Upregulated surface expression of intracellularly sequestered Igepsilon receptors (FcepsilonRII/CD23) following activation in human peripheral blood eosinophils

Human eosinophils and mast cells: Birds of a feather flock together

While the origin of the phrase "birds of a feather flock together" is unclear, it has been in use for centuries and is typically employed to describe the phenomenon that people with similar tastes or interests tend to seek each other out and congregate together. In this review, we have co-opted this phrase to compare innate immune cells of related origin, the eosinophil and mast cell, because they very often accumulate together in tissue sites under both homeostatic and inflammatory conditions. To highlight overlapping yet distinct features, their hematopoietic development, cell surface phenotype, mediator release profiles and roles in diseases have been compared and contrasted. What emerges is a sense that these two cell types often interact with each other and their tissue environment to provide synergistic contributions to a variety of normal and pathologic immune responses.

CD23-dependent transcytosis of IgE and immune complex across the polarized human respiratory epithelial cells

IgE-mediated allergic inflammation occurs when allergens cross-link IgE on the surface of immune cells, thereby triggering the release of inflammatory mediators as well as enhancing Ag presentations. IgE is frequently present in airway secretions, and its level can be enhanced in human patients with allergic rhinitis and bronchial asthma. However, it remains completely unknown how IgE appears in the airway secretions. In this study, we show that CD23 (FcεRII) is constitutively expressed in established or primary human airway epithelial cells, and its expression is significantly upregulated when airway epithelial cells were subjected to IL-4 stimulation. In a transcytosis assay, human IgE or IgE-derived immune complex (IC) was transported across a polarized Calu-3 monolayer. Exposure of the Calu-3 monolayer to IL-4 stimulation also enhanced the transcytosis of either human IgE or the IC. A CD23-specific Ab or soluble CD23 significantly reduced the efficiency of IgE or IC transcytosis, suggesting a specific receptor-mediated transport by CD23. Transcytosis of both IgE and the IC was further verified in primary human airway epithelial cell monolayers. Furthermore, the transcytosed Ag-IgE complexes were competent in inducing degranulation of the cultured human mast cells. Because airway epithelial cells are the first cell layer to come into contact with inhaled allergens, our study implies CD23-mediated IgE transcytosis in human airway epithelial cells may play a critical role in initiating and contributing to the perpetuation of airway allergic inflammation.

Anti-CD23 monoclonal antibody, lumiliximab, inhibited allergen-induced responses in antigen-presenting cells and T cells from atopic subjects

BACKGROUND

CD23 plays a role in the regulation of IgE production and allergy-induced immune and inflammatory responses. A novel anti-CD23 monoclonal antibody, lumiliximab, is a potential therapeutic antibody recently demonstrated to be safe in human beings.

OBJECTIVE

This study investigated the effects of lumiliximab on allergen-induced immune responses from atopic subjects compared with blocking HLA-DR and costimulatory molecules, CD80 and CD86.

METHODS

Allergen-stimulated PBMCs from atopic subjects were pretreated with lumiliximab or antibodies to CD80, CD86, and HLA-DR. Cultures were analyzed for cell proliferation and IL-1beta, TNF-alpha, and IL-5 cytokine secretion. An allergen-specific T-cell line was developed and analyzed for lymphocyte proliferation in response to allergen with or without lumiliximab. Lumiliximab's effect on CD86 expression was evaluated by flow cytometry in the U937 monocytic cell line.

RESULTS

Lumiliximab reduced allergen-induced PBMC proliferation by 50% (n = 6; P = .006). In addition, cultures pretreated with lumiliximab had a reduction in the proinflammatory cytokines IL-1beta (P < .003) and TNF-alpha (P = .05) and the T(H)2 cytokine IL-5 (P = .002). Blocking CD86 resulted in greater reduction in proliferation than lumiliximab (P = .003) but similar effects in cytokine secretion. The anti-CD80 blocking antibody had no effect on cytokine production but did reduce proliferation. Furthermore, the addition of lumiliximab to cytokine stimulated U937 cells reduced surface expression of CD86 (P = .012).

CONCLUSION

These results indicate that the anti-CD23 mAb, lumiliximab, may be involved in modulating antigen presenting cells and reducing TH2-type immune responses. The use of this antibody may provide clinical benefit for treating allergic diseases.

Quantitation of secretory group V phospholipase A(2) in human tissues by sandwich enzyme-linked immunosorbent assay

We have developed a sensitive sandwich ELISA (sELISA) for quantitative determination of group V phospholipase A(2) (gVPLA(2)). This assay utilizes three monoclonal antibodies (mAbs) directed against human gVPLA(2) (MCL-1B7, MCL-2A5, and MCL-3G1), which recognize specifically different epitopes of gVPLA(2). A mixture of MCL-1B7 and MCL-2A5 was used as the capture mAb, and MCL-3G1 as the detector mAb; purified human gVPLA(2) was used as the standard protein. The limit of detection of the sELISA is 2 ng/ml; the intra- and inter-coefficients of variation were 4.97+/-0.81% and 8.42+/-3.4%. The validity of the sELISA was assured by the recovery of exogenous recombinant gVPLA(2), which was 99.7% to 102%, and demonstration of noninterference of the gVPLA(2) assay by a high concentrations of other protein from murine lung and heart. To assess the usefulness of this sELISA for tissue measurements, the amount of gVPLA(2) in cultured human epithelial cells and isolated human eosinophils was determined. Total gVPLA(2) mass in epithelial cells was 2.83+/-0.33 ng/10(7) cells; gVPLA(2) was not detected in eosinophils. The presence of high concentration of gVPLA(2) in epithelial cells was confirmed by immunoprecipitation/Western blot analysis and by flow cytometry. This assay allows for convenient differentiation between the highly homologous 14-kDa secretory PLA(2)s, gVPLA(2), gIIaPLA(2), gIbPLA(2) and gXPLA(2), and accurate quantitation of gVPLA(2) in biological samples.

The relationship between serum IgE and surface levels of FcepsilonR on human leukocytes in various diseases: correlation of expression with FcepsilonRI on basophils but not on monocytes or eosinophils

BACKGROUND

Expression of receptors for IgE (FcepsilonR) have been mainly studied on mast cells and blood basophils in the context of allergic disease. Some reports have noted limited expression of FcepsilonR on other leukocytes, including blood monocytes and eosinophils in certain patients. An association between human blood basophil expression of FcepsilonRIalpha and serum IgE has been noted among allergic subjects.

OBJECTIVE

Recent evidence supports regulation of FcepsilonRIalpha by free IgE on both mast cells and basophils. We hypothesized that this relationship would exist across an extremely wide range of IgE levels for human basophils, irrespective of underlying disease. We further examined whether a similar relationship existed between serum IgE and FcepsilonRIalpha or FcepsilonRII (CD23) expression on monocytes and eosinophils in these same subjects.

METHODS

Blood was obtained from nonallergic subjects (n = 3) and subjects with allergic asthma (n = 5), atopic dermatitis (n = 3), hypereosinophilic syndromes (n = 7), hyper-IgE syndrome (n = 6), helminth infestation (n = 6), or IgE myeloma (n = 1). Levels of serum IgE were determined by using RIA and ranged from 3 to 4.7 mg/mL. Levels of cell surface FcepsilonRIalpha, FcepsilonRII, and IgE were measured by using immunofluorescence and flow cytometry.

RESULTS

Basophil surface IgE density and FcepsilonRIalpha expression correlated with serum IgE levels (r = 0. 67 and r = 0.46, respectively; P <.01; n = 31) regardless of the disease state. In contrast, monocyte FcepsilonRIalpha expression did not correlate with serum IgE (r = 0.09, P >.5, n = 29), and low-level eosinophil FcepsilonRIalpha expression was only detected in a single asthmatic subject. CD23 expression was not detected on basophils or eosinophils, except for the eosinophils from the donor with IgE myeloma. CD23 was present on monocytes from some donors but did not correlate with serum IgE levels.

CONCLUSIONS

In a variety of disease states, FcepsilonRIalpha expression by basophils, but not monocytes or eosinophils, correlated with serum IgE levels across a 6-log range of IgE. These data support the concept of in vivo regulation of FcepsilonRIalpha on basophils by serum IgE and further demonstrate that this is independent of allergic disease per se.