Comparison of lesional skin c-KIT mutations with clinical phenotype in patients with mastocytosis.

BACKGROUND: Activating c-KIT mutations cause abnormal mast cell growth and appear to play a role in mastocytosis. However, the correlation of c-KIT mutations with disease phenotypes is poorly characterized. AIM: To evaluate the correlation of c-KIT mutations with clinical presentations and laboratory findings. METHODS: Total cellular RNA was isolated from the skin lesions of 43 adults and 7 children with mastocytosis, and PCR amplicons of cDNA were sequenced for c-KIT mutations. RESULTS: The most common activating mutation, KIT-D816V, was identified in 72% of adults and 57% of children. Additional activating mutations, namely, V560G and the internal tandem duplications (ITDs) 502-503dupAY, were detected in 12% of adults and 8% of children. V560G occurred more commonly in our patients than previously reported, and it appeared to be associated with more advanced disease. Otherwise, the presence or absence of activating mutations did not correlate with skin lesion morphology, disease extent or total serum tryptase levels. Four adults had expression only of wild-type KIT, while two others had expression of a truncated KIT lacking tyrosine kinase activity; yet these patients were clinically indistinguishable from those patients with activating c-KIT mutations. CONCLUSIONS: Activating c-KIT mutations exist in a significant portion of patients with mastocytosis, but not all patients showed expression of these mutations. Except for V560G, the presence or absence of activating c-KIT mutations did not predict the extent of disease. These observations suggest that although activating c-KIT mutations are associated with mast cell growth, other genes probably play a role in the cause of mastocytosis.

Distinct signalling pathways for mutated KIT(V560G) and KIT(D816V) in mastocytosis.

BACKGROUND: The activating mutations KIT(V560G) and KIT(D816V) are associated with mastocytosis. Thus, identifying and inhibiting the signalling pathways associated with mutated KIT gene offers a potentially important strategy for the treatment of mastocytosis. AIM: To correlate KIT mutations with specific signalling pathways in human mast-cell lines using pathway inhibitors. METHODS: Human mast-cell (HMC) lines expressing KIT(V560G) (the cell line HMC-1) and KIT(V560G and D816V) (HMC-1.2) were treated with specific signalling pathway inhibitors for 1-5 days, and the inhibitory effects on growth were determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell-proliferation assay, western blotting and flow cytometry. RESULTS: Growth inhibitory assays and western blot analyses showed that the Janus kinase 3/signal transducer and activator of transcription (JAK3/STAT) pathway is the preferential signalling pathway for KIT(V560G), whereas the mechanistic target of rapamycin complex 1/4E-binding protein 1 (mTORC1/4E-BP1) pathway is preferentially linked to KIT(D816V). Inhibition of these critical signalling pathways results in programmed cell death. CONCLUSIONS: KIT(V560G) and KIT(D816V) use different signalling pathways that promote mast-cell growth. Inhibitors of these specific pathways might be effective in treating mastocytosis.

Mutations in the PSTPIP1 gene and aberrant splicing variants in patients with pyoderma gangrenosum.

BACKGROUND: Pyoderma gangrenosum (PG) is a rare, noninfectious form of skin ulceration, typically accompanied by neutrophilic infiltration. Several familial cases have been reported, suggesting the involvement of genetic factors in the aetiology of PG. Two mutations (A230T and E250Q) in the PSTPIP1 gene, encoding proline-serine-threonine phosphatase-interacting protein (PSTPIP)1 have been identified in patients with PAPA (pyogenic sterile arthritis with PG and acne) syndrome, a rare autoinflammatory disorder with autosomal dominant inheritance. AIM: The aim of this study was to sequence PSTPIP1 complementary cDNA and genomic DNA for mutations, and to identify genetic polymorphisms in the promoter region of PSTPIP1 in patients with PG. METHODS: The genomic region and cDNA of the PSTPIP1 gene were sequenced from peripheral blood leucocytes of 14 patients with PG and 20 healthy controls. RESULTS: One patient (PG1) had aberrant splicing variants of the PSTPIP1 transcript with deletions of exons 9, 11 and 12 and of exons 9-12 together, and all other patients with PG carried deletions of exon 11 and of 11-12. We also identified a novel mutation (G258A) in patient PG3, and novel polymorphisms [(CCTG)(6) and (CCTG)(8) tandem repeats] in the promoter region of the PSTPIP1 gene. CONCLUSION: All combinations of aberrant splicing variants had frame shifts and premature stop codons leading to truncated proteins and loss of function of PSTPIP1. The (CCTG)(n) tandem repeats in the promoter region of PSTPIP1 had no association with PG. The mutations G258A and R52Q are predicted by the improved prediction algorithm to have a possibly damaging effect on PSTPIP1 function.

Pharmacological characterizations of adrenergic receptors in human adipocytes.

Three types of adrenergic receptors, beta, alpha-1, and alpha-2, were identified in human adipocytes, isolated from properitoneal adipose tissue, using both the binding of radioactive ligands and the effects of adrenergic agents on receptor-specific biochemical responses. Adrenergic binding studies showed the following results: [(3)H]dihydroalprenolol binding (beta adrenergic) B(max) 280 fmol/mg protein, K(D) 0.38 nM; [(3)H]para-aminoclonidine binding (alpha-2 adrenergic) B(max) 166 fmol/mg protein, K(D) 0.49 nM; [(3)H]WB 4101 binding (alpha-1 adrenergic) B(max) 303 fmol/mg protein, K(D) 0.86 nM. In adipocytes from subcutaneous adipose tissue, [(3)H]dihydroergocryptine binding indicated the presence of alpha-2 but not alpha-1 receptors. Beta and alpha-2 adrenergic receptors appeared to be positively and negatively coupled to adenylate cyclase, respectively. Cells or cell membranes were incubated with epinephrine (10 muM) alone and in combination with the antagonists yohimbine (alpha-2) and prazosin (alpha-1). Epinephrine alone prompted a modest increase in adenylate cyclase activity, cyclic AMP, and glycerol release, an index of lipolysis. Yohimbine (0.1 muM) greatly enhanced these actions whereas prazosin was without effect. The beta agonist, isoproterenol, stimulated glycerol release, whereas the alpha-2 agonist, clonidine, inhibited lipolysis and cyclic AMP accumulation. To assess further alpha-1 receptors, cells were incubated with [(32)P]phosphate and epinephrine (10 muM) alone and in combination with prazosin and yohimbine. Epinephrine alone caused a three- to fourfold increase in (32)P incorporation into phosphatidylinositol. Prazosin (0.1 muM) blocked this action whereas yohimbine (0.1 muM) was without effect. Thus, in a homogeneous cell preparation, the human adipocyte appears to have three different adrenergic receptors, each of which is coupled to a distinct biochemical response.

The interaction between mast cells and endothelial cells.

Mast cells (MC) are widely distributed throughout different organs with a relative predilection for potential portals of entry into the host. In tissues, MC are generally concentrated around small blood vessels and lymphatics, as well as nerves and glandular tissue. This close association with vascular structures suggests an important interaction between MC and endothelial cells (EC). Tissue MC are known to generate and release a number of mediators including histamine, prostaglandin D2, and leukotrienes that induce vasodilatation and increased vascular permeability. These MC-mediated effects on vessels may enhance responses to tissue injury or infection by facilitating the deposition of plasma components and inflammatory cells into involved sites. Important interactions between MC, EC, and peripheral nerves also occur. MC-derived histamine and possibly other mediators induce axon reflexes in unmyelinated sensory nerves leading to the release of neurotransmitters such as substance P, calcitonin gene-related peptide, and adenine nucleotides. These neurotransmitters exert direct effects on blood vessels, and in some instances, may act as MC stimulators. In vitro studies indicate that MC also affect EC growth and new blood vessel formation. Mast cell-derived heparin has been implicated as an important cofactor in tumor-induced angiogenesis, whereas histamine has been reported to augment human dermal EC growth in culture. The recent identification of a tumor necrosis factor-like peptide in MC and the reported cytostatic effects of TNF on EC suggest that MC may inhibit the proliferation of these cells under certain conditions. Taken together, these observations indicate that the interactions between MC and EC are important in both physiologic and pathologic events.

Rat mast cell protease I alters cell metabolism.

Rat connective tissue mast cells are known to store significant amounts of mast cell protease I (RMCP I), which suppresses normal cell growth and mediates cytotoxicity against tumor cell lines, including the fibrosarcoma cell line FL. To better define its effects on FL cells, RMCP I was added to FL cultures for 30 min. Analysis of de novo nuclear protein synthesis revealed that RMCP I suppressed the expression of three proteins (41, 46, and 69 kD) and enhanced the expression of two other proteins (25 and 32 kD). Treatment of FL cells with diisopropylfluorophosphate (DFP)-inactivated RMCP I proved that these effects were largely independent of the protease catalytic site. Western blot hybridization, using a monoclonal antibody to phosphotyrosine-containing proteins, revealed that RMCP I inhibited phosphorylation of a nuclear and a cytoplasmic 81-kD tyrosylprotein. Inhibition of nuclear tyrosine kinase activity by RMCP I appeared to be catalytic site dependent, whereas cytoplasmic tyrosine kinase inhibition was independent of RMCP I proteolytic activity. Biotinylated RMCP I was used to identify potential surface-binding proteins. Three specific binding complexes (130, 150, and 210 kD) were detected. The binding of biotinylated RMCP I to these surface proteins was inhibited by excess unlabeled RMCP I, but not by trypsin or chymotrypsin. We speculate that the binding proteins may be critical in initiating RMCP I-induced metabolic changes on FL cells. The ability of RMCP I to alter the metabolism of cells suggests that it may have an important role in regulating their functions.

Conjugated avidin identifies cutaneous rodent and human mast cells.

Avidin conjugated to the fluorescent dyes rhodamine or fluorescein binds to mast cell granules in rodent and human skin. Sequential staining of tissue mast cells first with conjugated avidin, and then with a metachromatic stain demonstrated that both techniques identify the same mast cell granules. Specificity for mast cells was confirmed by the absence of avidin-positive cells in the skin of mast cell-deficient (W/Wv) mice. Binding of conjugated avidin to mast cells was inhibited by pretreating tissue specimens with unconjugated avidin but not by pretreating conjugated avidin with biotin, indicating that avidin does not bind to biotin or a biotin-like molecule. Within murine dermis, unique patterns of mast cell distributions were observed, with a prominent perivascular localization in ear skin, and a complete absence of mast cells underlying the scales in tail skin. In tissue sections of guinea pig skin undergoing basophil hypersensitivity reactions and in murine and human skin specimens infiltrated with eosinophils, conjugated avidin selectively stained only dermal mast cells, demonstrating specificity for mast cells in sites of inflammation. Conjugated avidin also readily stained rat peritoneal mast cells, demonstrating its utility for identifying extracutaneous mast cells. Unlike the metachromatic stains, avidin binding to mast cells in tissues is not limited by methods of fixation or special embedding and cutting procedures. Thus, mast cell identification with conjugated avidin is a reliable, specific, and simple method with important clinical and investigative applications.

Rodent epidermal Langerhans cells demonstrate greater histochemical specificity for ADP than for ATP and AMP.

Langerhans cells (LCs) in mammalian epidermis possess the ectoenzyme Ca++/Mg++-dependent adenosine triphosphatase (ATPase), which has served as a useful histochemical marker for these dendritic cells in a variety of tissue preparations. Since ATPase represents only one of several potential cell surface polyphosphatases, we investigated the capacities of 3 related adenine nucleotide substrates to identify rodent epidermal LCs. Cell surface ATPase activity was not inhibited in the presence of ouabain and was observed to be strictly divalent cation-dependent, with complete interchangeability between Ca++ and Mg++. Optimal staining in the presence of either cation occurred at a 20 mM concentration. Substrate concentration dependence was also observed, with optimal staining at 0.33 mM adenosine 5'-triphosphate (ATP). On an equimolar basis, however, adenosine 5'-diphosphate (ADP) was superior to ATP for the identification of LCs both in whole mounts of epidermis and in suspensions of disaggregated epidermal cells. The substrate adenosine 5'-monophosphate (AMP) stained follicular epithelial cells in both rodent species but failed to identify epidermal LCs in the mouse and only weakly stained these dendritic cells in rat epidermis. We conclude from these studies that ADP demonstrates greater specificity for LC surface polyphosphatase activity than ATP and that the inadvertent inclusion of AMP during identification procedures for epidermal cell suspensions will falsely identify cells other than LCs.

In vitro functional reactivities of cutaneous mast cells from patients with mastocytosis.

Cutaneous mast cells from 3 patients with mastocytosis were evaluated for their morphologic characteristics and in vitro functional reactivities to different secretory agonists. By electron microscopy, mastocytosis mast cells appeared larger than normal skin mast cells, frequently had atypical, highly indented or bilobed nuclei, and each contained numerous, elongated cytoplasmic projections. Suspensions of mastocytosis mast cells were obtained from lesional skin biopsy specimens, and their response to both immunologic and nonimmunologic secretagogues was compared with mast cells from normal skin. Lesional skin mast cells had a net histamine release of 12.3% (+/- 1.3 SEM) and 31.1% (+/- 6.0 SEM) following stimulation with the purified human anaphylotoxin C3a and mouse monoclonal antihuman IgE antibodies, respectively. This specific release was similar to the responses observed in normal skin mast cells (11.5% +/- 4.5 SEM and 16.7% +/- 2.1 SEM, respectively). Mast cells from cutaneous lesions of mastocytosis also responded to the nonimmunologic secretagogues, morphine sulfate and calcium ionophore A23187 with a specific histamine release of 15.1% (+/- 1.2 SEM) and 39.8% (+/- 8.7 SEM), respectively. The results of this study demonstrate that mast cells from lesions of mastocytosis are morphologically atypical, but have a histamine content similar to normal skin mast cells and retain their functional reactivities to clinically relevant secretory stimuli.

Studies of connective tissue mast cell-mediated cytotoxicity.

Although mast cells have been implicated in mediating antitumor activity, the kinetics, mechanism(s), and suspectibility of different tumors to mast cell-mediated cytotoxicity have not been defined. Rat connective tissue mast cells (CTMC) of greater than or equal to 99% purity were investigated in vitro and found to express maximal spontaneous cytotoxicity against the mouse fibrosarcoma cell line WEHI-164 (56.0% +/- 2.1 SEM), the ultraviolet B (UVB)-induced, cutaneous fibrosarcoma 5C25 (34.7% +/- 3.4 SEM), and the human renal cell tumor Currie (26.8% +/- 2.0 SEM) at an effector to target (E:T) ratio of 80:1. Kinetic studies of CTMC-mediated cytotoxicity demonstrated significant detectable lysis against these tumors within 8 h, which was maximal by 16 h. Binding experiments showed that CTMC formed conjugates with all three lytic-sensitive targets; however, CTMC also attached to the lytic-resistant target YAC-1, indicating that conjugate formation alone is not sufficient for mast cell-mediated cytotoxicity. At two different concentrations, mast cell granules (MCG) lysed WEHI-164 (36.5% +/- 6.8 SEM) and 5C25 (34.4% +/- 6.9 SEM), but were only slightly cytotoxic (5.7% +/- 2.9 SEM) against Currie. A potential role for tumor necrosis factor-alpha (TNF-alpha) in CTMC-mediated cytotoxicity also was investigated. Polyclonal antibodies to TNF-alpha greatly reduced CTMC and TNF-mediated lysis of WEHI-164, but only partially inhibited CTMC killing of the slightly TNF-sensitive 5C25 tumors, and had no effect on CTMC cytolysis of Currie. Thus, this study demonstrates that CTMC mediate cytotoxicity in vitro by both TNF-associated and TNF-independent mechanisms. We conclude that CTMC are capable of mediating antitumor activity and that this effect may be important for tumor surveillance in the skin and other sites.

alpha-Adrenergic receptors in human adipocyte membranes: direct determination by [3H]yohimbine binding.

The presence of alpha 2-adrenergic receptors in membranes derived from human sc adipose tissue was directly demonstrated with a new alpha 2-selective ligand, [3H]yohimbine. Binding of this radiolabeled antagonist to adipocyte membranes was of high affinity (Kd = 3.9 +/- 2.4 nM) and saturable. Computer modelling of [3H]yohimbine saturation curves demonstrated that it binds to a homogeneous class of sites with a density of 145.0 +/- 33.8 fmol/mg protein. Adrenergic agonists competed with [3H]yohimbine in the order expected of alpha-receptors, and their binding was strongly influenced by guanine nucleotides. Competition of alpha-antagonists with this radioligand demonstrated yohimbine to be more potent than prazosin, indicative of alpha 2-receptors. Antagonist binding was unaffected by guanine nucleotides. Paired saturation curves in these adipocyte membranes with the alpha 2-selective [3H]yohimbine and the nonsubtype selective alpha-antagonist [3H]dihydroergocryptine demonstrated similar receptor concentrations. [3H]Dihydroergocryptine has been previously shown to label both alpha 3- and alpha 2-receptors with equal affinity. Therefore, these data indicate that the vast majority of alpha-receptors in human sc fat are of the alpha 2-subtype. [3H]Yohimbine with its alpha 2-selectivity and high specific binding will provide an excellent tool for the clinical investigation of human adipocyte alpha-receptor mechanisms in both normal and pathological states.

Conjugated avidin binds to mast cell granules.

The glycoprotein, avidin, conjugated either to the enzyme horseradish peroxidase, or to the fluorochrome dyes, fluorescein or rhodamine, identifies the granules of mast cells in both tissues and cell suspensions. In the absence of prior fixation, mast cells were not identified with conjugated avidin; however, granules released from these cells were stained with this labeled glycoprotein. The specificity of avidin for mast cells was confirmed by the absence of conjugated avidin-positive cells in the skin of mice (S1/S1d) deficient in mature dermal mast cells. Electron microscopic studies confirmed that avidin binds specifically to individual mast cell granules rather than to other cellular structures. Rodent and human mast cells were readily stained with avidin conjugated to horseradish peroxidase or to either of the fluorochrome dyes. The conjugated avidin staining technique is a reliable and simple method for identifying rodent and human mast cells, one that is useful as both an investigative and a clinical tool.

New insights into the second generation antihistamines.

Second generation antihistamines are recognised as being highly effective treatments for allergy-based disease and are among the most frequently prescribed and safest drugs in the world. However, consideration of the therapeutic index or the benefit/risk ratio of the H1 receptor antagonists is of paramount importance when prescribing this class of compounds as they are used to treat non-life threatening conditions. There are many second generation antihistamines available and at first examination these appear to be comparable in terms of safety and efficacy. However, the newer antihistamines in fact represent a heterogeneous group of compounds, having markedly differing chemical structures, adverse effects, half-life, tissue distribution and metabolism, spectrum of antihistaminic properties, and varying degrees of anti-inflammatory effects. With regard to the latter, there is growing awareness that some of these compounds might represent useful adjunct medications in asthma therapy. In terms of safety issues, the current second generation grouping includes compounds with proven cardiotoxic effects and others with the potential for adverse drug interactions. Moreover, some of the second generation H1 antagonists have given cause for concern regarding their potential to cause a degree of somnolence in some individuals. It can be argued, therefore, that the present second generation grouping is too large and indistinct since this was based primarily on the concept of separating the first generation sedating compounds from nonsedating H1 antagonists. Although it is too early to talk about a third generation grouping of antihistamines, future membership of such a classification could be based on a low volume of distribution coupled with a lack of sedating effects, drug interactions and cardiotoxicity.

Diagnosis of mastocytosis subsets using a morphometric point counting technique.

Mastocytosis, a disease that varies in its clinical presentation, is usually documented by histologic examination of lesional skin. However, no universally accepted histopathologic criteria exist for establishing the diagnosis of this disease. We have combined the method of morphometric point counting with the mast cell-specific stain, conjugated avidin, to accurately quantify mast cells in cutaneous tissue sections of mastocytosis. Using this histologic approach, we found that macules, papules, and nodules of mast cell disease had from ninefold to nearly a 160-fold greater mast cell content than was observed in normal skin and in several other cutaneous disorders. This technique also permitted the objective histologic stratification of mastocytosis skin lesions according to their mast cell density. Morphometric point counting in conjunction with conjugated avidin offers a simple and accurate method for establishing the diagnosis of mastocytosis.

A role for mast cells in the progression of Duchenne muscular dystrophy? Correlations in dystrophin-deficient humans, dogs, and mice.

Dystrophin deficiency has been shown to be the underlying cause of Duchenne muscular dystrophy. Although dystrophin-deficient homologous animal models have been identified (dog, mouse, and cat), the clinical expression of the biochemical defect is species-specific. Thus, while the genetics and biochemistry of Duchenne dystrophy is understood, the pathophysiological cascade leading to muscle weakness in only humans and dogs remains obscure. To begin to dissect the pathophysiology at the histological level, we undertook a systematic study of mast cells in normal and dystrophin-deficient muscle. Mast cells have been implicated in the development of fibrosis in other disorders, and progressive fibrosis has been hypothesized to mediate the failure of muscle regeneration in human and dog dystrophin deficiency. Our results show a strong correlation between mast cell content and localization, and the clinico-histopathological progression in humans, dogs and mice. The mast cell increases were disease specific: other dystrophic myopathies with normal dystrophin generally did not show substantial increases in mast cell content or degranulation. Our data suggest that mast cell accumulation and degranulation may cause the grouped necrosis characteristic of dystrophin deficiency in all species.

IgE and immediate hypersensitivity.

Tissue mast cells play a central role in immediate hypersensitivity reactions. The clinical manifestations of these reactions appear to be dependent, in large part, on the anatomic location of the stimulated mast cells and the type of mediators released. In vivo and in vitro studies indicate that the tissues in which mast cells reside may greatly influence their biochemical composition, expression of surface receptors, and response to potential stimuli. Although all human mast cells in different organs store similar concentrations of histamine, heparin, and tryptase, cutaneous mast cells appear to be the predominant source of mast cell-derived chymase. Furthermore, at the time of stimulation, human skin mast cells predominantly form PGD2, whereas lung and intestinal mast cells generate LTB4, LTC4, and PGD2. Functional studies indicate that human cutaneous mast cells differ from human lung, heart, and intestinal mast cells. Skin mast cells are responsive to a variety of immunologic and nonimmunologic stimuli in vitro, whereas human pulmonary, cardiac, and intestinal mast cells are relatively refractory to many of these stimulatory signals. Taken together, these observations indicate that mast cells may assume different, and possibly specialized, functions within a specific tissue. Such site-to-site variation potentially could have important clinical significance, to the extent that information gained from mast cells in one organ may not be applicable to a mast cell population in a different tissue. Furthermore, these differences among human mast cells may not be confined to their biochemical composition and responses to various stimuli, but also may extend to the effectiveness of different anti-allergic preparations. Therefore, these observations underscore the importance of continued detailed investigation of human mast cells from different anatomic sites.

Mastocytosis.

Mastocytosis represents a heterogeneous group of clinical disorders resulting from the infiltration of mast cells in the skin and other organs. Although mastocytosis was first described over 130 years ago, the pathophysiologic mechanisms responsible for this disease have been identified only recently. This article discusses the salient clinical features of the disease, the mechanisms responsible for its development, and provides treatment approaches that have proven useful for managing patients with this disorder.

Mast cell and myofibroblast in wound healing.

Growing evidence in the literature indicates that mast cells are integrally involved in the process of dermal wound repair. They are resident cells of the normal dermis and have several cytokines stored in their granules that are stimulatory to fibroblasts. They also contain serine proteases that may be involved in remodeling of the extracellular matrix during healing. Mast cells are found in increased numbers in acute wounds and in certain chronic fibrotic diseases. Their influence on fibroblast growth and collagen production may be an important element in fibrosis. The effects of mast cell mediators on dermal fibroblasts are currently being explored by our laboratory and others. Myofibroblasts are implicated in the phenomenon of wound contraction. These phenotypically altered fibroblasts express some features of smooth muscle cells, notably actin filaments, and are abundant in granulation tissue. It has been proposed that they are responsible for wound contraction and possibly certain types of contracture. However, this hypothesis has been challenged by studies demonstrating the presence of myofibroblasts in wounds that do not contract, or the process of contraction in vitro in the absence of myofibroblasts. At this time the issue remains open to debate and further research.

The spectrum of mastocytosis.

Mastocytosis represents a spectrum of clinical disorders that results from an aberrant proliferation of tissue mast cells. This disease process may be confined to the skin (cutaneous mastocytosis) or may involve multiple organs (systemic mastocytosis). Parameters that are useful in differentiating cutaneous from systemic disorders include patient age, symptom complex, and clinical signs. A wide range of clinical symptoms may be encountered in patients with mastocytosis which result from the release of pharmacologically potent mast cell mediators. Distinct cutaneous patterns resulting from skin mast cell infiltrates can be helpful in identifying patients with systemic involvement. The diagnosis of mastocytosis is confirmed by demonstrating increased tissue mast cells in involved organs. The overall prognosis for patients with proliferative mast cell disease is relatively good, although a small percentage are at risk for developing a fatal neoplastic disorder (malignant mastocytosis). Treatment of mastocytosis is directed at both inhibiting mast cell degranulation and blocking the potential systemic effects of released secretory products. Future therapeutic advances depend upon an improved understanding of the basic mechanisms involved in mast cell mediator release and the forces that govern mast cell growth and development.

A comparison of twice-daily and once-daily administration of fluticasone propionate cream, 0.05%, in the treatment of eczema.

This multicenter, double-blind, randomized, parallel, four-week, vehicle-controlled study compared the efficacy and safety of once- and twice-daily application of fluticasone propionate cream, 0.05%, over a twenty-eight-day treatment period in 238 patients with moderate-to-severe eczema. Clinical evaluations, which included the physician's gross assessment, the severity of signs and symptoms, and the patient's subjective evaluation, were conducted at baseline and at weekly intervals following initiation of treatment. Both fluticasone QD and BID were found to be superior to vehicle at each evaluation. Application of fluticasone BID was found to be superior to once-daily application at day 22 based on the physician's gross assessment, and at days 15 and 22 based on the patient's subjective assessment. There were, however, no statistically significant differences between QD and BID application at day 8 and at the end of the twenty-eight-day treatment period. The results of this study suggest that QD application may be recommended for the treatment of moderate-to-severe eczema in most patients. As always, treatment effectiveness should be monitored periodically and BID application may be necessary to maximize therapeutic benefits in some patients.