We previously postulated that desensitization of human basophils was due to endocytosis or shedding of IgE and/or its Fc receptor. We report here, however, that during a 3-hr desensitization of purified basophils, there was no loss of cell surface antigen-specific IgE. The specific desensitization induced by antigen persists for at least 24 hr whereas simultaneously occurring nonspecific desensitization can recover during the same time interval. Therefore, we suggested that specific desensitization may result from a permanent modification of the Fc receptor or some closely associated protein. On the basis of elution studies of 125I-labeled BPO-HSA, we also suggest the antigen antibody reaction matures to aggregates of increasing size, and we propose that these large aggregates, unable to initiate a release signal, cause an additional component of desensitization.
Background Desloratadine is a non‐sedating, clinically effective, anti‐allergic therapy that has been shown to exhibit anti‐inflammatory properties that extend beyond its ability to antagonize histamine at H 1 ‐receptor sites. This latter effect has been shown in vitro to be both IgE‐dependent and ‐independent. Objective In this study, we addressed the ability of desloratadine to inhibit the in vitro generation of interleukin (IL)‐4 and IL‐13 from human basophils while concurrently comparing its efficacy in preventing mediator release by these cells. Methods Basophil‐enriched suspensions were treated with various concentrations of desloratadine for 15 min before stimulating with either anti‐IgE antibody, calcium ionophore, IL‐3 or phorbol ester. Histamine (fluorimetry), LTC 4 (RIA) and IL‐4 (ELISA) were all assayed using the same 4‐h culture supernatants. IL‐13 (ELISA) was measured in supernatants harvested after 20 h incubation. IL‐4 mRNA expression (dilutional RT‐PCR) was also examined. Results Desloratadine was found to be nearly six–seven times more potent in preventing the secretion of IL‐4 and IL‐13 induced by anti‐IgE than it was at inhibiting the release of histamine and LTC 4 . These cytokines were equally inhibited by desloratadine following activation with ionomycin despite the lack of an effect on the histamine induced with ionomycin. Desloratadine had a lesser effect regarding inhibition of the IL‐13 secreted in response to IL‐3 and PMA. There was no evidence that desloratadine mediated its inhibitory effects by causing decreased cell viability. Finally, IL‐4 mRNA accumulation was remarkably inhibited, by as much as 80%, following pretreatment with desloratadine. Conclusion While capable of inhibiting histamine and LTC 4 release by human basophils, desloratadine is more effective at targeting the signals regulating IL‐4 and IL‐13 generation in these cells. This inhibitory effect on cytokine generation provides additional evidence that this antihistamine exerts anti‐inflammatory properties.
An inverse relationship between cAMP content and effector function is ascribed generally to immune and inflammatory cells. Previous reports imply, however, that human polymorphonuclear leukocytes (PMN) are less responsive than other inflammatory cells to adenylate cyclase (AC) agonists. We therefore examined the effects of isoproterenol, prostaglandin E1 (PGE1), adenosine, and histamine on the adenosine 3',5'-monophosphate (cAMP) content of PMN and on particle-stimulated lysosomal enzyme release. For comparison, the effect of AC agonists on the cAMP content of human peripheral lymphocytes was evaluated in parallel. Although potent stimuli for cAMP accumulation in lymphocytes, the AC agonists produced only marginal increases in the cAMP content of PMN; this difference in responsiveness was independent of agonist concentration or length of incubation. Inhibition of lysosomal enzyme release by the AC agonists was likewise marginal (< 20%). The addition of theophylline with isoproterenol produced additive inhibition without significant cAMP increases. Hydrocortisone, which caused a small increase in the cAMP content, markedly potentiated the effects of AC agonists on the cAMP level in PMN; the synergistic increases in cAMP were accompanied by additive effects on lysosomal enzyme release. It is concluded that human lymphocytes and PMN exhibit differential sensitivity to AC agonists and that this difference may provide a basis for the selective modulation of individual PMN- or lymphocyte-mediated events.
The relationship between the intensity of the signal for antigen-induced immunoglobulin E-mediated histamine release from human basophils and the concentration of agonist needed to inhibit release has been determined. The agonists, prostaglandin E1, dimaprit, fenoterol, isobutylmethylxanthine and dibutyryl cyclic AMP, all act by increasing the cyclic AMP level. Each agonist was 10- to 1000-fold more potent (relative ID50) at low levels of histamine release (5-10% of total histamine) than at high levels (50-80%). Thus, the inhibitory potential of a drug is a function of the concentration of antigen used to initiate the response. Our results are now more in accord with the inhibitory profile of these drugs in human lung tissue. It is suggested that in vivo release is likely to be low and that this is the level at which to evaluate drugs in vitro.
Abstract Human lung macrophages obtained from surgical specimens spontaneously secreted a factor(s) (which we term macrophage factor) during 24-hr culture that induced calcium-dependent histamine release from human basophils and lung mast cells. Macrophage factor induced noncytotoxic histamine release from purified (85%) basophils. The kinetics of release were relatively slow and similar to that of anti-IgE. We performed a series of experiments to test the IgE dependence of macrophage factor-induced release. Preincubation of basophils with anti-IgE in calcium-free medium resulted in complete desensitization to macrophage factor-induced histamine release (i.e., when calcium and macrophage factor were added to the basophils, no histamine release occurred), and preincubation with macrophage factor in calcium-free medium resulted in partial desensitization to anti-IgE-induced histamine release. Pretreatment of basophils with pH 3.9 lactic acid buffer, which dissociates basophil IgE from its receptors, markedly reduced the capacity of basophils to release histamine in response to macrophage factor. Basophils that were incubated with IgE myeloma (but not with IgG) after lactic acid treatment partially or completely regained their capacity to release histamine in response to macrophage factor. Fluid-phase IgE myeloma (15 micrograms/ml) (but not IgG) inhibited basophil histamine release induced by two macrophage-derived supernatants, whereas IgE myeloma (200 micrograms/ml) did not inhibit release due to other supernatants. IgE-affinity columns removed the histamine-releasing activity of five macrophage-derived supernatants, and IgG-affinity columns had similar effects. However, neither affinity column removed the histamine-releasing activity of three other macrophage-derived supernatants. On Sephadex G-75 chromatography, nearly all of the histamine-releasing activity migrated as single peak with an apparent m.w. of 18,000. These results suggest that, although macrophage factor are heterogeneous, they are related, as they are a IgE-dependent factors that induce histamine release by interacting with cell surface IgE. These macrophage factors may be responsible for stimulation of basophil/mast cell mediator release in chronic allergic reactions.
Histamine has long been considered to be an important chemical mediator in the pathogenesis of immediate hypersensitivity reactions. We evaluated the efficacy of antihistamines to determine the physiological role of histamine in canine anaphylaxis. Either a saline vehicle (control group), an H1 antihistamine (chlorpheniramine, 10 mg/kg), or this H1 antihistamine and an H2 antihistamine (cimetidine, 30 mg/kg) was administered to three separate groups of anesthetized dogs (n = 8). Cardiopulmonary responses and plasma histamine levels were measured after the separate intravenous injection of Ascaris suum antigen and histamine. Results were analyzed only from the animals demonstrating physiological responses or histamine release after antigen injection. In the control group, antigen produced a 43 +/- 15% (mean +/- SE) decrease in mean arterial blood pressure, a 34 +/- 13% fall in cardiac output, and a 19 +/- 9% decrease in lung compliance, whereas pulmonary vascular resistance increased 161 +/- 87% and airway resistance rose 114 +/- 66%. Similar physiological abnormalities were observed with histamine shock. However, peak plasma histamine levels were, in most cases, greater after histamine injection than after antigen injection. An H1 antihistamine alone or in combination with an H2 antihistamine did not alter the physiological changes associated with systemic anaphylaxis. In contrast, the combined use of H1 and H2 antihistamines prevented the cardiopulmonary responses associated with the intravenous administration of histamine.(ABSTRACT TRUNCATED AT 250 WORDS)
