Mast cell numbers in incisional wounds in rat skin as a function of distance, time and treatment

Micronuclei in germ cells of hybrid frogs from Pelophylax esculentus complex contain gradually eliminated chromosomes

In most organisms, cells typically maintain genome integrity, as radical genome reorganization leads to dramatic consequences. However, certain organisms, ranging from unicellular ciliates to vertebrates, are able to selectively eliminate specific parts of their genome during certain stages of development. Moreover, partial or complete elimination of one of the parental genomes occurs in interspecies hybrids reproducing asexually. Although several examples of this phenomenon are known, the molecular and cellular processes involved in selective elimination of genetic material remain largely undescribed for the majority of such organisms. Here, we elucidate the process of selective genome elimination in water frog hybrids from the Pelophylax esculentus complex reproducing through hybridogenesis. Specifically, in the gonads of diploid and triploid hybrids, but not those of the parental species, we revealed micronuclei in the cytoplasm of germ cells. In each micronucleus, only one centromere was detected with antibodies against kinetochore proteins, suggesting that each micronucleus comprises a single chromosome. Using 3D-FISH with species-specific centromeric probe, we determined the role of micronuclei in selective genome elimination. We found that in triploid LLR hybrids, micronuclei preferentially contain P. ridibundus chromosomes, while in diploid hybrids, micronuclei preferentially contain P. lessonae chromosomes. The number of centromere signals in the nuclei suggested that germ cells were aneuploid until they eliminate the whole chromosomal set of one of the parental species. Furthermore, in diploid hybrids, misaligned P. lessonae chromosomes were observed during the metaphase stage of germ cells division, suggesting their possible elimination due to the inability to attach to the spindle and segregate properly. Additionally, we described gonocytes with an increased number of P. ridibundus centromeres, indicating duplication of the genetic material. We conclude that selective genome elimination from germ cells of diploid and triploid hybrids occurs via the gradual elimination of individual chromosomes of one of the parental genomes, which are enclosed within micronuclei.

The Importance of Mast Cells in Dermal Scarring

Significance: Mast cells are resident inflammatory cells present in high numbers in the skin. They are one of the first cell types to respond to damage and they do so by quickly releasing a variety of preformed mediators that are stored within mast cell granules. Mast cells are not only active early on, where they help induce inflammation, but they also stimulate the proliferation of several important cell types and influence the production and remodeling of collagen. Recent Advances: Recent studies have highlighted the importance of mast cells in determining the amount of scar tissue that forms as a result of the repair process. Mast cells are found in low numbers and in a less activated state in scarless wounds, whereas high numbers of activated mast cells are associated with scarring and fibrosis. Furthermore, animals that lack mast cells or have been treated with degranulation inhibitors or drugs that block the activity of mast cell proteases have been shown to heal with reduced scar tissue. Critical Issues: Despite evidence suggesting that mast cells regulate scar tissue development, the entire range of mast cell activities during wound repair and scar formation has not been completely characterized. In addition, the potential therapeutic benefits of targeting mast cells clinically have yet to be fully explored. Future Directions: More studies are needed to determine whether inhibiting mast cell activation and blocking the function of mast cell mediators are viable options to prevent or reduce the appearance of scars.

Blockade of mast cell activation reduces cutaneous scar formation

Damage to the skin initiates a cascade of well-orchestrated events that ultimately leads to repair of the wound. The inflammatory response is key to wound healing both through preventing infection and stimulating proliferation and remodeling of the skin. Mast cells within the tissue are one of the first immune cells to respond to trauma, and upon activation they release pro-inflammatory molecules to initiate recruitment of leukocytes and promote a vascular response in the tissue. Additionally, mast cells stimulate collagen synthesis by dermal fibroblasts, suggesting they may also influence scar formation. To examine the contribution of mast cells in tissue repair, we determined the effects the mast cell inhibitor, disodium cromoglycate (DSCG), on several parameters of dermal repair including, inflammation, re-epithelialization, collagen fiber organization, collagen ultrastructure, scar width and wound breaking strength. Mice treated with DSCG had significantly reduced levels of the inflammatory cytokines IL-1α, IL-1β, and CXCL1. Although DSCG treatment reduced the production of inflammatory mediators, the rate of re-epithelialization was not affected. Compared to control, inhibition of mast cell activity caused a significant decrease in scar width along with accelerated collagen re-organization. Despite the reduced scar width, DSCG treatment did not affect the breaking strength of the healed tissue. Tryptase β1 exclusively produced by mast cells was found to increase significantly in the course of wound healing. However, DSCG treatment did not change its level in the wounds. These results indicate that blockade of mast cell activation reduces scar formation and inflammation without further weakening the healed wound.

Mast cells and the liver aging process

It has now ascertained that the clinical manifestations of liver disease in the elderly population reflect both the cumulative effects of longevity on the liver and the generalized senescence of the organism ability to adjust to metabolic, infectious, and immunologic insults. Although liver tests are not significantly affected by age, the presentation of liver diseases such as viral hepatitis may be subtler in the elderly population than that of younger patients.

Human immunosenescence is a situation in which the immune system, particularly T lymphocyte function, deteriorates with age, while innate immunity is negligibly affected and in some cases almost up-regulated.

We here briefly review the relationships between the liver aging process and mast cells, the key effectors in a more complex range of innate immune responses than originally though.

Involvement of mast cell chymase in burn wound healing in hamsters

Mast cells play a significant role in the late stage of wound healing following burn injuries. In the present study, the possible role of mast cell chymase in burn wound healing was examined using a mast cell membrane stabilizer, ketotifen, in hamsters. A total of 28 hamsters were randomly divided into two groups (n=14), termed as the control and ketotifen groups. A deep partial-thickness burn injury was made on the back skin of the hamsters. The control group was orally administered physiological saline (1 ml) and the ketotifen group was orally administered ketotifen (4 mg/kg) once daily, two days prior to and two days subsequent to the burn. The results showed that concentrations of angiotensin II (Ang II), TGF-β1, collagens I and III and interleukin (IL)-1β were significantly decreased in the ketotifen group compared with those in the control group. However, there was no significant difference in fibroblast apoptosis between the two groups. The release of mast cell chymase was inhibited by the mast cell membrane stabilizer ketotifen. Taken together, these results suggest that mast cell chymase may participate in the process of burn wound healing. Chymase may therefore be a promising therapeutic target for the treatment of burn wounds.

Antagonists of CD117 (cKit) signaling inhibit mast cell accumulation in healing skin wounds

Mast cells (MCs) have important functional roles in leukocyte recruitment, pain, and wound healing, and increased tissue resident MC function has been associated with several fibrotic diseases. Consequently, the study of MCs in situ can be a direct approach to studying the pharmacodynamic impact of MC-directed therapeutics in tissues. Here we describe an automated laser scanning cytometry assay that was used to characterize the kinetics of MC accumulation in healing skin wounds and to study the effect of inhibiting CD117 (cKit) signaling. The number of tryptase-positive MCs approximately doubled 14 days after cutaneous injury in nonhuman primates. Treatment of animals with anti-CD117 or imatinib mesylate (Gleevec) reduced MC accumulation at the edge of healing wounds in mice and nonhuman primates, respectively. In translating this MC assay to become a biomarker for human studies, no differences in dermal MC numbers were evident between genders, ages or body mass index from 20 healthy donors. These data suggest that skin is a practical and useful tissue for tracking pharmacodynamic effects of MC-directed therapies.

Mast cell concentration in the wound healing process of incisions made by different instruments

The aim of this study was to compare the concentration of mast cells (MCs) in the healing process of incisions. Thirty rats were submitted to six linear incisions each, performed in the dorsal skin by carbon dioxide (CO(2)) and diode lasers, electrocautery and conventional scalpel. The animals were euthanized at intervals of 0 h, 24 h, 48 h, 72 h, 7 days and 14 days after the incisions had been made. Histological sections were obtained and stained with toluidine blue for identification of MCs, which were manually counted by conventional microscopy in 20 microscopic fields in the border of the incision, near the granulation tissue, or in the area of new collagen formation, depending on intervals. The concentration of MCs was significantly higher in the wounds made by scalpel than in those made by other techniques at 48 h and 72 h. After 72 h the number of MCs was also significantly higher after electrocautery than after incisions made by 4 W CO(2) laser. On days 7 and 14, there was no significant difference in the MC count among the different types of incisions. In summary, the MC concentration varied after different surgical incisions at early phases of wound healing. At the end of the healing process, however, there were similar MC concentrations around the incisions, suggesting that, in standard incisions in the surgical techniques studied, the wound healing process ultimately occurred in a similar pattern.

The complex functions of mast cells in chronic human liver diseases

Mast cells (MCs) are multifunctional effector cells of the immune system. MCs were originally thought to be involved in IgE-associated immediate hypersensitivity and allergic disorders, but it is now known that they contain or elaborate an array of mediators with a multitude of effects on many other cells. A number of studies have found that MCs are involved in various liver diseases. Although still controversial, they seem to be involved in the liver's fibrotic response to chronic inflammation and parasitic infection. Hepatic fibrosis is the most frequent liver response to toxic, infectious, or metabolic agents. During the establishment of this pathological condition, there is an increase in the components of the basement membrane that leads to continuous basement membrane-like structures being raised within Disse's space and a decrease in the number of sinusoid endothelial fenestrae. This leads to a complex process called "sinusoidal capillarization." At the cellular level, liver fibrogenesis is initiated by hepatocyte necrosis, which induces the recruitment of a large number of inflammatory cells, including MCs, which can be considered the primary effectors of the process changing sinusoidal endothelial cells into capillary-type endothelial cells. We review the roles played by MCs in hepatic chronic diseases and describe a biopsy section of hepatic tissue taken from a patient with chronic C virus-related hepatitis showing diffuse sinusoidal capillarization and a high density of MCs. This observation has led us to hypothesize a relationship between these highly specialized cells and sinusoidal capillarization.

Mast cell accumulation and cytokine expression in the tight skin mouse model of scleroderma

The tight skin (Tsk) mouse develops many pathological changes seen in human scleroderma, such as increased collagen content and mast cell density. Although associations between mast cell expansion and skin fibrosis have been reported, the mechanisms underlying mast cell accumulation remain unclear. In this study, we have measured the density of skin mast cells in Tsk mice and their normal littermates (pa/pa) of 4-36 weeks of age, and in the skin heterografted between Tsk and pa/pa mice. Cytokines related to mast cell differentiation, proliferation and migration were examined by using RNase protection assays. Skin mast cell density in Tsk mice was significantly increased from 12 weeks of age, compared to that in pa/pa mice. The expression of transforming growth factor-beta1 (TGF-beta1), and to a lesser extent, stem cell factor (SCF) and interleukin-15 (IL-15) mRNA was higher in Tsk mice, compared to that in control mice. Mast cell density was unchanged in Tsk skin grafted onto pa/pa hosts, but dramatically increased in pa/pa skin grafted onto Tsk hosts. This latter mast cell hyperplasia was associated with the increases in mRNA levels of TGF-beta1, SCF and IL-15, whereas little change in cytokine levels was seen in heterografted Tsk skin. These results suggest that locally produced cytokines in Tsk skin influence mast cell accumulation in this animal model of human scleroderma.

Therapeutic applications of chymase inhibitors in cardiovascular diseases and fibrosis

Chymase activates not only angiotensin I to angiotensin II but also latent transforming growth factor-beta-binding protein to transforming growth factor-beta. In dog grafted veins, chymase activity and angiotensin II concentration along with vascular proliferation were significantly increased, while they were significantly suppressed by a chymase inhibitor. After balloon injury in dog arteries, chymase activity was significantly increased in the injured artery, and a chymase inhibitor and an angiotensin AT(1) receptor antagonist were effective in preventing the vascular proliferation, but an angiotensin-converting enzyme inhibitor was ineffective. In fibrotic models, the tissue fibrosis was reduced by chymase inhibitors. In adhesion models, the transforming growth factor-beta concentration and adhesion formation were suppressed by chymase inhibitors. Therefore, chymase inhibitors may be useful for preventing cardiovascular diseases and fibrosis via inhibition of angiotensin II formation and transforming growth factor-beta activation.

Mast cells in tissue response to dentistry materials: an adhesive resin, a calcium hydroxide and a glass ionomer cement

Synthetic materials used in dentistry may trigger various inflammatory responses. In order to evaluate biocompatibility, standardized implants of Calcium Hydroxide (CH), Glass Ionomer Cement (GIC) and Light-activated Dental Adhesive (LDA) were surgically introduced into Wistar rats' back bone. Six (experimental) animal groups, five each, and two Sham (S) groups were studied after 15 and 30 days from surgery. In each animal, the density of mast cells and interstitial fibrosis volume was evaluated by quantitative light microscopy. In addition, the interaction between the disk material and its fibrous capsule was evaluated by scanning electron microscopy. The density of mast cells per area (N(A)[mast cells]) was lower in CH group than in LDA group. GIC group displayed N(A)[mast cells] results intermediate between CH and LDA groups (p<0.05). The smallest interstitial fibrosis volume density (Vv[f]) was observed in CH group, then in GIC group, while the greatest in LDA group. After 30 days, the fibrosis in LDA group was 30% higher than in CH group (p<0.05). In S group, discreet fibrosis restricted to surgical area was present, with few mast cells near the vessels. Significant interaction between fibrous capsule and the surrounding disk material was most evident in CH group. The implanted materials induced mast cell migration, distinct fibrosis development, suggesting that CH is the most biocompatible material among those tested.

Mast cells modulate the inflammatory but not the proliferative response in healing wounds

Upon stimulation, mast cells release a heterogeneous group of factors that promote inflammation and influence cell proliferation. Mast cells accumulate at sites of injury, further suggesting a critical role in wound healing. To assess the importance of mast cells in tissue repair, we compared wound healing in mast cell-deficient WBB6F1/J-KitW/KitW-v (KitW/KitW-v) and wild type WBB6F1/++ (WT) mice. During the inflammatory phase, neutrophil infiltration into wounds of the KitW/KitW-v mice was significantly less than that of WT mice (84.6 +/- 10.3 vs. 218 +/- 26.0 cells/10 high-power fields at day 3, p < 0.001), while wound macrophage and T cell infiltration were similar in both strains. The decrease in neutrophils could not be explained by changes in tumor necrosis factor-alpha or macrophage inflammatory protein-2 levels, because the amounts of these two neutrophil chemoattractants were similar in both KitW/KitW-v and WT mice. Surprisingly, the absence of mast cells had no effect on the proliferative aspects of wound healing, including reepithelialization, collagen synthesis, and angiogenesis. Although mast cells are known to release proangiogenic mediators, vascular endothelial growth factor levels were similar in WT and KitW/KitW-v mice. Moreover, levels of fibroblast growth factor-2 were increased in KitW/KitW-v mice (4206 +/- 107 vs. 1865 +/- 249 pg/ml, p < 0.01). These results suggest that mast cells modulate the recruitment of neutrophils into sites of injury, yet indicate that mast cells are unlikely to exert a major influence on the proliferative response within healing wounds.

Role of mast cells and myofibroblasts in human peritoneal adhesion formation

OBJECTIVE

To study fibroblasts and mast cells in human peritoneal adhesions and to evaluate whether their interaction plays a role in adhesion development.

SUMMARY BACKGROUND DATA

Myofibroblasts play a critical role in wound repair/fibrosis. Mast cells influence the formation of peritoneal adhesions in a rat model, and they are modulators of fibroblast functions.

METHODS

Peritoneal adhesion biopsies were processed for either histology (H&E, toluidine blue) or immunohistochemistry (tryptase, laminin, collagen type IV and VIII, and alpha-SMA) or grown as explants for obtention of fibroblasts. The effects of mast cell (HMC-1) sonicate and selected mast cell mediators and cytokines on fibroblast proliferation ([ (3)H]thymidine) and collagen synthesis ([ (3)H]proline) and on fibroblast contractile activity (tridimensional collagen lattice) were evaluated. Mast cell mediators influencing fibroblast proliferation were partially characterized by enzymatic susceptibility and FPLC gel filtration column chromatography.

RESULTS

Most of the fibroblasts in peritoneal adhesions were identified as alpha-SMA-positive myofibroblasts. Mast cell hyperplasia was observed and more than one third of the mast cells were degranulated. Few mast cells showed a faint staining for laminin or collagen type IV and VIII. Mast cell sonicate increased fibroblast proliferation and contractile activity while decreasing collagen synthesis. Mast cell sonicate proliferating activities were found to be proteinase-sensitive with a molecular weight of more than 158 kd, of approximately 40 kd, and of less than 10 kd. TGF-beta and tryptase enhanced collagen synthesis; TNF-alpha and chymase decreased it. None of the selected mediators increased fibroblast proliferation.

CONCLUSIONS

Myofibroblasts are the main connective tissue cells present in human peritoneal adhesions, and mast cells play a direct role in peritoneal adhesion formation.

Chymase inhibitor, BCEAB, suppressed peritoneal adhesion formation in hamster

BACKGROUND

Mast cells are closely related to adhesion formation, while it has been unclear which factor in mast cells plays an important role in the development of adhesion formation. To clarify the role of chymase produced from mast cells in adhesion formation, we investigated the preventive effect of a specific chymase inhibitor, BCEAB, on adhesion formation in a hamster experimental model.

MATERIALS AND METHODS

Hamsters were administered orally once daily with 100 mg/kg of BCEAB or placebo from the operated day to 1 week after the operation. The uterus was grasped and denuded by a swab.

RESULTS

One week after the operation, the scores for adhesion formation in the chymase inhibitor-treated group were significantly decreased in comparison with those in the placebo-treated group (placebo-treated group, 2.80 +/- 0.20; chymase inhibitor-treated group 1.60 +/- 0.31: P < 0.01). The chymase activity in the injured uterus was also significantly suppressed in the chymase inhibitor-treated group (placebo-treated group, 17.3 +/- 2.69 mU/mg protein; chymase inhibitor-treated group 9.60 +/- 0.89: P < 0.05). After scraping the utelus, the level of transforming growth factor-beta in the peritoneal fluid was significantly increased in the placebo-treated group, while it was suppressed to 70% by the treatment with BCEAB.

CONCLUSIONS

The specific chymase inhibitor BCEAB may be a useful drug for prevention of adhesion formation.

Oral administration of a novel chymase inhibitor, NK3201, prevents peritoneal adhesion formation in hamsters

We investigated the preventive effect of an orally active chymase inhibitor, NK3201 (2-(5-formylamino-6-oxo-2-phenyl-1,6-dihydropyrimidine-1-yl)-N-[[3,4-dioxo-1-phenyl-7-(2-pyridyloxy)]-2heptyl]acetamide), on the adhesion formation in a hamster experimental model. Hamsters were administered orally once daily with 30 mg/kg of NK3201 or placebo from 3 days before uterus scraping to 7 days after it. A significant increase of chymase activity in the injured uterus was reduced by treatment with NK3201. The score of adhesion formations in the chymase inhibitor-treated group was significantly decreased in comparison with that in the placebo-treated group (P < 0.01). Oral administration of NK3201 may be a useful drug for prevention of peritoneal adhesion formation.

Chymase inhibitors may prevent postoperative adhesion formation

OBJECTIVE

To clarify the role of chymase produced from mast cells in adhesion formation, we measured chymase activity level and investigated the preventive effect of a chymase inhibitor, Suc-Val-Pro-Phe(p)(OPh)(2), on the postoperative adhesion formation.

DESIGN

Prospective randomized study using a surgical model for adhesion formation.

SETTING

Clean hamsters in an academic research environment.

ANIMAL(S)

Sixty-seven female Syrian hamsters.

INTERVENTION(S)

Hamsters were given a lesion, produced by uterus scraping, and the chymase inhibitor (10 microM) or placebo was injected into the abdomen. Chymase activities in uteri were measured 3 days after the operation, and the scores of adhesion formations were assessed at 2 weeks.

MAIN OUTCOME MEASURE(S)

Measurement of chymase activity and scoring of adhesion formation were performed.

RESULT(S)

A significant increase of chymase activity in the injured uterus reduced by treatment with the chymase inhibitor. The scores of adhesion formations in the chymase inhibitor-treated group were significantly decreased in comparison with those in the placebo-treated group.

CONCLUSION(S)

Chymase contained in mast cells plays an important role in adhesion formation, and a chymase inhibitor may be a useful drug for prevention of adhesion formation.

Chymase inhibitor suppresses adhesion formation in a hamster experimental model

To clarify the role of chymase produced by mast cells in adhesion formation, we investigated the preventive effect of a specific chymase inhibitor, Suc-Val-Pro-Phe(p) (OPh)2, on adhesion formation in a hamster experimental model. Hamsters underwent resection of the right uterine body and then 10 microM Suc-Val-Pro-Phe(p) (OPh)2 or placebo was injected into the abdomen. Two weeks after the operation, the scores for adhesion formation in the chymase inhibitor-treated group were significantly lower than that in the placebo-treated group (placebo-treated group, 3.60+/-0.22; chymase inhibitor-treated group, 2.10+/-0.22; P<0.01). This specific chymase inhibitor, Suc-Val-Pro-Phe(p) (OPh)2, significantly suppressed the scores for adhesion formation in a hamster experimental model. Thus, chymase may play an important role in the adhesion formation.

The mast cell in wound healing

This review describes the role of the mast cell in the pathobiology of skin healing. After illustrating its main morphofunctional characteristics, with special reference to the dog and cat, we consider the involvement of the mast cell in the various phases of skin repair. With the aid of a wide array of newly formed or preformed mediators released by degranulation, the activated mast cell controls the key events of the healing phases: triggering and modulation of the inflammatory stage, proliferation of connective cellular elements and final remodelling of the newly formed connective tissue matrix. The importance of the mast cell in regulating healing processes is also demonstrated by the fact that a surplus or deficit of degranulated biological mediators causes impaired repair, with the formation of exuberant granulation tissue (e.g. keloids and hypertrophic scars), delayed closure (dehiscence) and chronicity of the inflammatory stage.

Inhibition of keratinocyte growth in cell culture and whole skin culture by mast cell mediators

Mast cells are suggested to participate in regenerative processes, but their influence on epithelialization and wound healing has not been well studied. Since mast cells can be found in contact with epidermis in chronic inflammatory skin diseases and venous ulcers, the effect of mast cells on keratinocyte growth was studied. Keratinocytes were cultured in serum-free conditions with (complete medium) or without (basal medium) epidermal growth factor (EGF) and bovine pituitary extract (BPE) to reach subconfluence in a 24-well plate, and the cells were treated with different mast cell mediators histamine, heparin and tryptase, or lysate from HMC-1 cells, a human leukemic mast cell line. Whole skin cultures were used as a model for in vitro wounds to study the effect of mast cells on epithelial outgrowth from skin specimens. Histamine inhibited 3H-thymidine incorporation of keratinocytes dose-dependently by 29% at 1 mM, and 89% at 5 mM histamine. In whole skin culture, histamine inhibited epithelial outgrowth dose-dependently by 64% already at 0.1 mM histamine and maximally (91%) at 1 mM histamine. Heparin inhibited 3H-thymidine incorporation dose-dependently by up to 33% at 2 microg/ml in the absence, but not in the presence, of EGF/BPE. In contrast, in whole skin culture, heparin first inhibited the epithelial outgrowth by up to 27% at 2 microg/ml, but then reversed the inhibition to 30% stimulation at 200 microg/ml. Skin tryptase (0.0285 to 2.85 microg/ml) with or without heparin (0.5 to 20 microg/ml) did not affect thymidine incorporation in keratinocytes. Lysate from HMC-1 cells, but not that from control, neuroblastoma cells, inhibited 3H-thymidine incorporation in keratinocytes dose-dependently, and maximal (47%) inhibition was reached with 16,700 lysed HMC-1 cells/ml. In whole skin culture, HMC-1 lysate inhibited the epithelial outgrowth by up to 36% at 67,000 lysed cells/ml. The results show that mast cells and their mediators are inhibitory to keratinocyte 3H-thymidine incorporation and epithelial outgrowth in vitro, although, the inhibitory effect of histamine was seen at high concentrations suggesting a requirement for close morphologic vicinity of mast cells to keratinocytes. Thus, mast cells are assumed to control epidermal regeneration and to impair epithelialization of chronic ulcers.

Association between the expression of mast cell chymase and intraperitoneal adhesion formation in mice

BACKGROUND

Adhesion formation is a major source of postoperative morbidity and mortality. Mast cells and their major protease, chymase, have been shown to participate in the healing process as well as in tissue remodeling. We aimed to identify the role of mast cells in intraperitoneal adhesion formation and to assess whether there is an association between the expression of mast cell chymase and adhesion formation.

MATERIALS AND METHODS

Both mast cell-deficient W/W(V) mice and congenic +/+ mice received a standardized lesion produced by cecal scraping and the application of 95% ethanol. Adhesions were assessed blindly 1 week later using a standardized scale. In addition, histamine content, mast cell numbers, and chymase activity in cecum as well as at the healing sites were evaluated before and 7 days after surgical injury.

RESULTS

A significant reduction in adhesion formation was seen in mast cell-deficient W/W(V) mice (P < 0.05). In the normal cecum, histamine content did not significantly differ between W/W(V) and +/+ mice. Chymase activity in cecum was detected in control +/+ mice, but not in W/W(V) mice. Mast cell numbers and chymase activity levels at the healing sites of +/+ mice were significantly increased 7 days after surgery.

CONCLUSIONS

Our results indicate that mast cells contribute to intraperitoneal adhesion formation in mice, and suggest that chymase originating from mast cells is important in the development of adhesions.

A theoretical model based upon mast cells and histamine to explain the recently proclaimed sensitivity to electric and/or magnetic fields in humans

The relationship between exposure to electromagnetic fields (EMFs) and human health is more and more in focus. This is mainly because of the rapid increasing use of such EMFs within our modern society. Exposure to EMFs has been linked to different cancer forms, e.g. leukemia, brain tumors, neurological diseases, such as Alzheimer's disease, asthma and allergy, and recently to the phenomena of 'electrosupersensitivity' and 'screen dermatitis'. There is an increasing number of reports about cutaneous problems as well as symptoms from internal organs, such as the heart, in people exposed to video display terminals (VDTs). These people suffer from subjective and objective skin and mucosa-related symptoms, such as itch, heat sensation, pain, erythema, papules and pustules. In severe cases, people can not, for instance, use VDTs or artificial light at all, or be close to mobile telephones. Mast cells (MCs), when activated, release a spectrum of mediators, among them histamine, which is involved in a variety of biological effects with clinical relevance, e.g. allergic hypersensitivity, itch, edema, local erythema and many types of dermatoses. From the results of recent studies, it is clear that EMFs affect the MC, and also the dendritic cell, population and may degranulate these cells. The release of inflammatory substances, such as histamine, from MCs in the skin results in a local erythema, edema and sensation of itch and pain, and the release of somatostatin from the dendritic cells may give rise to subjective sensations of on-going inflammation and sensitivity to ordinary light. These are, as mentioned, the common symptoms reported from patients suffering from 'electrosupersensitivity'/'screen dermatitis'. MCs are also present in the heart tissue and their localization is of particular relevance to their function. Data from studies made on interactions of EMFs with the cardiac function have demonstrated that highly interesting changes are present in the heart after exposure to EMFs. One could speculate that the cardiac MCs are responsible for these changes due to degranulation after exposure to EMFs. However, it is still not known how, and through which mechanisms, all these different cells are affected by EMFs. In this article, we present a theoretical model, based upon observations on EMFs and their cellular effects, to explain the proclaimed sensitivity to electric and/or magnetic fields in humans.

Altered expression of mast cell chymase and tryptase and of c-Kit in human cutaneous scar tissue

In order to explore a possible involvement of mast cells during human wound healing, we studied sections from scars (4-369-d-old) (N = 20) and normal skin (N = 10) for mast-cell-specific tryptase and chymase by enzyme histochemistry, for the stem cell factor receptor c-Kit and the melanosomal marker TA99 by immunohistochemistry, and for simultaneous c-Kit expression and avidin fluorescence by double staining. Enzyme activities and mRNA expression were also studied in tissue extracts. Chymase-reactive mast cell numbers as well as chymase activity and mRNA expression were reduced in all scars, whereas overall numbers of tryptase-reactive cells did not differ from normal skin, although tryptase activity and mRNA expression were increased in scar extracts. In contrast, numbers of c-Kit positive cells were significantly increased in old scars, and in the mid and lower dermis of all scars. A marked reduction of c-Kit reactivity was noted, however, in avidin-positive dermal mast cells and in epidermal basal cells, despite unchanged numbers of melanosome-positive cells, with an associated overall decrease of c-Kit mRNA in scar extracts. These data thus show that numbers of resident mast cells are very low in human cutaneous scars, suggesting massive mediator release from these cells into fresh wounds. Downregulation of stem cell factor receptors may also prevent these cells from increasing in number even in old scars. Instead, scar tissue is populated by a mast cell subpopulation that is chymase-, avidin-, tryptase +, c-Kit +, reflecting most probably an increased immigration and/or proliferation of immature mast cells and their precursors.

Mast cell involvement in normal human skin wound healing: expression of monocyte chemoattractant protein-1 is correlated with recruitment of mast cells which synthesize interleukin-4 in vivo

Mast cells (MCs) are known as key cells of immediate type hypersensitivity reactions. It has recently been shown that MCs regulate fibroblast proliferation by heterotypic cell-cell contact and secretion of interleukin-4 (IL-4) in vitro. It was therefore hypothesized that MCs may contribute to wound repair in vivo. Using immunohistology and in situ hybridization, the time course of mast cell recruitment and the expression of MC-attractant chemokines were analysed in a human skin wound-healing model, and the production of IL-4 by MCs in vivo was investigated. The data obtained indicate that the five-fold increase of the tryptase+ MCs at the fibrotic border of the wound within the first 10 days is the result of increased recruitment/survival of MCs or MC precursors, but not of increased local proliferation. Recruitment of MCs is paralleled by the expression of monocyte chemoattractant protein-1 (MCP-1), but not by other chemokines such as RANTES (regulated on activation, normal T cell expressed and secreted) and/or MIP (macrophage inflammatory protein)-1alpha/beta. Notably, 60-70% of MCs exhibited strong and selective IL-4 immunoreactivity, whereas other resident and passenger cells were rather quiescent. The data suggest that MC contribute significantly to the cytokine network of wound repair via MC-derived IL-4 and stimulation of fibroblast proliferation.

Expression of midkine in normal and burn sites of rat skin

Expression of midkine (MK), a retinoic acid-inducible heparin binding growth factor, was examined immunohistochemically in normal and burn sites of rat skin. In the normal skin, MK was localized in the epidermis and dermal appendages such as hair follicles and sebaceous glands. Mast cells in the subdermal connective tissue also accumulated MK. After burn injury, MK-positive cells began to infiltrate into subdermal connective tissue, and the number of MK-positive cells in the region increased to a maximum at postburn day two and then decreased gradually. Western blotting analysis of both normal and postburn skin revealed a 30 kDa band reactive with anti-MK antibody; this band was concluded to be a dimer of MK. These findings were discussed from the viewpoint of the possible role of MK in wound healing.

Mast cells and their mediators in cutaneous wound healing--active participants or innocent bystanders?

Mast cells are traditionally viewed as effector cells of immediate type hypersensitivity reactions. There is, however, a growing body of evidence that the cells might play an important role in the maintenance of tissue homeostasis and repair. We here present our own data and those from the literature elucidating the possible role of mast cells during wound healing. Studies on the fate of mast cells in scars of varying ages suggest that these cells degranulate during wounding, with a marked decrease of chymase-positive cells, although the total number of cells does not decrease, based on SCF-receptor staining. Mast cells contain a plethora of preformed mediators like heparin, histamine, tryptase, chymase, VEGF and TNF-alpha which, on release during the initial stages of wound healing, affect bleeding and subsequent coagulation and acute inflammation. Various additional vasoactive and chemotactic, rapidly generated mediators (C3a, C5a, LTB4, LTC4, PAF) will contribute to these processes, whereas mast cell-derived proinflammatory and growth promoting peptide mediators (VEGF, FGF-2, PDGF, TGF-beta, NGF, IL-4, IL-8) contribute to neoangiogenesis, fibrinogenesis or re-epithelization during the repair process. The increasing number of tryptase-positive mast cells in older scars suggest that these cells continue to be exposed to specific chemotactic, growth- and differentiation-promoting factors throughout the process of tissue remodelling. All these data indicate that mast cells contribute in a major way to wound healing. their role as potential initiators of or as contributors to this process, compared to other cell types, will however have to be further elucidated.

Differential cellular response within the rabbit tendon unit following tendon injury

The cellular changes in the epitenon, endotenon and synovial sheath were investigated in a rabbit model after a partial transverse laceration was made on the plantar aspect of the flexor digitorum profundus proximal to the synovial sheath (which was not injured). Fibroblasts, macrophages and mast cells within the epitenon, endotenon and synovial sheath were counted on electron micrographs. The epitenon and uninjured synovial sheath became engorged with fibroblasts and macrophages following injury. The number of synovial fibroblasts showed the greatest increase during the first week after injury. In comparison, the endotenon exhibited a delay in cellular response with initial apoptosis, as judged by positive P53 staining. However, hypercellular activity was seen within the endotenon at 12 weeks postoperatively.

Histamine-containing mast cells and their relationship to NGFr-immunoreactive nerves in prurigo nodularis: a reappraisal

The mast cell, which is a histamine-containing cell, has been found to have far more functions in skin inflammation than hitherto understood. To investigate the appearance of mast cells in prurigo nodularis, histamine immunohistochemistry in combination with nerve growth factor receptor (NGFr) double-staining as well as electron microscopic studies were performed. The results revealed that the histamine-containing cell number was increased in the lesional dermis. The mast cell size was also increased and the shape had become more dendritic. They tended to contact the epidermis and even infiltrated into it. In the histamine and NGFr double-staining, both an increased histamine-containing mast cell number and an increased number of NGFr-immunoreactive nerve fiber profiles were revealed in the upper dermis of the prurigo nodularis lesional skin. Mast cells were seen in close vicinity to NGFr-positive nerves and sometimes even seemingly to contact single nerve fibers. At the ultrastructural level, it is obvious that the mast cell bodies become larger, having more abundant cytoplasm and organelles (e.g. mitochondria), but comparatively fewer characteristic granules. Mast cells were often observed to sprout long dendrites, with or without granules. The cells were also frequently seen to contact other cell types, and a mast cell infiltration into the epidermis was also found. The statistical results of mast cell numbers showed a significant increase in prurigo nodularis lesional skin compared to the normal controls. The present results further indicate that mast cells, together with cutaneous nerve fibers, are actively involved in the pathogenesis of the disease.

Mast cells, eosinophils and fibrosis

We have presented results that increase our understanding of the roles MC and EOS play in modulating fibrotic processes. In vitro studies have provided clear-cut evidence for the direct involvement of these two inflammatory cells in enhancing proliferation, and either enhancing or decreasing collagen synthesis in human fibroblasts isolated from different anatomical locations. In addition, we have shown that MC and EOS interactions can also take part in modulating fibrosis. In vivo studies in murine and human cGVHD showed that MC activation is detrimental, and that MC stabilization therapy may be helpful in treating the fibrotic outcome of this disease. Much is still obscure. It is, for example, important to define the MC and EOS mediators involved in the modulation of fibroblast properties, and their pattern of influence, keeping in mind the ultimate goal of defining new therapeutic targets for the treatment of fibrotic diseases.

Histamine immunohistochemistry is superior to the conventional heparin-based routine staining methodology for investigations of human skin mast cells

Conventional studies of mast cells are limited by methodological restrictions such as a selective fixative-dependent routine staining blockage. This is thought to depend on the biochemical differences of the mast cell granule contents suggesting a cellular heterogeneity. Investigations of human mast cells, using routine methods, also suffer from the problem of a low signal-to-noise ratio. In the present study, normal human skin was used to compare an immunohistochemical method for histamine with two recommended mast-cell fixatives and a new commercial fixative in combination with three routine stains. Mast cells were found throughout the dermis with all the routine stains used. However, immunohistochemistry gave profoundly better results. Small structures, such as thin cytoplasmatic extensions and single granules, were readily detectable. Double-staining (immunohistochemistry followed by routine staining) revealed differences in staining capacity. All immunoreactive cells were not stained by routine stains and sometimes the opposite was also seen. This supports earlier reported evidence of heterogeneity, not only between skin and intestinal mast cells but also among skin mast cells themselves. Furthermore, by focusing on histamine, instead of heparin, we probably overcame the problems of the selective fixative-dependent routine staining blockage. Finally, the immunofluorescence technique provides a high signal-to-noise ratio and is an excellent method for making high-quality microphotographs of human mast cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Histochemical heterogeneity of mast cells in rat dermis

The dermal mast cells of Wistar rats were studied following fixation in either 10% phosphate buffered formalin or Carnoy's solution and staining with either toluidine blue or alcian blue:safranin O. Granules of mast cells appeared heterogeneous following fixation with formalin and staining with alcian blue:safranin O, but not when stained with toluidine blue. The number of mast cells observed in skin fixed in Carnoy's solution was greater than the number observed in equivalent samples of skin fixed in formalin (p < 0.01) when both samples were stained with toluidine blue. In formalin fixed skin stained with alcian blue:safranin O, there were three populations of mast cells designated as "blue," "red" or "mixed." "Blue" mast cells, containing only alcian blue stained granules, "red" mast cells, containing only safranin O stained granules, and "mixed" mast cells, containing both alcian blue and safranin O stained granules accounted for 77.6 +/- 3.0, 6.6 +/- 2.5 and 15.8 +/- 2.5% of the total mast cell population, respectively. In skin specimens fixed in Carnoy's solution and stained with alcian blue:safranin O the mast cells contained only blue granules (alcian blue positive). The number of mast cells observed in Carnoy's fixed skin sections was less than the number seen in formalin fixed skin sections when both were stained with alcian blue/safranin O. This indicates that there is a group of mast cells which do not stain with safranin O after fixation with Carnoy's solution.

Investigation of basophil cell proteinase release in progressive systemic sclerosis

The aim of this study was to evaluate the function of basophil granulocytes in 37 patients with progressive systemic sclerosis (PSS). The in vitro proteinase release test using Chromozyme TH as a chromogenic substrate was performed to measure the basophil cell releasability. Anti-IgE, calcium-ionophore (A 23187) and N-formyl-methyonil-leucyl-phenylalanine were used as activatory agents. Our results showed that the reactivity pattern to those agents did not differ in PSS compared to controls. Patients whose basophil cells release proteinases to all of the 3 activators tended to have more severe organ symptoms compared to the rest of the patients, while teleangiectasia was significantly less frequently (p < 0.02) found in cases with proteinase release. These findings suggest that there may be a certain relationship between basophil function and severity of the PSS.

Eccrine syringofibroadenoma (Mascaro): an ultrastructural study

To confirm the eccrine acrosyringeal differentiation of eccrine syringofibroadenoma (ESFA) and to elucidate the histogenesis of its angiofibrotic stroma, a case of ESFA from a 45-year-old man was examined by light and electron microscopy. Histologically, the parenchyma featured anastomosing, slender epithelial cords containing small cuboidal cells and occasional duct-like structures. The stroma had increased numbers of mast cells, increased capillaries with swollen endothelial cells, and prominent fibrosis. Ultrastructurally, the following findings were characteristic of ESFA: a) abundant glycogen particles in epithelial cells, b) numerous intracytoplasmic and extracellular spaces lined with microvilli, c) intraepithelial duct formation, consisting of microvilli, vesicles, rod-shaped dense bodies, multivesicular dense bodies, and peripheral network of tonofilaments, and d) large numbers of mast cells, closely associated with fibroblasts, surrounding increased numbers of capillaries containing swollen endothelial cells. These ultrastructural features support the acrosyringeal differentiation of ESFA. We hypothesize that mast cell hyperplasia and degranulation may play an important role in the formation of the angiofibrotic stroma.

Dermal mast cell granules bind interstitial procollagenase and collagenase

In order to identify structures in human skin that bind collagenase, sections from frozen or paraffin-embedded skin were incubated with either procollagenase or activated collagenase. After washing, bound procollagenase or collagenase was detected by immunofluorescence microscopy. In normal skin, procollagenase bound only to isolated granular dermal cells that were identified as mast cells on the basis of staining with fluoresceinated avidin and pinacyanol erythrosinate. When mast cells were degranulated by exposure to the ionophore A23187, extracellular granules bound procollagenase. Of various pathologic conditions examined, the highest binding of procollagenase occurred in specimens of urticaria pigmentosa. Procollagenase bound to granular cells and to abundant granules scattered throughout the dermis. Binding could be abolished by pre-treatment of tissue sections with heparinase or by pre-incubation of procollagenase with soluble heparin, suggesting that heparin is the binding agent in the granules. Activated collagenase also bound to dermal mast cells but in addition bound strongly to the dermal collagen. Enzymatic activity of activated collagenase was not inhibited by heparin in concentrations up to 10 mg/ml. There is evidence that mast cell tryptase can contribute to procollagenase activation. This study further supports a role for mast cells in collagenolysis by demonstrating that heparin from mast cells binds procollagenase and possibly serves as a reservoir for procollagenase, which may then subsequently be activated.

Morphological study of bovine lung grafted into the hamster cheek pouch

The hamster cheek pouch has been used extensively to study the modulation of microvascular responsiveness of native and transplanted tissues, because it is immunologically privileged. The purpose of this study was to determine the structural changes that occur over time in bovine lung tissue (donor) that was grafted into the hamster cheek pouch (recipient). Lungs from adult cows were cut into 1-mm-thick slices and grafted into the cheek pouch of adult Syrian golden hamsters (n = 60). After induction of anesthesia, bovine lung tissue was placed under the avascular tissue covering the cheek pouch, and the overlying skin was sutured. Intravital microscopy (IM) and transmission electron microscopy (TEM) of the cheek pouch and grafted tissue were performed 1, 7, 14, and 28 days after grafting. By using IM, we found blood flow throughout the grafted bovine lung tissue between days 7 and 14 post-transplantation. Both IM and TEM showed that the grafted tissue contained patent microvessels anastomosing with cheek pouch microvessels, alveolar structures, and interstitial tissue. Mast cell infiltration around microvessels of the grafted tissue was evident in all animals between days 14 and 28 post-grafting. No other inflammatory cells were identified throughout the observation period. By day 28 post-grafting, the entire lung tissue became fibrotic. We conclude that bovine lung tissue can be successfully transplanted into the hamster cheek pouch, that blood flow is established throughout the graft, and that prominent mast cell infiltration is associated with fibrosis of the graft 28 days after transplantation. We suggest that this model can be useful in studying pulmonary microvascular responses in situ.

Mast cells and tissue reaction to intraperitoneally implanted polymer capsules

The inflammatory reaction to implanted biomaterials often compromises the clinical usefulness of implantable devices. Dexamethasone, an anti-inflammatory agent, acts on macrophages to decrease production of inflammatory mediators, and on mast cells to prevent degranulation. Systemic administration of dexamethasone (dms) in rats decreases the tissue reaction to intraperitoneally implanted vinyl chloride-acrylic copolymer capsules. Local release of even smaller amounts of dms from a polymeric substrate placed inside an acrylic copolymer capsule may control the tissue reaction while avoiding the undesirable side effects of systemic treatment. Such a system also allows investigation of the local effect of soluble molecules on tissue-material interactions without altering the surface properties of the implant or adding the effect of a releasing material. In the present study, we investigated the effect of dms released from ethylene vinyl acetate (EVAc) rods placed in acrylic copolymer capsules and implanted in the peritoneal cavity of rats. In vitro the release of dms from EVAc rods was quasilinear for 5 weeks. When implanted intraperitoneally into rats, polymer capsules containing EVAc/dms rods generated a tissue reaction that was significantly thinner and featured fewer fibroblast and collagen layers than that around capsules containing pure EVAc rods at all time points studied. The tissue reaction layer was also thinner than that previously described in rats treated systemically with dms. The trabeculae of implants with dms-loaded EVAc rods contained significantly more intact mast cells than implants with EVAc alone, suggesting that degranulation of mast cells is involved in the tissue reaction to intraperitoneal polymer implants.

The effect of electrical stimulation on the number of mast cells in healing wounds

Many cutaneous disorders are associated with activation or increased numbers of mast cells. Electrical stimulation has been shown to be effective in treating many of these disorders. This study is designed to examine the effect of electrical stimulation on mast cells in acute wounds. Four pathogen-free pigs received 20 wounds, each of which was subjected to biopsy at various times after wounding. Half of the wounds were treated with electrical stimulation and the other half were treated with a sham electrode. The biopsy specimens were fixed in Carnoy's medium and stained with alcian blue and Nuclear Fast Red. Mast cells from both sets of wounds were counted and analyzed. Highly significant reductions in the number of mast cells were seen with electrical stimulation on days 1 and 2 compared with nonstimulated control wounds. Electron microscopy was performed to compare the stimulated and control mast cells for characteristic features in morphology, location, and evidence of degranulation. Electrical stimulation did not appear to induce degranulation. The ability of electrical stimulation to decrease the number of mast cells may be related to a reduction of either proliferation or migration of these cells and may prove to be a valuable therapeutic technique.

The mast cell in health and disease

The presence of mast cells, often in an activated state or increased numbers, has been noted in various cutaneous disorders. Recent studies suggest that mast cells are of primary importance in these conditions and their presence does not merely represent a secondary event. This review focuses on atopic dermatitis, contact hypersensitivity reactions, bullous pemphigoid, fibrosing conditions, neurofibromatosis, wound healing, polycythemia vera, and psoriasis, in which there is significant evidence to indicate a pathophysiologic role for mast cells.

Mast cells, nerves and fibrosis in the appendix: a morphological assessment

Mast cells are closely associated with nerves in the mucosa of the appendix vermiformis, and obliteration of the appendiceal lumen by fibrous tissue is accompanied by neurogenous hyperplasia. However, changes in the density of mast cells in this process have not been reported. Accordingly, fibrosis was graded in haematoxylin and eosin sections from 46 samples of human appendix. This was compared with mast cell number in toluidine blue-stained slides and nerve density in PGP9.5-immunoreactive sections. In the mucosa, the mast cell number in the samples with minimal fibrosis was three times greater than in those classified as normal (P less than 0.0001), and this declined in the more fibrotic samples. The mucosal nerve scores paralleled the mucosal mast cell changes, and stereological analysis revealed a correlation of mast cell number and nerve density within the lamina propria of the same specimens (r = 0.49-0.90). In the submucosa, mast cell numbers and nerve scores were not significantly different in the different histological grades and obliterated samples resembled normal submucosa, except that a dense axial block of nerve staining was often present. The progressive fibrotic changes in appendices provide a human model for studying the relationships of nerves, mast cells, and fibrosis in the gastrointestinal tract.

Mast cells enhance migration and proliferation of fibroblasts into an in vitro wound

The effects of mast cells (MC) in an in vitro wound model were studied. The model consisted of rat peritoneal MC cultured on confluent monolayers of 3T3 fibroblasts (MC/3T3). A linear wound was performed by cutting along the midline and scraping one half of the monolayer. After 42 h fibroblasts were counted in the scraped area of the wound. In the MC/3T3 cocultures 27.6 +/- 2.1 fibroblasts were found compared to 16.6 +/- 0.9 in the 3T3 cultures. The most significant increase in the number of fibroblasts was obtained upon activation of the MC with anti-IgE antibodies immediately after wound production (39.9 +/- 2.1). Stimulation with compound 48/80 had a weaker effect (32.7 +/- 1.5). Incubation of 3T3 wounded monolayers with supernatants of anti-IgE- or compound 48/80-activated MC, or with sonicated MC, induced an increase in fibroblast number similar to that found in unactivated MC/3T3. [3H]Thymidine incorporation followed by autoradiography was performed to assess fibroblast mitosis. The highest number of labeled fibroblasts beyond the wound line was found in immunologically activated MC/3T3 (29.7 +/- 4.4), followed by compound 48/80-activated MC/3T3 (18.4 +/- 1.5), MC/3T3 (15.1 +/- 3.6), and 3T3 (10.6 +/- 2.6). After addition of aphidicolin, which inhibited fibroblast mitosis, MC were still effective in enhancing fibroblast migration. In all the cocultures MC were observed to have migrated alongside fibroblasts. Thus merely the presence of MC adhering to wounded fibroblast monolayers significantly enhanced migration and proliferation of the fibroblasts. A further increase was achieved by immunological activation of the MC. We therefore suggest that MC have a facilitating role in this in vitro wound model.

The human skin mast cell

The abundance of mast cells in human dermis, together with their ability to release a variety of vasoactive and pro-inflammatory mediators following cross-linkage of their cell-surface receptors for IgE, enables these cells to provide an effective defence mechanism within this organ. A similar defensive function is attributed to mast cells of other human organs such as intestine and lung which are in contact with the external environment and therefore susceptible to infiltration by foreign allergens and micro-organisms. However, mast cells of the skin apparently differ from those present in lung and intestine in being activated for histamine release by a variety of endogenous neuropeptides which stimulate the rapid release of histamine in the virtual absence of eicosanoids. This would provide a mechanism of neurogenic control of a variety of homeostatic functions such as blood flow, angiogenesis and fibroblast proliferation. Such processes would aid in the remodelling of tissue during wound healing, and increased numbers of mast cells have been noted around healing wounds of rat skin and areas of developing fibrosis. Neuropeptides modulate the activity of a variety of immuno-competent leucocytes including macrophages, monocytes and lymphocytes. The findings that skin mast cells are activated by neuropeptides suggest that these cells may also be included amongst those involved in neuro-immune interactions. Activation of skin mast cells by non-immunological stimuli may contribute to the aetiology of some forms of skin disease. Patients with chronic idiopathic urticaria appear to have enhanced vascular responsiveness to intradermal injections of the histamine liberator codeine suggesting that this disease may involve hyper-responsiveness of their mast cells to endogenous non-immunological stimuli. The findings of large increases in histamine accompanied by small increases in PGD2 in venous effluent of thermally challenged limbs of patients with cold- or heat-induced urticaria may suggest that their mast cells had been activated by a non-immunological stimulus. However, the interpretation of results gained using such relatively complex in-vivo systems are difficult, as the cellular origin of the detected mediators is by no means clear. However, it is hoped that in the future the alliance of newly developed in-vitro techniques to investigate mast cell function together with in-vivo methods to investigate their interaction with elements in their tissue environment will greatly increase our understanding of the role of the human skin mast cell in health and disease.