Melanocyte transformation requires complete loss of all pocket protein function via a mechanism that mitigates the need for MAPK pathway activation.

Deregulation of p16INK4A is a critical event in melanoma susceptibility and progression. It is generally assumed that the major effect of loss of p16 function is mediated through the CDK-cyclin pathway via its influence on the pocket protein (PP) pRb. However, there are also two other PPs, p107 and p130, which, when phosphorylated by CDK-cyclin complexes, play a role in permitting cell progression. Cohorts of mice carrying melanocyte-specific knockouts (KOs) of various combinations of the three PPs were generated. Mice null for pRb, p107, p130 or any combination of double mutants did not develop melanoma. Surprisingly, melanocyte-specific loss of all three PPs facilitated melanoma development (median age of onset 308 days, penetrance 40% at 1 year). Tumorigenesis was exacerbated by Trp53 co-deletion (median age of onset 275 days, penetrance 82% at 1 year), with cell culture studies indicating that this difference may result from the apoptotic role of Trp53. Melanomas in PP;Trp53-deficient mice lacked either Ras or Braf mutations, and hence developed in the absence of constitutive MAPK pathway activation. The lag period between induction of total PP or PP/Trp53 KO and melanoma development indicates that additional genetic or epigenetic alterations may account for neoplastic progression. However, exome sequencing of PP;Trp53 KO melanomas failed to reveal any additional recurrent driver mutations. Analysis of the putative mutation signature of the PP;Trp53 KO melanomas suggests that melanocytes are primed for transformation via a mutagenic mechanism involving an excess of T>G substitutions, but not involving a preponderance of C>T substitutions at CpG sites, which is the case for most spontaneous cancers not driven by a specific carcinogen. In sum, deregulation of all three PPs appears central to neoplastic progression for melanoma, and the customary reference to the p16INKA/CDK4/pRB pathway may no longer be accurate; all PPs are potentially critical targets of CDK-cyclins in melanoma.

Murine melanomas accelerated by a single UVR exposure carry photoproduct footprints but lack UV signature C>T mutations in critical genes.

Ultraviolet radiation (UVR) exposure increases malignant melanoma (MM) risk, but in the context of acute, not cumulative exposure. C>T and CC>TT changes make up the overwhelming majority of single base substitutions (SBS) in MM DNA, as both precursor melanocytes and melanocytic lesions have incurred incidental exposures to sunlight. To study the mutagenic mechanisms by which acute sunburn accelerates MM, we sequenced the exomes of spontaneous and neonatal UVB-induced Cdk4-R24C::Tyr-NRASQ61K mouse MMs. UVR-induced MMs carried more SBSs than spontaneous MMs, but the levels of genomic instability, reflected by translocations and copy number changes, were not different. C>T/G>A was the most common SBS in spontaneous and UVR-induced MMs, only modestly increased in the latter. However, they tended to occur at the motif A/GpCpG (reflecting C>T transition due to spontaneous deamination of cytosine at CpG) in spontaneous MMs, and T/CpCpC/T (reflecting the effects of pyrimidine dimers on either side of the mutated C) in UVR-induced MMs. Unlike MMs associated with repetitive exposures, we observed no CC>TT changes. In addition, we also found UVR 'footprints' at T>A/A>Ts (at NpTpT) and T>C/A>G (at CpTpC). These footprints are also present in MMs from a chronic UVR mouse model, and in some human MMs, suggesting that they may be minor UVR signature changes. We found few significantly somatically mutated genes (~6 per spontaneous and 15 per UVR-induced melanoma) in addition to the Cdk4 and NRAS mutations already present. Trp53 was the most convincing recurrently mutated gene; however, in the UVR-induced MMs no Trp53 mutations were at C>T/G>A, suggesting that it was probably mutated during tumour progression, not directly induced by UVR photoproducts. The very low load of recurrent mutations convincingly induced by classical UVB-induced dimer photoproducts may support a role for cell extrinsic mechanisms, such as photoimmunosuppression and inflammation in driving MM after acute UVB exposure.

Melanoma susceptibility as a complex trait: genetic variation controls all stages of tumor progression.

Susceptibility to most common cancers is likely to involve interaction between multiple low risk genetic variants. Although there has been great progress in identifying such variants, their effect on phenotype and the mechanisms by which they contribute to disease remain largely unknown. We have developed a mouse melanoma model harboring two mutant oncogenes implicated in human melanoma, CDK4(R24C) and NRAS(Q61K). In these mice, tumors arise from benign precursor lesions that are a recognized strong risk factor for this neoplasm in humans. To define molecular events involved in the pathway to melanoma, we have for the first time applied the Collaborative Cross (CC) to cancer research. The CC is a powerful resource designed to expedite discovery of genes for complex traits. We characterized melanoma genesis in more than 50 CC strains and observed tremendous variation in all traits, including nevus and melanoma age of onset and multiplicity, anatomical site predilection, time for conversion of nevi to melanoma and metastases. Intriguingly, neonatal ultraviolet radiation exposure exacerbated nevus and melanoma formation in most, but not all CC strain backgrounds, suggesting that genetic variation within the CC will help explain individual sensitivity to sun exposure, the major environmental skin carcinogen. As genetic variation brings about dramatic phenotypic diversity in a single mouse model, melanoma-related endophenotype comparisons provide us with information about mechanisms of carcinogenesis, such as whether melanoma incidence is dependent upon the density of pre-existing nevus cells. Mouse models have been used to examine the functional role of gene mutations in tumorigenesis. This work represents their next phase of development to study how biological variation greatly influences lesion onset and aggressiveness even in the setting of known somatic driver mutations.

Proteomics identifies enhanced expression of stefin A in neonatal murine skin compared with adults: functional implications.

BACKGROUND: Skin develops through a process of epidermal proliferation, maturation, and remodelling of the epidermis and dermis. This period also involves the maturation of the skin immune system, such that antigen applied though the skin of a neonatal mouse always results in immunosuppression, whereas in adults, immunity will occur. OBJECTIVES: Using proteomics, to identify proteins uniquely involved in the development of the skin and skin immune system. METHODS: Proteins were extracted from whole skin of mice aged 4 and 21 days, and separated using two-dimensional electrophoresis. RESULTS: Of the 25 proteins that were sequenced by peptide mass fingerprinting with matrix-assisted laser desorption/ionization-time of flight-mass spectrometry, three were known markers of keratinocyte differentiation and proliferation. These were cyclophilin A, epidermal fatty acid binding protein 5 and stefin A. Of interest were the two isoforms of stefin A, an intracellular protease inhibitor, found in neonatal skin. The strong expression of stefin A in neonates was confirmed by immunohistochemical analysis, suggesting an important role in the development of the epidermis. Additionally, Western blotting identified two larger isoforms in adult skin, revealing a change in the stefin A during development. CONCLUSIONS: We propose that stefin A is involved in development of the skin, that development of the skin and of immune function is linked, and that stefin A has an important function in neonatal skin and potentially the neonatal immune response.

Lack of augmentation of tumor spectrum or severity in dual heterozygous Men1 and Rb1 knockout mice.

To identify possible genetic interactions between the mechanisms of tumor suppression of menin and pRb, we intercrossed mice with targeted deletions of Men1 and Rb1, and compared tumor development in cohorts of animals carrying single or dual mutations of these tumor-suppressor genes. In mice lacking one copy of Men1, pancreatic islet and anterior pituitary adenomas are common. In animals lacking one copy of Rb1, intermediate pituitary and thyroid tumors occur at high frequency, with less frequent development of pancreatic islet hyperplasia and parathyroid lesions. In mice heterozygous for both Men1 and Rb1, pancreatic hyperplasia and tumors of the intermediate pituitary and thyroid occurred at high frequency. Serum measurements of calcium and glucose did not vary significantly between genotypic groups. Loss of heterozygosity at the Rb1 locus was common in pituitary and thyroid tumors, whereas loss of menin was observed in pancreatic and parathyroid lesions. The tumor spectrum in the double heterozygotes was a combination of pathologies seen in each of the individual heterozygotes, without decrease in age of onset, indicating independent, non-additive effects of the two mutations. Together with the lack of increased tumor spectrum, this suggests that menin and pRb function in a common pathway of tumor suppression.

Abrogation of delayed type hypersensitivity response to Candida albicans produced by a molecular mimic of phosphorylated prolactin.

The effects of two major forms of prolactin (PRL) were examined on delayed type hypersensitivity (DTH) responses to Candida albicans. Unmodified PRL (U-PRL) had no effect on the DTH response, whereas a molecular mimic of phosphorylated PRL (S179D PRL) significantly inhibited immune responses to this robust antigen. This effect of S179D PRL was not accompanied by gross alterations in splenic T cell numbers, CD4/CD8 ratios, or T and B cell activation markers, but did produce a decrease in splenocyte apoptosis. Using gld animals, Fas ligand (FasL) was implicated in the suppressive effects of S179D PRL. Circulating IgG1 and IgG2 antibody levels were increased in response to treatment with both forms of PRL, but the effects of S179D PRL were most pronounced. Cytokine changes in the popliteal lymph nodes specific to S179D PRL treatment showed an inhibition of pro-inflammatory cytokines. In conclusion, mice treated with a molecular mimic of phosphorylated prolactin showed a profound inhibition of DTH responses to Candida correlating with an absence of GM-CSF, IL-4, and IL-13 production and a marked reduction in IL-12p70 synthesis.

Impaired CD40-signalling in Langerhans' cells from murine neonatal draining lymph nodes: implications for neonatally induced cutaneous tolerance.

Cutaneous tolerance to antigens may be induced in mice through application of antigen during the first few days following birth. The mechanism governing this neonatally induced tolerance remains uncertain. We employed a contact hypersensitivity model to analyse dendritic cell (DC) function and the expression of classical and non-classical lymphocyte populations within the neonate. Examination of draining lymph node DC after antigenic challenge of the skin revealed these DC to be significantly deficient in their ability to stimulate antigen-specific T cell proliferation. Co-stimulatory molecule (CD40, CD80 and CD86) expression of these cells was deficient in comparison to adult DC, and functional tests revealed these cells to possess a critical absence of CD40 signalling. A numerical analysis of classical and non-classical lymphocyte expression demonstrated that while the neonatal spleen is devoid of T cells, the lymph nodes have a normal repertoire of T, B, gammadelta and CD4+CD25+ lymphocytes but an increased expression of natural killer (NK) cells. This study indicates that functionally deficient DC are likely contributors to neonatally induced cutaneous tolerance.

UV irradiation augments lymphoid malignancies in mice with one functional copy of wild-type p53.

Epidemiological studies have suggested an association between exposure to solar UV radiation and the incidence of lymphoid malignancies, which has increased substantially worldwide during the last two decades. Findings from animal studies have raised the question of whether UV radiation might influence the development of lymphoid malignancies by means of its immunosuppressive effect. In this study, we examined the effect of UV irradiation on the development of lymphoid malignancies in mice with no or only one functional copy of p53. Mice that lack both copies of p53 spontaneously develop high frequency of lymphoid malignancies in the thymus and spleen. p53 heterozygous mice with only one copy of the wild-type allele also develop lymphoid malignancies, but with a much lower frequency and a long latent period. In our study using mice of the C57BL/6 background, only one of the unirradiated mice lacking one copy of p53 (p53(+/-)) spontaneously developed a lymphoid tumor (6%), whereas 88% of UV-irradiated p53(+/-) mice developed lymphoid tumors in the spleen or liver. None of the control or UV-irradiated p53 wild-type mice developed lymphoid tumors during the 60-week observation period. Both UV-irradiated and unirradiated mice lacking both copies of p53 (p53(-/-)) rapidly developed thymic lymphomas and/or lymphoid tumors in spleen or liver. All of the lymphoid tumors tested were of T cell type. The immune responses of the mice to contact sensitization were identical and were suppressed to the same extent by UV irradiation regardless of the genotype. These results indicate that differences in immune reactivity do not account for the different effects of UV radiation on lymphoid malignancies and, in addition, that p53 is not required for generation of T cell-mediated immunity. Interestingly, whereas p53 mutations or loss of heterozygosity did not account for the accelerated development of lymphoid tumors in UV-irradiated p53(+/-) mice, deletions in the p16(INK4a) gene were quite common. These data provide the experimental evidence that UV irradiation induces lymphoid neoplasms in genetically susceptible mice and support the hypothesis that extensive sunlight exposure contributes to the induction of lymphoma in humans.

Prevention of autoimmunity by induction of cutaneous tolerance.

Autoimmune gastritis develops in 20-60% of BALB/c mice following thymectomy at 3 days after birth (3dnTx). Previously we identified the gastric H+/K+ ATPase as the causative autoantigen and mapped the immunoreactive T cell epitope to a carboxyl-terminal peptide on the gastric H+/K+ ATPase beta subunit. Here we show that autoimmune gastritis can be suppressed by immunizing 3dnTx mice through neonatal skin with the beta subunit peptide, in combination with the contact sensitizer TNCB. When spleen cells were transferred from suppressed mice to nude mice a proportion of recipient mice developed gastritis. These results indicate that pathogenic T cells were still present in the 3dnTx mice but the absence of gastritis indicates that their activity can be regulated following induction of cutaneous tolerance by immunizing through neonatal skin. We propose that cutaneous tolerance is induced through mediation of immature Langerhans cells in neonatal skin and that this tolerance prevented the autoreactivity of pathogenic T cells. This procedure will have implications for strategies to suppress autoimmunity.

Ultraviolet light induced injury: immunological and inflammatory effects.

This article reviews many of the complex events that occur after cutaneous ultraviolet (UV) exposure. The inflammatory changes of acute exposure of the skin include erythema (sunburn), the production of inflammatory mediators, alteration of vascular responses and an inflammatory cell infiltrate. Damage to proteins and DNA accumulates within skin cells and characteristic morphological changes occur in keratinocytes and other skin cells. When a cell becomes damaged irreparably by UV exposure, cell death follows via apoptotic mechanisms. Alterations in cutaneous and systemic immunity occur as a result of the UV-induced inflammation and damage, including changes in the production of cytokines by keratinocytes and other skin-associated cells, alteration of adhesion molecule expression and the loss of APC function within the skin. These changes lead to the generation of suppressor T cells, the induction of antigen-specific immunosuppression and a lowering of cell-mediated immunity. These events impair the immune system's capacity to reject highly antigenic skin cancers. This review gives an overview of the acute inflammatory and immunological events associated with cutaneous UV exposure, which are important to consider before dealing with the complex interactions that occur with chronic UV exposure, leading to photocarcinogenesis.

Loss of Fas-ligand expression in mouse keratinocytes during UV carcinogenesis.

Skin cells containing excessive ultraviolet (UV) radiation-induced DNA damage are eliminated by apoptosis that involves the p53 pathway and Fas/Fas-Ligand (Fas-L) interactions. To determine whether dysregulation of apoptosis plays a role in skin cancer development through disruption of Fas/Fas-L interactions, hairless SKH-hr1 mice were exposed to chronic UV irradiation from Kodacel-filtered FS40 lamps for 30 weeks. Their skin was analyzed for the presence of sunburn cells (apoptotic keratinocytes) and for Fas and Fas-L expression at various time points. A dramatic decrease in the numbers of morphologically identified sunburn cells and TUNEL-positive cells was detected as early as 1 week after chronic UV exposure began. After 4 weeks of chronic UV exposure, these cells were barely detectable. This defect in apoptosis was paralleled by an initial decrease in Fas-L expression during the first week of chronic UV irradiation and a complete loss of expression after 4 weeks. Fas expression, however, increased during the course of chronic UV exposure. p53 mutations were detected in the UV-irradiated epidermis as early as 1 week after irradiation began and continued to accumulate with further UV exposure. Mice exposed to chronic UV began to develop skin tumors after approximately 8 weeks, and all mice had multiple skin tumors by 24 weeks. Most of the tumors expressed Fas but not Fas-L. We conclude that chronic UV exposure may induce a loss of Fas-L expression and a gain in p53 mutations, leading to dysregulation of apoptosis, expansion of mutated keratinocytes, and initiation of skin cancer.

Induction of primary cutaneous melanomas in C3H mice by combined treatment with ultraviolet radiation, ethanol and aloe emodin.

The role of ultraviolet (UV) radiation in the induction of nonmelanoma skin cancer is widely accepted, although its precise contribution to the development of primary cutaneous melanoma skin cancer requires further definition. We found that painting aloe emodin, a trihydroxyanthraquinone from Aloe barbadensis, in ethyl alcohol vehicle on the skin of mice in conjunction with exposure to UVB (280-320 nm) radiation results in the development of melanin-containing skin tumors. C3H/HeN mice were treated thrice weekly with aloe emodin in a 25% ethanol in water vehicle and exposed to 15 kJ/m2 UV radiation. Neither ethanol vehicle nor aloe emodin alone induced skin tumors in the absence of UV radiation. In two separate experiments, 20-30% of the mice treated with a combination of UV radiation and ethanol vehicle and 50-67% of the UV-irradiated animals given aloe emodin in ethanol vehicle developed primary cutaneous melanin-containing tumors. The diagnosis of melanoma was established using Fontana silver stain for melanin; these tumors were negative for vimentin and keratin. Melanin-containing melanosomes were observed by transmission electron microscopy in tumors diagnosed as melanomas. Although the mechanism of carcinogenesis in these mice is currently unknown, our findings have led to the development of the first facile murine model for the induction of primary melanoma. This model has the potential to clarify the role of UV radiation in the etiology of malignant melanoma.

Temporal events in skin injury and the early adaptive responses in ultraviolet-irradiated mouse skin.

We examined the effects of ultraviolet (UV) radiation on the time course for induction of sunburn (apoptotic) cells and expression of proteins known to be associated with growth arrest and apoptosis in SKH-hr1 mouse skin. Mice were irradiated with a single dose (2.5 kJ/m(2)) of UV from Kodacel-filtered (290-400 nm) FS40 sunlamps and the skin tissues were analyzed at various times after irradiation for the presence of apoptotic cells and expression of p53, p21(Waf-1/Cip1), bcl-2, bax, and proliferating cell nuclear antigen. The results indicated that p53 expression was induced early in the epidermis, reaching maximum levels 12 hours after irradiaton, and p21(Waf-1/Cip1) expression in the epidermis peaked at 24 hours after irradiation. In contrast, UV radiation induced high levels of bax at 24 to 72 hours after irradiation with a concomitant decrease in bcl-2 expression. Coinciding with these changes, apoptotic cells began to appear 6 hours after irradiation and reached a maximum at 24 hours after irradiation. Interestingly, proliferating cell nuclear antigen expression, which was initially confined to the basal layer, became dispersed throughout the basal and suprabasal layers of the skin at 48 hours and paralleled marked hyperplasia. These results suggest that UV irradiation of mouse skin induces apoptosis mediated by the p53/p21/bax/bcl-2 pathway and that the dead cells are replaced by hyperproliferative cells, leading to epidermal hyperplasia. This implies that UV-induced apoptosis and hyperplasia are closely linked and tightly regulated and that dysregulation of these two events may lead to skin cancer development.

Carcinogen-modified dendritic cells induce immunosuppression by incomplete T-cell activation resulting from impaired antigen uptake and reduced CD86 expression.

Exposure of the skin to environmental stimuli, such as chemical or physical carcinogens, modifies the local skin environment, including depletion of epidermal Langerhans' cells (LC). Any subsequent exposure of the LC-depleted skin to antigen results in the generation of antigen-specific tolerance. In this study we evaluated the antigen-bearing cells in the draining lymph nodes by capitalizing on the fluorescent nature of the contact sensitizer, fluorescein isothiocyanate (FITC). When FITC was applied to the skin of normal mice, two distinct populations of antigen-bearing cells were identified in the draining lymph nodes. They were classified as either FITChi or FITClo on the basis of their fluorescence intensity and thus the amount of antigen they internalized. Only FITClo cells were detected in the lymph nodes draining FITC-treated murine skin that had been depleted of epidermal LC by prior treatment with the complete carcinogen 9,10-dimethyl 1,2-benzanthracene (DMBA). Functional analysis of these cells revealed that the FITChi cells, but not the FITClo cells, induced antigen-specific T-cell proliferation. Further analysis of the FITClo cells from the DMBA-treated mice demonstrated that these cells had reduced levels of CD80 expression, had substantially reduced levels of CD86 expression and performed poorly as co-stimulator cells in an anti-CD3-mediated proliferative assay. Nonetheless these cells still induced early signs of T-cell activation and interleukin-12 production. Consequently the FITClo cells migrating from the LC-depleted skin, through a combination of reduced antigen presentation and reduced co-stimulatory activity, induced a state of unresponsiveness or anergy in the responder T cells in a similar manner to that observed when antigen presentation occurs in the absence of co-stimulation. We propose that these unresponsive, or anergic cells, account for the antigen-specific tolerance observed in these experiments.

Richard Charles Nairn, Foundation Professor of Pathology and Immunology at Monash University.

Richard Charles Nairn was the Founding Professor of Pathology and Immunology at Monash University, Melbourne, Australia, from 1963 to 1984. He built an outstanding teaching and research department and inaugurated the first Australian diagnostic laboratory in clinical immunology based at the Alfred Hospital, Melbourne. As the first Chief Examiner in Immunology for the Royal College of Pathologists of Australasia (RCPA) and first Chair of the Joint Specialist Advisory Committee in Immunology for the Royal Australasian College of Physicians (RACP) and the RCPA, he initiated and guided the early years of laboratory and clinical immunology in Australasia. His contributions to immunopathology, particularly in cancer immunology and the technology of immunofluorescence were significant, and he was an excellent Editor and the Associate Editor of Pathology for 17 years. Richard Nairn's legacy to Australian pathology and the RCPA is the vibrant specialty of clinical immunology.

p53 protects against skin cancer induction by UV-B radiation.

To assess the role of the p53 tumor suppressor gene in skin carcinogenesis by UV radiation, mice constitutively lacking one or both copies of the functional p53 gene were compared to wild-type mice for their susceptibility to UV carcinogenesis. Heterozygous mice showed greatly increased susceptibility to skin cancer induction, and homozygous p53 knockout mice were even more susceptible. Accelerated tumor development in the heterozygotes was not associated with loss of the remaining wild-type allele of p53, as reported for tumors induced by other carcinogens, but in many cases was associated with UV-induced mutations in p53. Tumors arose on the ears and dorsal skin of mice of all three genotypes, and homozygous knockout mice also developed ocular tumors, mainly melanomas. Skin tumors in the p53 knockout mice were predominately squamous cell carcinomas and were associated with premalignant lesions resembling actinic keratoses, whereas those in the heterozygous and wild-type mice were mainly sarcomas. These results demonstrate the importance of p53 in protecting against UV-induced cancers, particularly in the eye and epidermis.

Induction of peripheral tolerance in neonatally thymectomized mice by immunization through chemical carcinogen-altered skin.

BALB/c mice thymectomized 3 days after birth (3dnTx) are prone to the development of autoimmune gastritis. As this outcome may be a consequence of altered immunoregulatory mechanisms, we set out to determine the immunological status of these mice and their capacity to acquire antigen-specific peripheral tolerance. The latter was assessed by the capacity of these mice to suppress a contact sensitivity response to 2,4,6-trinitrochlorobenzene (TNCB) following treatment of the skin by the carcinogen, DMBA. The 3dnTx mice had a reduced number of CD4(+) and CD8(+) T cells and a reduced lymphocyte proliferative response to PHA, but a normal contact sensitivity response to TNCB. After treatment of the skin with DMBA these mice failed to develop contact sensitivity to TNCB. Adoptive transfer of splenocytes from these mice to naive mice transfered antigen-specific suppression, irrespective of whether the 3dnTx mice had developed autoimmune gastritis. We conclude that despite thymectomy at day 3 and the attendant immunosuppression, the capacity of BALB/c mice to generate antigen-specific peripheral tolerance to TNCB was retained. These results suggest that precursor T cells which mediate suppression to antigens such as TNCB are present in 3dnTx mice and that these cells are likely to have developed in the thymus and exported to the periphery before 3 days after birth.

The use of spectrophotometry to estimate melanin density in Caucasians.

The density of cutaneous melanin may be the property of the skin that protects it from damage by solar radiation, but there is not an accepted, noninvasive method of measuring it. To determine whether the density of cutaneous melanin can be estimated from reflectance of visible light by the skin, reflectance of 15-nm wavebands of light by the skin of the inner upper arm of each of 82 volunteers was measured at 20-nm intervals with a Minolta 508 spectrophotometer. A 3-mm skin biopsy was then taken from the same site, and four nonserial sections of it were stained with Masson Fontana for melanin. The melanin content of the basal area was calculated using the NIH Image analysis system. We show that cutaneous melanin in Caucasians can be estimated by the difference between two measurements of reflectance of visible light by the skin: those at wavelengths 400 and 420 nm. This new spectrophotometric measurement was more highly correlated (r = 0.68) with the histological measurements of cutaneous melanin than was skin reflectance of light of wavelength 680 nm (r = 0.33). Reflectances in the range of 650-700 nm have been used previously in skin cancer research. This relatively accurate measurement of melanin is quick and noninvasive and can be readily used in the field. It should provide improved discrimination of individual susceptibility to epidermal tumors in Caucasians and information about melanin's biological role in the causation of skin cancer.

Sun exposure, sunscreen and their effects on epidermal Langerhans cells.

This study examined the effects of chronic and current sun exposure on the number of Langerhans cells in epidermal sheets of UV-exposed and unexposed skin of the arms and assessed the effect of sunscreens. Participants were enrolled in a skin cancer prevention trial and had been using sunscreen daily for the previous 3 years. There were significantly fewer Langerhans cells on the exposed (463 cells/mm2) than on the unexposed forearm (528 cells/mm2) (P = 0.0001). High sun exposure in the previous 2 weeks and a history of predominantly outdoor occupations were both associated with a reduced number of Langerhans cells, although age and other biological indicators of chronic exposure were not associated. Sunscreen use was protective against the effects of current but not chronic sun exposure, with a suggestion of a greater effect at higher levels of exposure. Unexpectedly, people with a past history of nonmelanoma skin cancer had more Langerhans cells in both the exposed and the unexposed skin. These results emphasize the need for continued public health education to protect the immune system from the damaging effects of UV radiation.