Basophilic cell progenitors, nasal metachromatic cells, and peripheral blood basophils in ragweed-allergic patients

Modulating the Human Basophil Phenotype During Its Development and Maturation: Basophils Derived from In Vitro Cultures of CD34+ Progenitor Cells

Historically, the human basophil that is studied experimentally comes from peripheral blood. But there is evidence that only a short portion of the basophil life cycle related to IgE-mediated function occurs in the blood. The same evidence suggests that IgE-mediated functionality is present for 5-7 days in the bone marrow (or other tissues) during which the cell modulates its phenotype according to local conditions. It is suggested that to properly understand the nature of basophil behavior, a better understanding of its biology during maturation would be helpful. For example, one highly suggestive line of evidence for the relevance of understanding the maturation period is related to the change in basophil phenotype that occurs during treatment of patients with omalizumab. During this treatment, the intrinsic reactivity or sensitivity of the basophils is significantly increased despite, or perhaps because of, the dramatic reduction in FcεRI expression that accompanies this treatment. One of the critical signaling enzymes to increase expression selectively in basophils during treatment is SYK, which is one of the earliest signaling tyrosine kinases involved in translating the aggregation of FcεRI into secretion from the cell. Treatment with omalizumab increases SYK expression, and this observation focuses some attention of how SYK expression is regulated. It is possible that the key regulation occurs during maturation of the basophil. Regardless of the mechanisms operative in this particular treatment, understanding the process of maturation and the extrinsic factors that influence it may lead to better understanding of disease processes. Therefore, this chapter will discuss and present techniques to work with maturing human basophils.

Identifying regulatory pathways of spleen tyrosine kinase expression in human basophils

BACKGROUND

Expression levels of spleen tyrosine kinase (SYK), a critical signaling tyrosine kinase in basophils, are uniquely low relative to all other circulating leukocytes, and levels are highly variable in the population.

OBJECTIVE

We sought to determine whether transcriptional regulation of SYK through unique silencing of the SYK gene determines its basophil-specific expression patterns.

METHODS

Culture-derived basophils (CD34B cells) were derived from cultures of CD34⁺ progenitor cells by using 2 methods (G1 or G3). Peripheral blood basophils (PBBs; relative SYK protein level = 1), B cells (SYK = 8), CD34B-G1 cells (SYK = 11), and CD34B-G3 cells (SYK = 5) were examined by using assay for transposase-accessible chromatin sequencing (ATAC-seq) methods. In addition, the transcriptomes of 6 cell types, PBBs, peripheral blood eosinophils (SYK = 11), plasmacytoid dendritic cells (SYK = 30), CD34⁺ progenitors (SYK = 11), CD34B-G1 cells, and CD34B-G3 cells, were analyzed for patterns that matched patterns of SYK expression in these cells, with a focus on transcription factors.

RESULTS

ATAC-seq showed that PBBs have multiple open regions in the SYK gene, suggesting a nonsilenced state with 1 region unique to PBBs (low SYK expression), 1 region unique to both PBBs (low SYK expression) and both G1 and G3 CD34B cells (high and moderate SYK expression, respectively), and 5 regions unique to B cells (high SYK expression). SYK expression across the 6 cell types explored showed a unique pattern that was matched to expression patterns of 3 transcription factors: Kruppel-like factor 5 (KLF5), zinc-finger protein 608 (ZNF608), and musculoaponeurotic fibrosarcoma protein (c-MAF).

CONCLUSIONS

Two new potential regulatory pathways for SYK expression were identified. One appears independent of transcriptional regulation, and one appears to be dependent on transcriptional control in the SYK gene.

Hemopoietic progenitors: the role of eosinophil/basophil progenitors in allergic airway inflammation

Progenitor cells play important roles in the physiology and homeostasis of the overall hemopoietic system. The majority of hemopoietic activity takes place in the bone marrow, under the influence of resident marrow stromal cells, accessory cells, and/or their products. This constitutes the complex network of the hemopoietic inductive microenvironment, which is crucial for providing signals necessary for the maintenance of populations of progenitors at varying stages of lineage commitment. Accumulation of eosinophils and basophils in tissues is characteristic of allergic inflammation. A large body of evidence now exists which confirms that these tissue inflammatory events are coincident with relevant changes in progenitors; it has thus been hypothesized that the observed changes in mature cell numbers occur directly or indirectly as a result of differentiation of lineage-committed eosinophil/basophil, and perhaps other, progenitor cells. Differentiation and maturation of hemopoietic cells have traditionally been thought to be restricted to the bone marrow microenvironment. More recently, evidence has accumulated to suggest that some hemopoietic cells present in allergic tissue may be recruited from the bone marrow, traffic through the peripheral circulation and into tissues to participate in the ongoing inflammatory process at these distal sites. The clinical administration of monotherapy with topical corticosteroids, oral cysteinyl leukotriene antagonists and cytokine antagonists such as antibodies to interleukin-5, suggest that suppression of hemopoietic contributions to allergic inflammation may be necessary for full control of allergic inflammation and disease manifestations. In addition to progenitors being targets of therapy, they may well determine how and whether allergic inflammation is generated in early life, thus serving as biomarkers of disease.

Current Thinking on the Relationship Between Rhinosinusitis and Asthma

An observation made initially on clinical grounds and epidemiologic evidence, i.e., that rhinosinusitis and asthma are closely linked diseases is now supported by a growing body of scientific evidence. Most recent evidence supports the characterization of rhinosinusitis and asthma as two compartmental expressions of a common mucosal susceptibility to exogenous stimuli. In addition, there is evidence that the compartmental processes can affect and amplify each other via a systemic intermediary. The bone marrow is involved in this process, and IL-5 may be a key cytokine for orchestrating the systemic interaction. These facts argue that rhinosinusitis and asthma are not simply localized disease processes but part of a systemic inflammatory disease affecting the respiratory tract. They also provide a compelling rationale for combined treatment strategies with consideration of the treatment of rhinosinusitis as a means of improving asthma control and monitoring for signs of bronchial involvement in those with rhinosinusitis.

Eosinophil progenitors in airway diseases: clinical implications

Asthma, allergic rhinitis, nasal polyposis, chronic rhinosinusitis, and related forms of upper and lower airway diseases are often characterized by eosinophilic and basophilic inflammation, involving systemic processes. Eosinophil/basophil (Eo/B) lineage-committed progenitor cells in cord blood, peripheral blood, bone marrow, lung tissue, and sputum are up-regulated in the above conditions, and respond to allergen and other stimuli with increased differentiative and migratory capacity. A considerable body of evidence now exists showing that activation of such Eo/B-selective hemopoietic processes is not only associated with the onset and maintenance of allergic inflammation in atopic adults, but also with the development of the allergic diathesis. Moreover, eosinophilopoietic processes within hemopoietic compartments and, importantly, at mucosal tissue sites during an allergic inflammatory response provide novel targets for the treatment of allergy as a systemic process and disease.

Eosinophil progenitors in allergy and asthma - do they matter?

Allergic inflammation is associated with marked infiltration of eosinophils in affected tissues. The eosinophil is believed to be a key effector cells in allergen induced asthma pathogenesis. However, the role of eosinophils in the clinical manifestation of asthma has recently been questioned, since therapies directed against eosinophil infiltration (i.e. anti-interleukin-5) failed to improve clinical symptoms such as airways hyper-responsiveness (AHR) in patients with asthma. Although eosinophils in peripheral blood and the airways were largely depleted after anti-IL-5 treatment, residual eosinophilia in lung tissue persisted, which permits speculation that the remaining eosinophils may be sufficient to drive the asthma symptomatology. Furthermore, recent findings suggest that primitive eosinophil progenitor cells traffic from the bone marrow to sites of inflammation in response to allergen exposure. These progenitors may then differentiate in situ and thus provide an ongoing supply of mature pro-inflammatory cells and secretory mediators that augment the inflammatory response. In the present article, we will review the evidence for these findings, and discuss the rationale for targeting hematopoiesis and their migration pathways in the treatment of allergic diseases. Furthermore, this review will highlight the hypothesis that both IL-5- and CCR3-mediated signaling pathways may need to be targeted in order to control the inflammation and AHR associated with asthma.

In vitro effects of budesonide on eosinophil-basophil lineage commitment

IL-5 is the primary cytokine that stimulates the production and survival of eosinophils and basophils from progenitor cells. The inhaled glucocorticoid, budesonide, has been shown to exert a therapeutic effect via suppression of eosinophil/basophil progenitors in vivo. Since various steroids have exhibited the ability to enhance eosinophil/basophil progenitor differentiation, we examined the effects of budesonide in vitro. Bone marrow and cord blood samples were obtained and cultured in the presence of IL-5 alone or IL-5 plus budesonide. Eosinophil/basophil colony-forming units were enumerated from cultured nonadherent mononuclear cells and from purified CD34⁺ cells. CD34⁺ cells with and without budesonide were also examined for up-regulation of ERK1/2, MAPK and GATA-1 using real time-PCR.

RESULTS

i) up-regulation of eosinophil/basophil colony-forming units is due to the direct effects of budesonide on IL-5-stimulated progenitors; ii) GATA-1 is likely involved in the early amplification of eosinophil/basophil progenitor commitment leading to increased differentiation. A potential transcriptional pathway has been identified which may mediate the effects of budesonide on eosinophil/basophil lineage commitment.

Inhibition of the antigen provoked nasal reaction by second-generation antihistamines in patients with Japanese cedar pollinosis

BACKGROUND

Epinastine hydrochloride and fexofenadine hydrochloride, the second-generation antihistamines, are largely used in the indication of allergic rhinitis in Japan. The purpose of this study was to compare the protective efficacy of epinastine hydrochloride or fexofenadine hydrochloride using a nasal provocation test with Japanese cedar pollen allergen.

METHODS

A single-dose, placebo-controlled, single-blind crossover clinical study was conducted in patients with Japanese cedar pollinosis. The pollen exposure was done by the antigen provocation by disc method and involved repeated provocation five times per day.

RESULTS

Among the active agents studied-epinastine hydrochloride and fexofenadine hydrochloride-epinastine hydrochloride significantly decreased the number of sneezing attacks and the quantity of nasal discharge for 3 hours after drug administration compared with placebo, a finding supported by the quantity of nasal discharge in the nasal findings. In this study, fexofenadine hydrochloride showed no significant difference compared with placebo.

CONCLUSIONS

This study demonstrates better protection with epinastine hydrochloride than with fexofenadine hydrochloride or placebo in a nasal provocation test with Japanese cedar pollen allergen.

The effect of desloratadine on eosinophil/basophil progenitors and other inflammatory markers in seasonal allergic rhinitis: a placebo-controlled randomized study

BACKGROUND

Eosinophil/basophil (Eo/B) progenitors fluctuate in the peripheral circulation during seasonal allergen exposure in atopic subjects. Several drugs have been shown to modulate Eo/B progenitor levels in the peripheral blood but, to date, the possible effect of antihistamines on Eo/B progenitors has not been explored. Our objective was to evaluate whether the antihistamine desloratadine (DL) can modulate peripheral blood Eo/B progenitors or other markers of allergic inflammation.

METHODS

We performed a randomized double-blind placebo-controlled study on the effects of DL on peripheral blood Eo/B progenitors in subjects with symptomatic, seasonal allergic rhinitis during a ragweed pollen season. Forty-five subjects were randomized to treatment for 4 weeks with DL 20 mg daily or placebo.

RESULTS

The expected fall in the number of Eo/B progenitors from baseline to 2 weeks of treatment was seen in the placebo group [median drop of 1.0 colony-forming unit (CFU)/10(6) cells], and was greater than in the DL group (median drop of 0.0 CFU/10(6) cells) (p = 0.013). The change in histamine concentration per colony from baseline to 2 weeks of treatment was lower in the DL group (median decrease of 6.1 pg/colony) compared to placebo (median increase of 1.8 pg/colony) (p = 0.01). An increase in the nasal lavage eotaxin concentration from baseline to 4 weeks of treatment was statistically significant in the placebo group but not in the DL group. Eo/B CFU were not affected by varying in vitro concentrations of DL.

CONCLUSION

These results suggest that DL can modulate aspects of allergic inflammation in vivo through mechanisms other than simple blockade of H1 histamine receptors.

Haemopoietic mechanisms in murine allergic upper and lower airway inflammation

Eosinophil recruitment to the airways, including involvement of haemopoietic eosinophil-basophil progenitors (Eo/B-CFU), is primarily regulated by interleukin-5 (IL-5) and eotaxin. In this study, we investigated the haemopoietic mechanisms in upper and lower airway eosinophilic inflammation. Ovalbumin (OVA) sensitized and challenged BALB/c mice were used to establish isolated upper (UAC), isolated lower (LAC), or combined upper and lower airway (ULAC) inflammation. Airway, blood and bone marrow responses were evaluated in each model. Numbers of airway eosinophils and CD4(+) cells were increased significantly in the nasal mucosa in UAC and ULAC mice, and in the lung tissue in LAC and ULAC groups. Levels of IL-5 and eotaxin were increased significantly in the nasal lavage fluid (NL) in UAC and ULAC mice, and in the bronchoalveolar lavage fluid (BAL) in LAC and ULAC groups. The proportion of IL-5-responsive bone marrow Eo/B-CFU was significantly higher than the control in all treatment groups, but peaked much earlier in the ULAC group. Kinetic studies revealed that IL-5 and eotaxin in NL, BAL and serum peaked between 2 and 12 hr after OVA challenge in ULAC mice, and at 24 hr in UAC mice, related to the timing of maximal progenitor responses. These data support the concept that the systemic mechanisms linking rhinitis to asthma depend on the location and extent of airway allergen exposure.

The effect of cysteinyl leukotrienes on growth of eosinophil progenitors from peripheral blood and bone marrow of atopic subjects

BACKGROUND

The accumulation of eosinophils into the peripheral blood and airways of asthmatic subjects is, in part, dependent on cysteinyl leukotrienes (cysLTs). However, the effect of cysLTs on peripheral blood and bone marrow eosinophil pro-genitor cells in allergic subjects is not known.

OBJECTIVE

The purpose of this study was to evaluate the effects of leukotriene (LT) D(4) and LTE(4) and the cysLT(1) receptor antagonist montelukast on peripheral blood and bone marrow eosinophil-basophil progenitor growth and development in atopic subjects.

METHODS

Semisolid methylcellulose cultures for peripheral blood and bone marrow eosinophil-basophil colonies were counted after incubation with or without addition of LTD(4), LTE(4), and montelukast in the presence of suboptimal concentrations of GM-CSF, IL-3, and IL-5.

RESULTS

Peripheral blood eosinophil-basophil colony-forming unit cultures grown in the presence of GM-CSF and bone marrow eosinophil-basophil colony-forming units grown in the presence of IL-5 were significantly increased by the addition of LTD(4) (0.1 micromol/L). This increase was suppressed by montelukast (1 micromol/L).

CONCLUSION

This study has demonstrated that the cysLT LTD(4) can stimulate proliferation of eosinophil hematopoietic progenitor cells in the presence of eosinophilopoietic cytokines. The suppressive effect by montelukast demonstrates that this is a cysLT(1) receptor-mediated effect.

Anti-allergic therapies: effects on eosinophil progenitors

Marked eosinophilic infiltration is the typical inflammatory response associated with allergic inflammation. Previous research involving animal and human models has established a role for the eosinophil/basophil hematopoietic progenitor in a systemic process of allergic inflammation. In this article, we will review the evidence implicating eosinophil/basophil progenitors in this systemic response and will discuss the rationale for targeting this cell in the treatment of allergic disease. In this context, we discuss corticosteroid treatment of allergic diseases, such as asthma and its effects on hematopoietic mechanisms, the effects of therapies that inhibit the actions of cysteinyl leukotrienes, the effects of in vivo blockade of the eosinophil-active cytokine interleukin-5, and the effects of antihistamines on hematopoiesis. It is suggested that several anti-allergic therapies exert their beneficial effects on allergic inflammation by influencing eosinophil production systemically. Therefore, targeting the systemic hematopoietic response may provide additional, more beneficial, therapeutic effects.

Systemic aspects of allergic disease: the role of the bone marrow

In recent years, there has been an increasing appreciation of the important contribution of bone-marrow-related, hemopoietic mechanisms to allergic diseases. Eosinophil/basophil-progenitor levels fluctuate in the peripheral blood during allergen exposure and the cells home to peripheral tissue, where they differentiate. It is becoming apparent that several cytokines, particularly IL-5, have multiple effects on progenitors and allergic inflammation. Within the past few years, studies of the therapeutic implications of this bone marrow contribution to atopy have been initiated; the effects of corticosteroids, leukotriene-receptor blockers, antagonism of IL-5 and modulation of differentiation by retinoic acid on progenitors will be reviewed.

The trials and tribulations of IL-5, eosinophils, and allergic asthma

Eosinophils have been suggested to be part of the pathologic process that characterizes asthma, and their recruitment into the upper or lower airways appears to be essential for the clinical manifestations of allergen inhalation. IL-5 is a cytokine necessary for the development, differentiation, recruitment, activation, and survival of eosinophils. Allergen inhalation increases the production of IL-5 in the airways as measured in bronchoalveolar lavage cells and induced sputum. The relationship between IL-5 and the development of airway eosinophilia has been firmly established in IL-5 transgenic mice, with allergen challenge models in IL-5-deficient mice, and in mice treated with blocking anti-IL-5 antibodies. In addition, an accumulation of evidence suggests that treating mice with anti-IL-5 blocking antibodies prevents allergen-induced airway hyperresponsiveness. A recently reported study examined the effects of treatment with a humanized anti-IL-5 mAb (SB-240563) on allergen-induced airway responses and inflammation in atopic subjects. The authors of the study concluded that their results call into question the role of eosinophils in mediating the allergen-induced late asthmatic response and airway hyperresponsiveness; however, because of methodologic limitations, the study cannot be used either to support or to refute the concept of an important role for eosinophils in causing allergen-induced changes in airway function.

Allergen-induced murine upper airway inflammation: local and systemic changes in murine experimental allergic rhinitis

The role of inflammatory effector cells in the pathogenesis of airway allergy has been the subject of much investigation. However, whether systemic factors are involved in the development of local responses in both upper and lower airways has not been fully clarified. The present study was performed to investigate aspects of the pathogenesis of isolated allergic rhinitis in a murine model sensitized to ovalbumin (OVA). Both upper- and lower-airway physiological responsiveness and inflammatory changes were assessed, as well as bone marrow progenitor responses, by culture and immunohistological methods. Significant nasal symptoms and hyper-responsiveness appeared after intranasal OVA challenge (P < 0.0001 and P < 0.01, respectively), accompanied with significant nasal mucosal changes in CD4+ cells (P < 0.001), interleukin (IL)-4+ cells (P < 0.01), IL-5+ cells (P < 0.01), basophilic cells (P < 0.02) and eosinophils (P < 0.001), in the complete absence of hyper-responsiveness or inflammatory changes in the lower airway. In the bone marrow, there were significant increases in CD34+ cells, as well as in eosinophils and basophilic cells. In the presence in vitro of mouse recombinant IL-5, IL-3 or granulocyte-macrophage colony-stimulating factor (GM-CSF), the level of bone marrow eosinophil/basophil (Eo/Baso) colony-forming cells increased significantly in the OVA-sensitized group. We conclude that, in this murine model of allergic rhinitis, haemopoietic progenitors are upregulated, which is consistent with the involvement of bone marrow in the pathogenesis of nasal mucosal inflammation. Both local and systemic events, initiated in response to allergen provocation, may be required for the pathogenesis of allergic rhinitis. Understanding these events and their regulation could provide new therapeutic targets for rhinitis and asthma.

History and future perspectives of treating asthma as a systemic and small airways disease

Asthma is an inflammatory disorder in which the small airways of the lung play an important role. There is also evidence for the systemic nature of asthma. No current method adequately measures small airways function alone. Therefore, a combination of functional and clinical parameters should be used to ensure that patients with asthma are adequately treated with due consideration of the small airways. Previously therapeutic strategies have focused on bronchodilation and attenuation of airway inflammation. While early oral therapies had the advantage of reaching the small airways and treating the systemic aspect of asthma, they were associated with serious side-effects. Inhaled therapies were therefore developed to limit these effects. However, inhaled therapies have the disadvantage of limited penetration into the peripheral airways and an inability to treat the systemic component of asthma. They are also associated with local and systemic side-effects. The future for asthma treatment is likely to be a systemically administered medication with few side-effects targeting disease-specific mediators. The leukotriene receptor antagonists and anti-IgE monoclonal antibodies are examples of such therapies and the emergence of other new strategies is awaited.

Immunotherapy in atopic dermatitis

Atopic dermatitis (AD) is a common inflammatory disease involving the skin and often other organs and systems, mainly respiratory. A definitive general consensus on the AD pathogenesis has not yet been established, however several lines of evidence suggest that T-cells play a crucial role in priming AD early-stage lesions. Main topics involved in the disease pathogenesis have been reviewed, which considered the concept of local and systemic haemopoietic events as important contributors to allergic inflammation, a concept now achieving great acceptance. The recently recognised atopic nature of the skin inflammation in AD has raised increasing interest for treatment with allergen-specific immunotherapy. However, we only found eight studies using specific immunotherapy (SIT) in AD, two double-blind, placebo-controlled (DBPC) and six observational. One controlled and five observational reported favourable outcomes. The one unique study providing negative results was flawed by the ineffective oral route of extract administration. Despite being encouraging, the reported results do not allow definitive conclusions based on meta-analytic techniques because the amount and quality of information in the literature is not sufficient. The highly promising sub-lingual immunotherapy (SLIT) is discussed with its potential capability of controlling not only the skin lesion severity but also its capability of preventing the development of atopic dermatitis into asthma.

The effects of inhaled budesonide on circulating eosinophil progenitors and their expression of cytokines after allergen challenge in subjects with atopic asthma

Allergen inhalation by dual responder subjects with atopic asthma is associated with an increase in circulating eosinophil/basophil colony-forming units (Eo/B CFU) and granulocyte-macrophage colony- stimulating factor (GM-CSF) immunolocalization in Eo/B colony cells grown in vitro. The current study examined the effect of the inhaled corticosteroid, budesonide, on the number of allergen- induced circulating eosinophils and Eo/B CFU, and immunolocalization of GM-CSF and interleukin-5 (IL-5) in Eo/B colony cells grown in vitro. Sixteen subjects with mild atopic asthma were treated for either 7 or 8 d with 200 microg inhaled budesonide or placebo twice a day. Peripheral blood was collected before and 24 h after allergen inhalation challenge and nonadherent mononuclear cells (NAMC) were grown in methylcellulose culture. Eo/B CFU were enumerated after 14 d in culture, and prepared on slides for immunocytochemistry. Budesonide attenuated the allergen-induced increase in circulating eosinophils (4.0 +/- 0.4 x 10(5)/ml versus 6.5 +/- 0.7 x 10(5)/ml, p = 0.0001), circulating Eo/B CFU (12.4 +/- 2.3/10(6) NAMC versus 18.8 +/- 4.6/10(6) NAMC, p = 0.05), and immunolocalization of GM-CSF in Eo/B colony cells (11.8 +/- 1.9% positive versus 18.0 +/- 2.2%, p = 0.01) but not immunolocalization of IL-5 (7.9 +/- 1.4% versus 4.5 +/- 0.6%, p > 0.05). Inhaled budesonide attenuated the number of allergen-induced circulating eosinophils and their progenitors grown in the presence of GM-CSF, which may partially be a result of regulating eosinophil progenitor expression of the autocrine growth factor GM-CSF.

Systemic immunologic and inflammatory aspects of allergic rhinitis

Allergic rhinitis is a common chronic condition that is characterized by inflammation of the nasal mucosa. Although allergic rhinitis is a condition with upper respiratory symptoms, there is a growing body of evidence to suggest that allergic rhinitis may be linked to the development of systemic allergic manifestations that include allergic asthma. The evidence reveals that individuals with allergic rhinitis are sensitized to the eliciting allergens and exhibit cutaneous and respiratory hypersensitivity responses on exposure to the allergen. On exposure to a nasal allergen, circulating immunoglobulin E levels increased and remained elevated 2 weeks after the initial provocation. Patients with allergic rhinitis exhibit peripheral eosinophilia and basophilia, the magnitude of which correlates with the severity of symptoms. Additionally, there are several links between allergic rhinitis and asthma. First, 85% to 95% of patients with allergic asthma report rhinitis symptoms, and the severity of the 2 conditions increases in parallel on exposure to an allergen. Second, nasal administration of allergens can provoke impaired lower airway airflow in 25% to 30% of individuals and cause airway eosinophilia, as evidenced by increased numbers of eosinophils in sputum and mucosal biopsy specimens. Third, the treatment of seasonal allergic rhinitis with both systemic (eg, antihistamines) and local agents (eg, glucocorticosteroid analogues) can alleviate the symptoms of asthma. In summary, evidence that associates allergic rhinitis with systemic immunologic and inflammatory processes is growing, thereby warranting further in-depth investigation.

Bone marrow events in animal models of allergic inflammation and hyperresponsiveness

Allergic inflammation is associated with the marked infiltration of eosinophils in affected tissues. Eosinophilia, in turn, is a hallmark clinical feature associated with allergic rhinitis, atopic dermatitis, sinusitis, and asthma. There is considerable evidence in animal models and humans that the bone marrow plays an integral role in allergic inflammation. Evidence shows that, in response to allergen exposure in the airway, bone marrow (white blood cell) progenitors proliferate and differentiate, which leads to persistent increases in eosinophil numbers. These observations suggest that there is signaling between the lung and bone marrow after allergen exposure and provide further support for the proposition that allergy is a systemic disease. Although the nature of the signal-mediating activation of bone marrow after airway allergen exposure is unknown, several pathways have been implicated, including allergen-induced hemopoietic growth factors, cell trafficking, and stimulation of resident bone marrow cells. A common thread in all these pathways is the importance of IL-5. Evidence is reviewed in animal models for the role of bone marrow in allergic inflammation within the context of the systemic nature of allergic disease.

Systemic aspects of allergic disease: bone marrow responses

In patients with allergic diseases, allergen provocation can activate a systemic response that provokes inflammatory cell production by the bone marrow. After release and differentiation of progenitor cells, eosinophils, basophils, and mast cells are typically recruited to tissues in atopic individuals. An understanding at the molecular level of the signaling process that leads to these systemic responses between the target organ, especially the airways, and the bone marrow may open up new avenues of therapy for allergic inflammatory disease. Studies that support the critical involvement of the bone marrow in the development of eosinophilic inflammation of the airways point out the systemic nature of these conditions and their potential for biologic intervention. Hemopoietic events that originate in the bone marrow are potential targets of long-term therapy for rhinitis and asthma. For example, the "beneficial" systemic activity of cortico-steroids through modulation of hemopoietic mechanisms and inflammatory cell recruitment to the airways is essential for the optimal treatment of both upper and lower airway inflammation.

Molecular pathology of allergic disease: I: lower airway disease

Asthma is a complex disorder associated with eosinophil infiltration and the activation of T lymphocytes within the airways. Recent advances in the pathophysiologic mechanisms of asthma point to the importance of eosinophil-basophil progenitor cells and a family of transcription factors that underlie the development of T(H)2-type responses. Further research is needed to address the development of chronic inflammatory changes, the role of profibrotic cytokines, and especially their reliance on eosinophils in the lungs.

Bone marrow contribution to eosinophilic inflammation

Allergen-induced bone marrow responses are observable in human allergic asthmatics, involving specific increases in eosinophil-basophil progenitors (Eo/B-CFU), measured either by hemopoietic assays or by flow cytometric analyses of CD34-positive, IL-3R alpha-positive, and/or IL-5-responsive cell populations. The results are consistent with the upregulation of an IL-5-sensitive population of progenitors in allergen-induced late phase asthmatic responses. Studies in vitro on the phenotype of developing eosinophils and basophils suggest that the early acquisition of IL-5R alpha, as well as the capacity to produce cytokines such as GM-CSF and IL-5, are features of the differentiation process. These observations are consistent with findings in animal models, indicating that allergen-induced increases in bone marrow progenitor formation depend on hemopoietic factor(s) released post-allergen. The possibility that there is constitutive marrow upregulation of eosinophilopoiesis in allergic airways disease is also an area for future investigation.

Enhanced expression of GM-CSF in differentiating eosinophils of atopic and atopic asthmatic subjects

Higher numbers of eosinophil/basophil colony-forming units (Eo/B CFU) are observed in blood of atopic individuals, and can be enhanced in atopic asthmatics by allergen-inhalation challenge. It is known that mature basophils and eosinophils synthesize cytokines relevant to allergic inflammation. To investigate the potential role of growth factors in allergic disease we examined the expression of the hemopoietic cytokines, granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-5, in differentiating Eo/B colony cells from normal and atopic individuals, and from atopic asthmatics before and after allergen-inhalation challenge. Peripheral blood was collected from two normal and 12 atopic individuals, and also from 25 atopic asthmatics before and 24 h after allergen challenge. Nonadherent mononuclear cells were isolated and grown in semisolid growth medium. Eo/B colonies were selected and cytospins were prepared for immunocytochemical analysis of colony cells. Eo/B colonies, especially carbol chromotrope 2R+ cells, selected at Days 10, 14, and 18 from atopic donors contained messenger RNA for GM-CSF by combined in situ reverse transcription-polymerase chain reaction and cytochemistry, and demonstrated time-dependent expression of GM-CSF by immunocytochemistry (P = 0.007). Atopic individuals demonstrated a higher percentage of cells expressing GM-CSF than did normal subjects under all growth conditions when examined at Day 14 (P = 0. 04). Atopic asthmatics challenged with inhaled allergen who demonstrated a dual airway response, an increase in the number of blood eosinophils (P = 0.0001), and an increase in the number of Eo/B CFU (P = 0.02) also demonstrated a significant increase in the percentage of colony cells expressing immunostainable GM-CSF (P = 0. 0009), but only a variable effect on those expressing IL-5, 24 h after allergen. These results suggest that GM-CSF expression by differentiating Eo/Bs may provide an additional stimulus in vivo to enhance Eo/B progenitor differentiation in atopic and asthmatic individuals, especially after allergen challenge. The concept of microenvironmental differentiation, where blood progenitor cells may aid in their own differentiation, is supported by these ex vivo findings.

Allergen challenge increases cell traffic between bone marrow and lung

Increases in inflammatory-cell progenitors have been demonstrated in the bone marrow (BM) after inhalation of Ascaris suum in dogs at the time of allergen-induced airway hyperresponsiveness (AHR). The aim of this study was to evaluate the effect of allergen challenge on trafficking of inflammatory cells and their progenitors from the BM to the lung, using a marker of proliferating cells, bromodeoxyuridine (BrdU). BrdU is a thymidine analogue taken up by the DNA of dividing cells, and can be detected with immunohistochemistry (IHC). The development of AHR was assessed through acetylcholine (ACh) airway responsiveness before and after allergen inhalation. Two groups of dogs were matched for the degree of AHR after a screening allergen challenge. On the study day, one group inhaled allergen (n = 8) and one group inhaled diluent (n = 8). All dogs received equal bolus injections of BrdU before and at 5 h after challenge. Blood samples were taken before challenge and at 5 h and 24 h after challenge, and BM aspirate and bronchoalveolar lavage (BAL) samples were taken 24 h after challenge. BrdU-positive cells were detected in cytospin preparations of these samples, using IHC. Allergen inhalation caused AHR (P < 0.05) at 24 h after allergen challenge, and also an increase in BrdU-positive cells in blood, which was 5.7 +/- 0.6% (mean +/- SEM) after allergen challenge and 2.5 +/- 0.7% after diluent (P < 0.005); in BM the increase in BrdU-positive cells was 27.0 +/- 3.4% after allergen challenge and 18.9 +/- 3.2% after diluent (P = 0.1); and in BAL the increase was 3.2 +/- 0.4% after allergen challenge and 0.8 +/- 0.3% after diluent (P < 0.005). There was a significant correlation between the number of BAL neutrophils and the percentage of BrdU-positive BAL cells (r2 = 0.54, P < 0.05). These results demonstrate an allergen-induced increase in proliferating cells, probably in the BM, and indicate that such cells traffic through the circulation into the lungs in response to allergen inhalation.

Regulation of Allergic Inflammation and Eosinophil Recruitment in Mice Lacking the Transcription Factor NFAT1: Role of Interleukin-4 (IL-4) and IL-5

Transcription factors of the NFAT (nuclear factor of activated T cells) family regulate the expression of many genes encoding immunoregulatory cytokines and cell surface proteins during the immune response. The NFAT protein NFAT1 (NFATp) is expressed and functional in T cells, B cells, mast cells, and natural killer cells. Here we report a detailed analysis of the enhanced eosinophil responses of NFAT1-deficient mice, observed in an in vivo model of allergic inflammation. In addition to the pleural eosinophilia described previously, NFAT1−/− mice that have been sensitized with antigen display a significant increase, relative to wild-type mice, in the numbers of eosinophils in bone marrow and peripheral blood. After restimulation with antigen in vitro, antigen-responsive T cells from the draining lymph nodes of NFAT1−/− mice show increased expression of mRNA encoding the Th2 cytokines interleukin-4 (IL-4), IL-5, and IL-13. Consistent with this finding, there is a pronounced increase in the levels of IL-5 and IL-13 in the pleural cavities of sensitized NFAT1−/− mice after allergen challenge in vivo. Furthermore, development of eosinophilia depends on overexpression of IL-4 and IL-5, because it is strongly inhibited by administration of neutralizing antibodies to either of these cytokines. These results indicate that NFAT1-deficient mice are prone to develop a classically allergic phenotype characterized by eosinophilia and increased production of Th2 cytokines. Thus, the presence of NFAT1 might inhibit the allergic response, perhaps by interfering with the development of Th2 immune responses, and the lack or dysfunction of NFAT1 could potentially underlie certain cases of atopic disease.

Regulation of Allergic Inflammation and Eosinophil Recruitment in Mice Lacking the Transcription Factor NFAT1: Role of Interleukin-4 (IL-4) and IL-5

Transcription factors of the NFAT (nuclear factor of activated T cells) family regulate the expression of many genes encoding immunoregulatory cytokines and cell surface proteins during the immune response. The NFAT protein NFAT1 (NFATp) is expressed and functional in T cells, B cells, mast cells, and natural killer cells. Here we report a detailed analysis of the enhanced eosinophil responses of NFAT1-deficient mice, observed in an in vivo model of allergic inflammation. In addition to the pleural eosinophilia described previously, NFAT1−/− mice that have been sensitized with antigen display a significant increase, relative to wild-type mice, in the numbers of eosinophils in bone marrow and peripheral blood. After restimulation with antigen in vitro, antigen-responsive T cells from the draining lymph nodes of NFAT1−/− mice show increased expression of mRNA encoding the Th2 cytokines interleukin-4 (IL-4), IL-5, and IL-13. Consistent with this finding, there is a pronounced increase in the levels of IL-5 and IL-13 in the pleural cavities of sensitized NFAT1−/− mice after allergen challenge in vivo. Furthermore, development of eosinophilia depends on overexpression of IL-4 and IL-5, because it is strongly inhibited by administration of neutralizing antibodies to either of these cytokines. These results indicate that NFAT1-deficient mice are prone to develop a classically allergic phenotype characterized by eosinophilia and increased production of Th2 cytokines. Thus, the presence of NFAT1 might inhibit the allergic response, perhaps by interfering with the development of Th2 immune responses, and the lack or dysfunction of NFAT1 could potentially underlie certain cases of atopic disease.

Changes in bone marrow inflammatory cell progenitors after inhaled allergen in asthmatic subjects

Increases in inflammatory cell progenitors, particularly eosinophil/basophil colony-forming cells (Eo/B-CFU), occur in peripheral blood after allergen provocation. The role of bone marrow (BM) in these reactions is unclear. We examined the effect of allergen challenge on human bone marrow progenitor cell growth. Fifteen asthmatic subjects, eight dual responders (DR) and seven isolated early responders (IER), were challenged with inhaled allergen. BM aspirates were taken before and 24 h after challenge and progenitors were enumerated by a colony-forming assay. Eo/B-CFU numbers increased in both groups after allergen challenge (p < 0.0001). For DR, the increases were significant for BM incubated with optimal GMCSF and IL-5, but not with IL-3. For IER, the increases were significant for all three cytokines tested. At a suboptimal concentration of IL-5, there was a significant increase in the number of Eo/B-CFU after allergen in the DR, from 5.25 +/- 1.2 to 9.68 +/- 2.1 per 2.5 x 10(5) cells plated (p < 0.01), which was not demonstrated in the IER (p = 0.94). The responses at this concentration of IL-5 were different between groups (p < 0.05). These results demonstrate that inhaled allergen increases BM Eo/B-CFU, and that the bone marrow of dual responders is more responsive to IL-5 after allergen.

Retinoic acid modulation of induced basophil differentiation

Current models of the regulation of hematopoiesis postulate a combination of both factor-directed cell differentiation/survival acting through intracellular signaling pathways, and factor-independent differentiation along intrinsically set, default pathways. Recent reports have indicated that eosinophil/basophil (Eo-Baso) differentiation may represent one default pathway. Because of the strong modulating effect of all trans-retinoic acid (ATRA) on hematopoietic differentiation, we have investigated the role of ATRA in regulating Eo-Baso differentiation from pluripotent progenitors. Our results indicate that ATRA inhibits Eo-Baso maturation at early stages of lineage commitment. Because allergic responses may depend on the continued recruitment and differentiation of such inflammatory mediators, the ability to modulate this pathway may eventually prove to have a therapeutic role in allergic inflammation.

Clinical implications of the pharmacological profile of Tilarin

The pharmacological activity of nedocromil sodium is extensive and the compound should affect a variety of inflammatory processes by preventing activation of the involved cells or blocking release of their mediators. Some in vitro actions of nedocromil sodium are particularly relevant to the mechanisms of allergic rhinitis, and the response of the nasal epithelium to pollutants such as ozone. The effects of nedocromil sodium on mucosal mast cells, eosinophils, sensory nerves and nasal epithelial cells can each be linked to its potential clinical effectiveness by our own biopsy studies from patients with active allergic rhinitis. Nedocromil sodium has been shown to modulate production of a number of powerful cytokines, such as GM-CSF and TNF alpha, which are produced by the human nasal epithelium, as well as by involved inflammatory cells and lymphocytes, and which orchestrate the inflammatory response to allergen or to pollutant provocation. So, in addition to inhibiting activated mast cells and eosinophils, nedocromil sodium acts on the nasal epithelium itself to prevent further accumulation of these cells and thus to break the inflammatory chain of events. On this evidence of its preclinical activity, nedocromil sodium promises to become a very useful topical treatment for allergic rhinitis.

The role of the bone marrow in allergy and asthma

The above studies have begun to address the fundamental question of the mechanisms of bone marrow involvement and response to allergen challenge in allergic asthmatics. Further studies in this area should complement our investigations in human asthma--which suggest that a particular bias toward differentiation of Eo-Baso progenitors characterizes the atopic state--as well as our findings in the dog model of allergen-induced airway hyperresponsiveness, which indicate that the bone marrow responds to inhalation of allergen or corticosteroids. Taken in the context of previous indications that IgE and bronchial responsiveness may both be transferrable through bone marrow transplantation (109), these findings indicate a physiologic role for the bone marrow in allergic inflammation. Likewise, these concepts provide a basis for making certain predictions regarding management and novel therapeutic interventions in atopy and asthma.

Microenvironmental influences on inflammatory cell differentiation

Airways inflammation involves accumulation of inflammatory cells such as eosinophils, basophils and mast cells, which are derived from progenitors in marrow and blood. The inflamed tissue of the airways, through its structural (epithelium, stroma) and inflammatory cell components, produces an array of cytokines which can influence the differentiation of inflammatory cell progenitors. It is particular mechanism that we have investigated, showing that molecules such as GM-CSF, G-CSF, IL-6, IL-8 and SCF can be produced by airways epithelial cells and fibroblasts in quantities sufficient to induce hemopoietic events, either systemically or locally. Corticosteriods may act therapeutically, at least in part, to block inflammatory cell differentiation, and thus recruitment, into the allergic inflammatory process in the airways.

Proteinase content of mast cells of nasal mucosa; effects of natural allergen exposure and of local corticosteroid treatment

The distribution and density of metachromatic cells (MCC) and mast cells containing chymase plus tryptase (MCTC) or tryptase alone (MCT) were studied in the nasal mucosa by dye-binding methods and immunohistochemical analysis. Biopsies were obtained from 17 subjects with birch pollen allergy before and during the peak season and from nine healthy controls. Six patients were treated with an intranasal glucocorticosteroid before and during the season in an open study. Hay fever patients, even when asymptomatic, showed signs of mast cell system activation, exhibiting an increased number of mast cells in the nasal epithelium. Basophils, lacking immunohistochemically detectable tryptase, were not a major component of the mast cell response. MCT, most conspicuous in the epithelium, were found to be the most frequent mast-cell type in the nasal mucosa of allergic, but not of normal, subjects. Only 33% of the epithelial, but 90% of the stromal, immunopositive cells in the atopic mucosa before as well as during the season were MCC. Intraepithelial MCT thus displayed a low capacity to stain metachromatically, indicating a relative deficiency of the glycosaminoglycan (heparin) component of the granules. Intraepithelial mast cells also appeared to be markedly sensitive to steroid treatment and aldehyde fixation. The findings suggest that the lack of chymase, the characteristic feature of MCT, may reflect a functional activation of the mast cells, rather than a stable phenotypic differentiation related to anatomic site.

Immunocytologic analysis of nasal cells obtained by nasal lavage: a comparative study with a standard method of cell identification

For evaluation of two methods of nasal cell identification, cell morphology and immunocytologic analysis, nasal lavage was performed in 16 healthy subjects and 29 patients suffering from rhinitis. Nasal lavage smears were stained with May-Grünwald-Giemsa (MGG), and cells were identified according to their structure as epithelial cells, neutrophils, lymphocytes, eosinophils, and metachromatic cells (basophils and mast cells). Immunocytologic analysis was performed with monoclonal antibodies by the immunoalkaline phosphatase method. The following monoclonal antibodies were used: CK1, EG2, and CD3, which identify epithelial cells, activated eosinophils, and T lymphocytes, respectively; CD15, which recognizes mature granulocytic cells; and CD14, which reacts with monocytes and macrophages. A significant difference was observed between the two methods in the number of identified epithelial cells, in both controls (64.6 +/- 7.8% with MGG, 14.2 +/- 3.5% with CK1 analysis) and patients with rhinitis (56.9 +/- 7.6% with MGG, 18.2 +/- 3.7% with CK1 analysis). In contrast, no significant differences were found in eosinophil and neutrophil counts when the two methods were compared. After nasal allergic provocation, a significant increase in the number of eosinophils was observed with both methods in seven patients with rhinitis. The results of this study indicate that: 1) MGG staining is a useful method to identify the cells obtained by nasal lavage, and 2) immunocytologic analysis with monoclonal antibodies accurately identifies granulocytic cells, while only a low proportion of epithelial cells are detected, probably because anticytokeratin monoclonal antibody reacts only with viable cells.

Histochemical and immunohistochemical characteristics of mast cells in nasal polyps

In surgically excised nasal polyps, most epithelial mast cells were formalin sensitive, chloroacetate esterase (CAE) negative, and chymase negative. Thus, this represents a population of mast cells not identified by staining for CAE. On the other hand, most stromal mast cells were formalin resistant and CAE positive, and although there was some polyp-to-polyp variability in their content of neutral protease, most of these cells were positive for both tryptase and chymase. The percentage of metachromatic cells in the epithelium and the number of metachromatic cells per unit area of polyp tissue did not correlate with an index of allergy skin test reactivity or the serum IgE concentration. The percentage of mast cells surrounded by pericellular tryptase, suggesting activation/degranulation, was significantly higher in the stroma than in the epithelium. The findings demonstrate differences between the stroma and the epithelium in phenotype and state of activation of mast cells; these are postulated to be due to distinct microenvironmental factors that affect mast cells at these sites.

The pathobiology of bronchial asthma

Early studies of patients dying from status asthmaticus revealed marked inflammation of the bronchial tree. Subsequent histological studies of the airways and examination of bronchoalveolar lavage fluid of subjects with mild asthma have confirmed the presence of airway inflammation in life. There is epithelial edema and desquamation, subepithelial deposition of collagen and fibronectin, and an inflammatory cell infiltrate in the mucosa. There are increased numbers of activated eosinophils, CD25-positive T lymphocytes, and immature macrophages with the phenotypic characteristics of blood monocytes. An increased expression of HLA class II is present on epithelium, macrophages, and other infiltrating cells. The severity of clinical asthma correlates with several measurements of the severity of the inflammatory response, suggesting a crucial role for airway inflammation in the pathophysiology of the disease. There is considerable interest and research into the mechanisms underlying the pathogenesis and maintenance of the inflammatory response in asthma. The development and maintenance of the inflammatory response in asthma is likely to be a consequence of a complicated interaction between various cells and the mediators they generate. The characterization of an ever-increasing number of cytokines is of particular interest. Interleukin-3, interleukin-5, and granulocyte-macrophage colony-stimulating factor are hematopoietic growth factors that increase the survival of eosinophils in culture and enhance certain eosinophil functions, such as mediator generation and toxicity. Alveolar macrophages derived from asthmatic subjects produce twofold to threefold more GM-CSF than do those from normal control subjects. Using in situ hybridization, the presence of IL-5 mRNA has been demonstrated in bronchial biopsies from asthmatic subjects. Thus IL-3, IL-5, and GM-CSF influence eosinophil function and survival, and may be generated by T lymphocytes and/or alveolar macrophages within the airways in asthma. In addition to these three cytokines, IL-4 and interferon-gamma may be crucial to the regulation of IgE biosynthesis. TNF-alpha and IL-1 are potentially important in the up-regulation of endothelial adhesion molecules. An important step in the recruitment of leukocytes to an inflammatory focus is margination to the vascular endothelium. Our understanding of the molecular events involved in migration of leukocytes to an inflammatory focus has been advanced by the discovery and characterization of a variety of cell adhesion molecules. The potential role of ELAM-1 and ICAM-1 in allergic inflammation is suggested by their up-regulation on vascular endothelium in association with late cutaneous responses to allergen and by their role in certain primate models of asthma.(ABSTRACT TRUNCATED AT 400 WORDS)

Monocyte-macrophage differentiation induced by human upper airway epithelial cells

We examined the ability of conditioned medium (CM) generated by human upper airway epithelial (Ep) cells from normal (NN) and inflamed, allergic rhinitis (AR) and nasal polyp (NP) tissues to induce monocytic differentiation of hemopoietic progenitors of the HL-60 myeloid leukemia cell line in vitro. In HL-60 cells cultured in RPMI with 10% FBS, there was differentiation to 0.4 +/- 0.4% monocytic cells. NN-, AR-, and NP-EpCM induced differentiation to 23 +/- 6%, 42 +/- 11%, and 71 +/- 10% monocytic cells, respectively. EpCM also induced isolated peripheral blood nonadherent mononuclear cells to express monocyte/macrophage-specific antigens as detected by immunohistochemistry using FMC-32 monoclonal antibodies (anti-CD14). We also examined the cytokine content of these EpCMs and found that they contained granulocyte/macrophage colony-stimulating factor (GM-CSF): 126 +/- 35, 198 +/- 22, and 489 +/- 118 pg/ml for NN-, AR-, and NP-EpCM, respectively. These CMs also contained granulocyte-CSF (G-CSF) and interleukin-6 (IL-6), but there were no significant differences between normal and inflamed tissue-derived cell supernatants. No macrophage-CSF (M-CSF) was detected in these EpCMs. Recombinant human GM-CSF, G-CSF, and IL-6, alone and in combinations, at doses similar to or greater than those found in the EpCMs, did not induce comparable monocytic differentiation of HL-60 cells. Preincubation of the EpCM with neutralizing anti-GM-CSF, anti-G-CSF, or anti-IL-6 antibodies did not significantly inhibit the monocytic differentiation induced by the EpCM.(ABSTRACT TRUNCATED AT 250 WORDS)