Evaluation of the effect of narrow band‐ultraviolet B on the expression of tyrosinase,TYRP‐1, and TYRP‐2 mRNA in vitiligo skin and their correlations with clinical improvement: A retrospective study

Narrowband‐ultraviolet B (NB‐UVB) is considered one of the main therapeutic tools in vitiligo, which is able to induce repigmentation and halt depigmentation. However, little remains known about the effect of NB‐UVB on TYR gene family, the main pigmentary genes, in vitiligo patients. To assess the effect of NB‐UVB on expression of some genes related to the pigmentary problem of vitiligo; tyrosinase (TYR), tyrosinase related protein 1 (TYRP1) and tyrosinase related protein 2 (TYRP2), mRNA levels of those genes were quantitatively evaluated by Real‐Time quantitative Polymerase Chain Reaction (RT‐qPCR) in skin biopsies obtained from 30 patients with nonsegmental vitiligo and five healthy controls. Vitiligo patients were classified into two groups; group 1, involving 12 untreated vitiligo patients and group 2, including 18 vitiligo patients treated by NB‐UVB. The levels of TYR, TYRP‐1, and TYRP‐2 mRNAs in untreated group were significantly lower than in control subjects (P < .001). In NB‐UVB treated group, the three genes were significantly higher than in group 1 (P < .001), however, they were still significantly lower than in the control subjects (P < .001). A significant positive correlation was detected between TYR and TYRP‐2 genes in group 2 (P = .03). This study demonstrated that mRNA level of TYR, TYRP‐1, and TYRP‐2, which decreased in vitiligo, was significantly increased upon treatment with NB‐UVB. Accordingly, the mechanism of depigmentation in vitiligo disease and repigmentation by NB‐UVB treatment may be related to the changes in the expression of these genes.     

黄芩甙对紫外线诱导人正常黑素细胞黑素合成的抑制作用研究

体外培养黑素细胞（MC）分别经隔日长波紫外线（UVA）或中波紫外线（UVB）照射和（或）黄芩处理后，观察细胞增殖情况，测定酪氨酸酶活性和黑素含量。结果：（1）UVA使细胞增殖增快，但剂量较大时增殖减发电量；UVB使细胞增殖减慢。二者均可使细胞酪氨酸酶活性和黑素含量高于对照组。（2）黄芩具有抑制UVA和UVB诱导的MC增殖、酪氨酸酶活性及黑素合成改变的作用。提示黄芩能抑制UVA和UVB诱导的细胞反应，还可通过抑制酪氨酸酶减少MC黑素合成。     

Preliminary evaluation of vitiligo using in vivo reflectance confocal microscopy

BACKGROUND: Vitiligo is the most common pigmentary disorder with a global incidence from 0.1% to 2% in different geographical areas. Histopathology and histochemistry have shown the reduction of melanocytes in achromic patches, but microscopic changes of lesional and non-lesional skin are still not completely understood. Reflectance confocal microscopy (RCM), based on the different light reflectance index of cutaneous structures, allowed in vivo, en face microscopic evaluation of superficial skin layers with a resolution similar to skin histology. AIM: The purpose of this study was to evaluate RCM features of lesional and non-lesional skin of vitiligo patients. Moreover, re-pigmented areas were taken into consideration in order to evaluate melanocyte response to ultraviolet B (UVB) radiation. SUBJECTS AND METHODS: Sixteen patients of different phototypes affected by active non-segmental vitiligo and 10 controls were enrolled in the study. In vivo skin imaging was done using a commercially available RCM (Lucid, Vivascope 1500. Re-pigmented areas from 6 to 16 patients (after UVB narrow-band therapy) were also examined. RESULTS: Vitiligo lesions showed the disappearance of the bright rings normally seen at the dermo-epidermal junction. Moreover, non-lesional skin of vitiligo patients showed unexpected changes as the presence of half-rings or scalloped border-like features of the bright papillary rings. In re-pigmented areas after UVB narrow band therapy, the presence of activated, dendritic melanocytes was seen. CONCLUSIONS: Considering our results, and following further studies, RCM clinical applications could be used in the therapeutic monitoring and evaluation of the evolution of vitiligo.     

Increased micronucleus frequency in phytohaemagglutinin-stimulated blood cells of patients with vitiligo

Background Vitiligo is a relatively common, acquired pigmentary disorder characterized by areas of depigmented skin resulting from loss of melanocytes in the epidermis. Although several hypotheses have been proposed for the aetiology and pathogenesis of vitiligo, the cause of vitiligo remains unclear. Objective To evaluate spontaneous micronucleus (MN) frequency using the cytokinesis block MN assay to determine damages at the DNA or chromosome level in phytohaemagglutinin (PHA)‐stimulated blood cells of patients with vitiligo and healthy control subjects. Methods Peripheral blood samples were obtained and cultured from 21 patients with vitiligo (mean age: 21.48 ± 9.78 years) and 21 age‐ and sex‐matched healthy control subjects (mean age: 21.52 ± 9.80 years). MN values were scored in binucleated cells obtained from whole‐blood cultures of patients and control subjects. Results MN frequencies (mean ± SD) in PHA‐stimulated blood cells of patients with vitiligo and control subjects were 0.94 ± 0.58 and 0.58 ± 0.32, respectively. Compared with control subjects, MN frequencies of patients with vitiligo were found significantly higher than those of the control subjects (P = 0.012). Conclusion Our results indicate unexpectedly some chromosomal/DNA damage in whole‐blood cultures of patients with vitiligo. We do not know, however, if these chromosome/DNA instabilities observed in the cells of vitiligo patients resulted from the cause or from the consequences of the disorder.     

Combination treatment by 10 600 nm ablative fractional carbon dioxide laser and narrowband ultraviolet B in refractory nonsegmental vitiligo: a prospective, randomized half-body comparative study

Background Vitiligo is a common acquired depigmentation disorder caused by the loss of melanocytes. Despite the numerous treatment modalities available for vitiligo, responses to treatment are still unsatisfactory. For this reason, new treatment modalities and approaches are needed. Objectives To investigate the effects of fractional carbon dioxide (CO₂) laser therapy followed by systemic narrowband ultraviolet B (NB‐UVB) phototherapy on nonsegmental vitiligo (NSV) as a prospective and randomized left‐right comparative study. Methods Ten patients with NSV who presented symmetrical vitiligo lesions with no further improvement despite more than 1 year of conventional treatment were enrolled. Two sessions of half‐body fractional CO₂ laser therapy were performed at a 2‐month interval. NB‐UVB phototherapy was then administered to the entire body 5 days after each fractional laser treatment twice a week, increasing the dose incrementally by 15% at each session. Objective clinical assessments were made by two blinded dermatologists using a quartile grading scale, and the patients’ overall satisfaction was evaluated using a 10‐point visual analogue scale. Results Two months after the last treatment, mean improvement scores, assessed by physicians, were significantly higher for those treated with half‐body fractional CO₂ laser therapy followed by NB‐UVB phototherapy, compared with those treated with NB‐UVB alone (P = 0·034). In addition, according to subjective assessment, the half‐body laser treatment followed by NB‐UVB showed significantly higher improvements compared with NB‐UVB treatment alone (P = 0·023). Noticeable adverse events, such as infection, scarring and Koebner phenomenon, were not found in any patient. Conclusions This study suggests that fractional CO₂ laser therapy followed by NB‐UVB phototherapy could be used effectively and safely as an alternative modality for the treatment of refractory vitiligo.     

Ultrastructural Study of Vitiligo

Background. Vitiligo is a relatively common skin disease characterised by development of patchy depigmented macules. A comparative ultrastructural study was undertaken between early developing (2–6 months duration) and long standing (1–5 years duration) lesions of vitiligo in a series of ten patients. Methods. Skin biopsy specimens from the ten patients were fixed, stained, and examined under an electron microscope. Results. No melanocytes were found in the sections taken from long standing lesions. The sections from early lesions showed junctional melanocytes exhibiting various cellular abnormalities. The epidermal keratinocytes were normal in all sections; however, some sections from the periphery of early lesions exhibited minor degenerative changes. Conclusions. We can assume that because of the absence of melanocytes in long standing lesions, repigmentation may occur only from the melanocytic reservoir in the hair follicles. Repigmentation may also occur in lesions of short duration by reactivation of melanocytes present in the area, so an attempt should be made to treat vitiligo lesions in their early stage.     

Basic fibroblast growth factor promotes melanocyte migration via increased expression of p125(FAK) on melanocytes

Vitiligo is an acquired pigmentary disorder characterized by depigmentation of skin and hair. Melanocyte migration is an important event in re-pigmentation of vitiligo. We have demonstrated that narrow-band ultraviolet B (UVB) irradiation stimulated cultured keratinocytes to release a significant amount of basic fibroblast growth factor (bFGF). Furthermore, narrow-band UVB enhanced migration of melanocytes via increased expression of phosphorylated focal adhesion kinase (p125(FAK)) on melanocytes. The aim of this study was to investigate the effect of recombinant human bFGF (rhbFGF) on melanocyte migration. The relationship between the expression of p125(FAK) and melanocyte migration induced by rhbFGF was also studied. Our results demonstrated that rhbFGF significantly enhanced migration of melanocytes and p125(FAK) expression on melanocytes. Herbimycin A, a potent p125(FAK) inhibitor, effectively abolished rhbFGF-induced melanocyte migration. The combined results indicated that p125(FAK) plays an important role in the signal transduction pathway of melanocyte migration induced by bFGF.     

芪白合剂对黑素细胞作用的研究

目的：研究芪白合剂对黑素细胞的影响，探讨其治疗白癜风的药理作用。方法：将兔含药血清加入传代培养的正常人黑素细胞，用MTT法、多巴氧化法及NaOH法测定含药血清对黑素细胞的增殖、酪氨酸酶的活性及黑素合成的影响。结果：未灭活组含药血清可以促进黑素细胞增殖，上调酪氨酸酶活性以及增加黑素合成，效果较灭活组显著。结论：芪白合剂直接作用于黑素细胞，促进黑素细胞增殖，上调酪氨酸酶的活性，增加黑素合成，可用于白癜风的治疗。     

Comparison of the effect of 8-methoxypsoralen (8-MOP) plus UVA (PUVA) on human melanocytes in vitiligo vulgaris and in vitro.

In this study, we examined the various effects of PUVA treatment on cultured human melanocytes, and it revealed that 1) the higher the dose of PUVA treatment, the more significant the inhibition of cell DNA and protein synthesis; 2) the higher the dose of PUVA treatment, the more significant the depletion of epidermal growth factor receptor (EGFR) expression; 3) PUVA treatment at 124 mJoule/cm2 depleted the vitiligo-associated melanocyte antigens (VAMA) immediately after irradiation, and both the VAMA and EGFR expression progressively recovered at 24 or 72 h after PUVA; 4) PUVA treatment stimulated tyrosinase activity, but not in a dose-dependent fashion. In vitiligo vulgaris, PUVA treatment may stimulate the regrowth of melanocytes from hair follicles, but deplete the epidermal Langerhans cells in depigmented lesion of patients with stable vitiligo. Comparing the above results obtained from in vivo and in vitro studies, it reveals significantly different biologic responses. Although the precise therapeutic mechanism of PUVA treatment in vitiligo is still not well known, it is proposed that 1) PUVA treatment may stimulate the other components of skin, such as keratinocytes, to release inflammatory mediators and some of them may act as melanocyte growth-stimulatory factors (MGSF), which further enhance the proliferation of remaining melanocytes in hair follicle; and 2) PUVA treatment may deplete the VAMA expression on cell membrane of melanocytes and also deplete epidermal Langerhans cells, which may result in blocking the progressing of antibody-dependent cell-mediated cytotoxicity to melanocytes in vitiligo.     

白癜风表皮黑素细胞超微结构及小眼畸形相关转录因子转录调控研究

目的 研究白癜风黑素细胞超微结构和小眼畸形相关转录因子 （MITF）及其转录调控的酪氨酸酶相关蛋白（TRP）与白癜风临床类型与病程的相关性。方法 选择不同病程的寻常型白癜风（VV）12例和节段型白癜风（SV）8例,分别取白斑区、白斑边缘正常肤色区和远离白斑正常肤色区的表皮片,经组织学确定其表皮的完整性。透射电镜观察10例患者（VV 6例,SV 4例）不同区表皮黑素细胞的超微结构特点。对所有20例远离白斑正常肤色区的表皮片黑素细胞进行培养,应用免疫印迹方法检测 MITF及其转录调控的酪氨酸酶（TYR）、酪氨酸酶相关蛋白1（TYRP1）和酪氨酸酶相关蛋白2（TYRP2）的表达水平。结果 白癜风表皮黑素细胞超微结构病理改变：10例中7例白斑区表皮内未见黑素细胞,1例短病程和2例长病程VV分别可见少量黑素体显著减少或缺失的黑素细胞;白斑边缘正常肤色区,6例VV中,3例病程小于15个月者可见黑素细胞超微结构异常,而4例SV中仅1例异常;远离白斑正常肤色区,10例黑素细胞超微结构均正常。白癜风表皮黑素细胞MITF及其转录调控TRP的表达：VV的MITF表达下调与TYR、TYRP1、TYRP2的表达下调一致;SV存在MITF显著表达下调,而TYR、TYRP1、TYRP2几均正常表达。结论 VV和SV可能存在不同的表皮黑素细胞超微结构病理改变和MITF转录调控机制。     

Expression and modulation of apoptosis regulatory molecules in human melanocytes: significance in vitiligo

Although the aetiology of the hypopigmentary disorder vitiligo is ill understood, it is clear that pigment producing cells are absent from vitiliginous lesional skin. The present study was designed to investigate the possible role of melanocyte-expressed apoptosis regulatory molecules in melanocyte disappearance. Flow cytometric evaluation of p53, p21, Bcl-2 and Bax revealed no differences in in vitro expression levels between normal control and non-lesional melanocytes. Moreover, no in situ immunohistological differences were observed in melanocytes present in control, non-lesional and perilesional skin. However, an enhanced number of p53+ nuclei, in the absence of detectable p21 expression, was detected in involved areas. The observed p53 expression pattern did not involve melanocytes and could be the result of ultraviolet (UV) A irradiation. Further, we showed that UVB is capable of modulating melanocyte-expressed apoptosis regulatory molecules. Consequently, a lethal dose of UVB was given to two groups of cultured normal control and non-lesional melanocytes. No significant differences were found when comparing the percentages and kinetics of UVB-induced apoptosis in these groups. In conclusion, our results indicate that the relative apoptosis susceptibility of melanocytes in vitiligo is comparable with that of normal control cells. It is therefore unlikely that vitiligo is causally related to dysregulation of apoptosis regulatory molecules.     

过氧化氢对培养白癜风黑素细胞超微结构的影响

目的 探讨白癜风黑素细胞对外源性氧化剂的敏感性及氧化应激在白癜风发病中的作用.方法 以0.5mmol/L过氧化氢分别处理4例白癜风患者外观正常皮肤及6例正常对照皮肤培养的黑素细胞,采用透射电镜观察细胞的形态学变化,并应用图像分析技术和形态计量学方法,测定线粒体、粗面内质网及黑素小体的超微结构变化.结果 0.5mmol/L过氧化氢对正常人黑素细胞形态学及主要细胞器超微结构无明显影响.过氧化氢处理后的白癜风黑素细胞线粒体、内质网分别与处理前及正常对照处理后比较,数量明显减少,差异均有统计学意义(P<0.01).线粒体局部空化,内质网扩张.部分黑素小体体积显著增大,但黑素小体数量与过氧化氢处理前及正常对照处理后比较,差异无统计学意义(P>0.05).结论 过氧化氢可能通过破坏细胞的能量代谢和蛋白合成系统,使黑素细胞功能逐渐减退,促使白癜风的发生.     

热处理对UVB辐射后体外培养人黑素细胞活性的影响

目的 探讨热处理与窄谱中波紫外线（NB-UVB）联合作用对正常人黑素细胞活性的影响。 方法 分别以20、30、50、70、90、120、180 mJ/cm2 NB-UVB辐射体外培养的正常人黑素细胞,采用四甲基偶氮唑蓝比色法（MTT）检测细胞增殖活性并选择最佳照射剂量;以42 ℃,1 h为热处理干预剂量,将黑素细胞分为4组：正常对照组、UVB组、加热组、UVB + 加热组,连续干预3 d,以左旋多巴为底物测定酪氨酸酶活性,NaOH法测定黑素含量,流式细胞仪检测细胞周期变化。结果 NB-UVB照射呈剂量依赖性减少黑素细胞存活率,选择50 mJ/cm2作为最佳照射剂量;黑素细胞经不同干预后,UVB组、UVB+加热组的酪氨酸酶活性分别为0.244 ± 0.018、0.310 ± 0.015,较对照组（0.235 ± 0.018）分别增长3.8%和31.9%（P < 0.05）,两组黑素含量分别为0.201 ± 0.016、0.286 ± 0.019,较对照组（0.171 ± 0.016）分别增长17.5%和67.3%（P < 0.05）;UVB组和UVB+加热组处于G1期的黑素细胞较对照组分别减少23.94%和33.51%（P < 0.05）,S期细胞分别增加15.35%（P < 0.05）和17.76%（P > 0.05）,G2期分别增加11.93%（P < 0.05）和16.08%（P > 0.05）。 结论 热处理与NB-UVB可以协同增加黑素细胞的酪氨酸酶活性,促进黑素合成及细胞的增殖分化。     

Vitiligo: interplay between oxidative stress and immune system

Vitiligo is a multifactorial polygenic disorder with a complex pathogenesis, linked with both genetic and non‐genetic factors. The precise modus operandi for vitiligo pathogenesis has remained elusive. Theories regarding loss of melanocytes are based on autoimmune, cytotoxic, oxidant–antioxidant and neural mechanisms. Reactive oxygen species (ROS) in excess have been documented in active vitiligo skin. Numerous proteins in addition to tyrosinase are affected. It is possible that oxidative stress is one among the main principal causes of vitiligo. However, there also exists ample evidence for altered immunological processes in vitiligo, particularly in chronic and progressive conditions. Both innate and adaptive arms of the immune system appear to be involved as a primary event or as a secondary promotive consequence. There is speculation on the interplay, if any, between ROS and the immune system in the pathogenesis of vitiligo. The article focuses on the scientific evidences linking oxidative stress and immune system to vitiligo pathogenesis giving credence to a convergent terminal pathway of oxidative stress–autoimmunity‐mediated melanocyte loss.     

Ultrastructural studies in stable vitiligo

Vitiligo is a disease of melanocytes characterized by achromic lesions in the skin, affecting the epidermis and the pilosebaceous follicle. We performed an ultrastructural analysis of biopsy specimens from four patients with noninflammatory, stable vitiligo of long duration (three had generalized vitiligo and one had segmental vitiligo). The samples were taken from the oldest achromic lesions, and the biopsy sites were far from normal skin. In all cases we noted alterations in keratinocytes, Langerhans cells, and melanocytes. We also found lymphocytes in the epidermis, and these cells and macrophages were noted in the dermis. The basal membrane disappeared at some points, and sometimes it was possible to see dermal cells with processes that engulfed either granular material or vesicles of epidermal origin in such areas. Our studies suggest that even in stable vitiligo, achromia implies intense cytologic activity, probably involving cell-mediated cytotoxicity, and ultrastructural findings resemble those of a lichenoid reaction.     

In vitro growth characteristics of melanocytes obtained from adult normal and vitiligo subjects

The in vitro growth characteristics of melanocytes obtained from uninvolved and perilesional skin of vitiligo vulgaris subjects have been investigated in comparison to those from healthy adult donors. Normal human melanocytes have been found to grow exponentially in the presence of 10(-11) M cholera toxin and 10 ng/ml of 12-O-tetradecanoylphorbol-13-acetate in routine tissue culture media. They could be trypsinized up to 3-4 passages. Melanocytes of the uninvolved skin of vitiligo subjects manifested a lag of 8-11 days for the onset of growth and they could not be passaged. Melanocytes obtained from both hypo- and hyper-pigmented perilesional skin failed to grow under these conditions. Only in a few cases where the perilesional skin was normally pigmented did the melanocytes manifest some growth after a lag of 15 days. The initial seeding capacity of the melanocytes from uninvolved and perilesional skin of vitiligo patients were, respectively, 50% and 25% of the normal individuals. Vitiligo lesions themselves gave rise to unidentified dendritic cells that survived for 10-15 days without manifesting any growth. Our results suggest that melanocytes of individuals with vitiligo are defective. This fact has to be taken into account in any theory on the etiology of vitiligo.     

Vitiligo patients from India (Mumbai) show differences in clinical,demographic and autoantibody profiles compared to patients in western countries

Background Vitiligo is a common, idiopathic skin disorder characterized by depigmented skin due to the loss of cutaneous melanocytes. Several studies have reported the clinical and demographic characteristics of Indian vitiligo patients, however, none has characterized their antibody profiles. Objective To establish the clinical, demographic and serological details of a population of vitiligo patients from Mumbai, India, and to evaluate the data for any associations between clinical presentations and the occurrence of antibody responses. Methods Vitiligo patients (n = 79) were recruited to the study and their clinical and demographic details recorded. Serum antibodies, including those against melanocyte‐specific antigens, thyroid antigens and keratinocytes, were evaluated. Results The prevalence of vitiligo was independent of sex, and non‐segmental vitiligo was the most common form of the disease occurring in 65% of the patients. Patients with segmental vitiligo (mean age = 14.4 ± 4.6 years) presented at a younger age than those with non‐segmental disease (mean age = 32.5 ± 17.8 years). Personal and family histories of other autoimmune diseases occurred in 3% and 8% of patients, respectively. Antibodies were detected against tyrosinase, tyrosine hydroxylase, thyroid peroxidase, thyroglobulin and keratinocytes at frequencies of 11%, 22%, 18%, 24% and 27%, respectively. Overall, antibodies were more common in patients with non‐segmental vitiligo (50–67%) than in those with segmental disease (0–17%), and were detected more frequently in patients with shorter disease durations (<10 years). Conclusion Our study provides novel information relative to the clinical details, demographic features and serological parameters of a population of vitiligo patients from Mumbai, India. Important distinctions from similar surveys conducted in European patients were evident such as an infrequency of family history, a low prevalence of clinical autoimmune disease, and an absence of particular antibody specificities. These differences may have a bearing on the pathogenesis and course of the disease in Indian patients.     

Growth defects of melanocytes in culture from vitiligo subjects are spontaneously corrected in vivo in repigmenting subjects and can be partially corrected by the addition of fibroblast-derived growth factors in vitro

Summary Melanocytes cultured from uninvolved skin of untreated vitiligo subjects have decreased initial seeding capacities, manifest a lag period for the onset of the growth phase, and cannot be passaged. In contrast, melanocytes obtained from uninvolved and perilesional skin of vitiligo subjects actively repigmenting under 8-methoxy psoralen plus sunlight (PUVA) therapy have higher initial seeding capacities, grow faster without a lag period, and can be passaged to more than 12 passages. Extracts of a fetal lung fibroblast cell line (PMR-GF) that promote the growth rates and passage capacities of melanocytes from normal adult donors have been found also to promote the growth rates and passage capacities of melanocytes from the uninvolved skin of vitiligo subjects. Extracts of a fetal lung fibroblast cell line (PMR-GF), however, did not have any further stimulatory effect on the growth of melanocytes obtained from repigmenting vitiligo subjects. Melanocytes cultured from normal and untreated vitiligo subjects grew individually dispersed in the absence of PMR-GF, but tended to grow in clusters in its presence. Melanocytes from the repigmenting vitiligo subjects, however, tended to grow in clusters even in the absence of PMR-GF. These results indicate that the defective in vitro growth characteristics of melanocytes from vitiligo subjects may be related to the pathogenesis of this disease. It is possible that growth factors may be involved in the process of repigmentation in vitiligo subjects.     

Additive effect of heat on the UVB-induced tyrosinase activation and melanogenesis via ERK/p38/MITF pathway in human epidermal melanocytes

Heat is known as an environmental factor that causes significant skin pigmentation, but its effects on melanogenesis have been poorly studied. It has been shown that mitogen-activated protein kinase (MAPK) is involved in ultraviolet B (UVB) and stress-induced melanogenesis in melanocytes. In this study, we investigated the effects of heat and UVB, on melanocyte melanogenesis, differentiation, and MAPK phosphorylation. The results showed that heat (1 h at 40 °C for 5 days) increased cell dendrites, enlarged cell bodies, and induced extracellular signal-regulated kinases (ERK)/p38/MITF activation but did not influence melanogenesis of human epidermal melanocytes from skin phototype III. UVB irradiation (20 mJ/cm² for 5 days) induced melanogenesis and c-jun N-terminal kinases (JNK)/p38/MITF/tyrosinase activation in melanocytes from skin phototype III. UVB combined with heat resulted in much more significant tyrosinase activation and melanogenesis as compared with UVB alone in melanocytes from skin phototype III. Furthermore, heat treatment and UVB irradiation induced JNK, ERK, and p38 activation but not melanogenic and morphological changes in melanocytes from skin phototype I. These findings suggested that heat promoted melanocyte differentiation, probably via heat-induced ERK/p38/MITF/activation. Furthermore, heat had an additive effect on the UVB-induced tyrosinase activation and melanogenesis. These results provide a new clue for dermatologists for the treatment of hypopigmented skin disease with heat combined with UVB irradiation.