Functional expression of transmembrane 4 superfamily molecules on human eosinophils

Flow cytometric immunophenotypic differentiation patterns of bone marrow eosinophilopoiesis

BACKGROUND

Flow cytometry has been widely used to study immunophenotypic patterns of maturation of most hematopoietic lineages in normal human bone marrow aspirates, thus allowing identification of changes in patterns in many myeloid malignancies. Eosinophils play an important role in a wide variety of disorders, including some myeloid neoplasms. However, changes in flow cytometric immunophenotypic patterns during normal and abnormal bone marrow eosinophilopoiesis have not been well studied.

METHODS

Fresh bone marrow aspirates from 15 healthy donors, 19 patients with hypereosinophilic syndromes (HES), and 11 patients with systemic mastocytosis (SM) were analyzed for candidate markers that included EMR-1, Siglec-8, CCR3, CD9, CD11a, CD11b, CD11c, CD13, CD16, CD29, CD34, CD38, CD45, CD44, CD49d, CD49f, CD54, CD62L, CD69, CD117, CD125 (IL-5Rα), HLA-DR, using 10 parameter flow cytometry. Putative CD34-negative immature and mature normal eosinophil populations were first identified based on changes in expression of the above markers in healthy donors, then confirmed using fluorescence-based cell sorting and morphological evaluation of cytospin preparations. The normal immunophenotypic patterns were then compared to immunophenotypic patterns of eosinophilopoiesis in patients with HES and SM.

RESULTS

The eosinophilic lineage was first verified using the human eosinophil-specific antibody EMR-1 in combination with anti-IL-5Rα antibody. Then, a combination of Siglec-8, CD9, CD11b, CCR3, CD49d, and CD49f antibodies was used to delineate normal eosinophilic maturational patterns. Early stages (eosinophilic promyelocytes/myelocytes) were identified as Siglec-8 dim/CD11b dim to moderate/CD9 dim/CCR3 dim/CD49d bright/CD49f dim, intermediate stages (eosinophilic myelocytes/metamyelocytes) as Siglec-8 moderate/CD11b moderate to bright/CD9 moderate/CCR3 moderate/CD49d moderate/CD49f moderate and mature bands/segmented eosinophils as Siglec-8 bright/CD11b bright/CD9 bright/CCR3 bright/CD49d dim/CD49f bright. Overall maturational patterns were also similar in patients with HES and SM; however, the expression levels of several surface markers were altered compared to normal eosinophils.

CONCLUSION

A novel flow cytometric antibody panel was devised to detect alterations in immunophenotypic patterns of bone marrow eosinophil maturation and evaluated in normal, HES and SM samples. This approach will allow us to elucidate changes in immunophenotypic patterns of bone marrow eosinophilopoiesis in other hematological diseases.

Mass Cytometry Phenotyping of Human Granulocytes Reveals Novel Basophil Functional Heterogeneity

Basophils, the rarest granulocyte, play critical roles in parasite- and allergen-induced inflammation. We applied mass cytometry (CyTOF) to simultaneously asses 44 proteins to phenotype and functionally characterize neutrophils, eosinophils, and basophils from 19 healthy donors. There was minimal heterogeneity seen in eosinophils and neutrophils, but data-driven analyses revealed four unique subpopulations within phenotypically basophilic granulocytes (PBG; CD45+HLA-DR-CD123+). Through CyTOF and fluorescence-activated cell sorting (FACS), we classified these four PBG subpopulations as (I) CD16lowFcεRIhighCD244high (88.5 ± 1.2%), (II) CD16highFcεRIhighCD244high (9.1 ± 0.4%), (III) CD16lowFcεRIlowCD244low (2.3 ± 1.3), and (IV) CD16highFcεRIlowCD244low (0.4 ± 0.1%). Prospective isolation confirmed basophilic-morphology of PBG I-III, but neutrophilic-morphology of PBG IV. Functional interrogation via IgE-crosslinking or IL-3 stimulation demonstrated that PBG I-II had significant increases in CD203c expression, whereas PBG III-IV remained unchanged compared with media-alone conditions. Thus, PBG III-IV could serve roles in non-IgE-mediated immunity. Our findings offer new perspectives in human basophil heterogeneity and the varying functional potential of these new subsets in health and disease.

Combined Smooth Muscle and Melanocytic Differentiation in Lymphangioleiomyomatosis

Pulmonary lymphangioleiomyomatosis (LAM) is characterized by abnormal proliferation of immature-looking smooth muscle (SM)-like cells (LAM cells), leading to lung destruction and cyst formation. In addition to expressing some SM markers, scattered LAM cells express the melanocytic maker gp100, which is recognized by antibody HMB45, suggesting that at least a few LAM cells may have melanocytic differentiation. Here we immunostained 26 LAM samples for several melanocyte-related proteins. These studies showed that all LAM cells express tetraspanin CD63, a melanoma-associated protein that belongs to the transmembrane 4 superfamily. The majority of LAM cells also immunoreacted with PNL2, an antibody against a yet uncharacterized melanocytic antigen. Furthermore, we examined the co-expression of PNL2 and Ki-67, an indicator of cell proliferation, and found that PNL2-positive LAM cells showed a significantly lower proliferation rate compared with their negative counterparts. Our findings shed new light on the nature of the LAM cells by demonstrating their combined SM and melanocytic differentiation and the existence of subpopulations with different proliferative potential. Furthermore, these studies provided two new antibodies useful in the diagnosis of LAM.

Chemotactic responses of peripheral blood eosinophils to prostaglandin D2 in atopic keratoconjunctivitis

BACKGROUND

Eosinophils appear to be key cells in the pathogenesis of conjunctival inflammation in atopic keratoconjunctivitis (AKC). Chemoattractant receptor homologous molecule expressed on TH2 cells (CRTH2) mediates prostaglandin D2 (PGD2)-dependent migration of eosinophils. However, it is unclear whether CRTH2/PGD2-dependent eosinophil migration is upregulated in allergic diseases.

OBJECTIVE

To compare the chemotactic responses of peripheral blood eosinophils to prostaglandin D2 in patients with severe AKC and healthy individuals.

METHODS

We used an enzyme immunoassay system to measure PGD2 levels in tears and blood samples from healthy individuals and patients with AKC. CRTH2 expression on peripheral blood eosinophils was determined using reverse-transcriptase polymerase chain reaction (RT-PCR), flow cytometry, and an oligonucleotide array system. Chemotaxis experiments were performed using a modified Boyden chamber technique and an optical assay system.

RESULTS

The PGD2 concentrations were higher in tears from patients with severe AKC compared with healthy individuals. RT-PCR (severe and mild cases), flow cytometry (mild cases), and GeneChip analyses revealed a significantly higher expression of CRTH2 on peripheral blood eosinophils in patients with AKC than in healthy individuals. PGD2 and its stable metabolite 13,14-dihydro-15-keto-PGD2, a CRTH2 agonist, induced chemotaxis of eosinophils from patients with AKC; chemotaxis was significantly enhanced in eosinophils from patients with severe AKC compared with those from healthy individuals.

CONCLUSION

CRTH2 is more abundantly expressed on eosinophils from patients with AKC and promoted PGD2-dependent migration to a greater extent than in healthy individuals.

MHC Class II and CD9 in human eosinophils localize to detergent-resistant membrane microdomains

Eosinophils function in murine allergic airways inflammation as professional antigen-presenting cells (APCs). In murine professional APC cell types, optimal functioning of MHC Class II depends on its lateral association in plasma membranes and colocalization with the tetraspanin CD9 into detergent-resistant membrane microdomains (DRMs). With human eosinophils, we evaluated the localization of MHC Class II (HLA-DR) to DRMs and the functional significance of such localization. In granulocyte-macrophage colony-stimulating factor-stimulated human eosinophils, antibody cross-linked HLA-DR colocalized by immunofluorescence microscopy focally on plasma membranes with CD9 and the DRM marker ganglioside GM1. In addition, HLA-DR coimmunoprecipitates with CD9 after chemical cross-linking of CD9. HLA-DR and CD9 were localized by Western blotting in eosinophil DRM subcellular fractions. DRM disruption with the cholesterol-depleting agent methyl-β-cyclodextrin decreased eosinophil surface expression of HLA-DR and CD9. We show that CD9 is abundant on the surface of eosinophils, presenting the first electron microscopy data of the ultrastructural immunolocalization of CD9 in human eosinophils. Disruption of HLA-DR-containing DRMs decreased the ability of superantigen-loaded human eosinophils to stimulate CD4(+) T-cell activation (CD69 expression), proliferation, and cytokine production. Our results, which demonstrate that eosinophil MHC Class II localizes to DRMs in association with CD9 in a functionally significant manner, represent a novel insight into the organization of the antigen presentation complex of human eosinophils.

Eosinophils as antigen-presenting cells in allergic upper airway disease

PURPOSE OF REVIEW

The recognition of eosinophils as complex immunomodulatory cells has been increasing in recent years. One prominent novel immunomodulatory function of eosinophils is their role as antigen-presenting cells (APCs). This review will examine the evidence that has enhanced the understanding of eosinophils as APCs in the context of allergic inflammation, with a focus on data applicable to allergic upper airway disease.

RECENT FINDINGS

Recent studies expand on prior findings that eosinophils can express major histocompatibility complex class II and costimulatory molecules. Eosinophils have also been found to traffic to regional lymph nodes and act as professional APCs in various experimental settings.

SUMMARY

Accumulating evidence of the ability of eosinophils to act as APCs suggests that eosinophils may have more complex immunomodulatory roles in allergic upper airway disease than previously appreciated.

CpG oligodeoxynucleotide prolongs eosinophil survival through activation of contaminating B cells and plasmacytoid dendritic cells in vitro

BACKGROUND

In our previous study, oligodeoxynucleotides containing unmethylated CpG motifs (CpG ODNs) significantly prolonged eosinophil survival without inducing active release of eosinophil-derived neurotoxin or interleukin 8. In addition, this survival-promoting activity was nuclear factor-kappaB dependent. However, some eosinophil preparations from different donors hardly responded to CpG ODNs at all. To clarify why CpG ODN-induced nuclear factor-kB activation in eosinophils does not cause eosinophil-derived neurotoxin or interleukin 8 release and why the survival-promoting activity of CpG ODNs was not found in some eosinophil preparations, we determined the effect of extensive removal of contaminating B cells and plasmacytoid dendritic cells from human eosinophil preparations.

METHODS

Eosinophils were purified from the peripheral blood of healthy or slightly allergic donors by gradient sedimentation and negative selection with anti-CD16 alone or a combination of anti-CD16, anti-CD19 and anti-blood dendritic cell antigen 4 (BDCA4) immunomagnetic beads. Eosinophil survival was measured with FITC-conjugated annexin V and propidium iodide by FACS after incubation with synthetic CpG 2006(CpG-B), CpG 2216 (CpG-A) or their GpC control ODNs for 24 h.

RESULTS

The addition of anti-CD19 and anti-BDCA4 immunomagnetic beads reduced the number of contaminating CD19+ cells and CD123+ BDCA2+ cells in eosinophil preparations. CpG 2006 and CpG 2216, but not their GpC control ODNs, significantly prolonged survival of eosinophils purified with anti-CD16 immunomagnetic beads alone but not eosinophils purified with a combination of anti-CD16, anti-CD19 and anti-BDCA4 beads.

CONCLUSIONS

These results strongly suggest that contaminating B cells or plasmacytoid dendritic cells in eosinophil preparations critically regulate CpG ODN-mediated prolongation of eosinophil survival and that CpG ODNs do not activate eosinophils directly.

Translocation of the tetraspanin CD63 in association with human eosinophil mediator release

The tetraspanin CD63 (also known as LAMP-3) has been implicated in phagocytic and intracellular lysosome-phagosome fusion events. It is also present in eosinophils, with predominant expression on crystalloid granule membrane. However, its role in eosinophil function is obscure. We hypothesized that CD63 is associated with intracellular events involved in eosinophil activation and mediator release. We used a combination of confocal immunofluorescence microscopy, flow cytometry, and secretion assays, including beta-hexosaminidase, eosinophil peroxidase, and RANTES, to examine CD63 expression, intracellular localization, and its association with cell activation and mediator release. In resting eosinophils, CD63 immunoreactivity was localized to plasma and crystalloid granule membranes. In interferon-gamma (IFN-gamma)- or C5a/CB-stimulated cells (10 minutes), intracellular CD63 appeared to shift to the cell periphery and plasma membrane, while stimulation with a cocktail of interleukin-3 (IL-3)/IL-5/granulocyte-macrophage colony-stimulating factor induced the appearance of discrete intracellular clusters of CD63 immunoreactivity. IFN-gamma induced mobilization of CD63 to the cell periphery, which coincided with selective mobilization of RANTES prior to its release, implying CD63 association with piecemeal degranulation. Agonist-induced CD63 mobilization and cell surface up-regulation was associated with beta-hexosaminidase, eosinophil peroxidase, and RANTES release. Dexamethasone as well as genistein (a broad-spectrum inhibitor of tyrosine kinases) inhibited agonist-induced intracellular mobilization of CD63 and RANTES together with cell surface up-regulation of CD63 and mediator release. This is the first report of an association between CD63 mobilization and agonist-induced selective mediator release, which may imply the involvement of CD63 in eosinophil activation and piecemeal degranulation.

Systemic activation of basophils and eosinophils: markers and consequences

Basophils and eosinophils are important effector cells in human allergic diseases; they play a significant role in promoting allergic inflammation through the release of proinflammatory mediators (such as histamine, leukotriene C(4), major basic protein, eosinophil cationic protein, IL-4, and IL-13, among others). Notably, in allergic subjects, these cells exist in higher numbers and in a more activated state compared with nonatopic control subjects. Evidence for the greater activation state includes increased expression of intracellular and surface markers and hyperreleasability of allergy mediators. We have been interested in the phenotypic markers of effector-cell activation for many years. There is considerable overlap among activation markers, and few activation markers have been found that define a unique phenotype that is quantifiable in the assessment of the presence and severity of allergic disease. This review summarizes the existing evidence for systemic activation of human basophils and eosinophils in allergic diseases. The potential mechanisms responsible for functional and morphologic alterations in these effector cells and the specificity and utility of surface markers in the assessment of allergic disease activity or severity are also discussed.

Allergen-induced airway hyperreactivity is diminished in CD81-deficient mice

We demonstrated previously that CD81(-/-) mice have an impaired Th2 response. To determine whether this impairment affected allergen-induced airway hyperreactivity (AHR), CD81(-/-) BALB/c mice and CD81(+/+) littermates were sensitized i.p. and challenged intranasally with OVA. Although wild type developed severe AHR, CD81(-/-) mice showed normal airway reactivity and reduced airway inflammation. Nevertheless, OVA-specific T cell proliferation was similar in both groups of mice. Analysis of cytokines secreted by the responding CD81(-/-) T cells, particularly those derived from peribronchial draining lymph nodes, revealed a dramatic reduction in IL-4, IL-5, and IL-13 synthesis. The decrease in cytokine production was not due to an intrinsic T cell deficiency because naive CD81(-/-) T cells responded to polyclonal Th1 and Th2 stimulation with normal proliferation and cytokine production. Moreover, there was an increase in T cells and a decrease in B cells in peribronchial lymph nodes and in spleens of immunized CD81(-/-) mice compared with wild-type animals. Interestingly, OVA-specific Ig levels, including IgE, were similar in CD81(-/-) and CD81(+/+) mice. Thus, CD81 plays a role in the development of AHR not by influencing Ag-specific IgE production but by regulating local cytokine production.