Targeting adrenergic receptors to mitigate invariant natural killer T cells-induced acute liver injury

Invariant Natural Killer T (iNKT) cell activation by α-galactosylceramide (αGC) potentiates cytotoxic immune responses against tumors. However, αGC-induced liver injury is a limiting factor for iNKT-based immunotherapy. Although adrenergic receptor stimulation is an important immunosuppressive signal that curbs tissue damage induced by inflammation, its effect on the antitumor activity of invariant Natural Killer T (iNKT) cells remains unclear. We use mouse models and pharmacological tools to show that the stimulation of the sympathetic nervous system (SNS) inhibits αGC-induced liver injury without impairing iNKT cells' antitumoral functions. Mechanistically, SNS stimulation prevents the collateral effect of TNF-α production by iNKT cells and neutrophil accumulation in hepatic parenchyma. Our results suggest that the modulation of the adrenergic signaling can be a complementary approach to αGC-based immunotherapy to mitigate iNKT-induced liver injury without compromising its antitumoral activity.

Crotoxin down-modulates pro-inflammatory cells and alleviates pain on the MOG35-55-induced experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis

Multiple sclerosis (MS) is a Central Nervous System inflammatory demyelinating disease that has as primary symptoms losses of sensory and motor functions, including chronic pain. To date, however, few studies have investigated the mechanisms of chronic pain in animal models of MS since locomotor impairments render difficult its evaluation. It was previously demonstrated that in the MOG_35-55-induced EAE, an animal model of MS, the hypernociception appears before the onset of motor disability, allowing for the study of these two phenomena separately. Here, we evaluated the effect of crotoxin (CTX), a neurotoxin isolated from the Crotalus durissus terrificus snake venom that displays, at non-toxic dose, antinociceptive, anti-inflammatory and immunomodulatory effects, in the pain and in symptoms progression of EAE. The pain threshold of female C57BL/6 mice decreased at the 4th day after immunization, while the first sign of disease appeared around the 11st-12nd days, coinciding with the onset of motor abnormalities. CTX (40 µg/kg, s.c.) administered in a single dose on the 5th day after immunization, induced a long-lasting analgesic effect (5 days), without interfering with the clinical signs of the disease. On the other hand, when crotoxin was administered for 5 consecutive days, from 5th-9th day after immunization, it induced analgesia and also reduced EAE progression. The antinociceptive effect of crotoxin was blocked by Boc-2 (0.5 mg/kg, i.p.), a selective antagonist of formyl peptide receptors, by NDGA (30 μg/kg, i.p.), a lipoxygenase inhibitor and by atropine sulfate (10 mg/kg, i.p.), an antagonist of muscarinic receptors, administered 30 min before CTX. CTX was also effective in decreasing EAE clinical signs even when administered after its onset. Regarding the interactions between neurons and immunocompetent cells, CTX, in vitro, was able to reduce T cell proliferation, decreasing Th1 and Th17 and increasing Treg cell differentiation. Furthermore, in EAE model, the treatment with 5 consecutive doses of CTX inhibited IFN-γ-producing T cells, GM-CSF-producing T cells, reduced the frequency of activated microglia/macrophages within the CNS and decreased the number of migrating cell to spinal cord and cerebellum at the peak of the disease. These results suggest that CTX is a potential treatment not only for pain alteration but also for clinical progression induced by the disease as well as an useful tool for the development of new therapeutic approaches for the multiple sclerosis control.

Phyllanthus amarus does not affect hypernociception in experimental autoimmune encephalomyelitis

Multiple sclerosis is an inflammatory disease of the central nervous system. Chronic pain is one of the main symptoms, affecting many patients. Studies show that the lignans or the apolar extracts of Phyllanthus amarus have antinociceptive effects in different animal models. To evaluate the antihypernociceptive effect of a hexanic extract of P. amarus in experimental autoimmune encephalomyelitis in mice, the chemical composition of the hexanic extract was analyzed by gas chromatography mass spectrometry. After EAE induction, animals were treated with the hexanic extract of P. amarus for 26 consecutive days. Motor coordination and mechanical hypernociception were evaluated on alternate days. The principal lignans found were phyllanthin, niranthin, and 5-demethoxyniranthin. The hexanic extract of P. amarus at a dose of 100, 200, or 400 mg/kg did not affect the development of the disease. The motor coordination and pain threshold of the treated animals were not altered in this experiment. In conclusion, in this test, the hexanic extract of P. amarus did not show evidence of antihypernociceptive activity in experimental autoimmune encephalomyelitis.

Regulatory T cells migrate to airways via CCR4 and attenuate the severity of airway allergic inflammation

We have previously shown that regulatory T (Treg) cells that accumulate in the airways of allergic mice upregulate CC-chemokine receptor 4 (CCR4) expression. These Treg cells suppressed in vitro Th2 cell proliferation but not type 2 cytokine production. In the current study, using a well-established murine model of allergic lung disease or oral tolerance, we evaluated the in vivo activity of Treg cells in allergic airway inflammation with special focus on CCR4 function. We found that allergic, but not tolerant, mice treated with anti-CD25 Ab showed increased airway eosinophilia and IL-5- or IL-4-producing Th2 cells when compared with untreated mice. Notably, mice with CCR4 deficiency displayed an augmented airway allergic inflammation compared with wild-type or CCR2 knockout (KO) mice. The allergic phenotype of CCR4KO mice was similar to that observed in anti-CD25-treated mice. The exacerbated allergic inflammation of CCR4KO mice was directly associated with an impaired migration of Treg cells to airways and augmented frequency of pulmonary Th2 cells. Adoptive transfer of CD25(+)CD4(+) T cells expressing high levels of CCR4, but not CCR4KO CD25(+)CD4(+) T cells, attenuated the severe airway Th2 response of CCR4KO mice. Our results show that CCR4 is critically involved in the migration of Treg cells to allergic lungs that, in turn, attenuate airway Th2 activation and allergic eosinophilic inflammation.

Neural and behavioral correlates of food allergy

Food allergy accounts for a great number of reactions leading to diminished quality of life in western countries. There has been an abundance of reports of behavioral changes, as well as psychiatric conditions associated with food allergy over the past decades. Most of this field inspired little medical attention for its lack of a solid scientific ground. We review the literature on the association of food allergy and brain activity, leading to changes in emotion and behavior. Moreover, we describe an experimental paradigm employed to dissect the biological relevance of this association. Mice allergic to ovalbumin avoid a palatable sweet solution in order to escape contact with antigen. This choice is associated with increased levels of anxiety, compatible with a conflicting situation. These responses are associated with increased activity in brain areas associated with emotional and affective behavior, which are also important for anxiety and stress responses. Higher levels of corticosterone accompany these changes in behavior. These responses are mediated by specific antibodies and prevented by depletion or immunological tolerance. They are also partially mediated by C-sensitive afferents and mast cells. Far from anecdote, neural repercussions of food allergy should be considered when planning a therapeutic strategy in affected individuals.

Role of mast cell degranulation in the neural correlates of the immediate allergic reaction in a murine model of asthma

Experimental airway allergy in mice leads to increased activity in specific hypothalamic and amygdaloid nuclei, and behavioral changes. The experiments described here were designed to determine the role of anaphylactic antibodies, mast cell degranulation, and lung inflammation in the neural and behavioral correlates of an experimental murine asthma-like response. Animals were sensitized intraperitoneally with ovalbumin adsorbed to alum, and challenged by intranasal ovalbumin instillation or aerosol. To induce immunological tolerance, animals were fed ovalbumin in the drinking water for 5 consecutive days, along with primary sensitization. Depletion of IgE was also accomplished with a non-anaphylactic anti-IgE antibody. Mast cell degranulation was inhibited by cromolyn. In addition to BALB/c animals, C3H/HeJ mice were used for their relative resistance to lung allergic inflammation. We confirmed that ovalbumin challenge in allergic mice leads to increased activity in the paraventricular nucleus of the hypothalamus and central nucleus of the amygdala, and avoidance behavior towards an allergen-associated compartment. Moreover, these responses were precluded by oral tolerance or anti-IgE treatment, even in the presence of IgG1. Cromolyn abrogates both responses in the presence of anaphylactic antibodies. Finally, although sensitized C3H/HeJ mice did not develop airway inflammation, they exhibited brain and behavioral changes similar to BALB/c animals. The repercussions of murine allergic asthma on brain and behavior are IgE-dependent, mediated by mast cell degranulation, and do not require a pulmonary inflammatory infiltrate, suggesting that the early phase of this immediate allergic response suffices for the brain activation associated with avoidance behavior towards exposure to the allergen.

Neural correlates of IgE-mediated allergy

Although many authors have considered a direct interaction between allergic reactions and behavioral changes, supporting evidence has been elusive. In this series of studies we show that after oral or nasal ovalbumin (OVA) challenge, allergic mice present increased Fos expression in the paraventricular nucleus of the hypothalamus (PVN) and in the central nucleus of the amygdala (CeA). Mice with food allergy display higher levels of anxiety and increased serum corticosterone levels, and allergy-activated neurons express corticotropin-releasing factor (CRF) in the PVN and CeA. OVA-allergic mice develop aversion to an antigen-containing solution, and also avoid a dark compartment previously associated with nebulized OVA. Results on brain Fos expression and behavioral data seem compatible with adaptive responses. Removal of IgE by either antibody depletion or the development of oral tolerance precluded all responses analyzed here. C-sensitive fiber destruction by neonatal capsaicin inhibited the activation in the PVN, but not in the CeA, and decreased the magnitude of food aversion. Cromolyn, a mast cell stabilizer, completely blocked Fos expression in the PVN and CeA, and precluded the development of aversion to the dark compartment associated with nebulized OVA. Employing mice that do not develop an important inflammatory infiltrate following nasal OVA challenge, we found that inflammatory cells are not required at the site of challenge in order to trigger neural or behavioral correlates of murine experimental asthma. Altogether, we have built a solid foundation for understanding neuroimmune interactions during allergic responses that may contribute to the comprehension of psychological disorders associated with allergy.

Avoidance behavior and neural correlates of allergen exposure in a murine model of asthma

Allergic asthma is characterized by intermittent airway obstruction, inflammation, airway hyperreactivity, and increased production of IgE. The pathophysiology of asthma is well understood but little is known about its influences on brain activity and behavior. We recently described the neural correlates of food allergy and its associated modulation of behavior using an experimental model that also generates a T helper type 2 (Th2)-skewed response, with high levels of IgE. Here we show that mice allergic to ovalbumin (OVA) have an increase in the activity of the paraventricular nucleus of the hypothalamus (PVN) and in the central nucleus of the amygdala (CeA) following a single nasal OVA challenge. Moreover, we adapted a classical passive avoidance test using an OVA aerosol as the aversive stimulus. We found that allergic mice avoid entering the dark compartment of the apparatus that had been previously associated with nebulization of the allergen, while their non-immunized controls still move into the dark side of the test box. Thus, allergic mice have increased activity in areas of the CNS commonly associated with emotionality-related behavioral responses, such as the avoidance of a context previously associated with an unpleasant or harmful situation. Moreover, our findings on the avoidance test illustrate that previous experience with an airborne allergen can modify behavior.

Neural pathways involved in food allergy signaling in the mouse brain: role of capsaicin-sensitive afferents

There is increasing evidence supporting the notion that brain-gut communication is crucial for the manifestation of functional gastrointestinal (GI) disorders. Employing denervation by neonatal capsaicin treatment, we investigated here the role of unmyelinated C-fibers in food allergy signaling in the brain. We found that 90 min after oral ovalbumin (OVA) challenge, allergic mice present increased c-fos expression in emotionality-related brain areas such as the paraventricular nucleus of the hypothalamus (PVN) and the central nucleus of the amygdala (CeA). Food allergy also induced enhanced Fos immunoreactivity in the nucleus of tractus solitarii (NTS) of OVA-immunized animals. We also show that while the degree of Fos staining in the NTS of allergic mice was only diminished by neonatal capsaicin, it was completely blocked in the PVN. However, capsaicin did not modify food allergy-induced c-fos expression in the CeA. In conclusion, this study provides evidence showing that unmyelinated C-fibers are part of the neural pathways involved in food allergy-induced activation of specific brain areas, particularly the PVN and to a lesser extent the NTS.

Neural correlates of IgE-mediated food allergy

Although many authors have considered the possibility of a direct interaction between food allergy and behavioral changes, the evidence supporting this hypothesis is elusive. Here, we show that after oral ovalbumin (OVA) challenge, allergic mice present higher levels of anxiety, increased Fos expression in emotionality-related brain areas, and aversion to OVA-containing solution. Moreover, treatment with anti-IgE antibody or induction of oral tolerance abrogate both food aversion and the expression of c-fos in the central nervous system (CNS). Our findings establish a direct relationship between brain function and food allergy, thus creating a solid ground for understanding the etiology of psychological disorders in allergic patients.

Immune-induced flavor aversion in mice: modification by neonatal capsaicin treatment

OBJECTIVE

This study was designed to evaluate the role of c-sensitive fibers in the establishment of immune-induced flavor aversion in mice.

METHODS

Mice were treated neonatally with capsaicin in order to destroy c-sensitive fibers; after such treatment, adult animals, immunized or not with ovalbumin, were submitted to a two-bottle preference test, with a choice between water and a sweetened egg white solution.

RESULTS

Neonatal capsaicin treatment was unsuccessful in preventing the development of immune-induced aversion to the sweetened solution containing the antigen. Nonetheless, amongst immunized mice, those which had been previously treated with capsaicin showed a significant increment in the preference for the sweetened egg white solution. Furthermore, our data showed that neonatal capsaicin treatment did not interfere with either IgG1 or IgE production.

CONCLUSION

The present results suggest that c-sensitive fibers have a role in the transmission of the signals generated by this immune response to the central nervous system, thus contributing to the development of a flavor aversion in mice.