Definition, classification, and routine diagnosis of urticaria: a consensus report

Urticaria is a well-known disease entity; however, with an increasing understanding of the molecular mechanisms involved in its pathogenesis, there is also growing evidence for a heterogeneity of urticaria. Currently it is sometimes difficult to compare divergent data reported by different centers researching urticaria due to a lack of precisely described patient populations. A consensus definition and classification of the disease and its subtypes, taking into account new developments, are therefore needed. In addition, this consensus report provides a guideline for diagnostic procedures in different subtypes of urticaria.

Adhesion molecules and cellular infiltrate: histology of urticaria

Urticarial reactions are characterized by dermal capillary dilatation and edema, associated with a variably intense mixed inflammatory infiltrate consisting of neutrophils, eosinophils, T-helper lymphocytes, and activated macrophages. Mast cell numbers are moderately increased by a factor of 2.4, in contrast to mastocytosis where numbers are much higher (5-48-fold increase). In urticarial vasculitis there is in addition endothelial damage, leukocytoclasia, and fibrin and complement deposition. The emigration of leukocytes is regulated by vasoactive and chemotactic mediators released firom mast cells, inducing a sequential upregulation of endothelial adhesion molecules (P-selectin, E-selectin, ICAM-1, and VCAM-1), of beta2-integrins on leukocytes, and of cytokines on endothelial, epithelial, and infiltrating cells. In nonlesional skin, there is also an increase of mast cells and an upregulation of endothelial adhesion molecules, probably due to molecules in the circulation of which P-selectin and TNFalpha have so far been demonstrated. Whereas these data provide a molecular basis for the understanding of variations in mast cell-dependent pathology, they underline the fact that they are not diagnostic for different types of urticaria, except for urticarial vasculitis and mastocytosis.

Human skin mast cells rapidly release preformed and newly generated TNF-alpha and IL-8 following stimulation with anti-IgE and other secretagogues

Several groups have previously reported that rodent or human leukemic mast cells produce inflammatory cytokines such as TNF-alpha and IL-8 as well as the pro-allergic cytokines IL-4, IL-5 and IL-13. Comparatively little is known, however, regarding the ability of normal human skin mast cells to secrete these factors following either IgE-dependent or IgE-independent modes of activation. We therefore investigated whether normal human skin mast cells produce these cytokines following stimulation by a variety of secretagogues. Enriched isolated skin mast cells released both TNF-alpha and IL-8 following activation with either anti-IgE, SCF, substance P, compound 48/80 or A23187. This release was dose- and time-dependent, with maximal levels being reached within 4 h of stimulation involving, in part, the secretion of preformed stores of both cytokines. In accordance with this, using lysates of highly purified (>90%) skin mast cells, we could demonstrate that both TNF-alpha and IL-8 mRNA and protein were present in both unstimulated as well as stimulated mast cells. In stark contrast to these results, no significant levels of either IL-4, IL-5 or IL-13 were detected, regardless of the secretagogue used or the period of stimulation. These results show that human skin mast cells are capable of rapidly secreting pro-inflammatory cytokines like TNF-alpha and IL-8 following IgE-dependent activation and stimulation by the neuropeptide substance P, SCF and the basic polypeptide analogue compound 48/80. In contrast to other types of human mast cells however, human skin mast cells were incapable of secreting IL-4, IL-5 or IL-13 in these settings.

Angiotensin-converting enzyme inhibitors as inducers of adverse cutaneous reactions

Since adverse effects due to angiotensin-converting enzyme (ACE) inhibitors frequently occur in cutaneous locations, this review summarizes the spectrum of expected and unexpected adverse effects of these drugs, possible associated mechanisms, and their basic functions for dermatologists. ACE inhibitors block the activity of the metalloproteinase ACE by binding to its active site, thus displacing angiotensin I and preventing its conversion to vasopressive angiotensin II. Furthermore, ACE degrades bradykinin, substance P, enkephalins and some of the reproductive peptide hormones. The overall incidence of adverse effects to ACE inhibitors is estimated at 28%, approximately half of which occurs in the skin. General reactions are first-dose hypotension, hyperkalaemia and renal failure. Cutaneous reactions comprise life-threatening angioedema, pruritus, bullous eruptions, urticaria, other generalized rashes, photosensitivity and hair loss. ACE inhibitors thus mimic a broad variety of skin diseases, why these drugs should be thought of when sudden, unexplainable skin eruptions are observed.

Effect of granulocyte macrophage colony-stimulating factor in a patient with benign systemic mastocytosis

We report the in vitro and in vivo effects of granulocyte macrophage colony stimulating factor (GM-CSF), a known inhibitor of in vitro mast cell differentiation, in a patient with benign, adult-onset systemic mastocytosis. In vitro effects of GM-CSF on bone marrow cultures before the start of treatment showed a marked inhibition of mast cell marker expression [tryptase, Kit, and high-affinity IgE receptor (FcepsilonRIalpha)] at both protein and mRNA levels. Therefore, the patient was treated with daily injections of GM-CSF for 10 weeks. After an initial improvement, increasing worsening of clinical symptoms was noted, and the patient refused further treatment. Lesional skin biopsies showed an increase of toluidine blue-positive mast cells, compared with uninvolved skin, with further significant increase after treatment. Similar results were obtained on staining for mast cell-specific tryptase and Kit, as well as for CD1a and FcepsilonRIalpha. These findings show that GM-CSF inhibits human bone marrow mast cell differentiation in vitro, and also in mastocytosis. However, GM-CSF apparently enhances recruitment of mast cell as well as dendritic cell precursors into the tissue during systemic treatment. These findings and the observed adverse clinical effects in the present patient make it unlikely that GM-CSF monotherapy will be beneficial for the treatment of mastocytosis.

Acute herpes zoster neuralgia: retrospective analysis of clinical aspects and therapeutic responsiveness

BACKGROUND

Although the efficacy of modern antiviral agents for the treatment of herpes zoster is unquestioned, their ability to affect the associated pain remains controversial.

OBJECTIVE

We have therefore evaluated the inpatient hospital records of 550 patients with herpes zoster with regard to pain-related clinical aspects and therapeutic responsiveness.

METHODS

Intensity of pain was quantified by calculating a daily pain equivalence index (PEI) on the basis of different classes of pain medication and the number of tablets used in each category.

RESULTS

The mean age of patients was 66.7 years, cranial segments were predominantly involved (55%), 64% of patients suffered from associated diseases and 77% experienced herpes-related pain. The PEI was 0.90 in the entire patient population, with significantly higher values in women and in patients with 3 or more associated diseases. It was lower in sacral and cranial nerve involvement, and it decreased rapidly in patients prior to discharge from hospital. Although there were significant differences in hospital stay between patients who received aciclovir and those who did not (mean 20.3 vs. 23.8 days), and for high- versus low-dose oral or intravenous administration, no significant differences were noted between the two groups for initial PEI values and during the course of observation, irrespective of the route of administration or the dose of aciclovir and the individual patient's PEI value. The groups were otherwise closely similar with regard to basic demographic and clinical data. 23.3% predominantly aged female patients with more associated diseases than the total patient population had a persistently elevated PEI and stayed in hospital beyond 21 days (mean 35.1 days), representing patients who went on to postherpetic neuralgia.

CONCLUSION

These data further delineate clinical aspects of acute herpes zoster neuralgia, underline the unsolved therapeutic problems associated with this condition despite otherwise effective antiviral treatment, and characterise a subgroup of patients at risk to develop postherpetic neuralgia.

The ascomycin macrolactam pimecrolimus (Elidel, SDZ ASM 981) is a potent inhibitor of mediator release from human dermal mast cells and peripheral blood basophils

BACKGROUND

The ascomycin macrolactam pimecrolimus (Elidel, SDZ ASM 981) has recently been developed as a novel and cell-selective inhibitor of inflammatory cytokine secretion; it has fewer adverse effects than currently available drugs.

OBJECTIVE

In this study, we investigated the capacity of pimecrolimus to directly inhibit in vitro mediator release from human skin mast cells and basophils.

METHODS

Purified cutaneous mast cells or basophil-containing peripheral blood leukocytes were obtained from healthy human donors and preincubated with pimecrolimus (0.1 nmol/L to 1 micromol/L) in the absence or presence of its specific antagonist (rapamycin), cyclosporin A (100 nmol/L to 1 micromol/L), or dexamethasone (1 micromol/L) and then stimulated with anti-IgE or with calcium ionophore A23187 plus phorbol myristate acetate. Cell supernatants were kept for analysis of histamine, tryptase, LTC4, and TNF-alpha.

RESULTS

Pimecrolimus caused a strong and dose-dependent inhibition of anti-IgE--induced release of histamine from mast cells and basophils (maximally 73% and 82%, respectively, at 500 nmol/L pimecrolimus) and of mast cell tryptase (maximally 75%) and a less pronounced inhibition of LTC4 (maximally 32%) and of calcium ionophore plus phorbol myristate acetate--induced mast cell TNF-alpha release (90% maximum at 100 nmol/L pimecrolimus). In contrast, inhibition achieved during mast cell histamine release was maximally 60% with cyclosporin A and only 28% with dexamethasone.

CONCLUSION

These data demonstrate a marked inhibitory capacity of pimecrolimus on mediator release from human mast cells and basophils with a potency exceeding that of cyclosporin A and dexamethasone. Pimecrolimus might thus be expected to be effective in the treatment of mast cell-- and basophil-dependent diseases.

The pharmacologic profile of desloratadine: a review

Desloratadine is a new agent for the treatment of diseases such as seasonal allergic rhinitis and chronic urticaria. The pharmacologic profile of desloratadine offers particular benefits in terms of histamine H1-receptor binding potency and H1 selectivity. Desloratadine has a half-life of 21-24 h, permitting once-daily dosing. No specific cautions are required with respect to administration in renal or hepatic failure, and food or grapefruit juice have no effect on the pharmacologic parameters. No clinically relevant racial or sex variations in the disposition of desloratadine have been noted. In combination with the cytochrome P450 inhibitors, ketoconazole and erythromycin, the AUC and Cmax of desloratadine were increased to a small extent, but no clinically relevant drug accumulation occurred. With high-dose treatment (45 mg/day for 10 days), no significant adverse events were observed, despite the sustained elevation of plasma desloratadine levels. Specifically, desloratadine had no effects on the corrected QT interval (QTc) when administered alone, at high dose, or in combination with ketoconazole or erythromycin. Preclinical studies also show that desloratadine does not interfere with HERG channels or cardiac conduction parameters even at high dose. Desloratadine is nonsedating and free of antimuscarinic/anticholinergic effects in preclinical and clinical studies. Novel antiallergic and anti-inflammatory effects have also been noted with desloratadine, a fact which may be relevant to its clinical efficacy.

GM-CSF downmodulates c-kit, Fc(epsilon)RI(alpha) and GM-CSF receptor expression as well as histamine and tryptase levels in cultured human mast cells

GM-CSF is known primarily as a hematopoietic growth factor, but it has also been shown to inhibit mast cell differentiation in vitro. In order elucidate the mechanisms involved, we investigated the effects of GM-CSF in vitro on the differentiation of human leukemic mast cells (HMC-1 cells) and normal cord blood-derived mast cells (CBMC) under the influence of SCF, NGF, and fibroblast supernatant (FS). Under all culture conditions, GM-CSF induced a dose- and time-dependent reduction in intracellular histamine levels, tryptase activity, and numbers of cells immunoreactive for c-Kit and FcepsilonRIalpha. This effect leveled off between 10-100 ng/ml and after 4 days of culture. There was an associated decrease in mRNA expression for c-kit, FcepsilonRIalpha and tryptase. In contrast, no significant changes in the expression of the NGF receptor TrkA were noted under the same conditions. The GM-CSF receptor was found in HMC-1 cells and CBMC at both the mRNA and protein levels, but its expression decreased during culture with FS, and even more markedly during culture with GM-CSF. GM-CSF thus selectively inhibits in vitro induction and/or upregulation of all major mast cell characteristics in HMC-1 cells and CBMC irrespective of the growth factors present, and a concomitant downregulation of GM-CSF receptors can counteract these effects. GM-CSF may therefore function as a regulatory factor in mast cell growth and differentiation under normal and pathological conditions.

Mastocytosis: recent advances in defining the disease

Mastocytosis is a rare disease characterized by a primary pathological increase in mast cells in different tissues, which may present in a variety of clinical patterns. Major advances have been made in recent years in the understanding of the pathogenesis of mastocytosis. This review is aimed at familiarizing dermatologists with these recent findings, and at exploring their possible implications for the diagnosis and treatment of the condition. The heterogeneous clinical presentation of mastocytosis is detailed with respect to the type of skin lesions, age at onset, family history, organ systems involved, associated haematological disorders and prognosis. Recent genetic findings also indicate different pathogenetic forms of mastocytosis, as adult patients and those with associated haematological diseases usually express activating mutations of the stem cell factor receptor c-kit, whereas most cases of childhood-onset and familial mastocytosis seem to lack these mutations. Despite the presence of c-kit mutations, patients with cutaneous lesions generally have a good prognosis, even when there is involvement of other organs. Some patients, particularly those with childhood-onset disease, experience spontaneous remission, mostly by puberty. c-kit mutations do not explain the initial cause of mastocytosis, and their prognostic significance is as yet unclarified, as is the pathogenesis in patients without the mutations. Furthermore, these novel findings have as yet not resulted in a more effective treatment of the cause of the disease, so that counselling, prevention of exposure to mast cell secretory stimuli, and symptomatic treatment remain the mainstays of current patient management.

Retinoic acid up-regulates myeloid ICAM-3 expression and function in a cell-specific fashion--evidence for retinoid signaling pathways in the mast cell lineage

Investigation of mast cell responsiveness toward retinoic acid (RA) revealed selective promotion of ICAM-3 expression in the human mast cell line HMC-1. This process was dose- and time-dependent and detectable by flow cytometry, Western blot analysis, ELISA, and Northern blot analysis. ICAM-3 modulation was found to be cell-type dependent, detectable also for HL-60 cells and monocytes but not U-937 and only weakly for KU812 cells. Terminally differentiated skin mast cells also failed to up-modulate their ICAM-3, suggesting the requirement for some degree of immaturity for the process. RA-mediated effects on ICAM-1 expression, studied in parallel, were clearly distinct from those on ICAM-3. Investigation of retinoid receptor expression, known to mediate intracellular RA signaling, revealed presence of RAR alpha, RAR gamma, RXR beta, and RXR gamma transcripts in all cell lines studied, and HMC-1 cells were the only line lacking RXR alpha. RAR beta, not expressed at baseline, was induced by RA in a fashion obviously correlating with ICAM-3 up-regulation. Increased ICAM-3 expression was of functional significance, such that processes stimulated or co-stimulated via ICAM-3 (homotypic aggregation, IL-8 secretion) were clearly enhanced upon RA pretreatment, suggesting that RA may contribute via hitherto unrecognized pathways to immune function and host defense.

Expression of mast cell growth modulating and chemotactic factors and their receptors in human cutaneous scars

In order to explore possible mechanisms involved in the previously documented turnover of mast cell subpopulations in human cutaneous scars, we have examined selected factors known to stimulate and/or modulate mast cell hyperplasia (SCF, NGF, TGFbeta1, GM-CSF) and their receptors in human cutaneous scar tissue. On immunohistochemistry, numbers of SCF- and TGFbeta1-positive cells were significantly increased in the epidermis and throughout the dermis in scars (n = 27) of varying ages (4-369 d old), compared with normal skin (n = 12). Furthermore, TRbetaRI, II, and the NGF-p75 receptors were significantly increased in the epidermis, TRbetaRI and NGF-TrkA throughout the dermis, and TRbetaRII, NGF-p75, and GM-CSFR only in the mid- and lower dermis of scars. NGF and GM-CSF expression was in contrast scarce and weak, with no differences between normal skin and scars. In tissue extracts, mRNA levels of SCF, TGFbeta1, TRbetaI and II, and both NGF-receptors, but not GM-CSFR, were significantly increased as well. TRbetaI and II were identified in up to 90% and 83%, respectively, of isolated normal skin mast cells on flow cytometry, and GM-CSFR and NGFR-p75 were identified on 70% and 73%, respectively, of avidin-positive normal mast cells on double immunofluorescence microscopy. As described before for the SCF receptor KIT, GM-CSFR and NGFR-p75 were partly or entirely downregulated on avidin-positive mast cells in scars. The marked upregulation of TGFbeta1, its type I and II receptors, and SCF suggest that these factors play a major role in the orchestration of mast cell increase in human cutaneous scars whereas the role of NGF and GM-CSF is less clear, despite the significant upregulation of their receptors.

Novel unconventional therapeutic approaches to atopic eczema

Atopic eczema is a chronic, recurrent, multifactorial skin disease, and, accordingly, there are numerous therapeutic options for its symptomatic treatment. Conventional medications are however often unsatisfactory for many patients because of adverse effects on long-term use. For this reason, patients often readily welcome unconventional therapeutic approaches. We present here a selected number of such treatment modalities, namely gamma-linolenic acid, Chinese herbal tea, diets eliminating allergens, pseudoallergens, metal salts and sodium, and bioresonance. When stringent scientific criteria are applied in the evaluation of such study results, none of the reviewed alternative treatments provides unequivocal, convincing evidence of its efficacy, even when double-blind, placebo-controlled studies are available. With Chinese herbal tea, potentially serious adverse effects should be considered as well. Any new type of unconventional therapy should thus be thoroughly evaluated and shown to be equal or superior to conventional treatments with regard to both efficacy and tolerability before it is recommended for use in clinical practice.

Mast cells as initiators of immunity and host defense

Until recently, mast cells have been viewed primarily as harmful because of their key role as effector cells of allergic and potentially lethal anaphylactic reactions. Their contribution to human health appeared instead to be limited to the elimination of parasites. There is, however, growing evidence for additional beneficial functions of mast cells, particularly regarding the initiation of acquired immune reactions. Thus, mast cells can phagocytize diverse particles, take up antigens, and express a number of receptors, particularly MHC class I and II antigens, ICAM-1 and -3, CD43, CD80, CD86 and CD40L which allow them to interact with T and B lymphocytes. They can also secrete numerous cytokines that induce and enhance recruitment and functions of lymphocytes. Finally, there is good evidence that mast cells present e.g. pollen and bacterial antigens, respond to bacterial superantigens, but fail to react to endogenously produced antigens or superantigens. Mast cells can also activate B cells directly to produce IgE, but this activity and the ability to produce IL-4 or IL-13 is restricted primarily to basophil leukocytes and mucosal mast cells. Finally, recent evidence attributes a pivotal role to the cells in natural immunity to bacteria. There is also emerging evidence that mast cells can downmodulate the immune response. While these data require further clarification, the basic ability of mast cells to initiate innate and acquired immune reactions can no longer be questioned.

Effects of retinoids on in vitro and in vivo IgE production

BACKGROUND

Retinoids modulate the growth and number of different cell types, including B cells. We could previously show that retinoic acid (RA) strongly inhibits CD40 + IL-4-mediated IgE production in vitro. The aim of the present study was to extend these findings regarding the potential use of retinoids for the treatment of allergic diseases.

METHODS

In vitro IgE production was studied in anti-CD40 + IL-4-stimulated peripheral blood mononuclear cells (PBMC) from allergic donors in the presence of 10(-15)-10(-5) M all-trans and 13-cis RA and in ovalbumin (OVA)-sensitized BALB/c mice treated with RA (20 mg/kg) before and during sensitization. IgE and IgG1 levels were determined in the sera of the mice at day 21 after 2 injections (days 1 and 8) of aluminum hydroxide-absorbed OVA.

RESULTS

All-trans and 13-cis RA inhibited in vitro IgE production from PBMC in a dose-dependent manner, but were more efficient in atopic dermatitis patients with low total serum IgE levels (< 400 kU/ml), maximal inhibition for all-trans RA at 10(-7) M (87%) and for 13-cis RA at 10(-5) M (96%) compared to patients with high serum IgE levels (>2,000 kU/ml), maximal inhibition for both all-trans and 13-cis RA at 10(-5) M (53 and 39%, respectively). In contrast, the in vivo data from OVA-sensitized mice revealed comparable total IgE and IgG1 levels in control versus all-trans RA or CD336-treated groups, specific IgE was even higher in the CD336-treated group (n = 10, 2,814 ng/ml), and was comparable in mice treated with OVA alone or with additional all-trans RA (n = 10, 1,447 and 1,354 ng/ml, respectively).

CONCLUSIONS

These results indicate that the efficacy of retinoids to inhibit IgE production in vitro depends on the frequency of switched cells in the peripheral blood and that in an in vivo model using OVA-sensitized mice, retinoids fail to inhibit IgE production.

alpha-Melanocyte stimulating hormone acts as a selective inducer of secretory functions in human mast cells

In the present study, we have investigated the pro-opiomelanocortin (POMC)-derived neuropeptide alpha-MSH for its ability to modulate activation of human mast cells. The in vitro ability of purified human skin mast cells to secrete various types of mast cell mediators was monitored in response to alpha-MSH at the mRNA and at the protein level. Picomolar concentrations of alpha-MSH induced a dose-dependent release of histamine from isolated human skin mast cells and from skin punch biopsies. However, no effect of alpha-MSH was seen regarding the expression of IL-1, IL-6, IL-8, TGF-beta, and TNF-alpha. Melanocortin receptor MC-1 was identified at the transcriptional level by RT-PCR analysis but not at the protein level, whereas, in leukemic human mast cells (HMC-1), the mRNAs and the proteins for the MC-1 and MC-5 receptor were identified. These results suggest that alpha-MSH may selectively induce acute inflammatory effects via secretion of histamine.

Anti-FcepsilonRIalpha serum autoantibodies in different subtypes of urticaria

BACKGROUND

In recent years, a histamine-releasing anti-FcepsilonRIalpha autoantibody has been demonstrated in about one-third of patients with chronic urticaria. However, its clinical significance is still unclear. The objective was to detect a possible correlation between the occurrence of the anti-FcepsilonRIalpha autoantibody and the clinical type or cause of urticaria.

METHODS

Sera from 66 consecutively seen in- and outpatients with various types of urticaria and five healthy controls were examined for the presence of anti-FcepsilonRIalpha autoantibodies with a sandwich ELISA technique. In addition, basophil histamine release was studied in 13 autoantibody-positive sera.

RESULTS

Anti-FcepsilonRIalpha autoantibodies were found in 17/48 patients with chronic urticaria, in 2/4 with angioedema, in 1/2 with urticarial vasculitis, and in 2/11 with dermographic urticaria. However, no anti-FcepsilonRIalpha autoantibodies were detected in acute, cold, or delayed-pressure urticaria; in urticaria pigmentosa; or in normal controls. Of all chronic urticaria patients, 22 were classified as idiopathic since no underlying cause could be found. Of this group, seven were seropositive for anti-FcepsilonRIalpha. However, anti-FcepsilonRIalpha was also found in patients who went into remission after treatment of identified causes; namely, in one with type I allergy, one with drug intolerance, one with Helicobacter infection, and six with food intolerance. The autoantibody was also detected in 2/4 patients with associated autoimmune diseases. Functional activity was shown in basophil histamine release in 3/4 autoantibody-positive sera of patients with chronic idiopathic urticaria and in 4/6 autoantibody-positive sera of patients who went into remission after the treatment of underlying causes.

CONCLUSIONS

These data confirm that anti-FcepsilonRIalpha autoantibodies in urticaria are mostly found in chronic urticaria. Furthermore, their detection independently of the apparent cause of the urticaria suggests that as yet unidentified mechanisms must be operative, possibly related to the chronic inflammatory process and/or individual predispositions that favor their induction.

Preclinical diagnosis of pseudoxanthoma elasticum - methodological restrictions and ethical problems

Pseudoxanthoma elasticum (PXE) is an inherited connective tissue disease. Only recently, mutations in the MRP6 gene on chromosome 16p13.1 have been identified in PXE families. Up to now, predictive testing has not been available. Since ultrastructural connective tissue alterations in overtly normal skin of predilection sites have supported preclinical diagnosis in children of affected individuals, we have screened the daughters of a PXE patient for these alterations. The patient's biopsy from lesional skin revealed elastin and collagen fibril abnormalities, but biopsies from the clinically inconspicuous daughters showed only ultrastructural alterations of collagen fibrils. These findings are inconclusive regarding the diagnosis of PXE in the daughters. Predictive or preclinical diagnosis of incurable, late-onset disorders creates complex social, ethical, and legal problems which call for special management strategies.

Distribution and potential biologic function of the thrombin receptor PAR-1 on human keratinocytes

Thrombin has recently been shown not only to exert procoagulant activities, but also to induce mitogenic responses of different cell types involved in wound healing via binding to and cleavage of the thrombin receptor. In order to further explore these aspects of thrombin function, human keratinocytes (HaCaT cell line) were examined for their potential mitogenic responsiveness to thrombin and for the dependency of this process on the expression of the high-affinity thrombin receptor. Quiescent keratinocytes were stimulated in the mitogenic assay with alpha-thrombin and the thrombin receptor activating peptides TRAP42-55 (SFLLRNPNDKYEPY) and TRAP42-46 (SFLLR). A strong induction of cell proliferation was noted with alpha-thrombin, TRAP42-55 and TRAP42-46, but not with the "scrambled" peptide (FSLLR). These findings confirm that keratinocytes express the thrombin receptor and that the sequence of the first two amino acids of the generated neo-N-terminus are important for the activation of the receptor. Using cDNA fragments of the 5' coding sequence of the receptor, Northern blot analysis confirmed that HaCaT keratinocytes express the thrombin receptor. Expression of the receptor was also detected on normal human keratinocytes by immunohistochemistry and in situ hybridization. These data demonstrate the expression and biologic function of the human thrombin receptor on human keratinocytes, suggesting that thrombin, among other mediators, plays an important part in the orchestration of epidermal growth and repair processes.

Erythema elevatum diutinum--evidence for disease-dependent leucocyte alterations and response to dapsone

Erythema elevatum diutinum (EED) is a type of leucocytoclastic vasculitis of unknown aetiology. We report a patient with unusually widespread and disabling EED that had been unresponsive to corticosteroids and antibiotics, but resolved on dapsone. Biopsies of fresh lesions showed typical features of leucocytoclastic vasculitis, with prominent neutrophil infiltration, marked expression of the beta(2)-integrins CR3 and LFA-1, and increased mast cell numbers. Older lesions exhibited granulation tissue and fibrosis, macrophages were more dominant, beta(2)-integrins were expressed less markedly, and mast cell numbers were lower. In vitro chemotaxis of the patient's peripheral blood neutrophils prior to treatment showed increased random migration and directed migration towards interleukin-8 (by 424%), but a profoundly decreased responsiveness towards the bacterial peptide analogue N-formyl-methionyl-leucyl-phenylalanine (fMLP) (by 98%). These values returned to normal after dapsone treatment and clinical improvement 5 months later. These findings support the concept that in EED, activation via cytokines such as interleukin-8 allows a selective recruitment of leucocytes to tissue sites, while immune complexes and bacterial peptides sustain the persistent local inflammatory infiltrate and the leucocytoclastic vasculitis.