Detection of eosinophils in whole blood samples by flow cytometry

Oral Neutrophil Free Fatty Acid Receptors Expression May Link Oral Host and Microbiome Lipid Metabolism

In health, commensal bacteria from oral biofilms stimulate polymorphonuclear neutrophil (PMN) recruitment in gingival sulci and the oral cavity. Oral PMN (oPMN) is short-lived cells with low prosurvival gene expression. In periodontitis, oPMN accumulates in higher numbers, has extended lifespan, and sustains nonresolving inflammation. We hypothesize that short- and long-chain free fatty acids (SCFAs and LCFAs) and lipid mediator resolvin E1 (RvE1) modulate host ability to control biofilms and resolve inflammation. Our objective was to measure oPMN surface expression of receptors FFAR2 (binds bacteria-derived SCFA), FFAR4 (binds LCFA, EPA, and DHA), and ERV1 (binds RvE1) in health and to assess sex differences. We included 20 periodontally healthy individuals aged 20–80 years (10 males, 10 females), who were asked to (1) answer a targeted health nutritional questionnaire and (2) provide an oral saline rinse. oPMN isolated by sequential filtration was labeled with fluorophore-conjugated antibodies against CD11b, CD14, CD16, CD66b, ERV1, FFAR2, and FFAR4 and analyzed by flow cytometry. Statistical analyses were the following: two-way ANOVA, Tukey's test, and Pearson's correlation. Oral rinses contained 80% oPMN of which 60% were ERV1⁺ and FFAR2⁺, and 10% FFAR4⁺, with no sex differences. Females had more oPMN ERV1 compared to males. Both sexes had higher ERV1 compared to FFAR2 and FFAR4. CD66b⁺CD16^high oPMN expressed less ERV1 and FFAR2 compared to CD66b⁺CD16^low. There were positive correlations between oPMN ERV1 and FFAR2 expression and between ERV1⁺ and FFAR2⁺ oPMN and fish intake. These findings will help to better understand how oral host and microbiome interactions maintain periodontal health.

Autofluorescence of blood and its application in biomedical and clinical research

Autofluorescence of blood has been explored as a label free approach for detection of cell types, as well as for diagnosis and detection of infection, cancer, and other diseases. Although blood autofluorescence is used to indicate the presence of several physiological abnormalities with high sensitivity, it often lacks disease specificity due to use of a limited number of fluorophores in the detection of several abnormal conditions. In addition, the measurement of autofluorescence is sensitive to the type of sample, sample preparation, and spectroscopy method used for the measurement. Therefore, while current blood autofluorescence detection approaches may not be suitable for primary clinical diagnosis, it certainly has tremendous potential in developing methods for large scale screening that can identify high risk groups for further diagnosis using highly specific diagnostic tests. This review discusses the source of blood autofluorescence, the role of spectroscopy methods, and various applications that have used autofluorescence of blood, to explore the potential of blood autofluorescence in biomedical research and clinical applications.

Diffusion Mapping of Eosinophil-Activation State

Eosinophils are granular leukocytes that play a role in mediating inflammatory responses linked to infection and allergic disease. Their activation during an immune response triggers spatial reorganization and eventual cargo release from intracellular granules. Understanding this process is important in diagnosing eosinophilic disorders and in assessing treatment efficacy; however, current protocols are limited to simply quantifying the number of eosinophils within a blood sample. Given that high optical absorption and scattering by the granular structure of these cells lead to marked image features, the physical changes that occur during activation should be trackable using image analysis. Here, we present a study in which imaging flow cytometry is used to quantify eosinophil activation state, based on the extraction of 85 distinct spatial features from dark-field images formed by light scattered orthogonally to the illuminating beam. We apply diffusion mapping, a time inference method that orders cells on a trajectory based on similar image features. Analysis of exogenous cell activation using eotaxin and endogenous activation in donor samples with elevated eosinophil counts shows that cell position along the diffusion-path line correlates with activation level (99% confidence level). Thus, the diffusion mapping provides an activation metric for each cell. Assessment of activated and control populations using both this spatial image-based, activation score and the integrated side-scatter intensity shows an improved Fisher discriminant ratio rd = 0.7 for the multivariate technique compared with an rd = 0.47 for the traditional whole-cell scatter metric. © 2019 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

A field-applicable method for flow cytometric analysis of granulocyte activation: Cryopreservation of fixed granulocytes

Upon activation granulocytes upregulate several adhesion molecules (CD11b) and granule proteins (CD35, CD66b) and shed surface l-selectin (CD62L). These changes in expression, as assessed by flow cytometry, can be used as markers for activation. Whereas these markers are usually studied in fresh blood samples, a new method is required when samples are collected at a field site with no direct access to a flow cytometer. Therefore, we developed and tested a field-applicable method in which fixed leukocytes were cryopreserved. Using this method, the intensity of granulocyte activation markers was compared to samples that were either stained fresh, or fixed prior to staining but not cryopreserved. In addition, the response to an in vitro stimulation with fMLF was determined. While we observed differences in marker intensities when comparing fresh and fixed granulocytes, similar intensities were found between fixed cells that had been cryopreserved and fixed cells that did not undergo cryopreservation. Although fixation using FACS lysing solution might lead to membrane permeabilization, activation markers, and the responsiveness to fMLF or eotaxin could still be clearly measured. This method will, therefore, enable future studies of granulocyte activation in settings with limited resources and will allow simultaneous analysis of samples collected at different time points. © 2018 International Society for Advancement of Cytometry.

Functions of tissue-resident eosinophils

Eosinophils are a prominent cell type in particular host responses such as the response to helminth infection and allergic disease. Their effector functions have been attributed to their capacity to release cationic proteins stored in cytoplasmic granules by degranulation. However, eosinophils are now being recognized for more varied functions in previously underappreciated diverse tissue sites, based on the ability of eosinophils to release cytokines (often preformed) that mediate a broad range of activities into the local environment. In this Review, we consider evolving insights into the tissue distribution of eosinophils and their functional immunobiology, which enable eosinophils to secrete in a selective manner cytokines and other mediators that have diverse, 'non-effector' functions in health and disease.

Imaging Cytometry of Human Leukocytes with Third Harmonic Generation Microscopy

Based on third-harmonic-generation (THG) microscopy and a k-means clustering algorithm, we developed a label-free imaging cytometry method to differentiate and determine the types of human leukocytes. According to the size and average intensity of cells in THG images, in a two-dimensional scatter plot, the neutrophils, monocytes, and lymphocytes in peripheral blood samples from healthy volunteers were clustered into three differentiable groups. Using these features in THG images, we could count the number of each of the three leukocyte types both in vitro and in vivo. The THG imaging-based counting results agreed well with conventional blood count results. In the future, we believe that the combination of this THG microscopy-based imaging cytometry approach with advanced texture analysis of sub-cellular features can differentiate and count more types of blood cells with smaller quantities of blood.

Combination of CD157 and FLAER to Detect Peripheral Blood Eosinophils by Multiparameter Flow Cytometry

The identification of eosinophils by flow cytometry is difficult because most of the surface antigens expressed by eosinophils are shared with neutrophils. Some methods have been proposed, generally based on differential light scatter properties, enhanced autofluorescence, lack of CD16 or selective positivity of CD52. Such methods, however, show several limitations. In the present study we report a novel method based on the analysis of glycosylphosphatidylinositol (GPI)-linked molecules. The combination of CD157 and FLAER was used, since FLAER recognizes all GPI-linked molecules, while CD157 is absent on the membrane of eosinophils and expressed by neutrophils. Peripheral blood samples from normal subjects and patients with variable percentages of eosinophils (n = 31), and without any evidence for circulating immature myeloid cells, were stained with the combination of FLAER-Alexa Fluor and CD157-PE. A FascCanto II cytometer was used. Granulocytes were gated after CD33 staining and eosinophils were identified as CD157(-)/FLAER(+) events. Neutrophils were identified as CD157(+)/FLAER(+) events. The percentages of eosinophils detected by this method showed a very significant correlation both with automated counting and with manual counting (r = 0.981 and 0.989, respectively). Sorting assays were carried out by a S3 Cell Sorter: cytospins obtained from CD157(-)/FLAER(+) events consisted of 100% eosinophils, while samples from CD157(+)/FLAER(+) events were represented only by neutrophils. In conclusion, this method shows high sensitivity and specificity in order to distinguish eosinophils from neutrophils by flow cytometry. However, since CD157 is gradually up-regulated throughout bone marrow myeloid maturation, our method cannot be applied to cases characterized by immature myeloid cells.

Autofluorescence spectroscopy and imaging: a tool for biomedical research and diagnosis

Native fluorescence, or autofluorescence (AF), consists in the emission of light in the UV-visible, near-IR spectral range when biological substrates are excited with light at suitable wavelength. This is a well-known phenomenon, and the strict relationship of many endogenous fluorophores with morphofunctional properties of the living systems, influencing their AF emission features, offers an extremely powerful resource for directly monitoring the biological substrate condition. Starting from the last century, the technological progresses in microscopy and spectrofluorometry were convoying attention of the scientific community to this phenomenon. In the future, the interest in the autofluorescence will certainly continue. Current instrumentation and analytical procedures will likely be overcome by the unceasing progress in new devices for AF detection and data interpretation, while a progress is expected in the search and characterization of endogenous fluorophores and their roles as intrinsic biomarkers.

Enhanced expression of neuropeptide S (NPS) receptor in eosinophils from severe asthmatics and subjects with total IgE above 100IU/ml

Eosinophils are inflammatory cells of particular relevance to asthma exacerbations. Neuropeptide S (NPS) receptor was identified in a search for asthma susceptibility genes, where the risk haplotypes of the NPS receptor gene associated with total serum IgE above 100IU/ml and asthma. The aim of the present study was to investigate and compare expression of NPS receptor in human peripheral blood eosinophils derived from subjects with total serum IgE above and below 100IU/ml and patients with different phenotypes of asthma. Additionally, we aimed to study the function of NPS receptor in human eosinophils. We found higher NPS receptor protein expression in eosinophils derived from subjects with high IgE when compared to those from subjects with low IgE and the level of NPS receptor positively correlated with serum IgE. NPS receptor expression was also higher in eosinophils from patients with severe asthma than in cells from mild asthmatics or healthy controls. The receptor agonist NPS was a chemotactic agent for eosinophils. NPS also increased N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated CD11b integrin levels in eosinophils from subjects with high IgE. Furthermore, eosinophils from those subjects exhibited Ca(2+) mobilization but not cAMP rise in response to NPS. Altogether, NPS receptor may have a pathological role in individuals with severe asthma and/or elevated serum IgE levels as eosinophils from these patients express higher levels of NPS receptor protein and respond to NPS by enhanced migration and adhesion molecule expression.

Pathogen induced chemo-attractant hepoxilin A3 drives neutrophils, but not eosinophils across epithelial barriers

Pathogen induced migration of neutrophils across mucosal epithelial barriers requires epithelial production of the chemotactic lipid mediator, hepoxilin A3 (HXA3). HXA3 is an eicosanoid derived from arachidonic acid. Although eosinophils are also capable of penetrating mucosal surfaces, eosinophilic infiltration occurs mainly during allergic processes whereas neutrophils dominate mucosal infection. Both neutrophils and eosinophils can respond to chemotactic gradients of certain eicosanoids, however, it is not known whether eosinophils respond to pathogen induced lipid mediators such as HXA3. In this study, neutrophils and eosinophils were isolated from human blood and placed on the basolateral side of polarized epithelial monolayers grown on permeable Transwell filters and challenged by various chemotactic gradients of distinct lipid mediators. We observed that both cell populations migrated across epithelial monolayers in response to a leukotriene B4 (LTB4) gradient, whereas only eosinophils migrated toward a prostaglandin D2 (PGD2) gradient. Interestingly, while pathogen induced neutrophil trans-epithelial migration was substantial, pathogen induced eosinophil trans-epithelial migration was not observed. Further, gradients of chemotactic lipids derived from pathogen infected epithelial cells known to be enriched for HXA3 as well as purified HXA3 drove significant numbers of neutrophils across epithelial barriers, whereas eosinophils failed to respond to these gradients. These data suggest that although the eicosanoid HXA3 serves as an important neutrophil chemo-attractant at mucosal surfaces during pathogenic infection, HXA3 does not appear to exhibit chemotactic activity toward eosinophils.

Flow cytometric isolation and phenotypic characterization of two subsets of ED2(+) (CD163) hepatic macrophages in rats

AIMS

Macrophages in the liver are well known for their functional heterogeneity. However, subpopulations of the hepatic macrophages are not well defined.

METHODS

Two subsets of hepatic macrophages isolated from rats via FACS with immunolabeling of ED2 (anti-CD163) antibody were studied for phenotypic and functional characteristics.

RESULTS

A subset showed an ED2(high) and autofluorescence(high) (ED2(high)/AF(high)) phenotype, exhibiting characteristics consistent with the description of the Kupffer cells (KC). A second subset, displaying an ED2(dim)/AF(dim) phenotype, was smaller in size, monocyte-like and weak in phagocytosis. Transmission electron microscopy demonstrated that both subsets are phagocytes. Quantitative RT-PCR revealed that in addition to expression of macrophage-related surface markers such as CD14, ED1 (CD68), fucose receptor, and CD163, the ED2(dim)/ AF(dim) cells expressed mRNA encoding for myeloid lineage differentiation markers ERMP12 (PECAM) and ERMP20 (Ly-6C). These two subsets exhibited differential in gene expression of selected cytokines, extracellular matrix proteinases, and Toll-like receptor in normal livers, as well as significantly upregulated expression in cholestatic livers induced by bile duct ligation.

CONCLUSION

The data suggest that the ED2(high)/AF(high) population of the liver cells represent the conventional Kupffer cells. The ED2(dim)/AF(dim) cells, however, are small hepatic resident macrophages characteristically different from the conventional Kupffer cells.

Necator americanus infection: a possible cause of altered dendritic cell differentiation and eosinophil profile in chronically infected individuals

BACKGROUND

Hookworms survive for several years (5 to 7 years) in the host lumen, inducing a robust but largely ineffective immune response. Among the most striking aspects of the immune response to hookworm (as with many other helminths) is the ablation of parasite-specific T cell proliferative response (hyporesponsiveness). While the role of the adaptive immune response in human helminth infection has been well investigated, the role of the innate immune responses (e.g., dendritic cells and eosinophils) has received less attention and remains to be clearly elucidated.

METHODOLOGY/PRINCIPAL FINDINGS

We report on the differentiation/maturation of host dendritic cells in vitro and the eosinophil activation/function associated with human hookworm infection. Mature DCs (mDCs) from Necator americanus (Necator)-infected individuals showed an impaired differentiation process compared to the mDCs of non-infected individuals, as evidenced by the differential expression of CD11c and CD14. These same hookworm-infected individuals also presented significantly down-regulated expression of CD86, CD1a, HLA-ABC, and HLA-DR. The lower expression of co-stimulatory and antigen presentation molecules by hookworm-infected-derived mDCs was further evidenced by their reduced ability to induce cell proliferation. We also showed that this alternative DC differentiation is partially induced by excreted-secreted hookworm products. Conversely, eosinophils from the same individuals showed a highly activated status, with an upregulation of major cell surface markers. Antigen-pulsed eosinophils from N. americanus-infected individuals induced significant cell proliferation of autologous PBMCs, when compared to non-infected individuals.

CONCLUSION

Chronic N. americanus infection alters the host's innate immune response, resulting in a possible modulation of the maturation process of DCs, a functional change that may diminish their ability for antigen presentation and thus contribute to the ablation of the parasite-specific T cell proliferative response. Interestingly, a concomitant upregulation of the major cell surface markers of eosinophils was observed in hookworm-infected individuals, indicative of antigen-specific immune responses, especially antigen presentation. We showed that in addition to the postulated role of the eosinophils as effector cells against helminth infection, activated cells may also be recruited to sites of inflammation and contribute to the immune response acting as antigen presenting cells.

Evaluation of endocytic capacity and NADPH-oxidase activity from armadillo (Dasypus novemcinctus) eosinophils infected with microfilariae

Endocytic activity of phagocytic cells from armadillos infected with viruses, parasites or bacteria is unknown. This report shows that eosinophils from armadillos infected with microfilaria act against these helmintic parasites but have deficiencies in their oxygen-dependent bacteriocidal mechanisms and also in endocytic capacity against yeast.

Screening of anti-human leukocyte monoclonal antibodies for reactivity with equine leukocytes

Three hundred and seventy-nine monoclonal antibodies (mAbs) against various human CD molecules supplied to the HLDA8 animal homologues section (including four isotype controls) were analysed for cross-reactivity with equine leukocytes. First, flow cytometric identification of positively reacting mAbs was performed in one laboratory. Thereafter, a second round of flow cytometric evaluation was performed, involving three laboratories participating in the study. The first test-round indicated 17 mAbs as potentially positive. After the second round of flow cytometric analysis, 14 mAbs remained (directed against CD2, CD11a, CD18, CD44, CD45, CD49d, CD91, CD163 and CD172) where cross-reactivity was anticipated based on similarities between the human and equine staining pattern. Additionally, there was 1 mAb with weak likely positive reactivity, 12 mAbs with positive staining, which likely do not reflect valuable data, 5 mAbs with clear alternate expression pattern from that expected from humans, 5 mAbs with a questionable staining pattern itself, i.e. that was variable between the three labs, 32 mAbs with weak-positive expression and alternate staining pattern, and 279 negative mAbs (including the four isotype controls) were detected. In 31 cases, more appropriate target cells, such as thymocytes or stem cells, were not available for the screening. The results underline the value of this "cross-reactivity" approach for equine immunology. However, as only a few mAbs against leukocyte surface antigens reacted positively (approximately 4% of the mAbs submitted), the analysis of further anti-human mAbs and directed efforts to develop species-specific anti-CD mAb are still required.

Reduction of worm fecundity and canine host blood loss mediates protection against hookworm infection elicited by vaccination with recombinant Ac-16

Hookworm infection is one of most important parasitic infection of humans, occurring in 740 million people. Here we report the protective vaccination of dogs with Ac-16, an immunodominant surface antigen from the hookworm Ancylostoma caninum. We show that immunization with Ac-16 formulated with AS03 elicited specific humoral and cellular immune responses and provided partial protection against hookworm infection and morbidity as evidenced by a significant reduction of hookworm egg counts (64% reduction; P = 0.0078) and worm-induced blood loss (P < 0.05). Moreover, specific anti-Ac-16 antibodies recognized the native protein on the surface of third-stage larvae and blocked their migration through tissue in vitro. Our data support the use of Ac-16 as a potential candidate for vaccination against hookworm infection.

Cloning of the t(1;5)(q23;q33) in a myeloproliferative disorder associated with eosinophilia: involvement of PDGFRB and response to imatinib

Eosinophilia is common in myeloproliferative disorders (MPDs) with abnormalities of chromosome band 5q31-33, including those that present with t(1;5)(q23;q33). With the development of rational drug therapy, characterization of the molecular targets for these translocations could guide treatment and affect patient survival. We cloned the t(1;5)(q23;q33) and showed that it fuses platelet-derived growth factor receptor beta (PDGFRB) to the coiled-coil domains of a novel partner protein, myomegalin. Using two-color interphase fluorescence in situ hybridization (FISH), we also demonstrated that the eosinophils are clonal in these disorders. Imatinib mesylate has recently been shown to be efficacious in MPDs with PDGFR activation. Therefore, following our molecular studies, we were able to redirect this patient's treatment. Although she had refractory and progressive disease, once imatinib was started, complete clinical and hematologic remission, as well as major cytogenetic response, was achieved. Given the therapeutic implications, our findings stress the need to aggressively investigate the molecular basis of these diseases, with emphasis on the PDGFR family.

Expression of cell surface adhesion molecules by peripheral blood eosinophils during Trichostrongylus colubriformis infection in sheep

The effect of infection of sheep with the gastrointestinal nematode parasite Trichostrongylus colubriformis on expression of adhesion molecules CD11a, CD11b, CD11c, CD18, CD44, CD49d and CD62L by peripheral blood eosinophils was examined by flow cytometry. Initially, to establish the sensitivity of adhesion molecules to inflammatory signals, eosinophil-rich exudates were elicited in non-lactating mammary glands of immune sheep by infusion of 50 microg of soluble antigen extract from T. colubriformis third stage larvae. Eosinophils comprised 40.8% of mammary leucocytes and 4.5% of peripheral blood leucocytes. In comparison with blood, the percentage of eosinophils expressing CD18 increased and the percentage expressing CD62L decreased in exudates and the mean fluorescent intensity, an indicator of receptor number per cell, for CD11a and CD49d also decreased on exudate eosinophils. Peripheral blood eosinophils were examined over 8 weeks during trickle infection of immune sheep with infective or irradiated third stage larvae of T. colubriformis. During the last 3 weeks of infection, CD11a staining decreased in infected sheep and CD44 staining decreased in sheep receiving either infective or irradiated larvae. Other surface markers did not change. The results indicate that systemic changes in expression of adhesion molecules by eosinophils occur during T. colubriformis infection in sheep.

Flow cytometric discrimination between viable neutrophils, apoptotic neutrophils and eosinophils by double labelling of permeabilized blood granulocytes

Terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) is frequently used to detect apoptotic cells in tissues, cytospins and suspensions. Here we show that TUNEL staining of freshly isolated granulocytes results in non-specific positivity of a distinct population, which can be observed in the presence or absence of TdT. The morphological features of the false-positive cells examined in fluorescence microscopy suggest that the non-specifically stained cells are eosinophilic granulocytes. Granules of eosinophilic granulocytes were brightly stained by non-specific TUNEL reaction independent of TdT. This staining does not, therefore, indicate apoptosis and most likely reflects 'stickiness' of the permeabilized eosinophils. Immunofluorescence with phycoerythrin (PE)-labelled CD16 antibodies performed simultaneously with conventional TUNEL staining confirmed that the false-positive cells in TUNEL staining were CD16-negative eosinophils. In this report we describe a new procedure that allows: (i) the differentiation of neutrophilic and eosinophilic granulocytes in forward scatter versus log side scatter histograms after permeabilisation; (ii) the reliable discrimination between viable neutrophils, apoptotic neutrophils and eosinophilic granulocytes in cytofluorimetry.