GATA-2-deficient mast cells limit IgE-mediated immediate hypersensitivity reactions in human subjects

TH2-driven manifestations of inborn errors of immunity

Monogenic lesions in pathways critical for effector functions responsible for immune surveillance, protection against autoinflammation, and appropriate responses to allergens and microorganisms underlie the pathophysiology of inborn errors of immunity (IEI). Variants in cytokine production, cytokine signaling, epithelial barrier function, antigen presentation, receptor signaling, and cellular processes and metabolism can drive autoimmunity, immunodeficiency, and/or allergic inflammation. Identification of these variants has improved our understanding of the role that many of these proteins play in skewing toward TH2-related allergic inflammation. Early-onset or atypical atopic disease, often in conjunction with immunodeficiency and/or autoimmunity, should raise suspicion for an IEI. This becomes a diagnostic dilemma if the initial clinical presentation is solely allergic inflammation, especially when the prevalence of allergic diseases is becoming more common. Genetic sequencing is necessary for IEI diagnosis and is helpful for early recognition and implementation of targeted treatment, if available. Although genetic evaluation is not feasible for all patients with atopy, identifying atopic patients with molecular immune abnormalities may be helpful for diagnostic, therapeutic, and prognostic purposes. In this review, we focus on IEI associated with TH2-driven allergic manifestations and classify them on the basis of the affected molecular pathways and predominant clinical manifestations.

Novel insights into the ontogeny of basophils

Basophils are the least common granulocytes, accounting for <1% of peripheral blood leukocytes. In the last 20 years, analytical tools for mouse basophils have been developed, and we now recognize that basophils play critical roles in various immune reactions, including the development of allergic inflammation and protective immunity against parasites. Moreover, the combined use of flow cytometric analyses and knockout mice has uncovered several progenitor cells committed to basophils in mice. Recently, advancements in single-cell RNA sequencing (scRNA-seq) technologies have challenged the classical view of the differentiation of various hematopoietic cell lineages. This is also true for basophil differentiation, and studies using scRNA-seq analysis have provided novel insights into basophil differentiation, including the association of basophil differentiation with that of erythrocyte/megakaryocyte and the discovery of novel basophil progenitor cells in the mouse bone marrow. In this review, we summarize the recent findings of basophil ontogeny in both mice and humans, mainly focusing on studies using scRNA-seq analyses.

Pathogenic GATA2 genetic variants utilize an obligate enhancer mechanism to distort a multilineage differentiation program

Mutations in genes encoding transcription factors inactivate or generate ectopic activities to instigate pathogenesis. By disrupting hematopoietic stem/progenitor cells, GATA2 germline variants create a bone marrow failure and leukemia predisposition, GATA2 deficiency syndrome, yet mechanisms underlying the complex phenotypic constellation are unresolved. We used a GATA2-deficient progenitor rescue system to analyze how genetic variation influences GATA2 functions. Pathogenic variants impaired, without abrogating, GATA2-dependent transcriptional regulation. Variants promoted eosinophil and repressed monocytic differentiation without regulating mast cell and erythroid differentiation. While GATA2 and T354M required the DNA-binding C-terminal zinc finger, T354M disproportionately required the N-terminal finger and N terminus. GATA2 and T354M activated a CCAAT/Enhancer Binding Protein-ε (C/EBPε) enhancer, creating a feedforward loop operating with the T-cell Acute Lymphocyte Leukemia-1 (TAL1) transcription factor. Elevating C/EBPε partially normalized hematopoietic defects of GATA2-deficient progenitors. Thus, pathogenic germline variation discriminatively spares or compromises transcription factor attributes, and retaining an obligate enhancer mechanism distorts a multilineage differentiation program.

Genetic Changes in Mastocytes and Their Significance in Mast Cell Tumor Prognosis and Treatment

Mast cell tumors are a large group of diseases occurring in dogs, cats, mice, as well as in humans. Systemic mastocytosis (SM) is a disease involving the accumulation of mast cells in organs. KIT gene mutations are very often seen in abnormal mast cells. In SM, high KIT/CD117 expression is observed; however, there are usually no KIT gene mutations present. Mastocytoma (MCT)-a form of cutaneous neoplasm-is common in animals but quite rare in humans. KIT/CD117 receptor mutations were studied as the typical changes for human mastocytosis. In 80% of human cases, the KIT gene substitution p.D816H was present. In about 25% of MCTs, metastasis was observed. Changes in the gene expression of certain genes, such as overexpression of the DNAJ3A3 gene, promote metastasis. In contrast, the SNORD93 gene blocks the expression of metastasis genes. The panel of miR-21-5p, miR-379, and miR-885 has a good efficiency in discriminating healthy and MCT-affected dogs, as well as MCT-affected dogs with and without nodal metastasis. Further studies on the pathobiology of mast cells can lead to clinical improvements, such as better MCT diagnosis and treatment. Our paper reviews studies on the topic of mast cells, which have been carried out over the past few years.

CREB Is Activated by the SCF/KIT Axis in a Partially ERK-Dependent Manner and Orchestrates Survival and the Induction of Immediate Early Genes in Human Skin Mast Cells

cAMP response element binding protein (CREB) functions as a prototypical stimulus-inducible transcription factor (TF) that initiates multiple cellular changes in response to activation. Despite pronounced expression in mast cells (MCs), CREB function is surprisingly ill-defined in the lineage. Skin MCs (skMCs) are critical effector cells in acute allergic and pseudo-allergic settings, and they contribute to various chronic dermatoses such as urticaria, atopic dermatitis, allergic contact dermatitis, psoriasis, prurigo, rosacea and others. Using MCs of skin origin, we demonstrate herein that CREB is rapidly phosphorylated on serine-133 upon SCF-mediated KIT dimerization. Phosphorylation initiated by the SCF/KIT axis required intrinsic KIT kinase activity and partially depended on ERK1/2, but not on other kinases such as p38, JNK, PI3K or PKA. CREB was constitutively nuclear, where phosphorylation occurred. Interestingly, ERK did not translocate to the nucleus upon SCF activation of skMCs, but a fraction was present in the nucleus at baseline, and phosphorylation was prompted in the cytoplasm and nucleus in situ. CREB was required for SCF-facilitated survival, as demonstrated with the CREB-selective inhibitor 666-15. Knock-down of CREB by RNA interference duplicated CREB's anti-apoptotic function. On comparison with other modules (PI3K, p38 and MEK/ERK), CREB was equal or more potent at survival promotion. SCF efficiently induces immediate early genes (IEGs) in skMCs (FOS, JUNB and NR4A2). We now demonstrate that CREB is an essential partaker in this induction. Collectively, the ancient TF CREB is a crucial component of skMCs, where it operates as an effector of the SCF/KIT axis, orchestrating IEG induction and lifespan.

Incorporating Tryptase Genotyping Into the Workup and Diagnosis of Mast Cell Diseases and Reactions

The measurement of mast cell tryptase levels in serum has found utility in the diagnosis and management of both clonal mast cell disorders and severe mast cell-dependent systemic reactions in the form of anaphylaxis. A more recent discovery is that a majority of individuals with elevated basal serum tryptase levels have increased germline TPSAB1 gene copy number encoding α-tryptase. This genetic trait is referred to as hereditary α-tryptasemia (HαT) and affects nearly 6% of the general population. In clinical practice, the presence or absence of HαT should thus now be determined when defining what constitutes an abnormal serum tryptase level in the diagnosis of mastocytosis. Further, as rises in serum tryptase levels are used to support the diagnosis of systemic anaphylaxis, variability in baseline serum tryptase levels should be factored into how significant a rise in serum tryptase is required to confirm the diagnosis of a systemic allergic reaction. In practicality, this dictates that symptomatic individuals undergoing evaluation for a mast cell-associated disorder or reaction with a baseline serum tryptase level exceeding 6.5 ng/mL should be considered for tryptase genotyping in order to screen for HαT. This review provides detailed information on how to use the results of such testing in the diagnosis and management of both mastocytosis and anaphylaxis.

KIT as a master regulator of the mast cell lineage

The discovery in 1987/1988 and 1990 of the cell surface receptor KIT and its ligand, stem cell factor (SCF), was a critical achievement in efforts to understand the development and function of multiple distinct cell lineages. These include hematopoietic progenitors, melanocytes, germ cells, and mast cells, which all are significantly affected by loss-of-function mutations of KIT or SCF. Such mutations also influence the development and/or function of additional cells, including those in parts of the central nervous system and the interstitial cells of Cajal (which control gut motility). Many other cells can express KIT constitutively or during immune responses, including dendritic cells, eosinophils, type 2 innate lymphoid cells, and taste cells. Yet the biological importance of KIT in many of these cell types largely remains to be determined. We here review the history of work investigating mice with mutations affecting the white spotting locus (which encodes KIT) or the steel locus (which encodes SCF), focusing especially on the influence of such mutations on mast cells. We also briefly review efforts to target the KIT/SCF pathway with anti-SCF or anti-Kit antibodies in mouse models of allergic disorders, parasite immunity, or fibrosis in which mast cells are thought to play significant roles.

A Critical Function for the Transcription Factors GLI1 and GLI2 in the Proliferation and Survival of Human Mast Cells

Mast cell hyperactivity and accumulation in tissues are associated with allergy and other mast cell-related disorders. However, the molecular pathways regulating mast cell survival in homeostasis and disease are not completely understood. As glioma-associated oncogene (GLI) proteins are involved in both tissue homeostasis and in the hematopoietic system by regulating cell fate decisions, we sought to investigate the role for GLI proteins in the control of proliferation and survival of human mast cells. GLI1 transcripts were present in primary human mast cells and mast cell lines harboring or not activating mutations in the tyrosine kinase receptor KIT (HMC-1.1 and HMC-1.2, and LAD2 cells, respectively), while GLI2 transcripts were only present in HMC-1.1 and HMC-1.2 cells, suggesting a role for oncogenic KIT signaling in the regulation of GLI2. Reduction in GLI activity by small molecule inhibitors, or by shRNA-mediated knockdown of GLI1 or GLI2, led to increases in apoptotic cell death in both cultured human and murine mast cells, and reduced the number of peritoneal mast cells in mice. Although GLI proteins are typically activated via the hedgehog pathway, steady-state activation of GLI in mast cells occurred primarily via non-canonical pathways. Apoptosis induced by GLI silencing was associated with a downregulation in the expression of KIT and of genes that influence p53 stability and function including USP48, which promotes p53 degradation; and iASPP, which inhibits p53-induced transcription, thus leading to the induction of p53-regulated apoptotic genes. Furthermore, we found that GLI silencing inhibited the proliferation of neoplastic mast cell lines, an effect that was more pronounced in rapidly growing cells. Our findings support the conclusion that GLI1/2 transcription factors are critical regulators of mast cell survival and that their inhibition leads to a significant reduction in the number of mast cells in vitro and in vivo, even in cells with constitutively active KIT variants. This knowledge can potentially be applicable to reducing mast cell burden in mast cell-related diseases.

Understanding human mast cells: lesson from therapies for allergic and non-allergic diseases

Mast cells have crucial roles in allergic and other inflammatory diseases. Preclinical approaches provide circumstantial evidence for mast cell involvement in many diseases, but these studies have major limitations - for example, there is still a lack of suitable mouse models for some mast cell-driven diseases such as urticaria. Some approaches for studying mast cells are invasive or can induce severe reactions, and very few mediators or receptors are specific for mast cells. Recently, several drugs that target human mast cells have been developed. These include monoclonal antibodies and small molecules that can specifically inhibit mast cell degranulation via key receptors (such as FcεRI), that block specific signal transduction pathways involved in mast cell activation (for example, BTK), that silence mast cells via inhibitory receptors (such as Siglec-8) or that reduce mast cell numbers and prevent their differentiation by acting on the mast/stem cell growth factor receptor KIT. In this Review, we discuss the existing and emerging therapies that target mast cells, and we consider how these treatments can help us to understand mast cell functions in disease.

State-of-the-Art on Biomarkers for Anaphylaxis in Obstetrics

Anaphylaxis is an unpredictable systemic hypersensitivity reaction and constitutes a high risk of maternal and fetal morbidity and mortality when occurring during pregnancy. Currently, the acute management of anaphylaxis is based on clinical parameters. A total serum tryptase is only used to support an accurate diagnosis. There is a need to detect other biomarkers to further assess high-risk patients in obstetrics. Our objective is to present biomarkers in this complex interdisciplinary approach beyond obstetrician and anaesthetic management. Candidate biomarkers derive either from mediators involved in immunopathogenesis or upcoming molecules from systems biology and proteomics. Serum tryptase is determined by singleplex immunoassay method and is important in the evaluation of anaphylactic mast cell degranulation but also in the assessment of other risk factors for anaphylaxis such as systemic mastocytosis. Another category of biomarkers investigates the IgE-mediated sensitization to triggers potentially involved in the etiology of anaphylaxis in pregnant women, using singleplex or multiplex immunoassays. These in vitro tests with natural extracts from foods, venoms, latex or drugs, as well as with molecular allergen components, are useful because in vivo allergy tests cannot be performed on pregnant women in such a major medical emergency due to their additional potential risk of anaphylaxis.

Hymenoptera venom-induced anaphylaxis and hereditary alpha-tryptasemia

PURPOSE OF REVIEW

To discuss the association between the common dominantly inherited genetic trait hereditary alpha-tryptasemia (HαT) and hymenoptera venom-induced anaphylaxis (HVA).

RECENT FINDINGS

Elevated BST has been correlated with more severe systemic anaphylaxis in humans in a number of settings - most notably in HVA. Clonal mast cell disease, in particular, systemic mastocytosis, is frequently associated with elevated BST, and is a major risk factor for severe HVA. However, clonal mast cell diseases are believed to be rare, whereas HVA is relatively more common. HαT affects an estimated 3-5% of Western populations and is the common cause for elevated BST in these individuals. An association between HαT and severe HVA, as well as clonal mast cell disease has recently been demonstrated wherein this trait modifies reaction severity in venom allergic individuals. A mechanism underlying this association has been proposed through the identification of naturally occurring heterotetrameric tryptases and characterization of their unique physical attributes.

SUMMARY

Here we discuss the long-standing association between elevated BST and HVA severity, how HαT fits into this landscape, and review the clinical and mechanistic evidence that supports HαT as a modifier of HVA.

Sputum Gene Expression Reveals Dysregulation of Mast Cells and Basophils in Eosinophilic COPD

Purpose

The clinical and inflammatory associations of mast cells (MCs) and basophils in chronic obstructive pulmonary disease (COPD) are poorly understood. We previously developed and validated a qPCR-based MC/basophil gene signature in asthma to measure these cells in sputum samples. Here, we measured this gene signature in a COPD and control population to explore the relationship of sputum MCs/basophils to inflammatory and COPD clinical characteristics.

Patients and Methods

MC/basophil signature genes (TPSAB1/TPSB2, CPA3, ENO2, GATA2, KIT, GPR56, HDC, SOCS2) were measured by qPCR in sputum from a COPD (n=96) and a non-respiratory control (n=17) population. Comparative analyses of gene expression between the COPD and the control population, and between eosinophilic COPD and non-eosinophilic COPD were tested. Logistic regression analysis and Spearman correlation were used to determine relationships of sputum MC/basophil genes to inflammatory (sputum eosinophil proportions, blood eosinophils) and clinical (age, body mass index, quality of life, lung function, past year exacerbations) characteristics of COPD.

Results

MC/basophil genes were increased in COPD versus control participants (CPA3, KIT, GATA2, HDC) and between eosinophilic-COPD and non-eosinophilic COPD (TPSB2, CPA3, HDC, SOCS2). We found all MC/basophil genes were positively intercorrelated. In COPD, MC/basophil genes were associated with eosinophilic airway inflammation (GATA2, TPSB2, CPA3, GPR56, HDC, SOCS2), blood eosinophilia (all genes) and decreased lung function (KIT, GATA2, GPR56, HDC).

Conclusion

We demonstrate associations of MCs and basophils with eosinophilic inflammation and lower lung function in COPD. These findings are consistent with prior results in asthma and may represent a new tool for endotyping eosinophilic-COPD.

Inherited and acquired determinants of serum tryptase levels in humans

OBJECTIVE

To aid the clinician in correctly interpreting serum tryptase levels.

DATA SOURCES

Primary peer-reviewed literature.

STUDY SELECTIONS

Clinical and basic science peer-reviewed studies characterizing the genetic and physiological bases for tryptase generation, secretion, and elevation, including those describing serum tryptase levels in population-based cohort studies.

RESULTS

Clinically measured basal serum tryptase (BST) consists of ostensibly inactive alpha- and beta-tryptase precursors. The autosomal dominant genetic trait hereditary alpha-tryptasemia is the most often cause for elevated BST levels, with other acquired causes, such as renal failure and clonal myeloid diseases being far less common. Acute increases in serum tryptase levels resulting from release of mature tryptase from secretory granules is specific to mast cell degranulation but is not detected in all cases of systemic anaphylaxis.

CONCLUSION

Understanding the differences and distinguishing between acute increases in serum tryptase and chronic elevations in BST owing to inherited or acquired conditions is critical in the correct interpretation of this useful clinical biomarker.

Anaphylaxis: Focus on Transcription Factor Activity

Anaphylaxis is a severe allergic reaction, rapid in onset, and can lead to fatal consequences if not promptly treated. The incidence of anaphylaxis has risen at an alarming rate in past decades and continues to rise. Therefore, there is a general interest in understanding the molecular mechanism that leads to an exacerbated response. The main effector cells are mast cells, commonly triggered by stimuli that involve the IgE-dependent or IgE-independent pathway. These signaling pathways converge in the release of proinflammatory mediators, such as histamine, tryptases, prostaglandins, etc., in minutes. The action and cell targets of these proinflammatory mediators are linked to the pathophysiologic consequences observed in this severe allergic reaction. While many molecules are involved in cellular regulation, the expression and regulation of transcription factors involved in the synthesis of proinflammatory mediators and secretory granule homeostasis are of special interest, due to their ability to control gene expression and change phenotype, and they may be key in the severity of the entire reaction. In this review, we will describe our current understanding of the pathophysiology of human anaphylaxis, focusing on the transcription factors' contributions to this systemic hypersensitivity reaction. Host mutation in transcription factor expression, or deregulation of their activity in an anaphylaxis context, will be updated. So far, the risk of anaphylaxis is unpredictable thus, increasing our knowledge of the molecular mechanism that leads and regulates mast cell activity will enable us to improve our understanding of how anaphylaxis can be prevented or treated.

Mast cell tryptases in allergic inflammation and immediate hypersensitivity

Dysregulated mast cell-mediated inflammation and/or activation have been linked to a number of human diseases, including asthma, anaphylaxis, chronic spontaneous urticaria, and mast cell activation syndromes. As a major mast cell granule protein, tryptase is a biomarker commonly used in clinical practice to diagnose mast cell-associated disorders and -mediated reactions, but its mechanistic roles in disease pathogenesis remains incompletely understood. Here, we summarize recent advances in the understanding of human tryptase genetics and the effects that different genetic composition may have on the quaternary structure of tetrameric mature tryptases. We also discuss how these differences may impact clinical phenotypes including allergic inflammation, immediate hypersensitivity, and others seen in patients with mast cell-associated disorders. With the increased application of next-generation sequencing, we foresee that human genetic approaches will be a major focus of understanding human tryptase functions in various human mast cell disorders and in new therapeutic development.

The Genetic Basis and Clinical Impact of Hereditary Alpha-Tryptasemia

Hereditary alpha-tryptasemia (HαT) is an autosomal dominant genetic trait found in 4% to 6% of the general population and defined by excess copies of alpha-tryptase at TPSAB1. Elevated basal serum tryptase (sBT >8 ng/mL) is a defining feature of HαT and appears to result from increased pro-alpha-tryptase synthesis and secretion rather than mast cell activation. It is estimated that approximately one-third of individuals with HαT have associated symptoms, including cutaneous, gastrointestinal, atopic, musculoskeletal, autonomic, and neuropsychiatric manifestations. HαT is found at a disproportionately high rate in systemic mastocytosis and idiopathic anaphylaxis, and is a modifying factor that independently increases the incidence and severity of anaphylaxis. The varied phenotypes associated with HαT may, in part, result from coinheritance of other genetic variants, increased expression of α-/ß-tryptase heterotetramers, and/or overexpression of pro-alpha-tryptase, although further studies are needed. There is an accurate diagnostic test available to confirm HαT in patients that can be used in combination with sBT to help risk-stratify individuals in whom bone marrow biopsy is being considered. There is no specific treatment for symptoms associated with HαT, and management is focused on controlling clinical manifestations with mast cell mediator antagonists, aspirin, inhalers, epinephrine, omalizumab, and involvement of other specialists.

Genetic Regulation of Tryptase Production and Clinical Impact: Hereditary Alpha Tryptasemia, Mastocytosis and Beyond

Tryptase is a serine protease that is predominantly produced by tissue mast cells (MCs) and stored in secretory granules together with other pre-formed mediators. MC activation, degranulation and mediator release contribute to various immunological processes, but also to several specific diseases, such as IgE-dependent allergies and clonal MC disorders. Biologically active tryptase tetramers primarily derive from the two genes TPSB2 (encoding β-tryptase) and TPSAB1 (encoding either α- or β-tryptase). Based on the most common gene copy numbers, three genotypes, 0α:4β, 1α:3β and 2α:2β, were defined as “canonical”. About 4–6% of the general population carry germline TPSAB1-α copy number gains (2α:3β, 3α:2β or more α-extra-copies), resulting in elevated basal serum tryptase levels. This condition has recently been termed hereditary alpha tryptasemia (HαT). Although many carriers of HαT appear to be asymptomatic, a number of more or less specific symptoms have been associated with HαT. Recent studies have revealed a significantly higher HαT prevalence in patients with systemic mastocytosis (SM) and an association with concomitant severe Hymenoptera venom-induced anaphylaxis. Moreover, HαT seems to be more common in idiopathic anaphylaxis and MC activation syndromes (MCAS). Therefore, TPSAB1 genotyping should be included in the diagnostic algorithm in patients with symptomatic SM, severe anaphylaxis or MCAS.

Sputum mast cell/basophil gene expression relates to inflammatory and clinical features of severe asthma

BACKGROUND

Mast cells (MCs) and basophils are important in asthma pathophysiology, however direct measurement is difficult, and clinical and inflammatory associations in severe asthma are poorly understood. Transcriptomic hallmarks of MCs/basophils may allow their measurement in sputum using gene expression.

OBJECTIVES

This study sought to develop and validate a sputum MC/basophil gene signature and investigate its relationship to inflammatory and clinical characteristics of severe asthma.

METHODS

A total of 134 candidate MC/basophil genes (identified by the Immunological Genome Project Consortium) were screened in sputum microarray for differential expression among control subjects (n = 18), patients with eosinophilic (n = 29), and patients with noneosinophilic asthma (n = 30). Candidate genes were validated by confirming correlation of gene expression with flow cytometry-quantified sputum MCs and basophils in a separate asthma cohort (n = 20). The validated gene signature was measured in a severe asthma cohort (n = 81), and inflammatory and clinical associations were tested.

RESULTS

Through microarray screening and subsequent validation, we found quantitative PCR gene expression of 8 targets correlated with sputum MCs/basophils: TPSAB1/TPSB2, CPA3, ENO2, GATA2, KIT, GPR56, HDC, SOCS2. In severe asthma, MC/basophil genes were associated with eosinophilic airway inflammation (GATA2, TPSB2, CPA3, GPR56, HDC, SOCS2), blood eosinophils (TPSB2, CPA3, GATA2, SOCS2, FCER1A, HDC), fractional exhaled NO (GATA2, SOCS2), decreased lung function (KIT, ENO2), and moderate exacerbation history (GATA2, SOCS2).

CONCLUSIONS

Quantitative PCR-based measures reflect varying sputum MC/basophil abundance, demonstrating associations of MCs/basophils with eosinophilic inflammation, spirometry and exacerbation history in severe asthma.

Mast cell activation in the context of elevated basal serum tryptase: genetics and presentations

PURPOSE OF REVIEW

To describe inherited and acquired genetic variants and clinical entities associated with increased basal serum tryptase (BST), distinguish these levels from those which acutely rise due to mast cell activation, and finally to characterize the association between chronically elevated basal serum tryptase and episodic mast cell activation.

RECENT FINDINGS

Hereditary alpha-tryptasemia is a commonly inherited genetic cause for basally elevated serum tryptase and explains elevated BST in many individuals who do not have evidence of clonal myeloid or mast cell disease. When clonal myeloid disease is present, BST may be elevated and can be a biomarker of a number of disparate disorders of the myeloid compartment. Elevated BST is most commonly caused by hereditary alpha tryptasemia but may also be indicative of clonal myeloid disease. Clinical reports suggest that elevated BST is associated with increased risk for more severe systemic allergic reactions to a number of eliciting agents and exposures. Additional studies are needed to determine the role that inherited or acquired genetic variants associated with elevated BST and clonal or non-clonal myeloid diseases may play in these reactions.