Mobile phone radiation might alter protein expression in human skin

Background

Earlier we have shown that the mobile phone radiation (radiofrequency modulated electromagnetic fields; RF-EMF) alters protein expression in human endothelial cell line. This does not mean that similar response will take place in human body exposed to this radiation. Therefore, in this pilot human volunteer study, using proteomics approach, we have examined whether a local exposure of human skin to RF-EMF will cause changes in protein expression in living people.

Results

Small area of forearm's skin in 10 female volunteers was exposed to RF-EMF (specific absorption rate SAR = 1.3 W/kg) and punch biopsies were collected from exposed and non-exposed areas of skin. Proteins extracted from biopsies were separated using 2-DE and protein expression changes were analyzed using PDQuest software. Analysis has identified 8 proteins that were statistically significantly affected (Anova and Wilcoxon tests). Two of the proteins were present in all 10 volunteers. This suggests that protein expression in human skin might be affected by the exposure to RF-EMF. The number of affected proteins was similar to the number of affected proteins observed in our earlier in vitro studies.

Conclusion

This is the first study showing that molecular level changes might take place in human volunteers in response to exposure to RF-EMF. Our study confirms that proteomics screening approach can identify protein targets of RF-EMF in human volunteers.

Continuous wave and simulated GSM exposure at 1.8 W/kg and 1.8 GHz do not inducehsp16-1 heat-shock gene expression inCaenorhabditis elegans

Recent data suggest that there might be a subtle thermal explanation for the apparent induction by radiofrequency (RF) radiation of transgene expression from a small heat-shock protein (hsp16-1) promoter in the nematode, Caenorhabditis elegans. The RF fields used in the C. elegans study were much weaker (SAR 5-40 mW kg(-1)) than those routinely tested in many other published studies (SAR approximately 2 W kg(-1)). To resolve this disparity, we have exposed the same transgenic hsp16-1::lacZ strain of C. elegans (PC72) to higher intensity RF fields (1.8 GHz; SAR approximately 1.8 W kg(-1)). For both continuous wave (CW) and Talk-pulsed RF exposures (2.5 h at 25 degrees C), there was no indication that RF exposure could induce reporter expression above sham control levels. Thus, at much higher induced RF field strength (close to the maximum permitted exposure from a mobile telephone handset), this particular nematode heat-shock gene is not up-regulated. However, under conditions where background reporter expression was moderately elevated in the sham controls (perhaps as a result of some unknown co-stressor), we found some evidence that reporter expression may be reduced by approximately 15% following exposure to either Talk-pulsed or CW RF fields.

Ultraviolet-A radiation induces changes in cyclin G gene expression in mouse melanoma B16-F1 cells

Background

We have previously shown that ultraviolet-A (UVA) radiation enhances metastatic lung colonization capacity of B16-F1 melanoma cells. The aim of this study was to examine changes in expression profile of genes in mouse melanoma B16-F1 cells exposed to UVA radiation.

Results

B16-F1 melanoma cells were exposed to a single UVA radiation dose of 8 J/cm² and mRNA was isolated 4 h after the end of UVA exposure. Atlas™ Mouse Cancer 1.2 cDNA expression arrays were used for the large-scale screening to identify the genes involved in the regulation of carcinogenesis, tumor progression and metastasis. Physiologically relevant UVA dose induced differential expression in 9 genes in the UVA exposed melanoma cells as compared to the unexposed control cells. The expression of seven genes out of nine was upregulated (HSC70, HSP86, α-B-crystallin, GST mu2, Oxidative stress induced protein OSI, VEGF, cyclin G), whereas the expression of two genes was down-regulated (G-actin, non-muscle cofilin). The gene expression of cyclin G was mostly affected by UVA radiation, increasing by 4.85-folds 4 hour after exposure. The analysis of cyclin G protein expression revealed 1.36-fold increase at the 6 hour time point after UVA exposure. Cell cycle arrest in G2/M phase, which is known to be regulated by cyclin G, occurred at 4-h hour time-point, peaking 8 hours after the end of UVA irradiation, suggesting that cyclin G might play a role in the cell cycle arrest.

Conclusion

Our results suggest that UVA radiation-induces changes in the expression of several genes. Some of these changes, e.g. in expression of cyclin G, possibly might affect cell physiology (cell cycle arrest).

Questions and answers concerning applicability of proteomics and transcriptomics in EMF research

The applicability of high-throughput screening techniques of transcriptomics, proteomics and metabolomics in the search for biological and health effects of electromagnetic fields is a hotly debated issue. On the one hand, use of these modern screening technologies speeds up the discovery process and gives broader insight into biochemical events that follow the exposure to electromagnetic fields. On the other hand these modern screening technologies have the problem of reproducibility and variability between experiments and are prone to produce false positive results. These and other issues concerning the applicability of modern screening technologies were the topic of a workshop held at STUK in 2005 (30 October to 1 November) in Helsinki, Finland, and this Report summarizes the discussions at this workshop.

Mobile phone radiation causes changes in gene and protein expression in human endothelial cell lines and the response seems to be genome- and proteome-dependent

We have examined in vitro cell response to mobile phone radiation (900 MHz GSM signal) using two variants of human endothelial cell line: EA.hy926 and EA.hy926v1. Gene expression changes were examined in three experiments using cDNA Expression Arrays and protein expression changes were examined in ten experiments using 2-DE and PDQuest software. Obtained results show that gene and protein expression were altered, in both examined cell lines, in response to one hour mobile phone radiation exposure at an average specific absorption rate of 2.8 W/kg. However, the same genes and proteins were differently affected by the exposure in each of the cell lines. This suggests that the cell response to mobile phone radiation might be genome- and proteome-dependent. Therefore, it is likely that different types of cells and from different species might respond differently to mobile phone radiation or might have different sensitivity to this weak stimulus. Our findings might also explain, at least in part, the origin of discrepancies in replication studies between different laboratories.

Gene expression changes in human cells after exposure to mobile phone microwaves

Possible biological effects of mobile phone microwaves were investigated in vitro. In this study, which was part of the 5FP EU project REFLEX (Risk Evaluation of Potential Environmental Hazards From Low-Energy Electromagnetic Field Exposure Using Sensitive in vitro Methods), six human cell types, immortalized cell lines and primary cells, were exposed to 900 and 1800 MHz. RNA was isolated from exposed and sham-exposed cells and labeled for transcriptome analysis on whole-genome cDNA arrays. The results were evaluated statistically using bioinformatics techniques and examined for biological relevance with the help of different databases. NB69 neuroblastoma cells, T lymphocytes, and CHME5 microglial cells did not show significant changes in gene expression. In EA.hy926 endothelial cells, U937 lymphoblastoma cells, and HL-60 leukemia cells we found between 12 and 34 up- or down-regulated genes. Analysis of the affected gene families does not point towards a stress response. However, following microwave exposure, some but not all human cells might react with an increase in expression of genes encoding ribosomal proteins and therefore up-regulating the cellular metabolism.

Ultraviolet A exposure might increase metastasis of mouse melanoma: a pilot study

BACKGROUND

The major sources of long-wave ultraviolet A radiation (UVA; 320-400 nm) exposure are extensive sunbathing and tanning in solaria. While the carcinogenic effects of mid-wave ultraviolet B radiation (UVB; 280-320 nm) are well recognized, the potentially hazardous effects of UVA are less understood. Several studies have shown that a variety of physiological processes in the cell are modified by UVA exposure, some of which might be involved in the regulation of tumor metastasis. In this study we suggest that UVA radiation could lead to the increase of metastatic capability of melanoma cells in mice.

METHOD/RESULT

A pilot in vivo study was executed using C57BL/6 mice and syngeneic B16 melanoma cell lines. Mice were intravenously (i.v.) injected with either B16-F1 or B16-F10 melanoma cells into the tail vein and then immediately exposed to UVA. Fourteen days after melanoma injection, lungs were collected and the quantity and quality of metastases were determined under a dissecting microscope. As an outcome of the pilot study we observed that i.v. injected melanoma cells formed more lung metastases in the UVA-exposed mice in comparison with the control mice.

CONCLUSION

This result suggests that the UVA exposure of mice, with melanoma cells present in blood circulation, increases the formation of melanoma metastases in lungs. Further studies should determine whether a similar pro-metastatic effect, as observed in mice, could occur in humans and whether other than melanoma tumors might be susceptible.

Ultraviolet A exposure alters adhesive properties of mouse melanoma cells

BACKGROUND

We have examined whether ultraviolet A (UVA) irradiation could alter adhesive properties of melanoma cells. As an experimental in vitro model, we have used C57BL/6 mouse-derived B16- F1 and B16-F10 melanoma cell lines and the syngeneic MS-1 endothelial cell line.

METHOD/RESULT

The melanoma cells were exposed to different doses of UVA irradiation. We have determined that a single dose of UVA at 8 and 12 J/cm(2) causes an 88% (P<0.001) and a 32% (P<0.05) increase in B16-F1 melanoma cell adhesiveness to the non-irradiated endothelial monolayer, respectively. The peak of the response was 24 h after the irradiation. The UVA dose of 8 J/cm(2) delivered in four doses separated by 1 h intervals (4 x 2 J/cm(2)) had led to a caused 149% (P<0.001) increase of B16-F1 melanoma adhesiveness already at 1 h after the last dose of UVA. Besides the induction of increase in the melanoma-endothelial cell adhesion, UVA exposure has induced a rapid decline (1 h after exposure) in homotypic melanoma-melanoma cell adhesion (clustering). The clustering decline of B16-F1 cells with a single dose of UVA at 8 J/cm(2) was by 61% (P<0.05) and by 35% (P<0.05) with 4 x 2 J/cm(2). Pilot experiments have shown that the changes of the adhesive properties of melanoma cells were accompanied by an increase in N-cadherin expression and a decline in E-cadherin expression. Such a change in cadherin expression profile has been shown to be an indicator of the increased metastatic potential.

CONCLUSION

Our results suggest that UVA radiation appears to alter the adhesive properties of melanoma cells in vitro, by diminishing the melanoma-melanoma adhesion and by increasing melanoma adhesion to the endothelium. This suggests that UVA exposure might increase the metastatic capability of the melanoma cells.

Rapporteur report: cellular, animal and epidemiological studies of the effects of static magnetic fields relevant to human health

Three talks were presented in the session on "Cellular, Animal and Epidemiological Studies of the Effects of Static Magnetic Fields Relevant to Human Health". The first talk presented the in vitro effects of static magnetic fields on cell cultures. The second talk presented the in vivo evidence obtained from animal studies. The final, third talk, presented the evidence obtained from epidemiological studies. The overall conclusion of the three presentations and the following general discussion was that the scientific evidence available to date is weak and contains large gaps in knowledge either due to the poor quality of published studies or because of the lack of published research on certain health-related topics. It was emphasized that the rapid development of new technological applications of static magnetic fields (e.g. magnetic levitation trains or magnetic resonance imaging-MRI) results in the human population at large, in certain occupations, and in a selected population of clinical patients being exposed to ever increasing static magnetic field strengths. It is of concern that the knowledge presently available concerning the health effects of these strong static magnetic fields is lagging a long way behind technological development. In conclusion, it was suggested that there is an urgent need to perform new studies in all research areas (in vitro, in vivo and epidemiology) in order to fill the present gaps in knowledge and provide assurance that this technology will not cause any unwanted and unexpected health side effects.

Proteomics analysis of human endothelial cell line EA.hy926 after exposure to GSM 900 radiation

The human endothelial cell line EA.hy926 was exposed to mobile phone radiation and the effect on protein expression was examined using two-dimensional electrophoresis (2-DE). Up to 38 various proteins have statistically significantly altered their expression levels following the irradiation. Four proteins were identified with matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). Two of the affected proteins were determined to be isoforms of cytoskeletal vimentin. This finding supports our earlier presented working hypothesis which indicated that the mobile phone radiation might affect the cytoskeleton and might have an effect on the physiological functions that are regulated by the cytoskeleton.

Applicability of discovery science approach to determine biological effects of mobile phone radiation

We argue that the use of high-throughput screening techniques, although expensive and laborious, is justified and necessary in studies that examine biological effects of mobile phone radiation. The "case of hsp27 protein" presented here suggests that even proteins with only modestly altered (by exposure to mobile phone radiation) expression and activity might have an impact on cell physiology. However, this short communication does not attempt to present the full scientific evidence that is far too large to be presented in a single article and that is being prepared for publication in three separate research articles. Examples of the experimental evidence presented here were designed to show the flow of experimental process demonstrating that the use of high-throughput screening techniques might help in rapid identification of the responding proteins. This, in turn, can help in speeding up of the process of determining whether these changes might affect human health.*

Non-thermal activation of the hsp27/p38MAPK stress pathway by mobile phone radiation in human endothelial cells: molecular mechanism for cancer- and blood-brain barrier-related effects

We have examined whether non-thermal exposures of cultures of the human endothelial cell line EA.hy926 to 900 MHz GSM mobile phone microwave radiation could activate stress response. Results obtained demonstrate that 1-hour non-thermal exposure of EA.hy926 cells changes the phosphorylation status of numerous, yet largely unidentified, proteins. One of the affected proteins was identified as heat shock protein-27 (hsp27). Mobile phone exposure caused a transient increase in phosphorylation of hsp27, an effect which was prevented by SB203580, a specific inhibitor of p38 mitogen-activated protein kinase (p38MAPK). Also, mobile phone exposure caused transient changes in the protein expression levels of hsp27 and p38MAPK. All these changes were non-thermal effects because, as determined using temperature probes, irradiation did not alter the temperature of cell cultures, which remained throughout the irradiation period at 37 +/- 0.3 degrees C. Changes in the overall pattern of protein phosphorylation suggest that mobile phone radiation activates a variety of cellular signal transduction pathways, among them the hsp27/p38MAPK stress response pathway. Based on the known functions of hsp27, we put forward the hypothesis that mobile phone radiation-induced activation of hsp27 may (i) facilitate the development of brain cancer by inhibiting the cytochrome c/caspase-3 apoptotic pathway and (ii) cause an increase in blood-brain barrier permeability through stabilization of endothelial cell stress fibers. We postulate that these events, when occurring repeatedly over a long period of time, might become a health hazard because of the possible accumulation of brain tissue damage. Furthermore, our hypothesis suggests that other brain damaging factors may co-participate in mobile phone radiation-induced effects.

Laser-beam-triggered microcavitation: a novel method for selective cell destruction

We describe a new method of cell destruction that may have potential for use in antitumor therapy. Cells are loaded by phagocytosis with microparticles (<1 microm) and irradiated with short laser pulses. Absorption of laser energy by the microparticles causes localized vaporization of the fluid surrounding the microparticles, leading to the generation of transient vapor bubbles (microcavitation) around the microparticles. Using cultures of bovine aortic endothelial cells, we demonstrate that induction of intralysosomal microcavitation is an efficient, rapid and selective method of cell killing that is dependent on the number of microparticles, the number of laser pulses, and the fluence of the laser pulses. Cell killing by microcavitation is a very selective process that is restricted to cells containing microparticles, leaving other cells unaffected. Intracytoplasmic release of lysosomal hydrolases is, in part, responsible for cell death, because the protease inhibitors E64d and TLCK diminished cell killing. Using the broad-specificity caspase inhibitor Z-VAD-fmk, we determined that lysosomal hydrolases could induce apoptosis in a caspase-independent manner. We also examined the possibility of microcavitation-induced delayed effects in the cells that survived the treatment. Using flow cytometry, we determined that there was no delayed cell death between 1 and 4 days after microcavitation. Moreover, we did not observe changes in the cell cycle, in expression of the proteins BCL2, HSP70 and HSP27, or in PARP degradation. In conclusion, microcavitation induces rapid and specific cells death (limited only to cells containing microparticles), without producing delayed effects among the surviving cells.

Mast cell chymase induces apoptosis of vascular smooth muscle cells

In human coronary atheromas, the numbers of degranulated mast cells and of apoptotic smooth muscle cells (SMCs) are increased. Accordingly, the possibility exists that mast cells participate in the regulation of SMC apoptosis in the lesions. Mast cells isolated from the serosal cavities of rats were stimulated to release their secretory granules. The neutral protease chymase, present in the exocytosed granules, was found to induce apoptosis when added to rat aortic SMCs in culture. The chymase-induced apoptosis of SMCs was detected by flow cytometry, microscopic analysis of cellular morphology, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL), and electrophoretic demonstration of DNA laddering. Chymase induced SMC apoptosis in a dose- and time- dependent manner, and its proteolytic activity was essential for the proapoptotic effect. In addition to rat chymase, recombinant human chymase was also found to induce apoptosis of human coronary artery SMCs in culture. These results suggest that mast cells may participate in the apoptotic regulation of SMCs in atherosclerotic lesions.

Photodynamic therapy induces apoptosis in intimal hyperplastic arteries

Photodynamic therapy (PDT) generates free radicals through the absorption of light by photosensitizers. PDT shows promise in the treatment of intimal hyperplasia, which contributes to restenosis, by completely eradicating cells in the vessel wall. This study investigates the mechanisms of PDT-induced cell death. PDT, using the photosensitizer chloroaluminum-sulfonated phthalocyanine (1 mg/kg) and laser light (lambda = 675 nm) 100 J/cm(2) was administered to rat carotid arteries after balloon injury-induced intimal hyperplasia. Apoptosis was determined by cell morphology with light microscopy and transmission electron microscopy, DNA cleavage by terminal dUTP nick-end labeling staining, and nucleosomal fragmentation (ladder pattern) by DNA agarose gel electrophoresis. Four hours after PDT, apoptosis was observed in vascular cells, as evidenced by terminal dUTP nick-end labeling staining and transmission electron microscopy. Within 24 hours no cells were present in the neointima and media. Immunofluorescence using an alpha-smooth muscle cell actin antibody confirmed the disappearance of all neointimal and medial cells within 24 hours. No inflammatory cell infiltrate was observed during this time frame. Apoptosis was sharply confined to the PDT treatment field. These data demonstrate that vascular PDT induces apoptosis as a mechanism of rapid, complete, and precise cell eradication in the artery wall. These findings and the lack of inflammatory reaction provide the basis for understanding and developing PDT for a successful clinical application in the treatment of hyperplastic conditions such as restenosis.

Photodynamic therapy generates a matrix barrier to invasive vascular cell migration

Photodynamic therapy (PDT) inhibits experimental intimal hyperplasia. PDT results in complete vascular wall cell eradication with subsequent adventitia but minimal media repopulation. This study was designed to test the hypothesis that PDT alters the vascular wall matrix thereby inhibiting invasive cell migration, and as such, provides an important barrier mechanism to favorably alter the vascular injury response. Untreated smooth muscle cells (SMCs) and fibroblasts were seeded on control and PDT-treated (100 J/cm(2); photosensitizer was chloroaluminum-sulfonated phthalocyanine, 5 microg/mL) 3-dimensional collagen matrix gels. Invasive cell migration was temporally quantified by calibrated microscopy. Zymography and ELISA assessed SMC matrix metalloproteinase levels. Molecular changes of gel proteins and their susceptibility to collagenase were analyzed by SDS-PAGE and Western blot. Limited pepsin digestion and histology were used to assess the in vivo relevance of the model, using an established rat carotid artery model at 1 and 4 weeks after balloon injury and PDT. PDT of 3-dimensional matrix of gels led to a 52% reduction of invasive SMCs and to a 59% reduction of fibroblast migration (P<0.001) but did not significantly affect secretion of matrix metalloproteinases. PDT induced collagen matrix changes, including cross-linking, which resulted in resistance to protease digestion. PDT led to a durable 45% reduction in pepsin digestion susceptibility of treated arteries (P<0.001) and inhibition of periadventitial cell migration into the media. These data suggest that PDT of matrix gels generates a barrier to invasive cellular migration. This newly identified effect on matrix proteins underscores its pleiotropic actions on the vessel wall, and as such, PDT may be of considerable potential therapeutic value to inhibit restenosis.

Different effects of photodynamic therapy and gamma-irradiation on vascular smooth muscle cells and matrix : implications for inhibiting restenosis

gamma-Irradiation (gamma-RT) and photodynamic therapy (PDT) are known to inhibit intimal hyperplasia. The common mechanism is that both modalities produce free radicals, but unlike gamma-RT, PDT generates them through the absorption of light by photosensitizers. The purpose of this in vitro study was to assess the differences that PDT and gamma-RT have on the fibroproliferative response after vascular injury by comparing their effects on vascular smooth muscle cells (SMCs) and on the extracellular matrix (ECM). Mitochondrial activity (tetrazolium salt), proliferation ([(3)H]thymidine incorporation), and the mechanisms of cell death (terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labeling [TUNEL] staining) were used to assess differences between PDT (100 J/cm(2)) and gamma-RT (10 or 20 Gy) on SMC injury. The different effects on bioregulatory molecules were investigated by quantitating the proliferation of SMCs cultured with conditioned medium and on treated ECM. PDT of SMCs reduced proliferation and mitochondrial activity (0.5+/-0.75% and 1.7+/-4.25%, respectively, P<0.0001), whereas gamma-RT of SMCs decreased cell proliferation but did not affect metabolic activity. Stimulation with calf serum of gamma-RT-treated SMCs did not affect proliferation but increased mitochondrial enzyme activity (160+/-11%, P<0.0005). The conditioned medium, derived from PDT- but not gamma-RT-treated SMCs, did not stimulate effector SMC proliferation compared with gamma-RT-treated SMCs (16+/-4.1% versus 80+/-16.8%, P<0.0001). Apoptosis was the principle cytotoxic mechanism after PDT, whereas gamma-RT cells were growth arrested but viable. PDT of the ECM reduced effector SMC proliferation compared with controls and gamma-RT cells (18+/-6.5% versus 100+/-17.7% and 84+/-8.9%, respectively, P<0.0001). These data suggest that gamma-RT and PDT may inhibit restenosis but by different mechanisms. The effects of PDT are more diverse and may result in improved outcome while avoiding the teratogenic exposure due to ionizing irradiation.

Association of p53, K-ras and proliferating cell nuclear antigen with rat lung lesions following exposure to simulated nuclear fuel particles

Expression of p53, K-ras, and proliferating cell nuclear antigen (PCNA) and mutations of p53 and K-ras genes in lung lesions of Han/Wistar rats were investigated by immunohistochemistry and direct DNA sequencing following a long-term exposure of animals to neutron-activated UO2 particles. The p53 protein was overexpressed in all five malignant tumors, in 62% of benign tumors, and in 42% of hyperplastic lesions examined. K-ras protein and PCNA levels were only slightly elevated in all types of lung lesions. In three malignant tumors a C-->T transition was detected in codon 288 (human 290) of the p53 gene, but this mutation was not present in seven other tumors analyzed. No mutations were detected in codons 12/13 and 61 of the K-ras gene in any of the five tumors analyzed. Our findings suggest that K-ras overexpression is a rare alteration, whereas p53 protein overexpression (sometimes associated with mutated p53 gene), as assessed with the CM5 antibody, is a relatively common phenomenon in hot particle-induced preneoplastic and neoplastic rat lung lesions.

The effects of the broadband UVA radiation on myeloid leukemia cells: the possible role of protein kinase C in mediation of UVA-induced effects

We examined the effects of broadband UVA radiation (320-400 nm) on a rat myeloid leukemia cell line-chloroma (ChL). A Phillips face tanner model HB 171/A was used as a light source. Chloroma were irradiated through a 5 mm thick glass filter that cut off all of the UVB contamination. The irradiances were measured, from 250 to 400 nm, with a well-characterized and calibrated double-grating spectroradiometer Optronic 742. The overall uncertainty of dose evaluation was estimated to be +/-15% (2 sigma). The cells were irradiated with UVA doses of 4 and 8 J/cm2 and cultured thereafter for 24 h. After this period of time, a marked decline up to 50% was observed in cell proliferation in UVA-irradiated ChL cultures. The cell proliferation decline was found to be caused by simultaneously occurring G2/M phase cell cycle arrest and apoptosis in part of the UVA-irradiated ChL population. Concomitantly, with the decline in cell proliferation, an increase was observed in the expression of the major histocompatibility (MHC) class I and II antigens. Because protein kinase C (PKC) is known to regulate cell proliferation, apoptosis and expression of MHC antigens, and because UVA was shown to regulate PKC activity/expression, we therefore examined whether UVA irradiation has any effect on the expression of isozymes of PKC. Western blots revealed that ChL express alpha, beta I, delta, epsilon, eta, and zeta/iota isozymes of PKC and that expression of all isozymes declined 24 h after UVA irradiation (8 J/cm2). Finally, PKC activation in ChL by exposure to phorbol ester caused cell cycle arrest in G1 phase but did not induce apoptosis. This suggests that the previously shown UVA-induced PKC activation in ChL might be responsible for the induction of MHC antigens but the simultaneously observed ChL apoptosis is likely to be mediated by PKC down-regulation. All together, our results suggest that UVA, at irradiance levels that resemble the outdoor exposure, may have profound effects on the immune-related properties of leukocytes. Thus, we speculate that in vivo the immune functions of leukocytes passing through dermal capillaries might be altered by exposure to solar UVA radiation.