Schistosoma mansoni: IL-4 is necessary for concomitant immunity in mice.

To ask whether type-2 immune responses serve an essential role in concomitant immunity, that is the prevention of superinfection with Schistosoma mansoni, we compared resistance to a challenge infection in infected wild-type (WT) mice and in infected IL-4-/- mice, which are unable to mount Th2 responses during schistosomiasis. Although WT mice are protected from superinfection, resistance is abrogated in the absence of interleukin (IL)-4. We conclude that IL-4 or IL-4-dependent responses, or both, are necessary for resistance to S. mansoni superinfection in mice.

Interleukin 5 (IL-5) is not required for expression of a Th2 response or host resistance mechanisms during murine schistosomiasis mansoni but does play a role in development of IL-4-producing non-T, non-B cells.

During schistosomiasis, interleukin-5 (IL-5)-dependent eosinophil responses have been implicated in immunopathology, resistance to superinfection, synergistic interactions with chemotherapeutic agents, and the inductive phase of the egg-induced Th2 response. We examined these issues in IL-5-deficient (IL-5(-/-)) mice. IL-5(-/-) and wild-type (WT) mice were indistinguishable in terms of susceptibility to primary infections and the ability to resist secondary infections. Moreover, hepatic pathology was similar in both strains apart from a relative lack of eosinophils and, during chronic infection, a significantly larger mast cell component in the granulomas of IL-5(-/-) mice. Splenocyte cytokine production in response to soluble egg antigen (SEA) or anti-CD3 revealed no significant differences except for heightened tumor necrosis factor alpha production by cells from chronically infected IL-5(-/-) mice compared to WT animals. In contrast, ionomycin-stimulated non-B, non-T (NBNT) cells from IL-5(-/-) mice produced significantly smaller IL-4 amounts than did NBNT cells from WT animals. This difference was not apparent following plate-bound anti-immunoglobulin E or SEA stimulation. The absence of IL-5 failed to affect the induction of Th2 responses in naive mice. Peritoneal exudate cells recovered from egg-injected IL-5(-/-) or WT mice produced equivalent levels of IL-4 following restimulation with SEA or anti-CD3.

IL-4 protects against TNF-alpha-mediated cachexia and death during acute schistosomiasis.

To examine the role of the Th2-type response during schistosomiasis mansoni we compared disease progression in wild type (wt), and Th2-response deficient IL-4(-/-) mice. Whereas wt C57BL/6 mice tolerate infection and develop chronic disease, IL-4(-/-) C57BL/6 animals are highly susceptible, exhibiting severe acute cachexia followed by death. Data point toward morbidity in the IL-4(-/-) C57BL/6 mice being mediated by TNF-alpha, possibly through the uncontrolled production of nitric oxide in target organs such as the ileum. We propose that IL-4 prevents severe disease during schistosomiasis by regulating macrophage activation.

Schistosoma mansoni egg-induced early IL-4 production is dependent upon IL-5 and eosinophils.

The initial immune response to Schistosoma mansoni eggs presumably results in IL-4 production, as schistosome eggs are strong Th2-inducing antigens and the differentiation of antigen-specific Th2 cells is largely dependent on the presence of IL-4 during priming of naive Th cells. Consistent with this concept, intraperitoneal injection of mice with schistosome eggs results in an upregulation of IL-4 production by peritoneal exudate cells (PECs) within 12 h. Egg-induced IL-4 is rapidly bound by its receptor, suggesting that this cytokine is utilized by a cell type present at the site of antigen deposition or is complexed to soluble receptor. The peak of early IL-4 production is accompanied by a local eosinophilia and the apparent disappearance of mast cells. Studies utilizing either IL-4, IL-5, or mast cell-deficient mice indicate that the eosinophilia is dependent on mast cells and IL-5 and independent of IL-4. Strikingly, egg-induced IL-4 production is absent in animals lacking the early peritoneal eosinophilia. Immunocytochemical analysis of PEC following egg injection indicates that the eosinophils themselves make IL-4. These data strongly suggest that egg-induced IL-5 plays an essential role in recruiting eosinophils to the site of antigen deposition and that it is these eosinophils that then directly produce early IL-4.

Key role of alkanoic acids on the spectral properties, activity, and active-site stability of iron-containing nitrile hydratase from Brevibacterium R312.

Interaction of n-butyric acid with dialyzed nitrile hydratase from Brevibacterium R312, which is characterized by a charge-transfer band at 680 nm and EPR signals typical of a low-spin Fe(III) with delta g = 0.22, leads to a form displaying different spectral properties (lambda = 710 nm, delta g = 0.31). Butyric acid also acts as a competitive inhibitor of nitrile-hydratase-catalyzed hydration of acrylonitrile with a Ki value of 0.9 mM. Formation of the complex between the enzyme and butyric acid is highly dependent on the concentration of the latter and on pH. When stored with high levels of butyric acid, nitrile hydratase is completely inactive. The active uncomplexed enzyme is restored under the high dilution conditions used for the enzymatic assays, while the complexed form is favored at acidic pH and is not formed at pH above 8. Furthermore, the inhibitory potency of butyric acid decreases upon increasing pH (IC50 increases from 0.8 mM at pH 6.2 to 12 mM at pH 8.2). These data show that nitrile hydratase interacts with the acid form of butyric acid with a high affinity (Ki' approximately 4 microM at pH 7.2). At pH < 3, the visible spectrum of the enzyme disappears, presumably because of demetallation, whereas that of the complex exhibits a charge-transfer band shifted to 800 nm, the presence of butyric acid preventing nitrile hydratase from demetallation. Other linear carboxylic acids such as valeric and hexanoic acids behave similarly; they act as inhibitors of nitrile hydratase and protect the enzyme during storage. A structure of the nitrile hydratase active site interacting with butyric acid is tentatively proposed in which the latter is hydrogen-bonded to the Fe(III)-OH moiety. This interaction between butyric acid and nitrile hydratase should be considered when deducing the nature of nitrile hydratase active site and mechanisms, from spectral and enzymatic data, since most results published previously have been obtained on nitrile hydratase containing large amounts of butyric acid and interpreted without taking into account the presence of this acid in the active site.