IgG-, IgA-, and IgE-induced release of leukotriene C4 by monocytes isolated from patients with atopic dermatitis

Efficacy of traditional Chinese herbal therapy in vitro. A model system for atopic eczema: inhibition of CD23 expression on blood monocytes

Recently, there has been growing interest in the use of traditional Chinese herbal therapy (TCHT) decoctions for the treatment of atopic eczema (AE). The mode of action of this treatment is still unknown, and in order to investigate this we have analysed the effect of an extract of these herbs (TCHTE) on interleukin 4 (IL-4)-induced CD23 expression on peripheral blood monocytes from non-atopic subjects. We found that TCHTE inhibited CD23 expression up to 60% (P < 0.001), whereas the placebo extract had no significant effect on CD23 expression. This inhibition was dose-dependent, and TCHTE was effective at a concentration of 250 micrograms/ml (P = 0.001). If TCHTE or placebo was added after IL-4, the action of TCHTE could still be seen at 12 h. This inhibition was not due to cell death, as peripheral blood mononuclear cells (PBMCs) cultured with TCHTE or placebo at a concentration used in these experiments had a similar viability to control cultures. Down-regulation of the low affinity receptors for IgE on antigen-presenting cells in patients with AE may contribute to the benefit observed following treatment with TCHT.

Leukotriene B4 and C4 generation by blood leukocytes after ex vivo stimulation by Ca-ionophore and opsonized zymosan in children with atopic dermatitis

The ex vivo release of leukotrienes B4 (LTB4) and C4 (LTC4) from the leukocytes of children with atopic dermatitis (AD) was evaluated after stimulation with Ca-ionophore and opsonized zymosan and compared with that of control children of similar ages. The blood eosinophil counts and total serum IgE levels in AD children were significantly higher than those in control children. The production of LTC4, but not LTB4, was significantly higher in AD children than in control children. There was a significant correlation between the relative blood eosinophil count and LTC4 generation after stimulation with both Ca-ionophore and opsonized zymosan in all subjects. Calculations of the amount of LTC4 produced per eosinophilic cell showed that there was no significant difference between cells from AD children and control children in terms of their ability to produce LTC4. These findings suggest that the enhanced LTC4 generation is due to increased numbers of eosinophils rather than to enhanced releasability of these cells.

Receptors for IgA on phagocytic cells

IgA receptors have been detected on monocytes, polymorphonuclear neutrophils (PMNs) and eosinophils, and on phagocytic cells at mucosal sites. These receptors bind both secretory and serum forms of immunoglobulin A (IgA) and require the Ca2 region of the IgA molecule for ligand recognition. Monocytes and PMNs modulate their expression of the IgA receptor upon treatment with cytokines, such as granulocyto-macrophage colony-stimulating factor, and lipopolysaccharide. Purified IgA receptors appear as heavily glycosylated molecules with an average molecular weight of 60 kD, dropping to 32 and 36 kD upon treatment with N-glycanase. The cDNA sequence encoding the IgA receptor has been determined by expression cloning, and predicts that the receptor consists of two Ig-like extracellular domaines, a transmembrane region and a cytoplasmic tail of 41 residues. Ligation of IgA receptors on phagocytic cells by multivalent IgA complexes induces a variety of responses, including superoxide generation, release of inflammatory mediators, phagocytosis, and killing of various pathogenic microorganisms. Thus the apparent role of these receptors is to amplify the protective effects of the IgA antibody, a function of potential importance to mucosal defense.

IgE and IgG are synergistic in antigen-mediated release of thromboxane from human lung macrophages

The mechanism of IgE-mediated release of thromboxane A2 from human lung macrophages has been studied using a monoclonal chimeric human/mouse IgE antibody and its specific antigen. The cells could be sensitized at 37 degrees C but not at 4 degrees C by incubation with IgE, and released a significant amount of thromboxane A2 (TXA2), measured as the stable hydrolysis product TXB2, in response to an anti-chimeric IgE antibody. In contrast, stimulation of IgE-sensitized macrophages with the specific antigen produced less than 10% of this response. A similar time course for the release of TXB2 and the formation of inositol monophosphate in the presence of LiCl was observed. Cleavage of the Fc domain of the anti-chimeric IgE antibody substantially eliminated its capacity to stimulate IgE-sensitized cells. However, the weak or undetectable response to chimeric IgE plus specific antigen was substantially potentiated by an antigen-specific chimeric IgG antibody. IgG-sensitized macrophages did not respond to antigen challenge by the release of TXB2. Preincubation of the cells with a monoclonal antibody against the low affinity receptor for IgE (Fc epsilon RII/CD23) did not prevent IgE sensitization. We conclude that cell-bound IgE antibody cannot induce the release of TXB2 but has fixed antigen which then must interact with specific IgG antibody and IgG receptors to induce mediator release.

Production of tumor necrosis factor with IgE receptor triggering from sensitized lung tissue

Mast cells and basophils have been known to play a central role in allergic inflammation through the release of chemical mediators by cross-linkage of IgE receptors. The IgE receptor triggering and calcium ionophore A23187 have also been shown to induce gene expression and production of tumor necrosis factor (TNF) by rat basophilic leukemia cells. In the present study, we examined whether IgE receptor triggering could induce gene expression and production of TNF in rat lung tissue. The lung tissue released not only histamine but also cytotoxic activity on L929 cells 2 and 4 h after incubation with dinitrophenyl conjugated to ovalbumin (DNP-OVA) following passive sensitization with anti-DNP monoclonal rat IgE antibody, whereas neither DNP-OVA nor anti-DNP IgE antibody could induce the cytotoxic activity when used solely. Calcium ionophore A23187 also could induce both histamine release and cytotoxic activity. These activities induced by IgE receptor triggering, A23187, and lipopolysaccharide were completely neutralized by preincubation with anti-mouse TNF-rabbit serum, but not with normal rabbit serum. Northern blot analysis using cDNA probe of mouse TNF demonstrated expression of TNF gene as early as 2 h after IgE receptor triggering. These data demonstrating that IgE receptor triggering induced gene expression and production of TNF in lung tissue suggest the participation of TNF in the pathogenesis of late asthmatic response through its biologic activities such as the attraction and activation of neutrophils and eosinophils.

Fc receptors for IgE and interleukin-4 induced IgE and IgG4 secretion

IgE binds to two types of Fc receptors, called Fc epsilon R1 (or high-affinity Fc epsilon R) and Fc epsilon R2 (or low-affinity Fc epsilon R). The Fc epsilon R1 is composed of four polypeptide chains, one alpha, one beta, and two gamma chains. The alpha chain contains the IgE binding site and is a member of the immunoglobulin supergene family. The Fc epsilon R2, also called CD23, consists of one polypeptide chain which shows homology to animal lectin receptors. Fc epsilon R1 are expressed on mast cells and basophils. Crosslinking of the Fc epsilon R1 induces immediate release of mediators of inflammation such as histamine and leukotrienes and delayed secretion of interleukins 4, 5, and 6. Fc epsilon R2 are expressed on resting mu delta + B cells, monocytes/macrophages (M phi), eosinophils, and platelets but rarely on T cells. Interleukin-4 upregulates Fc epsilon R2 expression on B cells and M phi. The functions of Fc epsilon R2 on the different cell types are not fully established and are controversial. Fc epsilon R2 on M phi, eosinophils, and platelets mediate cytotoxicity to schistosomules, enhance phagocytosis, and induce the release of granule enzymes. However, M phi from patients with atopic dermatitis expressing significantly more Fc epsilon R2 than M phi from normals do not release more leukotriene C4, prostaglandin E2, or beta-glucuronidase after incubation with aggregated IgE than normal monocytes. Furthermore, aggregated IgG1 is much more efficient than IgE in inducing mediator release from M phi and IgG1 antibodies are not known to induce immediate-type hypersensitivity reactions. Therefore, definitive proof that Fc epsilon R2 are involved in the pathogenesis of allergic disorders is still lacking. IL-4 appears to play a central role in immediate-type hypersensitivity. It induces human B cells to secrete IgE and IgG4, Ig isotypes typical for antibodies to helminthic parasites and allergens. IL-4 stimulates mast cell growth and upregulates Fc epsilon R2 expression. Interferon-gamma and IL-2 inhibit the IL-4-induced IgG4 and IgE secretion. Whether the abnormally high IgE antibody production in atopic patients is the result of overproduction of IL-4 or deficient IFN-gamma/IL-2 production is presently unknown.

Allergen-stimulated release of thromboxane A2 and leukotriene E4 in humans. Effect of indomethacin

Allergen-stimulated release of a cyclooxygenase product (thromboxane [TX] A2) and a 5-lipoxygenase product (leukotriene [LT] E4) into the urine was measured in 10 atopic asthmatics undergoing allergen inhalation. Because indomethacin has been reported to increase allergic-stimulated 5-lipoxygenase product formation and to inhibit the late asthmatic response, we determined the effect of indomethacin (50 mg 3 times a day) or placebo on airway and biochemical responses to inhaled allergen in a randomized, blinded study. Urinary levels of the enzymatic metabolite of TXB2, 11-dehydro-TXB2, increased from 585 +/- 330 to 1,500 +/- 250 pg/mg creatinine (mean +/- SEM, p less than 0.05) 2 h after allergen. Urinary LTE4 increased from 190 +/- 37 to 1,100 +/- 400 (p less than 0.05) 2 h after challenge. The urinary levels of these eicosanoids were not elevated during the late response. Indomethacin significantly reduced urinary 11-dehydro-TXB2 levels without affecting the excretion of LTE4 or pulmonary function. Thus, we failed to obtain evidence for enhanced leukotriene formation during allergic stimulation in vivo in the presence of cyclooxygenase inhibition. Furthermore, we conclude that cyclooxygenase products are likely to play only a marginal role in allergic bronchoconstriction.

Atopic dermatitis

AD is a complex, multifactorial, cutaneous manifestation of the atopic diathesis. Observations from bone marrow transplantation cases have shown transmission of the disease from atopic donors [30] and indicate that the basic defect is carried in immune and inflammatory cells which infiltrate skin lesions. Mast cells appear to be important in the initiation of inflammatory events and eosinophils may have an important role in perpetuating the response. New evidence suggests that IL-4 may be a crucial factor controlling mast cells as well as IgE production in allergic disease. The significance of the Fc&RII/CD23 in regulating IgE synthesis and its role in Langerhans' cell/antigen interactions in atopic dermatitis represents an intriguing area in need of further study.