IL-4-induced apoptosis in peripheral blood eosinophils.

BACKGROUND: The regulation of eosinophil survival and apoptosis may play a major role in diseases demonstrating increased numbers of circulating and tissue eosinophils such as allergic reactions. Because few promoters of eosinophil apoptosis have been described so far, the objective of this study was to elucidate the role of endogenous factors on eosinophil survival and apoptosis. METHODS AND RESULTS: Highly purified peripheral blood eosinophils were analyzed in the time course from 24 up to 144 hours in culture. Eosinophil survival was assessed with trypan blue dye exclusion and apoptosis was determined by DNA fragmentation gel analysis and ELISA technique with anti-histone antibodies. We confirmed previous results demonstrating prolonged eosinophil survival and inhibited apoptosis by IL-3, IL-5, and GM-CSF. In contrast, eosinophil apoptosis was significantly enhanced by corticosteroids, particularly dexamethasone and hydrocortisone. However, IL-1beta, IL-8, IL-12, platelet-activating factor, TNF-alpha, and eotaxin had no effect on eosinophil survival or apoptosis when compared with culture medium alone. In contrast, IL-4 at concentrations of 100 U/mL or more inhibited eosinophil survival and induced apoptosis. This effect was time dependent and abrogated by preincubation with neutralizing anti-IL-4 antibodies. However, after 96 hours in coincubation, IL-4 did overcome the survival-prolonging effect of IL-3, IL-5, and GM-CSF. IL-4 did not enhance eosinophil surface expression of APO-1/Fas antigen (CD95). In assessing IL-4-mediated effects on eosinophil function, we found no response by means of the release of eosinophil cationic protein or reactive oxygen species. CONCLUSIONS: Taken together, our data present direct evidence for the presence of functional IL-4 receptors on human eosinophils and indicate that IL-4 may lead to resolution of chronic inflammation by induction of eosinophil apoptosis.

Delayed eosinophil programmed cell death in vitro: a common feature of inhalant allergy and extrinsic and intrinsic atopic dermatitis.

The present studies were undertaken to characterize the potential role of eosinophil programmed cell death (PCD) in atopic diseases. Peripheral blood eosinophil PCD was found to be delayed in inhalant allergy (p < 0.05) and delayed to an even greater extent in atopic dermatitis (AD) (p < 0.0001) when compared to nonatopic subjects. There was no difference in the occurrence of PCD between the extrinsic and the intrinsic type of AD, pointing to a secondary role of specific sensitization. Blockade of eosinophil PCD was not responsible for peripheral blood eosinophilia, because we found no obvious relationship of eosinophil survival to blood eosinophil count. Eosinophil supernatants of more patients with AD than of patients with inhalant allergy dose-dependently inhibited PCD in nonatopic eosinophils, and it was shown that this effect was possibly due to autocrine production of granulocyte-macrophage-colony stimulating factor, probably IL-5. Eosinophil expression of CD95 (Fas antigen) did not change over time in culture and was not modulated by cytokines prolonging eosinophil survival. In contrast, IL-3, IL-5, and granulocyte-macrophage-colony stimulating factor caused an upregulated expression of CD69. However, in AD, CD69 on eosinophils was upregulated without the need of exogenous growth factor or factors over time in culture, thus confirming an autocrine production of proeosinophilic cytokines. In conclusion, our data clearly indicate that eosinophil PCD is markedly delayed in the so-called atopic diseases irrespective of allergen sensitization and suggest that this effect is mediated by the autocrine production of growth factors by eosinophils.

Human HMC-1 mast cells exclusively express the Fc gamma RII subtype of IgG receptor.

Because of their localization at the interface of the internal and external environment mast cells play a crucial role in the immune response and in inflammatory reactions. Effects may be mediated not only by the high-affinity IgE receptor, but also by IgG receptors. Since in rodent mast cells signal transduction via the Fc gamma receptor family has been shown, we analysed the expression of surface receptors for IgG on the human mast cell line HMC-1. It was shown by flow cytometric analysis that HMC-1 constitutively expressed the Fc gamma RII/CD32 subtype whereas Fc gamma RI/CD64 and Fc gamma RIII/CD16 were not expressed. This exclusive expression of the Fc gamma RII subtype of IgG receptor is similar to the expression pattern of basophils, although concerning cell surface molecules HMC-1 rather seem to resemble monocytes. In contrast to monocytes the expression profile on HMC-1 did not change upon stimulation with IL-4, TNF alpha, IFN gamma, PMA or salbutamol. Moreover, the mast cell-activating cytokine SCF and the calcium ionophore A23187 did not modulate the Fc gamma R profile in this study. To assess the importance of the exclusive Fc gamma RIII expression on HMC-1, we investigated whether the production of the cytokine TNF alpha is modulated via Fc gamma RII activation or if an increase in intracellular calcium could be observed. No significant modulation of TNF alpha release or of intracellular free calcium after crosslinking of Fc gamma RII by heat-aggregated IgG or by a second antibody was observed. It remains to be clarified whether this low-affinity subtype for the IgG receptor is involved in antigen-dependent sensitization of human tissue mast cells resulting in secretion of immunoregulatory cytokines. This mechanism may be important for disease states associated with circulating or tissue-bound immune complexes.