The maintenance of a benign chronic Toxoplasma gondii infection is mainly dependent on the persistent presence of gamma interferon (IFN-␥) in the central nervous system (CNS). However, IFN-␥-activated microglia are paradoxically involved in parasitism control and in tissue damage during a broad range of CNS pathologies. In this way, nitric oxide (NO), the main toxic metabolite produced by IFN-␥-activated microglia, may cause neuronal injury during T. gondii infection. Despite the potential NO toxicity, neurodegeneration is not a common finding during chronic T. gondii infection. In this work, we describe a significant downmodulation of NO production by IFN-␥-activated microglia in the presence of conditioned medium of T. gondii-infected astrocytes (CMi). The inhibition of NO production was paralleled with recovery of neurite outgrowth when neurons were cocultured with IFN-␥-activated microglia in the presence of CMi. Moreover, the modulation of NO secretion and the neuroprotective effect were shown to be dependent on prostaglandin E 2 (PGE 2 ) production by T. gondii-infected astrocytes and autocrine secretion of interleukin-10 (IL-10) by microglia. These events were partially eliminated when infected astrocytes were treated with aspirin and cocultures were treated with anti-IL-10 neutralizing antibodies and RP-8-Br cyclic AMP (cAMP), a protein kinase A inhibitor. Further, the modulatory effects of CMi were mimicked by the presence of exogenous PGE 2 and by forskolin, an adenylate cyclase activator. Altogether, these data point to a T. gondii-triggered regulatory mechanism involving PGE 2 secretion by astrocytes and cAMP-dependent IL-10 secretion by microglia. This may reduce host tissue inflammation, thus avoiding neuron damage during an established Th1 protective immune response.

Macrophage migration inhibitory factor (MIF) is increased in asthmatic patients and plays a critical role in the pathogenesis of asthma. We show here that mice lacking MIF failed to develop airway hyper-responsiveness (AHR), tissue eosinophilia, and mucus metaplasia. Analysis of the bronchoalveolar fluids revealed a substantial reduction of IL-13, eotaxin and cysteinyl-leukotrienes. The lack of these cardinal features of asthma in MIF -/-mice occurs regardless of high concentrations of IL-4 in the lung and OVAspecific IgE in the serum. Antigen-specific lymphocyte proliferation and IL-13 production were similarly increased in the draining lymph nodes of OVA-immunized and challenged MIF -/-mice compared to WT, but were reduced in the spleen of MIF -/-, thus indicating differential roles of MIF in these compartments. Stimulation of naive CD4 + cells with anti-CD3 antibody demonstrated that MIF -/-cells produced increased amounts of IFN-c and IL-4 compared to WT CD4 + cells. Finally, treatment of sensitized BALB/c mice with neutralizing anti-MIF antibody abrogated the development of ARH and airway inflammation without affecting the production of Th2 cytokines or IgE. The present study demonstrates that MIF is required for allergic inflammation, adding important elements to our knowledge of asthma pathogenesis and suggesting that neutralization of MIF might be of therapeutic value in asthma. IntroductionAllergic asthma is a disorder characterized by chronic lung inflammation, reversible airway obstruction and increases in airway hyper-responsiveness (AHR) to nonspecific stimuli. Several studies have provided compelling evidences that the lung infiltrating leukocytes and the proinflammatory mediators they produce initiate cellular damage, amplify the immune response, cause airway physiological changes and tissue remodeling [1]. The airway inflammation of asthma has a predominance of Th2 CD4 + lymphocytes, eosinophils and mast cells infiltrating the lung interstitium. Several studies indicate the existence of a mechanism dependent on IL-5 and eosinophils that induce pulmonary damage and intensify AHR [3][4][5]. In other studies, however, the induction of AHR was observed despite the absence of infiltrating eosinophils, suggesting dissociation between these phenomena [6][7][8][9][10]. Macrophage migration inhibitory factor (MIF) is a pleiotropic molecule and critical mediator of innate and acquired immune responses [11,12]. Pre-formed MIF protein is present in many cell types and is released in response to different stimuli, such as infection and cytokine stimulation [12]. MIF exhibits several proinflammatory functions, including the induction of TNF-a, IL-1 and NO release from macrophages, and the production of arachidonic acid and eicosanoids through the induction of phospholipase A 2 and cyclooxygenase [13,14]. A unique property of MIF is its secretion by immune cells in response to physiological increase in glucocorticoid levels. Once released, MIF can counterregulate the anti-inflammatory effects of steroids on cyt...

Alloxan damages insulin-producing cells and has been used as an inducer of experimental diabetes in several animal species. In this study, administration of alloxan (40 mg/kg, i.v.) to rats was followed by a selective and time-dependent reduction in the number of pleural mast cells (50±2.2%, p<0.01; mean ± SEM), while mononuclear cell and eosinophil counts were not altered. As compared to naive rats, the reduction in mast cell numbers was first noted 48 h following alloxan administration and remained unaltered for at least 60 days. It is noteworthy, that the depletion in the mast cell population was not accompanied by alterations in the total amount of histamine stored per cell. Sensitized rats turned diabetic by alloxan treatment performed 72 h before challenge showed a less pronounced antigen-induced mast cell degranulation compared to nondiabetic rats. Moreover, rats injected with alloxan 72 and 48 but not 24 h before challenge, reacted to allergenic challenge with 50% reduction in the number of eosinophils recruited to the pleural cavity within 24 h. We found that the less pronounced eosinophil accumulation did not relate to an intrinsic cell locomotor abnormality since eosinophils from diabetic rats presented similar chemotactic responses to LTB4 and PAF in vitro as compared to matching controls. Insulin (3 IU/rat) restored basal levels of mast cells and reversed the subsequent inhibition of allergen-induced pleural eosinophilia, suggesting a causative relationship between these phenomena. Treatment with insulin also significantly increased the number of mast cells in the pleural cavity of naive rats (from 637±57 to 978±79 × 10³ cells/cavity, p<0.001). Consistently, previous depletion of mast cells by means of local treatment with compound 48/80 significantly reduced the antigen-induced eosinophil recruitment in sensitized animals. We conclude that the reduction in the pleural mast cell population noted in alloxan-treated rats could be directly implicated in the diminished pleural eosinophil influx following allergen challenge. This hyporesponsiveness is independent of an intrinsic abnormality of cell chemotaxis, but can be imitated by local mast cell depletion.

Inhaled lidocaine prevents eosinophilic inflammation, overproduction of mucus, and peribronchial fibrosis in a murine model of asthma, and impaired airway hyperreactivity, possibly by inhibiting allergen-evoked GATA-3 expression and the subsequent up-regulation of proinflammatory cytokines and chemokines.

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