppressor cells but not CD11b(+)F4/80(high) mature macrophages expanded in the peritoneal cavity of BALB/c mice implanted with Taenia crassiceps. Peritoneal cell populations from early stage-infected animals impaired T cell proliferation by secreting NO. Yet, they lost their ability to secrete NO in the late stage of infection. Concomitantly, their capacity to exert arginase activity and to express mRNAs coding for FIZZ1 (found in inflammatory zone 1), Ym, and macrophage galactose-type C-type lectin increased. Furthermore, cells from early stage-infected mice triggered T cells to secrete IFN-gamma and IL-4, whereas in the late stage of infection, they only induced IL-4 production. These data suggest that CD11b(+)GR-1(+) myeloid suppressor cells displaying an alternative activation phenotype emerged gradually as T. crassiceps infection progressed. Corroborating the alternative activation status in the late stage of infection, the suppressive activity relied on arginase activity, which facilitated the production of reactive oxygen species including H(2)O(2) and superoxide. We also document that the suppressive activity of alternative myeloid suppressor cells depended on 12/15-lipoxygenase activation generating lipid mediators, which triggered peroxisome proliferator-activated receptor-gamma. IL-4 and IL-13 signaling contributed to the expansion of myeloid suppressor cells in the peritoneal cavity of T. crassiceps-infected animals and to their antiproliferative activity by allowing arginase and 12/15-lipoxygenase gene expression.

Helminth parasites--masters of regulation

Immune regulation by parasites is a global concept that includes suppression, diversion, and conversion of the host immune response to the benefit of the pathogen. While many microparasites escape immune attack by antigenic variation or sequestration in specialized niches, helminths appear to thrive in exposed extracellular locations, such as the lymphatics, bloodstream, or gastrointestinal tract. We review here the multiple layers of immunoregulation that have now been discovered in helminth infection and discuss both the cellular and the molecular interactions involved. Key events among the host cell population are dominance of the T-helper 2 cell (Th2) phenotype and the selective loss of effector activity, against a background of regulatory T cells, alternatively activated macrophages, and Th2-inducing dendritic cells. Increasingly, there is evidence of important effects on other innate cell types, particularly mast cells and eosinophils. The sum effect of these changes to host reactivity is to create an anti-inflammatory environment, which is most favorable to parasite survival. We hypothesize therefore that parasites have evolved specific molecular strategies to induce this conducive landscape, and we review the foremost candidate immunomodulators released by helminths, including cytokine homologs, protease inhibitors, and an intriguing set of novel products implicated in immune suppression.

Effect of Cysticercus cellulosae on neutrophil function and death

Neutrophils, eosinophils and macrophages interact with invading parasites and naive hosts. The initial reaction of leukocytes is the generation of reactive oxygen species (ROS). The cytotoxic effects of extracts derived from intact Cysticercus cellulosae and from the scolex or membrane fractions on neutrophils were examined. DNA fragmentation of neutrophils was observed when cells were incubated with an extract from the intact metacestode; however, the addition of antioxidant enzymes to the incubation medium had a protective effect. The scolex and membrane extracts did not affect DNA fragmentation of neutrophils. Hydrogen peroxide production of neutrophils incubated with metacestode fractions from C. cellulosae increased by 190% (total extract), 120% (scolex) or 44% (membrane). An increase in antioxidant catalase activity (28%) concomitant with the increased production of ROS was observed in neutrophils incubated with metacestode fractions, which could be an attempt at self-protection. ROS production by neutrophils in the presence of the intact cysticerci extract did not alter phagocytosis. In contrast, the scolex and membrane fractions increased the phagocytic capacity of neutrophils by 44 and 28%, respectively. The results showed that the extract from intact C. cellulosae was toxic for neutrophils via ROS production, leading to DNA fragmentation and inhibition of phagocytic capacity, but neutrophils are able to protect themselves against oxidative stress by via catalase activity.

Blockade of macrophage migration inhibitory factor (MIF) in Schistosoma japonicum-infected mice results in an increased adult worm burden and reduced fecundity

Macrophage migration inhibitory factor (MIF), a cytokine produced by many cell types, modulates cellular and humoral immune responses. In schistosomiasis, ova in the portal circulation induce a delayed type hypersensitivity (DTH) that results in formation of hepatic granulomas (HG) which secrete MIF activity. Therefore, we hypothesized that endogenous MIF modulates immune responses in schistosomiasis. To test this hypothesis, Schistosoma japonicum-infected mice were injected with rabbit IgG or neutralizing rabbit IgG antibody to MIF 4.5-6.5 week post infection when HG form and female worms are laying eggs. Compared with controls, 6.5-7-week post-infection, antibody-treated mice had 1.7-3 times as many adult worms and half as many ova per worm pair in their livers. In contrast, antibody introduced before infection or 6-8 week post infection did not affect worm burden or fecundity. Thus, for the first time there is evidence that 4.5-6 week post-infection endogenous MIF somehow mediates reduction of adult worm burden and promotes fecundity. Splenocytes and HG cells from antibody-treated mice showed reduced intracellular expression of TNFalpha and/or IL-10. We hypothesize that endogenous MIF enhances adult worm attrition by up-regulating innate and adaptive immune responses by increasing expression of MHC-II, co-stimulatory, adhesion, receptor and cytokine molecules, and promotes fecundity by up-regulating TNFalpha expression.

Macrophage migration inhibitory factor: a regulator of innate immunity

Cytokines are essential effector molecules of innate immunity that initiate and coordinate the cellular and humoral responses aimed, for example, at the eradication of microbial pathogens.

Discovered in the late 1960s as a product of activated T cells, the cytokine macrophage migration inhibitory factor (MIF) has been discovered recently to carry out important functions as a mediator of the innate immune system.

Constitutively expressed by a broad spectrum of cells and tissues, including monocytes and macrophages, MIF is rapidly released after exposure to microbial products and pro-inflammatory mediators, and in response to stress. After it is released, MIF induces pro-inflammatory biological responses that act as a regulator of immune responses.

MIF activates the extracellular signal-regulated kinase 1 (ERK1)/ERK2–mitogen-activated protein kinase pathway, inhibits the activity of JUN activation domain-binding protein 1 (JAB1) — a co-activator of the activator protein 1 (AP1) — upregulates the expression of Toll-like receptor 4 to promote the recognition of endotoxin-expressing bacterial pathogens, sustains pro-inflammatory function by inhibiting p53-dependent apoptosis of macrophages and counter-regulates the immunosuppressive effects of glucocorticoids on immune cells.

As a pro-inflammatory mediator, MIF has been shown to be implicated in the pathogenesis of severe sepsis and septic shock, acute respiratory distress syndrome, and several other inflammatory and autoimmune diseases, including rheumatoid arthritis, glomerulonephritis and inflammatory bowel diseases.

Given its crucial role as a regulator of innate and acquired immunity, pharmacological or immunological modulation of MIF activity might offer new treatment opportunities for the management of acute and chronic inflammatory diseases.

For more than a quarter of a century, macrophage migration inhibitory factor (MIF) has been a mysterious cytokine. In recent years, MIF has assumed an important role as a pivotal regulator of innate immunity. MIF is an integral component of the host antimicrobial alarm system and stress response that promotes the pro-inflammatory functions of immune cells. A rapidly increasing amount of literature indicates that MIF is implicated in the pathogenesis of sepsis, and inflammatory and autoimmune diseases, suggesting that MIF-directed therapies might offer new treatment opportunities for human diseases in the future.

Altered T helper responses in CD40 and interleukin-12 deficient mice reveal a critical role for Th1 responses in eliminating the helminth parasite Taenia crassiceps

A key feature of helminth infections is the induction of strong Th2-biased immune responses in their hosts. We have previously found that Th2-like responses mediate susceptibility to the helminth parasite Taenia crassiceps, probably by inhibiting Th1 responses required for the development of protective immunity against this parasite. Here we show that mice lacking interleukin-12p35 (IL-12p35-/-) following T. crassiceps infection, failed to mount a Th1 response, but developed a strong Th2-type response, produced higher levels of IgG1, IgE, interleukin-4, interleukin-5 as well as interleukin-13 than wild-type mice, and became highly susceptible to the larval stage of this cestode. In contrast, similarly-infected CD40 deficient BALB/c mice (CD40-/-) displayed impairment of both Th1 and Th2-type responses associated with low levels of interferon-gamma as well as IgE, interleukin-4, interleukin-5 and interleukin-13, but efficiently controlled T. crassiceps infection. Together, these findings suggest a detrimental role for Th2-biased responses during the larval stage of T. crassiceps infection. Furthermore, they also suggest a pivotal role for CD40 in developing Th2-type responses.