Gleich, Gerald J.

AbstractThe cDNA for eosinophil granule major basic protein (MBP) encodes a prepromolecule with a total length of 222 amino acids (preproMBP). PreproMBP includes a secretory leader of 15 amino acids, an acidic propiece of 90 amino acids, and a basic MBP portion of 117 amino acids. The function of the propiece, which has a predicted pI of 3.9, is unknown, but it gives proMBP an overall acidic charge. Because proMBP is not found in mature eosinophils, we analyzed eosinophil differentiation in interleukin-5 (IL-5)–stimulated umbilical cord stem cells cultured for 24 days. By immunofluorescence, proMBP appeared by day 6 and peaked on day 18, whereas MBP was prominent at days 12 to 24. By day 6, Western blots detected heterogeneous glycosylated 33-kD proMBP; its peak expression occurred on day 12. Western blots showed sequential processing of 33-kD proMBP to an 18-kD intermediate form and finally to 14-kD MBP. By dual label immunoelectron microscopy, proMBP was localized primarily to large uncondensed eosinophil granules, whereas MBP was localized to granules containing a condensed central area. Thus, proMBP is likely expressed and processed as the granule condenses in a multistep process to 14-kD MBP in differentiating eosinophils.

The cDNA for eosinophil granule major basic protein (MBP) encodes a prepromolecule with a total length of 222 amino acids (preproMBP). PreproMBP includes a secretory leader of 15 amino acids, an acidic propiece of 90 amino acids, and a basic MBP portion of 117 amino acids. The function of the propiece, which has a predicted pI of 3.9, is unknown, but it gives proMBP an overall acidic charge. Because proMBP is not found in mature eosinophils, we analyzed eosinophil differentiation in interleukin-5 (IL-5)–stimulated umbilical cord stem cells cultured for 24 days. By immunofluorescence, proMBP appeared by day 6 and peaked on day 18, whereas MBP was prominent at days 12 to 24. By day 6, Western blots detected heterogeneous glycosylated 33-kD proMBP; its peak expression occurred on day 12. Western blots showed sequential processing of 33-kD proMBP to an 18-kD intermediate form and finally to 14-kD MBP. By dual label immunoelectron microscopy, proMBP was localized primarily to large uncondensed eosinophil granules, whereas MBP was localized to granules containing a condensed central area. Thus, proMBP is likely expressed and processed as the granule condenses in a multistep process to 14-kD MBP in differentiating eosinophils.

AbstractEosinophil-associated diseases (EADs) are rare, heterogeneous disorders characterized by the presence of eosinophils in tissues and/or peripheral blood resulting in immunopathology. The heterogeneity of tissue involvement, lack of sufficient animal models, technical challenges in working with eosinophils, and lack of standardized histopathologic approaches have hampered progress in basic research. Additionally, clinical trials and drug development for rare EADs are limited by the lack of primary and surrogate endpoints, biomarkers, and validated patient-reported outcomes. Researchers with expertise in eosinophil biology and eosinophil-related diseases reviewed the state of current eosinophil research, resources, progress, and unmet needs in the field since the 2012 meeting of the NIH Taskforce on the Research of Eosinophil-Associated Diseases (TREAD). RE-TREAD focused on gaps in basic science, translational, and clinical research on eosinophils and eosinophil-related pathogenesis. Improved recapitulation of human eosinophil biology and pathogenesis in murine models was felt to be of importance. Characterization of eosinophil phenotypes, the role of eosinophil subsets in tissues, identification of biomarkers of eosinophil activation and tissue load, and a better understanding of the role of eosinophils in human disease were prioritized. Finally, an unmet need for tools for use in clinical trials was emphasized. Histopathologic scoring, patient- and clinician-reported outcomes, and appropriate coding were deemed of paramount importance for research collaborations, drug development, and approval by regulatory agencies. Further exploration of the eosinophil genome, epigenome, and proteome was also encouraged. Although progress has been made since 2012, unmet needs in eosinophil research remain a priority.Review on eosinophil biology and eosinophil-related disorders (2012–2017) with a focus on continued unmet needs in eosinophil-associated diseases.

Abstract Unstained human eosinophils exhibit marked autofluorescence in comparison to other leukocytes due to a granule-associated fluorescent substance. Fluorescence spectroscopy of granule extracts reveals excitation maxima at ~380 and ~450 nm with a single emission at ~520, characteristic of flavins. The fluorescent material from eosinophil granule extracts was characterized by fluorescence, high-performance liquid chromatographic, and enzymatic analyses. First, acidification to pH 2.6 resulted in increased fluorescence, indicative of flavin adenine dinucleotide (FAD). Second, because flavin mononucleotide (FMN) and riboflavin cannot be distinguished by acidification, high-performance liquid chromatography was performed and revealed a predominance of FAD and smaller amounts (<15%) of both FMN and riboflavin. Third, the presence of FAD was clearly demonstrated by reconstitution of the activity of d-amino acid oxidase, a FAD-dependent enzyme, when granule extracts were added to the apoenzyme. Thus, we have identified FAD as the predominant fluorophore in eosinophil granules. The small amounts of FMN and riboflavin detected may result from the hydrolysis of FAD under the acidic conditions of granule extraction. Because fluorescent material is deposited onto target cells by eosinophils, it is possible that granule-associated flavoproteins may act as a source of hydrogen peroxide and/or superoxide, which, in conjunction with eosinophil peroxidase, could yield potent cytotoxic agents.

Abstract Eosinophil adhesion and degranulation appear to be associated with cell death. Eosinophils bound avidly and degranulated with secretory immunoglobulin A (slgA)- and IgG-coupled Sepharose 4B beads but bound poorly and did not degranulate with ovalbumin beads. Through the use of dye staining, we found that about 50% of the bound eosinophils were dead by 4 h, regardless of the protein coating. Colchicine and reduced calcium concentration inhibited binding to beads and eosinophil degranulation in a concentration-dependent manner but did not decrease the percentages of dead bound eosinophils. Electron microscopy showed that eosinophils bound to and spread over bead surfaces. Typical granule exocytosis with release of membrane-free granules occurred in about 20% of bound eosinophils. Eosinophil degeneration and lysis with release of membrane-coated granules occurred in about 50% of bound eosinophils; often only membrane-bound granules were present. Therefore, bound eosinophils degranulate both by classical exocytosis and by release after cytolytic degeneration. By increasing the numbers of bound cells, both IgG and sIgA increase the numbers of dying cells.

Abstract Use of the murine monoclonal antibodies EG1 and EG2 has been based on the assumption that EG2 recognizes activated eosinophils. We examined the reactivity of EG1 and EG2 with eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN), and stimulated and nonstimulated eosinophils from normal donors. By radioimmunoassay, EG1 recognized only ECP, whereas EG2 recognized both ECP and EDN. By Western blot, EG1 reacted with ECP, EG2 reacted with both ECP and EDN, but EG2 could not distinguish between lysates of stimulated and nonstimulated eosinophils. By immunofluorescence, EG1 and EG2 at 20 μg/mL stained 95–100% of nonstimulated eosinophils, regardless of fixative; EG1 and EG2 at 0.1 μg/mL stained 61–90% of acetone- and paraformaldehyde-fixed and only 5–21% of methanol-fixed nonstimulated eosinophils. Thus, the reactivity of EG1 and EG2 with eosinophils depends on the method of fixation and antibody concentration; and EG2, in contrast to previous reports, cannot reliably discriminate between resting and activated eosinophils. J. Leukoc. Biol. 66: 447–454; 1999.

Abstract Eosinophils contain four principal cationic proteins, major basic protein (MBP), eosinophil-derived neurotoxin (EDN), eosinophil cationic protein (ECP), and eosinophil peroxidase (EPO). To determine the quantities of these proteins in granulocytes and whether they are specific to eosinophils, their concentrations in ly- sates of human granulocytes were measured using specific radioimmunoassays. The effect of different methods for eosinophil lysis on the recovery of the proteins was also studied. Maximal recovery occurred at pH 2 for MBP and pH 5.6 for the other granule proteins. The proteins cosedimented with eosinophils and their concentrations (X ± SEM) in ng/106 eosinophils (and in nM/106 eosinophils) were: MBP, 8,982 ± 611 (641.6); EDN, 3,283 ± 116 (178.4); ECP, 5,269 ± 283 (250.9); and EPO, 12,174 ± 859 (171.5). Basophils from a normal person contained (in ng/106 cells) MBP, 2,374; EDN, 214; ECP, 77; and EPO, 17. Highly purified neutrophils contained (in ng/106 cells) MBP, 3 ± 0.5; EDN, 72 ± 9; and ECP, 50 ± 12. Therefore we conclude that these proteins are mainly expressed in eosinophils, but that certain ones are present in basophils and neutrophils.

Abstract Eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP) are generally regarded as eosinophil-specific proteins. We tested whether EDN and ECP are present in mature neutrophils. By indirect immunofluorescence, both eosinophils and neutrophils stained with antibodies to EDN and ECP. Lysates of purified (<0.1% eosinophil contamination) neutrophils contained EDN, 112 ± 4 ng/106 cells, and ECP, 163 ± 2 ng/106 cells, whereas eosinophil major basic protein (MBP) was not detectable. Electron microscopic examination of immunogold-labeled buffy coat cells stained with EDN antibody showed that EDN is localized to neutrophil granules. Finally, EDN mRNA was detected in lysates of highly purified neutrophils (0.001% eosinophil contamination) by the reverse transcription-polymerase chain reaction. We conclude that proteins that are either identical to or immunologically cross-reactive with EDN and ECP are present in neutrophils and that EDN is synthesized and localized to neutrophil granules. Thus, caution must be exercised in interpreting the presence of EDN and ECP as specific markers of eosinophil-associated inflammation in human disease.