UV Erythema Research Articles

Rodent models of dermatological disorders.

To assess the possible beneficial effects of drugs and drug candidates, different dermatological disease models are available in rodents. These models are able to mimic one or more characteristic features of the disorders, but not completely recapitulate the pathogenesis of the human skin diseases. Therefore, to improve the technology many new models have been developed both by genetic engineering and by chemical or physical induction. Currently the in vivo rodent models provide the physiologically most relevant approach to produce the pathology related to the majority of dermatological diseases. In this short review some widely used animal techniques (psoriasis, allergic contact dermatitis, atopic dermatitis, wound healing, melanoma and non-melanoma type skin cancers and UV erythema) are shown which are currently applied in pharmacological, pharmacokinetic, pharmaceutical and dermatological research. First the main points of the human pathomechanism are shown and afterwards the rodent models are briefly discussed. Finally critical evaluation is provided by the authors. However, according to the 3R rule the number of experimental animals is strongly suggested to be reduced, therefore the advanced in vitro and ex vivo techniques become more and more important contrary to in vivo preclinical methods also in dermatological research. As it is described in the outlook section, although the 2D/3D in vitro and skin on-a-chip techniques are promising and have many advantages they are not able to completely substitute the animal models in their vascular, immunological, secretory and neural complexity.

The impact of an extreme solar event on the middle atmosphere: a case study

Abstract. A possible impact of an extreme solar particle event (ESPE) on the middle atmosphere is studied for present-day climate and geomagnetic conditions. We consider an ESPE with an occurrence probability of about 1 per millennium. In addition, we assume that the ESPE is followed by an extreme geomagnetic storm (GMS), and we compare the contribution of the two extreme events. The strongest known and best-documented ESPE of 774/5 CE is taken as a reference example and established estimates of the corresponding ionization rates are applied. The ionization rates due to the energetic particle precipitation (EPP) during an extreme GMS are upscaled from analyzed distributions of electron energy spectra of observed GMSs. The consecutive buildup of NOx and HOx by ionization is modeled in the high-top 3D chemistry circulation model KArlsruhe SImulation Model of the middle Atmosphere (KASIMA), using specified dynamics from ERA-Interim analyses up to the stratopause. A specific dynamical situation was chosen that includes an elevated stratosphere event during January and maximizes the vertical coupling between the northern polar mesosphere–lower thermosphere region and the stratosphere; it therefore allows us to estimate a maximum possible impact. The particle event initially produces about 65 Gmol of NOy, with 25 Gmol of excess NOy even after 1 year. The related ozone loss reaches up to 50 % in the upper stratosphere during the first weeks after the event and slowly descends to the mid-stratosphere. After about 1 year, 20 % ozone loss is still observed in the northern stratosphere. The GMS causes strong ozone reduction in the mesosphere but plays only a minor role in the reduction in total ozone. In the Southern Hemisphere (SH), the long-lived NOy in the polar stratosphere, which is produced almost solely by the ESPE, is transported into the Antarctic polar vortex, where it experiences strong denitrification into the troposphere. For this special case, we estimate a NO3 washout that could produce a measurable signal in ice cores. The reduction in total ozone causes an increase of the UV erythema dose of less than 5 %, which maximizes in spring for northern latitudes of 30∘ and in summer for northern latitudes of about 60∘.

Sun Exposure and Vitamin D.

Vitamin D is generally accepted in its importance on the regulation of calcium homeostasis and bone metabolism. Moreover, further health effects due to vitamin D are under discussion. In its effect, vitamin D is more like a hormone. In the classic view, a vitamin is an essential nutrient, which cannot be synthesized independently in the body. Besides nutrition, vitamin D will be produced in the body itself. The skin contains the provitamin D3 7-dehydrocholesterol, a precursor of vitamin D. Provitamin D3 will be photoconverted to previtamin D3 by UVB radiation that penetrates the skin superficially. In this way, the vitamin D metabolism will be started independent of the nutrition. In everyday life, this photosynthesis will be carried out due to the solar UVB radiation penetrating the uncovered skin. In the same spectral waveband range of UVB radiation, which causes the beneficial health effect of starting the vitamin D metabolism, the UVB radiation causes simultaneously acute and chronic harmful health effects as UV erythema (sunburn), skin aging and skin cancer. There is no vitamin D production in the skin without simultaneous DNA damage in the skin. Against this background, risks and benefits have to be balanced carefully.

Estimation of exposure durations for vitamin D production and sunburn risk in Switzerland.

Although overexposure to solar ultraviolet radiation (UVR) is responsible for cutaneous melanoma and epithelial skin cancer and can cause negative health effects such as sunburn, a "little and often" exposure regime is often suggested to produce naturally recommended vitamin D levels, being essential for skeletal health. This study aimed to quantify solar UV doses needed to trigger 1000 International Units (IU) vitamin D doses and, at the same time, producing sunburn in Switzerland. Solar UV erythema irradiance (in mW/m2) measured at four meteorological stations in Switzerland for the period 2005-2017 were used to evaluate effective solar UV radiation producing 1000 IU vitamin D doses in skin phototype II and III individuals. Daily solar UV exposure durations (in minutes) needed to produce vitamin D with limited sunburn risk were estimated while considering mean vitamin D food intake of the Swiss population and seasonal skin coverage. In summer and spring, with 22% of uncovered skin, 1000 IU vitamin D doses are synthesized in 10-15 min of sun exposure for adults. Exposure durations between erythema risk and 1000 IU vitamin D production vary between 9 and 46 min. In winter and autumn, the recommended vitamin D production without sunburn risks often unachievable, since up to 6.5 h of sun exposure might be necessary considering 8-10% of uncovered skin surface. The vitamin D food intake only represented 10% of the recommended vitamin D production and remained unchanged throughout the year. These findings might clarify why vitamin D deficiency is common in Switzerland. Moreover, exposure durations between recommended vitamin D and increased sunburn risk might only differ by few minutes. Without additional oral vitamin D supplementation, daily doses of vitamin D (1000 IU) are not reachable in autumn and winter months in Switzerland.

Tannins from Potentilla officinalis display antiinflammatory effects in the UV erythema test and on atopic skin.

Rich in tannins, the rhizome of Potentilla officinalis (PO) has traditionally been used in the topical treatment of inflammatory disorders of the skin and mucous membranes. The objective of the present study was to examine the antiinflammatory effects of PO in the UV erythema test as well as in patients with atopic skin. Using the UV erythema test, the antiinflammatory effects of a PO extract (2%) -compared to 1 % hydrocortisone acetate - were assessed in a randomized, prospective, placebo-controlled double-blind study of 40 healthy volunteers. In the context of a prospective non-controlled trial, the efficacy and tolerability of 2 % PO cream (applied to defined test areas twice daily for two weeks) was evaluated in twelve adults and twelve children with atopic skin using a partial SCORAD. In addition, the effects on the degree of erythema in the test areas was measured photometrically. In the UV erythema test, PO cream significantly reduced the erythema index compared to the vehicle. The antiinflammatory effects of PO cream were comparable to those of 1% hydrocortisone acetate cream. The clinical study with atopic patients revealed a significant reduction in the partial SCORAD as well as erythema in the test areas. No adverse events were recorded. PO cream displays antiinflammatory effects in vivo. It is effective in and well tolerated by patients with atopic skin.

Analysis of Two Kinds of Tree as Physical Barriers Against Erythemal UVB Radiation Received

Differences between global radiation UVER (erythemal ultraviolet solar radiation) received under full sun and diffuse radiation received under the shadow of two types of tree are analyzed to check the importance of these components on human exposure to UV radiation. Blue Line spores dosimeters of VioSpor were used for measurement of erythemal dose of UV radiation (able to produce erythema in human skin.) The response profile of these devices is extremely similar to human skin, thus they are suitable to determine and predict the interactions between UV erythema and human skin. Measurements were obtained in relatively clear days from February to December 2009 between 9:30 and 15:30 h. Three dosimeters were placed on a horizontal surface: one in full sun and the other two under the shadow of each tree. Values of UVER in both cases, in full sun and under the shadow of pine and Sauce, were obtained. In addition, the comparison was made between values of dose received in each case and the exposure limits recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Finally, average daily irradiance received under the shadow of each tree in comparison with those received in full sun, was also analyzed using two PMA2100 radiometers situated on a horizontal surface.

To what extent does the radiation of a solar simulator meet a “reference sun”? A quantitative approach

Solar simulators generate radiation which should simulate a defined “reference sun” as perfectly as possible, and most important is the fitting to the spectral distribution. So far, the fitting is described verbally only, e.g. in standards concerning artificial weathering, and the user has to decide for himself whether the spectral distribution E(λ) indicated by the producer of the solar simulator agrees well enough with the “reference sun” for his specific application. Occasionally, the classification describes the fitting to a wanted “reference sun” only insufficiently (e.g. qualification approvals for photo voltaic modules).This paper deals with a procedure for the determination of factors characterising the grade of fitting in quantity. For various solar simulators which are commercially available (e.g. for artificial weathering tests or design qualification tests), characteristic factors for different wavelength ranges are indicated, and a proposal is made for a classification regarding the grade of fitting of the spectral distribution of solar simulators to a defined “reference sun”.As examples of characteristic factors regarding action spectra with especially distinct wavelength dependence, characteristic factors for the UV erythema and the CO formation of PE are given.

Miniature swine model of phototoxicity testing

This study determined the threshold doses for 'solar erythema' and for phototoxic responses to 8-methoxypsoralen (8-MOP) in white skin Hanford and grey skin Yucatan miniature swine. For threshold erythema determinations, the UVR exposures included both UVA (315-400 nm) and UVB (290-315 nm) radiation by positioning one fluorescent 'sunlamp' among 10 'PUVA' lamps. With this configuration the UVR exposures ranged from 0.5-2.8 times the 'instrumental MED' (MEDi) for Hanford and from 1.0-5.6 times the MEDi for Yucatan. For phototoxicity determinations (i.e., with and without topically-applied graduated concentrations of 8-MOP), the UVB component was minimized by extinguishing the sunlamp, thus permitting higher UVA exposures. The Hanford had the lower UV erythema dose threshold (1.0-1.4 times the MEDi) and the erythema that developed was readily observable. The exposure doses for the phototoxicity test were 5 J/cm(2) of UVA in 35 minutes or 10 J/cm(2) in 70 minutes. The phototoxic (vascular) response to 8-MOP was observed in the two highest concentrations (0.01% and 0.1%) in Hanford pigs, in a dose-related manner. Microscopic evidence of a dose-related response was also observed as the concentration of 8-MOP increased. This verified that the Hanford miniature swine is the preferable strain for phototoxic effects. In contrast, UVR exposure of the Yucatan pig skin produced tanning rather than erythema, confirming that the Yucatan is the more appropriate strain for studying the melanization response. Thus, Hanford and Yucatan miniature swine have cutaneous photobiological responses that reflect their respective strain differences.

Vitamin D in Oncology

The vitamin D system has been strongly conserved in evolution. It links sun exposure to a multitude of endocrine messages. In most body cells the active hormone calcitriol binds intracellularly to the vitamin D receptor and regulates the expression of specific gene products. Vitamin D deficiency is epidemic affecting some 1 billion people worldwide and is mainly caused by chronically inadequate sun exposure. This deficiency is associated with harmful effects on almost all tissues including a predisposition to cancer. In cancer patients vitamin D deficiency is associated with a worsening of the prognosis. The active hormone calcitriol has anti-tumor activity and is being investigated as an anticancer agent. There is general agreement that exposure to sunlight should be increased while carefully avoiding UV erythema. In addition, recent suggestions call for a health-promoting dietary intake of 25–100 mg (1,000–4,000 IU) of vitamin D3. While supplements of vitamin D improve musculoskeletal symptoms, proof is still lacking that these doses convey a protection from cancer. Interventional studies that administer vitamin D versus placebo in patients with cancer should be a high priority because of the hypothesized benefits and the low risk of supplementation with vitamin D.

European S3‐Guidelines on the systemic treatment of psoriasis vulgaris

Of the 131 studies on monotherapy or combination therapy assessed, 56 studies on the different forms of phototherapy fulfilled the criteria for inclusion in the guidelines. Approximately three-quarters of all patients treated with phototherapy attained at least a PASI 75 response after 4 to 6 weeks, and clearance was frequently achieved (levels of evidence 2 and 3). Phototherapy represents a safe and very effective treatment option for moderate to severe forms of psoriasis vulgaris. The onset of clinical effects occurs within 2 weeks. Of the unwanted side effects, UV erythema from overexposure is by far the most common and is observed frequently. With repeated or long-term use, the consequences of high, cumulative UV doses (such as premature aging of the skin) must be taken into consideration. In addition, carcinogenic risk is associated with oral PUVA and is probable for local PUVA and UVB. The practicability of the therapy is limited by spatial, financial, human, and time constraints on the part of the physician, as well as by the amount of time required by the patient. From the perspective of the cost-bearing institution, phototherapy has a good cost-benefit ratio. However, the potentially significant costs for, and time required of, the patient must be considered.

Comparative Study of the Gross Interpretation of Phototesting and Objective Measurement with Using a Spectrophotometer for Patients with Psoriasis and Vitiligo Treated with Narrow-band UVB

Determination of the minimal erythema dose (MED) is important for developing a phototherapy protocol and to diagnosis photosensitivity disorders. But obtaining a precise and reproducible MED is quite difficult because a phototest for erythema is based on subjective assessment. The objective of our study was to compare the gross interpretation of a phototest and the objective measurement using a spectrophotometer for determining the parameters of cutaneous narrow-band UVB (NBUVB) therapy. A total of 14 psoriasis and 10 vitiligo patients who receiving NBUVB phototherapy with skin types III and IV were selected for this study. To perform phototesting, ten sites on the skin of the back were vertically exposed to a series of 10 NBUVB doses among 14 doses between 340 and 1,400 mJ/cm(2). We interpreted the gross findings of erythema and measured the L*a*b* values with using a spectrophotometer at each phototest spot and at the control skin. Also, we evaluate the relationship between the gross presentation and the spectrophotometric analysis by delta E for the assessment of the minimal perceptible erythema (MPE) and MED. For all the subjects, the MEDs were measured in the 490~1,000 mJ/cm(2) range. The average of the colorimetric values for the control skin were L*: 64.8, a*: 7.9 and b*: 19.8. Among them, the L* value and MED value were shown to be inversely correlated, and as the L* value was decreased, the MED was increased. For the MPE, the delta E, which was the color difference of the normal skin and the phototest area, was within the range of 1.5~3.0 in 17 of the 21 patients, and 4 patients were within the range of 1.0~1.5. For the MED, among the 21 patients, the delta E of 17 patients was within the range of 3.0~6.0, and 4 patients were within the range of 6.0~12.0. A spectrophotometer enables UV erythema to be assessed objectively and quantitatively, and this can compensate for the disadvantages of subjective gross interpretation when determining the MED. Delta E is a good novel and objective indicator for determining the MPE and MED. So, a spectrophotometer is a very useful instrument for developing a phototherapy protocol for psoriasis and other dermatoses and for making the diagnosis of photosensitivity disorders.

Investigation of the Anti-Inflammatory Potential of Aloe vera Gel (97.5%) in the Ultraviolet Erythema Test

Background:Aloe vera is a natural product that is frequently used in soothing skin care products such as aftersun lotions. In the present study we aimed to explore the anti-inflammatory potential of a highly concentrated A. vera gel in the UV erythema test in vivo. Methods: 40 volunteers with skin types II and III were included in the randomized, double-blind, placebo-controlled, phase III monocenter study. Test areas on the back were irradiated with the 1.5-fold minimal erythema dose of UVB. Subsequently, the test areas were treated occlusively on 2 subsequent days with A. vera gel (97.5%), the positive controls (0.25% prednicarbate, 1% hydrocortisone in placebo gel and 1% hydrocortisone cream) and a placebo gel. Erythema values were determined photometrically after 24 and 48 h. Results:A. vera gel (97.5%) significantly reduced UV-induced erythema after 48 h, being superior to 1% hydrocortisone in placebo gel. In contrast, 1% hydrocortisone in cream was more efficient than A. vera gel. Conclusions: In this study after 48 h the A. vera gel (97.5%) displayed some anti-inflammatory effects superior to those of 1% hydrocortisone in placebo gel. The A. vera gel tested here might be useful in the topical treatment of inflammatory skin conditions such as UV-induced erythema.

UV Erythema Reducing Capacity of Mizolastine Compared to Acetyl-salicylic Acid or both Combined in Comparison to Indomethacin†¶

UV Erythema Reducing Capacity of Mizolastine Compared to Acetyl-salicylic Acid or both Combined in Comparison to Indomethacin†¶

Melanin differentially protects from the initiation and progression of threshold UV‐induced erythema depending on UV waveband

This study aimed to determine the relationship between various measures of constitutive skin pigmentation and erythema caused by solar-simulated UV (ssUV), 290 and 310 nm UV. Skin pigmentation was assessed clinically by skin typing as well as objectively by measurement of the melanin index (MI) by reflectance spectroscopy. Subjects having Fitzpatrick skin types I-IV were exposed to graded doses of ssUV and either narrowband 310 nm (n=70) or 290 nm (n=69) UV, and assessed 24 h after exposure. Minimal erythema dose (MED) was assessed visually as the lowest dose that caused minimally perceptible erythema. Susceptibility to further development of erythema with higher exposure doses was measured by the gradient of erythema dose-response curves. This was determined by linear regression using reflectance spectrometry data beyond the MED. Although there was considerable variation within each skin type, MI and ssUV MED increased with increasing Fitzpatrick skin type. MI correlated with ssUV MED and 310 nm UV MED, but not 290 nm UV MED. There was also a significant negative correlation between MI and erythema dose-response gradients caused by ssUV, 310 and 290 nm UV. Melanin situated near the basal epidermis may not protect from the initial development of threshold erythema caused by 290 nm UV because it penetrates poorly past the stratum corneum and is not well absorbed by melanin in vivo compared with 310 nm UV. Higher erythemal 290 nm UV doses may reach basal epidermal melanin, which may then afford protection against further 290 nm UV erythema.

Quantification of UV‐Induced Erythema and Pigmentation Using Computer‐Assisted Digital Image Evaluation

Photography has been used in human skin research for some time. With the advent of digital photography in recent years, its use has increased. However, the focus has now turned from documentation to actual analysis and quantification of skin color changes. The advantages of digital photography outweigh any shortcomings as long as consistent, standardized procedures are followed and quality control is implemented. We present a simple procedure to standardize images and discuss a computer-assisted digital image evaluation (CADIE) technique to quantify skin color changes following UV exposure. The CADIE approach is illustrated with examples from two different studies on UV responses in human skin. Using the Commission Internationale de l'Eclairage L*a*b* color coordinate system in combination with a personal computer and image-editing software, we analyzed digital images obtained in these two studies. We demonstrate the feasibility of using digital photography for objective evaluation of UV erythema in different racial/ethnic groups and for measuring pigmentation changes caused by repeated exposures over a period of several weeks. Our results indicate how objective assessment using CADIE can be an adjunct to visual and optical observation in clinical and scientific evaluations.

The Topical Isoflavonoid NV‐07α Reduces Solar‐simulated UV‐induced Suppression of Mantoux Reactions in Humans¶

AbstractUV radiation suppresses delayed‐type hypersensitivity responses to intradermally injected tuberculin purified protein derivative in Mantoux‐positive individuals. The effect of the topically administered isoflavonoid NV‐07α, a synthetic derivative of the isoflavonoid equol, on UV‐induced suppression of Mantoux reactions was assessed in 18 healthy Mantoux‐positive volunteers. A single, fixed dose of solar‐simulated UV radiation was delivered to the volunteers'lower backs. Different concentrations of NV‐07α or its vehicle were applied to different sites within the irradiated field immediately after UV exposure and again 24 h later. Forty‐eight hours after irradiation, Mantoux testing was performed at both the irradiated sites and adjacent, unirradiated sites. The intensity of Mantoux reactions was measured 72 h later with a reflectance erythema meter and by measuring the diameter of each reaction. Although lower concentrations of NV‐07α (0.5 and 2 mM) did not prevent UV immunosuppression, 4 mM NV‐07α partially but significantly attenuated UV‐induced suppression of Mantoux‐induced erythema. Minimal erythema doses were also determined for sites treated with NV‐07α or its vehicle immediately after UV exposure. NV‐07α had no significant effects on UV erythema. We conclude that 4 mM NV‐07α prevented the suppressive effects of UV radiation on Mantoux responses in humans but did not affect UV‐induced erythema at the concentrations used.

Impact of biomass burning aerosols on UV erythema—a case study from northeast region of India

Total spectral solar irradiance and biologically active solar ultraviolet radiation (UV ery, 280– 315 nm ) have been monitored during biomass burning period of moist deciduous forests in the Northeastern India. Aerosol optical depth values varied from 0.5 to 4.2 during different stages of burning. Total solar irradiance measurements suggested decrease in direct solar irradiance during burning with increase in diffused radiation. A statistical fit of AOD (500 nm) through UV ery shows negative gradient and for every 0.1 increase in aerosol optical depth during biomass burning period 0.01 W m −2 reduction in the ground reaching UV ery has been observed.

The Topical Isoflavonoid NV-07α Reduces Solar-simulated UV-induced Suppression of Mantoux Reactions in Humans¶

UV radiation suppresses delayed-type hypersensitivity responses to intradermally injected tuberculin purified protein derivative in Mantoux-positive individuals. The effect of the topically administered isoflavonoid NV-07alpha, a synthetic derivative of the isoflavonoid equol, on UV-induced suppression of Mantoux reactions was assessed in 18 healthy Mantoux-positive volunteers. A single, fixed dose of solar-simulated UV radiation was delivered to the volunteers' lower backs. Different concentrations of NV-07alpha or its vehicle were applied to different sites within the irradiated field immediately after UV exposure and again 24 h later. Forty-eight hours after irradiation, Mantoux testing was performed at both the irradiated sites and adjacent, unirradiated sites. The intensity of Mantoux reactions was measured 72 h later with a reflectance erythema meter and by measuring the diameter of each reaction. Although lower concentrations of NV-07alpha (0.5 and 2 mM) did not prevent UV immunosuppression, 4 mM NV-07alpha partially but significantly attenuated UV-induced suppression of Mantoux-induced erythema. Minimal erythema doses were also determined for sites treated with NV-07alpha or its vehicle immediately after UV exposure. NV-07alpha had no significant effects on UV erythema. We conclude that 4 mM NV-07alpha prevented the suppressive effects of UV radiation on Mantoux responses in humans but did not affect UV-induced erythema at the concentrations used.

Anti-Inflammatory Efficacy of Topical Preparations with 10% Hamamelis Distillate in a UV Erythema Test

In 40 volunteers the efficacy of three lotions with 10% hamamelis distillates from different suppliers, two vehicles, dimethindene maleate 0.1% gel, hydrocortisone 1% cream and hydrocortisone 0.25% lotion were investigated in a modified UV erythema test with three UV dosages (1.2, 1.4 and 1.7 MED). The test preparations were applied occlusively over a 48-hour period following irradiation. Chromametric measurement of redness and visual assessment were performed 24, 48 and 72 h after induction of erythema. The hydrocortisone formulations were most effective in erythema suppression. An anti- inflammatory effect was noted for all three hamamelis lotions as well as for the vehicles. A significantly greater suppression of erythema than seen with the vehicles was noted for one of the hamamelis lotions at 1.4 MED. The efficacy of the antihistamine dimethindene maleate did not surpass the hamamelis lotions or the vehicles. Even though the differences between the hamamelis lotions were slight, it was possible to make an objective selection of the best hamamelis distillate for aftersun purposes.

Microinjection of an antibody against HSP 72 in keratinocytes to study acute UV injury⊃

First, a method of microinjection of antibodies in primary human keratinocytes in culture was established. Second, in acute UV irradiation, the physiological role of heat shock protein (HSP) 72 in keratinocytes was studied with this method. Primary human keratinocytes in culture were injected with "controls" as fluorescent dyes, phosphate buffered saline (PBS), an irrelevant secondary antibody and an antibody against a protein with known protective function in UV erythema, HSP 72. UV irradiation was applied and survival, colony forming and immunohistochemistry for injected and non-injected keratinocytes were evaluated in a time course. Puncturing the plasma membrane with injections of "controls" as FITC, PBS and the IgG anti-mouse antibody did not result in reflux of injected material or any alteration in morphology or colony-forming ability for 24 h. Keratinocytes injected with an mAb to HSP 72 without UV irradiation survived microinjection for up to 12 days, while surprisingly, more than double of injected and irradiated ones died after 12 h compared to not injected and irradiated ones. Moreover, microinjection of the antibody to HSP 72 in the nucleus resulted in a loss of the immunohistochemical labeling for HSP 72 in these cells after 12 h. Microinjection of the "controls" did not harm the survival, forming of colonies and expression of HSP 72 in keratinocytes for 24 h. In contrast, microinjection of an mAb against HSP 72 led to an increase in cell death after UV irradiation, confirming that HSP 72 is important for UV protection. Microinjection of antibodies in human keratinocytes in culture might allow the study of the physiological role of some proteins.