Expression of stem cell factor in cutaneous mastocytosis

Stem cell factor has recently been identified as a potent growth factor for bone marrow stem cells, melanocytes and mast cells. In order to evaluate its possible role in human mastocytosis, skin lesions from 13 patients with urticaria pigmentosa and five patients with mastocytomas, and normal skin specimens from five healthy donors were studied by immunohistochemistry, using polyclonal and monoclonal (hkl-12) antibodies against stem cell factor, and a monoclonal antibody (YB5.B8) against its receptor, the c-kit proto-oncogene product. Stem cell factor expression was noted in all sections studied, with an equal distribution pattern for both antibodies, but a weaker intensity with the hkl-12 reagent. Cytoplasmic staining was noted in keratinocytes, Langerhans cells, sweat gland ductal lining cells, mast cells, endothelial cells and spindle-shaped dermal stromal cells. An intense, diffusely granular reaction pattern was noted in all cells, except for a sparse, coarsely granular pattern in mast cells and stromal cells. In urticaria pigmentosa, staining was weaker in keratinocytes, but more prominent in Langerhans cells. In all sections, toluidine blue-positive mast cells and TA 99-positive basal epidermal melanocytes were the only cells to react with the c-kit antibody. Mastocytomas and urticaria pigmentosa lesions thus exhibit different patterns of stem cell factor expression. However, a possible pathogenetic role of this factor in mastocytosis remains to be determined.     

Macrophage subsets in different types of urticaria

Summary Biopsy specimens from lesional and uninvolved skin of nine patients with delayed pressure urticaria, three patients with acute urticaria, six patients with chronic recurrent urticaria, and four patients with urticaria pigmentosa were analyzed by routine histology and by immunochemistry for their reactivity with monoclonal antibodies to three different subsets of macrophages. Skin from 12 healthy volunteers served as control. Uninvolved skin of patients did not differ from that of healthy volunteers. An antibody against activated macrophages (27E10) was reactive to a marked extent with macrophages in wheals of pressure urticaria, more variably in acute and chronic urticaria, and practically not at all in urticaria pigmentosa. Antibodies with specificities for macrophages in healing (RM3/1) and normal (25F9) tissue reacted more markedly in all but pressure urticaria lesions, compared with normal skin. These findings indicate an active involvement of inflammatory macrophages in whealing reactions while these cells play apparently no role in cutaneous mast cell proliferation (urticaria pigmentosa).     

Delayed pressure urticaria histologically resembles cutaneous late-phase reactions

In a recent study, all patients with delayed pressure urticaria (DPU) developed late cutaneous reaction (LCR) after intradermal injection of compound 48/80 and after skin testing with certain food antigens. In the present study, we analyzed the histologic changes in the pressure lesions and compared them with those found in normal skin injected with diluent and in LCR to 48/80. The study included five patients with DPU associated with chronic urticaria (CU) and four patients with CU but without DPU. Six to eight hours after pressure challenge and intradermal skin testing with 48/80 and diluent, skin biopsy specimens were obtained from the pressure lesions, the LCRs, and normal skin (diluent injection). Specimens were assessed by Giemsa staining of 1-micron sections and immunofluorescence of frozen sections. Total cells were counted in each specimen. Interstitial deposits of fibrin were observed by immunofluorescence in LCR and pressure lesions. The total numbers of infiltrating cells in the dermis among LCR sites and pressure lesions were not significantly different, while both LCR sites and pressure lesions contained significantly more infiltrating cells than did normal skin injected with saline diluent. The differential counts in LCR and DPU were mostly mononuclear cells. Infiltrates in the DPU and LCR were mostly perivascular. No histopathologic changes were seen at skin sites challenged with pressure in the control patients with CU without clinical manifestations of DPU. We conclude that lesions seen in DPU are morphologically similar to classic LCR.     

Comparative immunoreactivity of the eosinophil constituents MBP and ECP in different types of urticaria

In order to elucidate the role of eosinophil constituents in urticaria, we investigated major basic protein expression immunohistologically in comparison with that of eosinophilic cationic protein and the low-affinity IgE receptor in lesional and uninvolved skin of different types of urticaria. Eosinophil activation was studied with the markers EG1 and EG2. Different eosinophil constituents were found in all urticarial lesions except those of urticaria pigmentosa. MBP staining tended to be distributed diffusely throughout the tissue, whereas EG1 and EG2 antibodies were located at or close to individual cells. Staining with the low affinity IgE receptor antibody was rare. In uninvolved skin, major basic protein and particularly eosinophilic cationic protein reactivity was found in chronic recurrent urticaria, delayed pressure urticaria and, to a minor degree, in cholinergic urticaria. No correlation was found between antibody reactivity and eosinophil counts. Reactivity with either of the eosinophil constituents is thus a better marker for eosinophil involvement than routine H&E staining of the cells. The demonstration of eosinophil constituents in nonlesional skin of some urticaria patients suggests generalized eosinophil activation in certain subtypes of the disease.     

Photochemotherapy (PUVA) in the treatment of urticaria pigmentosa

Eight patients received PUVA for mastocytosis. Five women had typical adult-onset urticaria pigmentosa, without evidence of systemic disease. Another woman had suspected hepatic involvement while the remaining female had early-onset familial urticaria pigmentosa with morphologically atypical mast cells. The only male patient had cirrhosis with hepatic deposits of mast cells in addition to polycythaemia rubra vera. In all patients, except the man with systemic disease, there was reduced pruritus and wealing and partial to almost complete fading of the macules. The manifestations of urticaria pigmentosa recurred after treatment was discontinued. In both lesional and uninvolved skin there was no significant change in either the mean mast cell counts or mast cell ultrastructure after an average of twenty-seven PUVA exposures. In addition, PUVA did not cause a significant alteration in the histamine content of the skin. The beneficial effect of PUVA in urticaria pigmentosa therefore does not appear to be directly related to a change in mast cell numbers or morphology, or to the histamine concentration in the skin. Urticaria pigmentosa usually presents as a generalized maculo-papular rash which urticates on rubbing (Darier's sign). Many patients are troubled only by the unsightliness of the rash while some complain of pruritus, wealing or flushing. These symptoms are attributed to the release of histamine by mast cells which characteristically occur in increased numbers in the dermis. Symptomatic treatment is often unrewarding, but favourable results have been claimed for cimetidine with or without Hi blockers (Hirschowitz & Groarke, 1979; O'Laughlin & Bredfeldt, 1980) and for oral disodium cromoglycate (Soter, Austen & Wasserman, 1979; Czarnetski & Behrendt, 1981). In 1978, Christophers and colleagues reported that photochemotherapy (PUVA) produced symptomatic relief in all of ten adult patients with typical urticaria pigmentosa. Similarly encouraging results were subsequently reported from other centres (Ortonne et al., 1980; Allevato, Donatti & Cordero, 1980; Granerus, Roupe & Swanbeck, 1981; Väätäinen, Hannuksela & Karvonen, 1981). In this study we examined the effects of PUVA in eight adult patients with urticaria pigmentosa. Although PUVA produced a moderately good clinical response in seven out of these eight patients (reduced pruritus, reduced wealing and faded macules) quantitative studies failed to reveal a consistent effect of PUVA on either the mast cell population density or the histamine concentration in both lesional and clinically uninvolved skin. The findings arc discussed in relation to existing information concerning the effect of ultraviolet radiation (U VR) on mast cells and other constituents of the skin.     

The cosmetic treatment of urticaria pigmentosa with Nd:YAG laser at 532 nanometers

Background Urticaria pigmentosa is a cutaneous disorder involving infiltration of the skin with mast cells. Histologically the papillary dermis has an increased number of mast cells with an increase in basal layer pigmentation. In addition to possible systemic symptoms, patients with urticaria pigmentosa can suffer emotionally from the cosmetic nature of this skin disease. Objective The purpose was to investigate the use of a diode‐pumped Nd:YAG laser at 532 nm for the treatment of the cosmetic comorbidity of urticaria pigmentosa lesions. Methods A 19‐year‐old white male with urticaria pigmentosa had multiple lesions on the dorsum of the hands and forearms. A test site on the right inner arm was treated with a DioLite? 532 nanometer laser. Because of satisfaction with the treatment of the test site lesions, multiple lesions on the dorsal hands and forearms were also treated with the DioLite? 532 nanometer laser. Results There was a dramatic clinical reduction in the amount of lesions on the dorsum of the hands and forearms. The test site lesions on the right inner arm had not recurred. Conclusion The diode‐pumped Nd:YAG laser at 532 nanometers should be considered part of a dermatologist's armamentarium for the treatment of a patient's cosmetic concerns with lesions of cutaneous mastocytosis.     

Ultrastructural findings in tissue mast cells in urticaria pigmentosa

In a study on 10 patients suffering from urticaria pigmentosa, biopsies of skin lesions were electron microscopically investigated. In contrast to normal skin, the mast cells showed irregular, partly bilobed nuclei, prominent nucleoli, hypogranulation, and rather small granules; giant granules were rarely observed. In addition, we frequently found degranulation, and the development of microvilli was much more prominent than with normal mast cells. These deviations from normal skin represent at least in part functional alterations. However, some of the findings suggest that urticaria pigmentosa may be considered a neoplastic disease of the tissue mast cells, although clear evidence is still lacking. In any case, our findings show that mast cells in mastocytosis are not identical with those in normal skin.     

183例儿童皮肤型肥大细胞增生症临床及预后分析

目的 探讨儿童皮肤型肥大细胞增生症的临床特征及预后。 方法 回顾分析183例儿童皮肤型肥大细胞增生症患者的临床资料,并随访部分患者。 结果 183例患者中,色素性荨麻疹136例（74.3%）,肥大细胞瘤43例（23.5%）,弥漫性肥大细胞增生症4例（2.2%）;生后2岁内发病者179例（97.8%）。43例肥大细胞瘤患者中出生即发病者21例（48.8%）,出生后至6个月发病者17例（39.5%）,136例色素性荨麻疹患者中出生即发病者35例（25.7%）,出生至6个月发病者78例（57.3%）。伴随症状记录详细的33例患者中,10例出现伴随症状,其中9例为潮红发作。对45例患者随访3 ~ 6年（平均4年）,色素性荨麻疹患者1例于11岁时皮损完全消退,18例皮损部分消退;肥大细胞瘤患者1例皮损于8岁时完全消退,7例行皮肤活检后1年内皮损消退。口服抗组胺药可控制患者潮红、风团及水疱等症状;口服糖皮质激素可有效控制弥漫性肥大细胞增生症患儿反复发生的泛发水疱、大疱。 结论 儿童皮肤型肥大细胞增生症以色素性荨麻疹最常见,其次为肥大细胞瘤。肥大细胞瘤多于出生即发病,而色素性荨麻疹以出生后至6个月发病多见。口服抗组胺药可控制介质释放相关症状。严重的弥漫性肥大细胞增生症患者可口服糖皮质激素控制症状。     

Absence of MHC class II antigen on mast cells at sites of inflammation in human skin

Abstract Since the presence of major histocompatibility complex (MHC) antigens has recently been reported on murine and human mast cells under various conditions, we have investigated their expression on mast cells in different types of cutaneous inflammation. Cryostat sections from lesional biopsies of patients with psoriasis, atopic eczema, chronic urticaria, lichen planus, bullous pemphigoid and urticaria pigmentosa were immunohistochemically stained with monoclonal antibodies against MHC class I and class II antigens using a double staining APAAP/toluidine blue methodology. While strongly positive staining with the antibody directed against MHC class I antigens was found on nearly all mast cells in normal skin and in inflammatory dermatoses, reactivity for HLA-DR and HLA-DQ antigens on mast cells could not be detected, except for less than 2% of cells with doubtful staining. Human mast cells therefore probably play no significant rôle as antigen-presenting cells in the conditions studied.     

Diffuse cutaneous bullous mastocytosis with IgM deposits at dermo–epidermal junction

Cutaneous mastocytosis is a disease characterized by the infiltration and proliferation of mast cells in the skin. In children, the most common form of presentation is urticaria pigmentosa, while the diffuse cutaneous bullous mastocytosis is one of the rarest subtypes seen. The aim of this paper is to present a case of diffuse bullous mastocytosis with detection of IgM deposits at dermo–epidermal junction using direct immunofluorescence (DIF) microscopy. The diagnosis of diffuse bullous mastocytosis is a challenge, and DIF microscopy is necessary in order to exclude an autoimmune bullous disorder. However, IgM deposits at dermo–epidermal junction can be nonspecific, being found in a variety of skin disorders. A 6‐month‐old girl presented with bullous lesions and erosions on the scalp and the trunk. During hospitalization, further bullous lesions appeared, along with generalized erythrodermia. Skin biopsy revealed aspects of urticaria pigmentosa. Taking into account the clinical findings, the case was enclosed as bullous mastocytosis. Treatment included the avoidance of trigger factors, and administration of antihistamines along with a short‐term course of systemic steroids. The evolution was favorable, with remission of the existing lesions and without occurrence of new ones.     

Phenotypic characterization of skin lesions in urticaria pigmentosa and mastocytomas

In order to identify possible cellular abnormalities in human mastocytosis, sections from 13 urticaria pigmentosa lesions and 5 mastocytomas were compared with 5 normal skin specimens using histochemical, enzyme histochemical and immunohistochemical techniques. All toluidine blue-positive mast cells also reacted with FcRI and c-kit antibodies, almost all stained for tryptase, many for chymase and the myeloid workshop mast cell antibodies, few for FcRII and none for the proliferation marker Ki-67. Urticaria pigmentosa lesions contained fewer epidermal Langerhans cells and a lower percentage of avidin-positive mast cells than mastocytomas and normal skin. Mastocytomas exhibited generally weaker staining for mast cell markers and mostly lacked FcRI-bound IgE on mast cells and Langerhans cells, although the receptor was able to bind IgE in tissue sections. Most of the mast cell antibodies also reacted with other cell types. Only toluidine blue, avidin, tryptase and chymase stains were mast cell specific. Mast cells in mastocytosis thus differed only to a minor degree from normal mast cells, although distinct pathomechanisms may play a role in urticaria pigmentosa and mastocytosis.     

Perivascular mast cells in urticaria pigmentosa

We have quantified perivascular mast cells in cases of urticaria pigmentosa, urticaria, and dermal hypersensitivity reactions. To facilitate reproducibility, the mast cells were counted for a precisely defined vessel unit. These vessel units were divided arbitrarily into those ≤55μm and > 55μm in largest diameters. Urticaria pigmentosa showed an average of 6.4 ± 1.9 and 22.8 ± 13.2 masts cells for vessel unit ≤ 55μm and ≤ 55μm, respectively. Urticaria yielded a lower number of mast cells: 1.5 ± 0.2 and 2.9 ± 0.9 for the same respective vessel units. Dermal hypersensitivity reactions revealed an average of 1.6 ± 0.4 and 2.2 ± 0.7 mast cells, and the normal skin showed 1.5 ± 0.3 and 2.4 ± 0.6 mast cells for each of the vessel units of ≤ 55μm and > 55μm. The perivascular mast cell distributions of urticaria pigmentosa are statistically different from those of urticaria and dermal hypersensitivity reactions with p < 0.0001. No statistical difference was noted between urticaria, dermal hypersensitivity reactions, and normal skin. The percentages of vessel units ≤ 55μm with ≥ 5 mast cells and vessel units < 55μm with ≥ 10 mast cells were determined for each case. The average percentage of vessel units for the former and latter in urticaria pigmentosa was 82.6% and 58.9%, respectively. Urticaria yielded 0% and 0.2%, respectively. None of vessel units in the dermal hypersensitivity reactions or normal skin contained more than 5 mast cells in vessel units ≤ 55μm and more than 10 mast cells in vessel units > 55μm. Cases of urticaria pigmentosa can be distinguished from other cutaneous eruptions containing mast cells using a simple counting technique on Giemsa stained sections.     

Two novel mast cell phenotypic markers, monoclonal antibodies Ki-MC1 and Ki-M1P, identify distinct mast cell subtypes

Summary In order to identify more specific or selective mast cell markers, the reactivity of two monoclonal antibodies, Ki-MC1 and Ki-M1P, was studied by immunohistochemistry in two human cell lines (mast cell line HMC-1, basophilic cell line KU812), in mast cells cultured from blood precursors, in adherent mononuclear cells from peripheral blood, and in mast cells of tissue sections from 1 3 urticaria pigmentosa lesions, live mastocytomas and live normal skin specimens. Toluidine blue staining, fluorescence staining with FITC-conjugated avidin, and immunohistochemical staining (APAAP) with other mast cell reactive monoclonal antibodies, was performed for comparison. Double staining with the APAAP method, using the Ki-antibodies and toluidine blue, was also carried out. Both Ki-antibodies showed reactivity for skin mast cells, but with a different staining pattern. In addition, the Ki-MC1 antibody did not react with the cell lines, and reacted only with a few peripheral blood mononuclear cells and cultured mast cells. In contrast, the Ki-M1P antibody reacted with almost all cultured mast cells and blood mononuclear cells, but stained only about one-half of lesional and one-fifth of normal skin mast cells. Ki-M1P also reacted with many toluidine blue-negative dermal cells, particularly in urticaria pigmentosa. Ki-MC1 antibody can thus be considered as a useful additional marker for normal skin mast cells. In contrast, the Ki-M1 P antibody primarily identifies immature mast cells and monocytes/macrophages, suggesting that these cell types probably originate from the same bone marrow precursor.     

Okkulte kutane Mastozytose

Mastocytosis is diagnosed without difficulty if it presents with easily recognizable lesions of urticaria pigmentosa. Recently, we have identified hardly visible skin lesions of mastocytosis in Hymenoptera venom allergic patients ("occult mastocytosis"). In addition, in approximately 15% of the patients with typical cutaneous lesions, urticaria pigmentosa was at first mistaken for other conditions and thus not linked to simultaneous symptoms of systemic mastocytosis. In most patients with unrecognized mastocytosis, the diagnosis was supported by raised basal serum tryptase levels. Cutaneous mastocytosis is often overlooked and more frequent than assumed. Measurement of basal serum tryptase concentrations can make an important contribution to the diagnosis of mastocytosis, but it does not replace a meticulous skin examination.     

Cutaneous mastocytosis: demographic aspects and clinical features of 55 patients

BACKGROUND: Mastocytosis is a rare, heterogeneous group of disorder with abnormal increase of mast cells in one or more organ systems. OBJECTIVE: To evaluate the demographic and clinical features of cutaneous mastocytosis (CM). METHODS: Records of 55 patients with cutaneous mastocytosis were retrospectively analysed. RESULTS: Of the 22 females and 33 males, 80% had urticaria pigmentosa/maculopapular CM and 20% had mastocytoma. Of all cases, 81.8% had first lesions in childhood. The most common presentation was involvement of trunk together with extremities. Thirteen (23.6%) patients had history of bulla; Darier's sign was positive in 34 of 38 patients. Itching was the most common complaint, provocated by hot weather/bath. CONCLUSION: Clinical presentations of urticaria pigmentosa/maculopapular CM and mastocytoma are similar regarding gender, age of onset, age of diagnosis, and presence of Darier's sign and history of bulla. In contrast to mastocytoma, urticaria pigmentosa/maculopapular CM lesions were frequently located on trunk together with extremities.     

Urticaria pigmentosa. Systemic evaluation and successful treatment with topical steroids

Nine patients with adult-onset urticaria pigmentosa were studied for the incidence of extracutaneous mast cell involvement and the efficacy of potent topical corticosteroid therapy for cutaneous lesions. Seven of the nine patients had increased mast cells in the marrow biopsy specimens, and five patients had focal aggregates of mast cells. The bone scan was abnormal in one patient. Liver-spleen scans revealed a shift of colloid uptake from liver to spleen in four patients. No abnormal gastrointestinal tract roentgenograms were obtained. Urinary histamine metabolites correlated with nodular bone marrow involvement, but not with other parameters. Results of the psychoneurologic testing revealed significant deviation from the norm with a verbal memory deficit in all nine patients and abnormalities on the Minnesota Multiphasic Personality Inventory in four patients. All nine patients were treated with 0.05% betamethasone dipropionate ointment under occlusion over half of the body nightly for 6 weeks. Seven of nine patients treated responded with almost complete resolution of their lesions. Hypothalamic pituitary adrenal axis suppression was evaluated with intramuscular cosyntropin stimulation and metyrapone administration during treatment. Only two patients, both of whom used the medication improperly, developed transient abnormalities. Slow return of lesions was noted 6 months after completion of therapy. Remissions could be lengthened with single weekly applications of topical steroids. Systemic involvement is frequent in patients with cutaneous mast cell disease and it is best demonstrated by bone marrow biopsy. Mast cell lesions can be safely and effectively treated with topical steroids in motivated patients.     

Trioxsalen baths plus UV-A in the treatment of lichen planus and urticaria pigmentosa

Local photochemotherapy with trioxsalen baths and long-wave ultraviolet radiation (UV-A) was used in nineteen patients with lichen planus and five patients with urticaria pigmentosa. Widespread papular lichen planus healed totally in all sixteen patients. Hypertrophic lichen planus was more resistant to therapy; two out of three patients recovered completely and in one the result was good. The average total UV-A dose in papular lichen planus was only 6 J/cm^2. In urticaria pigmentosa good results were gained in all five patients treated with respect to whealing, itching and dermographism, and in one patient the lesions disappeared completely.     

Urticaria pigmentosa associated with acute stress and lesional skin mast-cell expression of CRF-R1

A 38-year-old woman presented with a pronounced increase in symptoms and proliferation of urticaria pigmentosa (UP) after acute psychological stress, which was quantified using the Spielberger's State–Trait Anxiety Inventory. Immunohistochemical examination of a skin biopsy from a new UP lesion showed a large number of activated mast cells expressing corticotrophin-releasing factor receptor-1 (CRF-R1) and there was high serum CRF. This is the first documented report to our knowledge of UP worsening associated with acute stress, possibly through activation of skin mast-cell CRF-R1.     

The skin in mastocytosis.

The most frequent site of organ involvement in patients with any form of mastocytosis is the skin. Cutaneous expressions include urticaria pigmentosa, mastocytoma, diffuse and erythrodermic cutaneous mastocytosis, and telangiectasia macularis eruptiva perstans. The cutaneous lesions tend to appear early in life. Although urticaria pigmentosa has been reported in 12 pairs of twins and one set of triplets, the majority of affected individuals have no familial association. Most patients with systemic mastocytosis have skin lesions; however, an occasional patient will have systemic disease with no other skin features than flushing. In lesional cutaneous sites and in non-lesional skin, there is an increase in the number of mast cells. Electron microscopy shows quantitative differences between lesional skin mast cells from patients with and without systemic disease. The mast cells from adult patients with systemic disease have a larger mean cytoplasmic area, nuclear size, and granule diameter. The granules contain predominantly grating/lattice structures. The cutaneous mast cells contain tryptase and chymase. They retain their functional reactivities to relevant secretory stimuli, such as C3a, morphine sulfate, and calcium ionophore A23187. Lesional skin contains histamine, leukotriene B4, prostaglandin D2, 5-hydroxyeicosatetraenoic acid, platelet-activating factor, and heparin. Treatment of the cutaneous manifestations includes the use of H1 and H2 antihistamines, oral disodium cromoglycate, psoralens plus ultraviolet A photochemotherapy, and potent topical corticosteroid preparations.     

Evidence for altered mast cell proliferation and apoptosis in cutaneous mastocytosis

BACKGROUND: Mastocytosis presents as a focal or generalized increase of mast cells, particularly in the skin, but also in other organs. Activating mutations of KIT (formerly c-kit), the receptor of the mast cell growth factor stem cell factor (SCF), appear to play a key role in the pathogenesis of sporadic adult onset mastocytosis. However, these mutations are not present in childhood-onset and familial mastocytosis and also fail to explain the heterogeneity of adult-onset disease. Other factors such as prolonged survival of mast cells may therefore participate in causing and modulating the pathological increase of mast cells in mastocytosis. OBJECTIVES: To examine the expression of proliferation and apoptosis markers in the mast cells of cutaneous mastocytosis lesions in order to gain further insight into the pathogenesis of mastocytosis. METHODS: Lesional cutaneous biopsies from eight infants with solitary mastocytomas, five children with multiple mastocytomas, 11 children with generalized urticaria pigmentosa, 12 adults with urticaria pigmentosa, and skin from seven normal controls were used in this study. Serial sections were stained with toluidine blue to quantify mast cell numbers and with antibodies against the proliferation marker Ki67 protein, the tumour suppressor protein p53, and the inhibitor of cyclins and cyclin-dependent kinases p21WAF1/CIP1, using the alkaline phosphatase antialkaline phosphatase technique. The terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labelling (TUNEL) method was used to assess apoptosis. RESULTS: Cutaneous mast cell counts were significantly increased in all patient sections, particularly in childhood lesions, and similarly, a small but significant increase of proliferation was found in the lesional mast cells of all patients. Enhanced mast cell numbers and proliferation was associated with a significant decrease of TUNEL staining, particularly in mastocytomas. p53 expression was highly variable, with an overall significant increase in all patient skin mast cells, whereas p21 expression was barely observed at all. CONCLUSIONS: These findings further support the concept that an imbalance of mast cell proliferation and apoptosis is prevalent in mastocytosis lesions that may account in part for the increased focal mast cell accumulation in this condition.