Evaluation of biologic activity of tryptase secreted from blast cells in acute myeloid leukemia

A number of autocrine and paracrine growth regulators are considered to be involved in the survival and proliferation of blast cells in acute myeloid leukemia (AML). We have recently shown that blast cells in a group of patients with AML produce and secrete the mitogenic enzyme tryptase. In the present study, we examined functional effects of tryptase in the context of AML. As assessed by 3H-thymidine uptake experiments, tryptase-containing serum from patients with AML as well as heparin-complexed recombinant tryptase were found to promote the proliferation of cultured bone marrow- and lung fibroblasts in a dose-dependent manner. A neutralizing antibody against human beta-tryptase was found to diminish these growth-stimulatory effects of serum-tryptase in all patients examined. Tryptase also induced the expression of mRNA for GM-CSF and SCF, two cytokines known to promote growth of AML cells, in cultured bone marrow fibroblasts. Neither recombinant tryptase nor tryptase-rich serum of AML patients, showed an effect on the growth of leukemic blast cells irrespective of the FAB category or expression of protease-activated receptor (PAR)-2, a putative molecular target of tryptase. Together, tryptase is secreted from AML blasts as a biologically active molecule that may exhibit paracrine rather than autocrine effects in AML.

Fc gamma RIIa, not Fc gamma RIIb, is constitutively and functionally expressed on skin-derived human mast cells

The expression of FcgammaR by human skin-derived mast cells of the MC(TC) type was determined in the current study. Expression of mRNA was analyzed with microarray gene chips and RT-PCR; protein by Western blotting and flow cytometry; function by release of beta-hexosaminidase, PGD(2), leukotriene C(4) (LTC(4)), IL-5, IL-6, IL-13, GM-CSF, and TNF-alpha. FcgammaRIIa was consistently detected along with FcepsilonRI at the mRNA and protein levels; FcgammaRIIc was sometimes detected only by RT-PCR; but FcgammaRIIb, FcgammaRI, and FcgammaRIII mRNA and protein were not detected. FcgammaRIIa-specific mAb caused skin MC(TC) cells to degranulate and secrete PGD(2), LTC(4), GM-CSF, IL-5, IL-6, IL-13, and TNF-alpha in a dose-dependent fashion. FcepsilonRI-specific mAb caused similar amounts of each mediator to be released with the exception of LTC(4), which was not released by this agonist. Simultaneous but independent cross-linking of FcepsilonRI and FcgammaRIIa did not substantially alter mediator release above or below levels observed with each agent alone. Skin MC(TC) cells sensitized with dust-mite-specific IgE and IgG, when coaggregated by Der p2, exhibited enhanced degranulation compared with sensitization with either IgE or IgG alone. These results extend the known capabilities of human skin mast cells to respond to IgG as well as IgE-mediated signals.

Diagnostic Value of Tryptase in Anaphylaxis and Mastocytosis

Serum (or plasma) levels of total and mature tryptase measurements are recommended in the diagnostic evaluation of systemic anaphylaxis and systemic mastocytosis, but their interpretation must be considered in the context of a complete workup of each patient. Total tryptase levels generally reflect the increased burden of mast cells in patients with all forms of systemic mastocytosis (indolent systemic mastocytosis, smoldering systemic mastocytosis, systemic mastocytosis associated with a hematologic clonal non-mast cell disorder, aggressive systemic mastocytosis, and mast cell leukemia) and the decreased burden of mast cells associated with cytoreductive therapies in these disorders. Causes of an elevated total tryptase level other than systemic mastocytosis must be considered, however, and include systemic anaphylaxis, acute myelocytic leukemia, various myelodysplastic syndromes, hypereosinophilic syndrome associated with the FLP1L1-PDGFRA mutation, end-stage renal failure, and treatment of onchocerciasis. Mature (beta) tryptase levels generally reflect the magnitude of mast cell activation and are elevated during most cases of systemic anaphylaxis, particularly with parenteral exposure to the inciting agent.

The tryptase positive compact round cell infiltrate of the bone marrow (TROCI-BM): a novel histopathological finding requiring the application of lineage specific markers

AIMS

Compact tryptase-positive round cell infiltrates of the bone marrow (TROCI-BM) are very rare histopathological findings and may pose challenging problems with regard to the cell type involved (either mast cells or basophilic granulocytes) and the exact diagnosis.

METHODS

A selected panel of immunohistochemical markers against mast cell and basophil related antigens, including CD25, CD34, CD117/Kit, and the 2D7 antigen (which is found only in basophilic granulocytes) on a total of 410 routinely processed bone marrow biopsy specimens (including 88 cases of systemic mastocytosis (SM), 20 cases of chronic myeloid leukaemia (CML), 92 cases of myeloid neoplasms other than CML, and 210 controls with normal/reactive bone marrows).

RESULTS

In total, 17 cases with TROCI-BM could be identified: 11 SM (including two cases of well-differentiated SM and two mast cell leukaemias; MCL), 2 myelomastocytic leukaemia (MML), 2 CML with excess of basophils (secondary basophilic leukaemia (CMLba)), and 2 tryptase positive acute myeloid leukaemia (AML). Regarding the cell types involved, TROCI-BM cells were found to express CD117/Kit in all cases of SM and MCL. In MML and tryptase postitive AML, TROCI-BM cells were found to coexpress CD34 and Kit. The basophil specific antigen 2D7 was only detected in CD34/Kit negative TROCI-BM cells in two patients with CMLba. The activating point mutation D816V was detected in 8/11 patients with SM but not in any of the other haematological malignancies.

CONCLUSIONS

In summary, a total of six rare myeloid neoplasms may present with a novel immunohistochemical phenomenon tentatively termed TROCI-BM.

Current options in the treatment of mast cell mediator-related symptoms in mastocytosis

Patients with mastocytosis have symptoms related to the tissue response to the release of mediators from mast cells (MC), local mast cell burden or associated non-mast cell hematological disorders. MC contain an array of biologically active mediators in their granules, which are preformed and stored. MC are also able to produce newly generated membrane-derived lipid mediators and are a source of multifunctional cytokines. Mediator-related symptoms can include pruritus, flushing, syncope, gastric distress, nausea and vomiting, diarrhea, bone pain and neuropsychiatric disturbances; these symptoms are variably controlled by adequate medications. Management of patients within all categories of mastocytosis includes: a) a careful counseling of patients (parents in pediatric cases) and care providers, b) avoidance of factors triggering acute mediator release, c) treatment of acute and chronic MC-mediator symptoms and, if indicated, d) an attempt for cytoreduction and treatment of organ infiltration by mast cells.

The B12 anti-tryptase monoclonal antibody disrupts the tetrameric structure of heparin-stabilized beta-tryptase to form monomers that are inactive at neutral pH and active at acidic pH

The novel tetrameric structure of human beta-tryptase faces each active site into the central pore, thereby restricting access of most biologic protease inhibitors. The mechanism by which the anti-tryptase mAb B12 inhibits human beta-tryptase peptidase and proteolytic activities at neutral pH, but augments proteolytic activity at acidic pH, was examined. At neutral pH, B12-beta-tryptase complexes are inactive. At acidic pH, B12 (intact and Fab) minimally affects peptidase activity when added to beta-tryptase tetramers, but does induce susceptibility to inhibition by soybean trypsin inhibitor and antithrombin III. Surprisingly, B12 Fab-beta-tryptase complexes formed at both neutral and acidic pH exhibit the apparent molecular mass of a complex with 1 beta-tryptase monomer and 1 Fab by gel filtration. B12 does not compete with heparin for binding to tryptase at either neutral or acidic pH. Thus, B12 directly disrupts beta-tryptase tetramers to monomers that are inactive at neutral pH, whereas at acidic pH, are active and more accessible to protein inhibitors and substrates.

Enumeration and immunohistochemical characterisation of bone marrow basophils in myeloproliferative disorders using the basophil specific monoclonal antibody 2D7

BACKGROUND

Basophils are highly specialised granulocytes that express a unique profile of antigens and increase in myeloproliferative disorders (MPD). In chronic myeloid leukaemia (CML), basophilia is a diagnostic and prognostic determinant. So far, however, no reliable approach for routine detection and enumeration of bone marrow basophils has become available.

OBJECTIVE

To detect and enumerate basophils in bone marrow sections in patients with CML and other MPD.

METHODS

The anti-basophil antibody 2D7 was applied to paraffin embedded bone marrow sections from normal/reactive subjects (n = 31), patients with CML (chronic phase, n = 37; accelerated phase, n = 9), and other MPD (chronic idiopathic myelofibrosis (CIMF), n = 20; polycythaemia vera (PV), n = 20; essential thrombocythaemia (ET), n = 20; indolent systemic mastocytosis (ISM), n = 7).

RESULTS

As assessed by serial section staining, 2D7(+) cells were found to co-express myeloperoxidase, histidine decarboxylase, CD9, and CD43, but did not express B cell or T cell restricted antigens. 2D7(+) bone marrow cells were found to increase in CML compared with normal/reactive bone marrow and other MPD (median numbers of 2D7(+) cells/mm(2): CML, 33; normal/reactive bone marrow, 6; CIMF, 10; PV, 6; ET, 5; ISM, 3; p<0.05). The highest basophil counts were recorded in accelerated phase CML (115/mm(2)).

CONCLUSIONS

A novel immunohistochemical procedure has been established for basophil detection in normal bone marrow and MPD. This approach should help in the quantification of bone marrow basophils at diagnosis and during anti-leukaemic treatment.

Identification of basophils by a mAb directed against pro-major basic protein 1

BACKGROUND

Basophils possess characteristics of both mast cells and eosinophils, and all 3 cell types often are found together, particularly during allergic reactions. A mAb (J175-7D4) generated against the recombinant pro-form of human eosinophil granule major basic protein 1 (rproMBP1) appeared to stain only basophils in tissue specimens.

OBJECTIVE

We investigated J175-7D4 to characterize its specificity for basophils.

METHODS

Fluid-phase immunoprecipitation, Western blotting, and immunocytochemistry and immunohistochemistry were used to establish the specificity of J175-7D4.

RESULTS

First, J175-7D4 binds to various glycosylated and proteolytically processed forms of rproMBP1, but not to major basic protein. Second, cells transfected with the rproMBP1 gene and human placental tissue (known to express the pro-form of major basic protein 1 [proMBP1]) stain specifically with J175-7D4. In contrast, although mature eosinophils contain substantial major basic protein, they lack proMBP1 and do not stain. Neutrophils, lymphocytes, monocytes, and skin mast cells also are not stained. However, blood basophils are stained by J175-7D4, anti-IgE, Wright-Giemsa (metachromatically), and a previously characterized basophil-specific mAb, 2D7. Finally, formaldehyde-fixed, paraffin-embedded basophils are identically detected by J175-7D4 and 2D7, and J175-7D4 also recognizes putative basophils in formaldehyde-fixed, paraffin-embedded tissue specimens from inflammatory dermatoses, such as atopic dermatitis and delayed pressure urticaria.

CONCLUSION

The J175-7D4 mAb recognizes proMBP1 as a novel marker for human basophils. J175-7D4 should prove useful for characterizing basophil involvement in human health and disease.

Analysis of MC(T) and MC(TC) mast cells in tissue

The MC(TC) and MCT types of human mast cells initially were recognized on the basis of the protease compositions of their secretory granules, with tryptase, chymase, carboxypeptidase A3, and cathepsin G in the former and only tryptase in the latter. Antibodies against chymase and tryptase traditionally have been used to distinguish these mast cell types from one another. Antitryptase antibodies label all mast cells; antichymase labels only the MC(TC) type. To identify both types in a tissue section, a sequential double-labeling scheme was developed to first stain chymase-positive cells, thereby blocking their recognition by the antitryptase antibody, which will label only the chymase-negative mast cells. In general, these immunocytochemical techniques are more sensitive and specific than classical histochemical techniques for detecting mast cells.

Structural and functional comparison of mast cells in the pregnant versus nonpregnant human uterus

OBJECTIVE

To characterize uterine mast cells and investigate uterine muscle strips contractile responses to challenge with an allergen in nonpregnant and pregnant women.

STUDY DESIGN

A double-antibody labeling technique was used to identify tryptase positive or chymase-tryptase-positive mast cells in uterine samples from term pregnant and nonpregnant women. Longitudinal myometrial strips were prepared from biopsies of hysterectomy specimens from patients undergoing procedures for benign indications and women who had elective cesarean sections. Responses to ragweed antigen were compared in uterine tissues from allergic and nonallergic patients and with passively sensitized tissues in the absence or presence of H1 receptor antagonist and a cyclooxygenase inhibitor.

RESULTS

Tryptase-chymase-positive mast cells were predominant in nonpregnant myometrium, whereas tryptase-positive cells were dominant in pregnant myometrium. Mast cell density was significantly higher in tissue from pregnant women than those of nonpregnant women. Studies in tissues from patients with known allergy to ragweed, as well as in passively sensitized tissues, showed an immediate and substantial increase in the frequency and force of myometrial contraction after a challenge with ragweed antigen. A similar response was observed to histamine. There was no contractile response to antigen challenge in tissues from nonallergic patients. An H1 receptor antagonist partially inhibited the response to antigen, whereas a cyclooxygenase inhibitor had no effect.

CONCLUSION

Sensitized isolated pregnant and nonpregnant human uterine tissue is capable of responding to antigen challenge with strong myometrial contractions. This ability, along with the increased density of mast cells in pregnant tissues as compared with nonpregnant tissues, indicates a possible role for mast cells in mediating uterine contractility in pregnancy.

Cytokine Production by Skin-Derived Mast Cells: Endogenous Proteases Are Responsible for Degradation of Cytokines

The current study characterizes the cytokine protein (ELISA) and mRNA (gene array and RT-PCR) profiles of skin-derived mast cells cultured under serum-free conditions when activated by cross-linking of Fc epsilonRI. Prior to mast cell activation, mRNA only for TNF-alpha was detected, while after activation mRNA for IL-5, IL-6, IL-13, TNF-alpha, and GM-CSF substantially increased, and for IL-4 it minimally increased. However, at the protein level certain recombinant cytokines, as measured by ELISAs, were degraded by proteases released by these skin-derived mast cells. IL-6 and IL-13 were most susceptible, followed by IL-5 and TNF-alpha; GM-CSF was completely resistant. These observations also held for the endogenous cytokines produced by activated mast cells. By using protease inhibitors, chymase and cathepsin G, not tryptase, were identified in the mast cell releasates as the likely culprits that digest these cytokines. Their cytokine-degrading capabilities were confirmed with purified chymase and cathepsin G. Soy bean trypsin inhibitor, when added to mast cell releasates, prevented the degradation of exogenously added cytokines and, when added to mast cells prior to their activation, prevented degradation of susceptible endogenous cytokines without affecting either degranulation or GM-CSF production. Consequently, substantial levels of IL-5, IL-6, IL-13, TNF-alpha, and GM-CSF were detected 24-48 h after mast cells had been activated, while none were detected 15 min after activation, by which time preformed granule mediators had been released. IL-4 was not detected at any time point. Thus, unless cytokines are protected from degradation by endogenous proteases, cytokine production by human mast cells with chymase and cathepsin G cells may be grossly underestimated.

Surface CD88 functionally distinguishes the MCTC from the MCT type of human lung mast cell

BACKGROUND

MC(T) and MC(TC) types of human mast cells (MCs) are distinguished from one another on the basis of the protease compositions of their secretory granules, but their functional and developmental relationships have been uncertain.

OBJECTIVE

These studies better define the functional properties and developmental relationship of MC(T) and MC(TC) cells.

METHODS

Mast cells were dispersed from human skin and lung, purified with anti-Kit antibody, and separated into CD88+ and CD88- populations by cell sorting. These cells were evaluated by immunocytochemistry with antitryptase and antichymase mAbs; for chymase and tryptase mRNA by real-time RT-PCR; for conversion of MC(T) to MC(TC) cells during cell culture with recombinant human stem cell factor and recombinant human IL-6; and for degranulation and leukotriene C 4 (LTC 4 ) secretion when stimulated with anti-FcepsilonRI, substance P, C5a, and compound 48/80.

RESULTS

Mature MC(T) and MC(TC) cells were separated from one another on the basis of selective expression of CD88, the C5aR, on MC(TC) cells. Lung MC(T) cells had negligible levels of chymase mRNA and retained their MC(T) phenotype in culture. Mature MC(TC) cells from skin and lung degranulated in response to FcepsilonRI cross-linking, C5a, compound 48/80, and substance P. Lung MC(TC) cells released LTC 4 on activation, but no LTC 4 was detected when skin-derived MC(TC) cells were activated. MC(T) cells from lung degranulated and released LTC 4 in response to anti-FcepsilonRI and substance P, but not to C5a and compound 48/80.

CONCLUSION

These observations functionally distinguish MC(T) from MC(TC) types of human mast cells and suggest important differences that may affect their participation in diseases such as asthma and urticaria.

TGF-beta 1 inhibits mast cell Fc epsilon RI expression

Mast cell activation through the high affinity IgE receptor (FcepsilonRI) is a critical component of atopic inflammation. The cytokine TGF-beta1 has been shown to inhibit IgE-dependent mast cell activation, possibly serving to dampen mast cell-mediated inflammatory responses. We present proof that TGF-beta1 inhibits mast cell FcepsilonRI expression through a reversible pathway that diminishes protein, but not mRNA, expression of the FcepsilonRI subunit proteins alpha, beta, and gamma. The stability of the expressed proteins and the assembled cell surface complex was unaltered by TGF-beta1 treatment. However, TGF-beta1 decreased the rate of FcepsilonRI beta-chain synthesis, arguing that this inhibitory cytokine exerts its effects at the level of mRNA translation. TGF-beta1 consistently diminished FcepsilonRI expression on cultured human or mouse mast cells as well as freshly isolated peritoneal mast cells. The related cytokines, TGF-beta2 and TGF-beta3, had similar effects. We propose that TGF-beta1 acts as a negative regulator of mast cell function, in part by decreasing FcepsilonRI expression.

Inflammatory basis of exercise-induced bronchoconstriction

RATIONALE

Exercise-induced bronchoconstriction (EIB) is a highly prevalent condition with unclear pathogenesis. Two competing theories of the pathogenesis of EIB differ regarding the inflammatory basis of this condition.

OBJECTIVES

Our goals were to establish whether epithelial cell and mast cell activation with release of inflammatory mediators occurs during EIB and how histamine and cysteinyl leukotriene antagonists alter the airway events occurring during EIB.

METHODS

Induced sputum was used to measure mast cell mediators and eicosanoids at baseline and 30 minutes after exercise challenge in 25 individuals with asthma with EIB. In a randomized, double-blind crossover study, the cysteinyl leukotriene antagonist montelukast and antihistamine loratadine or two matched placebos were administered for two doses before exercise challenge.

MAIN RESULTS

The percentage of columnar epithelial cells in induced sputum at baseline was associated with the severity of EIB. After exercise challenge, histamine, tryptase, and cysteinyl leukotrienes significantly increased and prostaglandin E(2) and thromboxane B(2) significantly decreased in the airways, and there was an increase in columnar epithelial cells in the airways. The concentration of columnar epithelial cells was associated with the levels of histamine and cysteinyl leukotrienes in the airways. Treatment with montelukast and loratadine inhibited the release of cysteinyl leukotrienes and histamine into the airways, but did not inhibit the release of columnar epithelial cells into the airways.

CONCLUSIONS

These data indicate that epithelial cells, mast cell mediators, and eicosanoids are released into the airways during EIB, supporting an inflammatory basis for EIB.

Heparin-induced recurrent anaphylaxis

BACKGROUND

Heparin-related immediate-type hypersensitivity reactions like urticaria, angio-oedema or bronchospasm are very rare, and only a few cases of anaphylaxis-like responses because of heparin have been described. However, the mechanisms underlying these reactions and the role of mast cells in their pathogenesis have not been elucidated.

OBJECTIVES

We report a patient with end-stage renal disease who presented with recurrent anaphylaxis after receiving heparin during haemodialysis. The underlying aetiology was obscured by the initiation of haemodialysis with its known anaphylactic-like side-effects. The diagnosis of hypersensitivity to heparin was confirmed by the clinical picture, positive skin tests and elevated serum tryptase levels.

MATERIALS AND METHODS

We performed prick and intradermal skin tests with heparin, enoxaparin and danaparoid heparinoid. Total and mature tryptase levels were measured in serum by ELISAs at 1, 24 and 36 h following the reaction.

RESULTS

An elevated mature tryptase level was found at 1 h, which returned to normal levels at 24 and 36 h. A high total tryptase level was detected at 1 h, but remained somewhat elevated at 24 h. Prick tests were negative with the three compounds. Intradermal skin tests with heparin and enoxaparin were both positive, while with danaparoid negative. Following negative skin test results, danaparoid was used as an anticoagulant during dialysis for the next 3 years without any adverse effects.

CONCLUSIONS

In conclusion, we report the first case of heparin-induced anaphylaxis confirmed by an elevated level of mature tryptase in serum. Following skin tests, the patient was treated with danaparoid during haemodialysis sessions three times a week without any adverse effects. Because of increasing use of heparin in daily medical practice, physicians should be aware of possible immediate hypersensitivity reactions to this medication and know how to diagnose and treat them.

Human β-Tryptase: Detection and Characterization of the Active Monomer and Prevention of Tetramer Reconstitution by Protease Inhibitors

beta-Tryptase is a trypsin-like serine protease stored in mast cell secretory granules primarily as an enzymatically active tetramer. The current study aims to determine whether monomeric beta-tryptase also can exhibit enzyme activity, as suggested previously. At neutral pH beta-tryptase tetramers in the absence of heparin or dextran sulfate spontaneously convert to inactive monomers. Addition of a polyanion to these monomers at neutral pH fails to convert them back to a tetramer or to an enzymatically active state. In contrast, at acidic pH addition of a polyanion resurrects enzyme activity. Whether this activity is associated with tetramers or monomers depends on the concentration of beta-tryptase. Under the experimental conditions employed at pH 6 in the presence of heparin, the monomer concentration at which 50% conversion to tetramers occurs is 193 ng/mL. Activity against tripeptide substrates by monomers is detected at pH 6 but not at pH 7.4, whereas tetramer activity is greater at pH 7.4 than pH 6.0. Active monomers are inhibited by soybean trypsin inhibitor, bovine pancreatic trypsin inhibitor, antithrombin III, and alpha2-macroglobulin, whereas active tetramers are resistant to these inhibitors. Active monomers form complexes with these inhibitors and cleave both antithrombin III and alpha2-macroglobulin. These inhibitors also prevent reconstitution of monomers to tetramers, indicating that inactive monomers become active monomers before becoming active tetramers. The ability of tryptase monomers to become active at acidic pH raises the possibilities of expanded substrate specificities as well as inhibitor susceptibilities where the low-pH environments associated with inflammation or poor vascularity are encountered in vivo.

Expression of alpha-tryptase and beta-tryptase by human basophils

BACKGROUND

Alpha and beta-tryptase levels in serum are clinical tools for the evaluation of systemic anaphylaxis and systemic mastocytosis. Basophils and mast cells are known to produce these proteins.

OBJECTIVE

The current study examines the effect of the alpha,beta-tryptase genotype on basophil tryptase levels and the type of tryptase stored in these cells.

METHODS

Tryptase extracted from purified peripheral blood basophils from 20 subjects was examined by using ELISAs measuring mature and total tryptase and by using an enzymatic assay with tosyl-Gly-Pro-Lys-p-nitroanilide. Tryptase genotypes (4:0, 3:1, and 2:2 beta/alpha ratios) were assessed by using a hot-stop PCR technique with alpha,beta-tryptase-specific primers. Total alpha,beta-tryptase mRNA was measured by means of competitive RT-PCR, and ratios of alpha to beta-tryptase mRNA were measured by means of hot-stop RT-PCR.

RESULTS

Tryptase in all but one of the basophil preparations was mature and enzymatically active. Tryptase quantities in basophils were less than 1% of those in tissue mast cells. Tryptase genotypes (beta/alpha) among the 20 donors were 4:0 in 7, 3:1 in 7, and 2:2 in 6. Tryptase protein and mRNA levels per basophil were not affected by the tryptase genotype.

CONCLUSION

Basophils from healthy subjects contain modest amounts of mature and enzymatically active tryptase unaffected by the tryptase genotype.

Diagnosis and classification of mast cell proliferative disorders: delineation from immunologic diseases and non–mast cell hematopoietic neoplasms

In mast cell (MC) disorders (mastocytosis), clinical symptoms are caused by the release of chemical mediators from MCs, the pathologic infiltration of neoplastic MCs in tissues, or both. Cutaneous mastocytosis is a benign disease in which MC infiltration is confined to the skin. In pediatric cases cutaneous mastocytosis might regress spontaneously. Systemic mastocytosis (SM) is more frequently diagnosed in adults and is a persistent (clonal) disease of bone marrow-derived myelomastocytic progenitors. The somatic c-kit mutation D816V is found in the majority of such patients. The natural clinical course in SM is variable. Whereas most patients remain at the indolent stage for many years, some have aggressive SM (ASM) at diagnosis. Other patients have an associated clonal hematologic non-MC lineage disease (AHNMD). MC leukemia (MCL) is a rare disease variant characterized by circulating MCs and fatal disease progression. The diagnoses of ASM, SM-AHNMD, and MCL might be confused with a variety of endocrinologic, vascular, or immunologic disorders. It is therefore of particular importance to be aware of the possibility of an underlying (malignant) MC disease in patients with unexplained vascular instability, unexplained (anaphylactoid) shock, idiopathic flushing, diarrhea, headache, and other symptoms that might be mediator related. An important diagnostic clue in such cases is an increased serum tryptase level. The current review provides an overview of mastocytosis and its subvariants and a practical guide that might help to delineate mastocytosis from unrelated systemic disorders.

Effect of sex and haplotype on plasma tryptase levels in healthy adults

BACKGROUND

The total level of alpha-tryptase and ss-tryptase in serum or plasma is used as a clinical indicator of the mast cell burden.

OBJECTIVE

The effect of the tryptase haplotype and of sex on the total tryptase level of healthy individuals was determined.

METHODS

A novel hot-stop PCR technique was used to determine the tryptase genotype, and a standard fluoroenzyme immunoassay was used to measure total plasma tryptase levels in 106 healthy subjects. Mx modeling and the QTL association routine of Mendel 5.0 were used to analyze the data.

RESULTS

Tryptase haplotypes exhibit a 1 (betaalpha/betaalpha):2 (betabeta/betaalpha):1 (betabeta/betabeta) distribution, monomorphic for ss at 1 position and allelic for ss and alpha at the other position. The betaalpha haplotype has a frequency of 0.49. The betaalpha haplotype increases total tryptase levels by 0.5 ng/mL from the overall mean, whereas female sex increases the level by 0.2 ng/mL from the mean.

CONCLUSION

The tryptase haplotype and sex each have a statistically significant effect on the total plasma tryptase level of healthy subjects.

Batroxobin reduces intracellular calcium concentration and inhibits proliferation of vascular smooth muscle cells

BACKGROUND

Batroxobin (BX), a serine protease used in defibrinogenation and thrombolysis, also has an effect on c-fos gene and growth factor. This study attempted to determine the effects of BX on the proliferation of vascular smooth muscle cells (VSMCs) and calcium metabolism.

METHODS

VSMCs were treated with BX at concentrations of 0.1, 0.3, or 1.0 mmol/L and cell numbers were determined at 0, 24, 48, and 72 hours. Intracellular calcium concentration ([Ca2+]i) was measured using direct fluorescence methods.

RESULTS

BX was found to suppress proliferation of VSMCs in a dose-dependent fashion with inhibition rates of 18% and 31% by 48 and 72 hours, respectively. In addition, BX decreases basal [Ca2+]i significantly. The basal level in untreated cells was 162.7 +/- 33.8 nmol/L, and decreased to 131.5 +/- 27.7 nmol/L, 128.3 +/- 28.5 nmol/L, and 125.6 +/- 34.3 nmol/L with the three concentrations of BX, respectively. Noradrenaline (NE)-induced [Ca2+]i stimulation was also attenuated by BX (0.1 mmol/L BX, 20% +/- 8% inhibition; 0.3 mmol/L BX, 54% +/- 11% inhibition; 1.0 mmol/L BX, 62% +/- 15% inhibition). The ability of NE to stimulate [Ca2+]i was attenuated in cultures in Ca(2+)-free medium, as was the ability of BX to blunt NE-induced stimulation.

CONCLUSION

These findings demonstrate that BX can effectively inhibit proliferation of VSMCs, probably by blocking the release and uptake of Ca2+, thus influencing [Ca2+]i.

Neutralizing endogenous IL-6 renders mast cells of the MCT type from lung, but not the MCTC type from skin and lung, susceptible to human recombinant IL-4-induced apoptosis

Human cord blood-derived mast cells undergo apoptosis upon exposure to recombinant human (rh)IL-4 and become resistant to rhIL-4-induced apoptosis when cultured in the presence of rhIL-6. The current study extends these effects of rhIL-4 to different populations of human mast cells, namely fetal liver-derived mast cells, lung-derived mast cells, and skin-derived mast cells. Endogenous production of IL-6 appears to protect fetal liver-derived mast cells and those of the MC(T) phenotype from rhIL-4-mediated apoptosis, because neutralization of IL-6 renders these mast cells sensitive. In contrast, mast cells of the MC(TC) phenotype from skin and lung were resistant to IL-4-mediated apoptosis, even after neutralization of endogenous IL-6. MC(TC) cells were CD124(low), whereas those of the MC(T) cells were CD124(high). These observations extend the phenotypic differences between MC(T) and MC(TC) types of human mast cells to include different functional responses to IL-4.

Recombinant human (rh) stem cell factor and rhIL-4 stimulate differentiation and proliferation of CD3+ cells from umbilical cord blood and CD3+ cells enhance FcepsilonR1 expression on fetal liver-derived mast cells in the presence of rhIL-4

We previously reported that rhIL-4 induced apoptosis and rhIL-6 mediated protection of human mast cells derived from cord blood mononuclear cells. Based on the result, we attempted to obtain the phenotypes and differentiation of CD3+ cells from cord blood by investigating their cell surface markers in the presence of rhSCF plus rhIL-4. The effect of co-cultured CD3+ cells on fetal liver mast cells (FLMCs) was also determined. Phenotypes from cord blood-derived cells were analyzed by flow cytometry and cell numbers were determined. Fetal liver mast cells were cultured with cord blood-derived cells (mainly CD3+) in the presence of rhSCF and/or rhIL-4 and were analyzed to determine cell number and expression of Kit+ and FcepsilonR1. The percentage of CD3+ cells from cord blood-derived cells on day 0 was about 41 +/- 13.5%, following monocytes and granulocytes. CD3+ cells increased in number (1.5-fold) and purity (90%), whereas other cell types did not survive. More than 60% of CD3+ cells from cord blood at day 0 were CD4(-)CD8-. These double-negative cells dramatically decreased by 1 week of culture, while CD4+CD8+ cells increased in number and purity through 3 weeks of culture, and then decreased as greater numbers of single-positive T cells emerged. We also found that FcepsilonR expression on FLMC increased in the presence of rhIL-4, but was not affected by the T cells that developed from cord blood mononuclear cells. The results indicate that IL-4, a Th2 type cytokine, together with rhSCF, can induce T cell proliferations, differentiation, and maturation from cord blood progenitor cells.

Effector cells of anaphylaxis: mast cells and basophils

Systemic anaphylaxis arises when mast cells, possibly along with other cell types, are provoked to secrete mediators that evoke a systemic response. Mast cells in perivascular, respiratory, gastrointestinal and cutaneous tissues are likely involved, regardless of whether IgE or non-IgE-dependent pathways are invoked. Alpha/beta tryptases are selectively and abundantly produced by mast cells. Tryptase levels in the circulation provide a precise indicator of mast cell involvement. Mature beta tryptase is stored in secretory granules and is released when the cells are activated to degranulate, as occurs in anaphylaxis. Alpha/beta pro/pro' tryptases are spontaneously secreted by mast cells. Consequently, mature tryptase levels in serum (normally 1 ng/ml) are elevated in systemic anaphylaxis. Total tryptase levels (mature plus precursor forms), normally 1-15 ng/ml in baseline serum samples, are elevated in patients with systemic mastocytosis (> 20 ng/ml), a disease that also predisposes one to anaphylactic reactions. The assessment of basophils in systemic anaphylactic reactions has been problematic, because an assay for a specific releasable marker from this cell type has not been developed. Nevertheless, in cases of anaphylaxis in which elevations of histamine, but not tryptase, have been detected, it is enticing to speculate that basophil-dependent anaphylaxis may have occurred.