A review of studies on the effects of ultraviolet irradiation on the resistance to infections: evidence from rodent infection models and verification by experimental and observational human studies

Sunshine duration and solar radiation contributed to severe Bell's palsy: An 11-year time series analysis based on a distributed lag non-linear model model

Although previous studies have suggested that meteorological factors are associated with Bell's palsy, articles on this topic are rare and the results are inconsistent. We aim to reveal the relationship between exposure to different meteorological factors and the onset of severe Bell's palsy (SBP) with daily data. A case-crossover study based on time-series data was applied, and the minimum risk value of each climatic factor was set as the reference value. We fitted a distributed lag non-linear model (DLNM) which applied quasi-Poisson regression to evaluate the exposure-response association and the lag-response association of meteorological factors on the occurrence of SBP. The mode value and per-decile interval value of each meteorological factor were all included in the analysis. Sensitivity analyses were conducted to test the robustness of results. A total of 863 SBP patients (474 males and 389 females) from 7 hospitals in the Shenzhen Futian District were selected from January 2009 to February 2020. The highest relations effect was tested in the cumulative exposure-response result shown as follows; mean temperature at the minimum value 15.3°C with RR of 10.370 (1.557-69.077) over lag 0 to 13; relative humidity at the 30th value 71% with RR of 8.041 (1.016-63.616) over lag 0 to 14; wind speed at the 90th value 31 (0.1 m/s) with RR of 1.286 (1.038-1.593) over lag 0; mean air pressure at the 30th value 1001.4 (pa) with RR of 9.052 (1.039-78.858) over lag 0 to 5; visibility at the 80th value 26.5 (km) with RR of 1.961 (1.005-1.423) over lag 0 to 2; average total cloud cover at the max value 100 (%) with RR 1.787 (1.014-3.148) over lag 0 to 2; sunshine duration at the 10th value 0.1 (h) with RR of 4.772 (1.018-22.361); daily evaporation shows no relationship in the cumulative result; daily average solar radiation at the minimum value 0 (W/m2) with RR of 5.588 (1.184-26.382). There is a relationship between wind speed and the onset of SBP, while mean air pressure, visibility, and average total cloud cover, especially sunshine duration and solar radiation which showed a strong effect, may be associated with severe clinical symptoms of SBP. Mean temperature and relative humidity may affect the course of SBP.

Association between season of vaccination and antibody levels against infectious diseases

Vaccination has reduced the disease burden of vaccine-preventable diseases. However, the extent to which seasonal cycles of immunity could influence vaccine-induced immunity is not well understood. A national cross-sectional serosurveillance study performed in the Netherlands (Pienter-2) yielded data to investigate whether season of vaccination was associated with antibody responses induced by DT-IPV (diphtheria, tetanus and poliomyelitis), MMR (measles, mumps and rubella) and meningococcus C (MenC) vaccines in children. In total, 434 children met the inclusion criteria to study DT-IPV immunity, 811 for MMR and 311 for MenC. Differences in log(antibody levels) by season of vaccination were investigated with linear multivariable regression analyses. Seroconversion rates varied according to season of vaccination for rubella (90% of autumn-vaccinated children vs. 99% of winter-vaccinated had concentrations above cut-off levels). Summer-vaccinated boys showed a slower decline of tetanus antibodies (6% per month), in comparison with winter-vaccinated boys. In conclusion, season of vaccination showed little association with immunological protection. However, a number of associations were seen with a P-value of about 0.03; and adding data from a just-completed nationwide serological study might add more power to the current study. Further immunological and longitudinal investigations could help understand the mechanisms of seasonal influence in vaccine-induced responses.

Are there differences in immune responses following delivery of vaccines through acutely or chronically sun-exposed compared with sun-unexposed skin?

The majority of human vaccines are administered above the deltoid muscle of the arm, a site that is chronically sun-exposed in many people. It is known that exposure of the skin to the UV wavelengths in sunlight stimulates systemic immunosuppression, an outcome that is associated with reduced immunity to microbial infections in animal models. Here we consider whether immunization of humans through a UV-irradiated skin site will lead to a less effective immune response compared with immunization through an unexposed site. Studies showing that the efficacy of vaccination can be reduced when surrogates of increased levels of sun exposure, such as latitude of residence and season of the year, are considered. Results from a limited number of intervention experiments in humans demonstrate a similar pattern. To provide an explanation for these findings, changes in the number and functional potential of immune cells in chronically sun-exposed compared with unexposed skin are outlined. UV radiation-induced changes to skin cells are also relevant when considering skin sites for administration of immune-tolerizing peptides. The review provides the basis for further research into the effects of acute and chronic UV radiation exposure on skin cells in the context of vaccination.

Factors That Influence the Immune Response to Vaccination

There is substantial variation between individuals in the immune response to vaccination. In this review, we provide an overview of the plethora of studies that have investigated factors that influence humoral and cellular vaccine responses in humans. These include intrinsic host factors (such as age, sex, genetics, and comorbidities), perinatal factors (such as gestational age, birth weight, feeding method, and maternal factors), and extrinsic factors (such as preexisting immunity, microbiota, infections, and antibiotics). Further, environmental factors (such as geographic location, season, family size, and toxins), behavioral factors (such as smoking, alcohol consumption, exercise, and sleep), and nutritional factors (such as body mass index, micronutrients, and enteropathy) also influence how individuals respond to vaccines. Moreover, vaccine factors (such as vaccine type, product, adjuvant, and dose) and administration factors (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important. An understanding of all these factors and their impacts in the design of vaccine studies and decisions on vaccination schedules offers ways to improve vaccine immunogenicity and efficacy.

The role of UV radiation and vitamin D in the seasonality and outcomes of infectious disease

The seasonality of infectious disease outbreaks suggests that environmental conditions have a significant effect on disease risk. One of the major environmental factors that can affect this is solar radiation, primarily acting through ultraviolet radiation (UVR), and its subsequent control of vitamin D production. Here we show how UVR and vitamin D, which are modified by latitude and season, can affect host and pathogen fitness and relate them to the outcomes of bacterial, viral and vector-borne infections. We conducted a thorough comparison of the molecular and cellular mechanisms of action of UVR and vitamin D on pathogen fitness and host immunity and related these to the effects observed in animal models and clinical trials to understand their independent and complementary effects on infectious disease outcome. UVR and vitamin D share common pathways of innate immune activation primarily via antimicrobial peptide production, and adaptive immune suppression. Whilst UVR can induce vitamin D-independent effects in the skin, such as the generation of photoproducts activating interferon signaling, vitamin D has a larger systemic effect due to its autocrine and paracrine modulation of cellular responses in a range of tissues. However, the seasonal patterns in infectious disease prevalence are not solely driven by variation in UVR and vitamin D levels across latitudes. Vector-borne pathogens show a strong seasonality of infection correlated to climatic conditions favoring their replication. Conversely, pathogens, such as influenza A virus, Mycobacterium tuberculosis and human immunodeficiency virus type 1, have strong evidence to support their interaction with vitamin D. Thus, UVR has both vitamin D-dependent and independent effects on infectious diseases; these effects vary depending on the pathogen of interest and the effects can be complementary or antagonistic.

Sun protection to improve vaccine effectiveness in children in a high ambient ultraviolet radiation and rural environment: an intervention study

BACKGROUND

Vaccination is a mainstay of preventive healthcare, reducing the incidence of serious childhood infections. Ecological studies have demonstrated an inverse association between markers of high ambient ultraviolet (UV) radiation exposure (e.g., sunny season, low latitude of residence) and reduction in the vaccination-associated immune response. Higher sun exposure on the day prior to and spanning the day of vaccination has been associated with a reduced antigen-specific immune response independent of skin pigmentation. The South African Department of Health's Expanded Programme on Immunisation provides free vaccinations in government primary health care clinics. In some areas, these clinics may have only a small waiting room and patients wait outside in full sun conditions. In rural areas, patients may walk several kilometres to and from the clinic. We hypothesised that providing sun protection advice and equipment to mothers of children (from 18 months) who were waiting to be vaccinated would result in a more robust immune response for those vaccinated.

METHODS

We conducted an intervention study among 100 children receiving the booster measles vaccination. We randomised clinics to receive (or not) sun protection advice and equipment. At each clinic we recorded basic demographic data on the child and mother/carer participants, their sun exposure patterns, and the acceptability and uptake of the provided sun protection. At 3-4 weeks post-vaccination, we measured measles IgG levels in all children.

DISCUSSION

This is the first intervention study to assess the effect of sun protection measures on vaccine effectiveness in a rural, real-world setting. The novel design and rural setting of the study can contribute much needed evidence to better understand sun exposure and protection, as well as factors determining vaccine effectiveness in rural Africa, and inform the design of immunisation programmes. (TRN PACTCR201611001881114, 24 November 2016, retrospective registration).

The potential impact of climate change and ultraviolet radiation on vaccine-preventable infectious diseases and immunization service delivery system

Climate change and solar ultraviolet radiation may affect vaccine-preventable infectious diseases (VPID), the human immune response process and the immunization service delivery system. We systematically reviewed the scientific literature and identified 37 relevant publications. Our study shows that climate variability and ultraviolet radiation may potentially affect VPID and the immunization delivery system through modulating vector reproduction and vaccination effectiveness, possibly influencing human immune response systems to the vaccination, and disturbing immunization service delivery. Further research is needed to determine these affects on climate-sensitive VPID and on human immune response to common vaccines. Such research will facilitate the development and delivery of optimal vaccination programs for target populations, to meet the goal of disease control and elimination.

Variations in total ozone column and biologically effective solar UV exposure doses in Bologna, Italy during the period 2005-2010

Variations in total ozone column and sun exposures able to cause erythema and damage the DNA molecules were observed by the narrow-band filter radiometer UV-RAD in Bologna, Italy from 2005 to 2010. The ozone columns determined from the UV-RAD measurements were found to be close to those provided by the satellite Ozone Monitoring Instrument (OMI) showing an average discrepancy of 1% with standard deviation of ± 6%. Analysis of the data highlights a well-marked annual cycle of the ozone column variations while the oscillations with periods of 8, 18 and 34 months present much smaller amplitudes. The influence of the frequency of solar irradiance measurements on the accuracy of the evaluated daily exposure dose has been studied and it was found that time intervals no longer than 5-10 min between the measurements of erythema and DNA damage effective UV irradiances provide a satisfactory assessment of the corresponding daily exposures. The latter do not present significant year-to-year variations for the period under study, while their annual distributions show slight changes likely due to the specific cloud cover and ozone column variability for different years. The annual erythemal exposure dose for 2007-2010 varied between 603.7 and 638.1 kJ m(-2), while the corresponding sun exposure affecting DNA changed from 6.38 to 7.91 kJ m(-2).

Prospective study of ultraviolet radiation exposure and mortality risk in the United States

Geographic variations in mortality rate in the United States could be due to several hypothesized factors, one of which is exposure to solar ultraviolet radiation (UVR). Limited evidence from previous prospective studies has been inconclusive. The association between ambient residential UVR exposure and total and cause-specific mortality risks in a regionally diverse cohort (346,615 white, non-Hispanic subjects, 50-71 years of age, in the National Institutes of Health (NIH)-AARP Diet and Health Study) was assessed, with accounting for individual-level confounders. UVR exposure (averaged for 1978-1993 and 1996-2005) from NASA's Total Ozone Mapping Spectrometer was linked to the US Census Bureau 2000 census tract of participants' baseline residence. Multivariate-adjusted Cox proportional-hazards models were used to estimate hazard ratios and 95% confidence intervals. Over 12 years, UVR exposure was associated with total deaths (n = 41,425; hazard ratio for highest vs. lowest quartiles (HRQ4 vs. Q1) = 1.06, 95% confidence interval (CI): 1.03, 1.09; Ptrend < 0.001) and with deaths (all Ptrend < 0.05) due to cancer (HRQ4 vs. Q1 = 1.06, 95% CI: 1.02, 1.11), cardiovascular disease (HRQ4 vs. Q1 = 1.06, 95% CI: 1.00, 1.12), respiratory disease (HRQ4 vs. Q1 = 1.37, 95% CI: 1.21, 1.55), and stroke (HRQ4 vs. Q1 = 1.16, 95% CI: 1.01, 1.33) but not with deaths due to injury, diabetes, or infectious disease. These results suggest that UVR exposure might not be beneficial for longevity.

Gene profiling of narrowband UVB-induced skin injury defines cellular and molecular innate immune responses

The acute response of human skin to UVB radiation has not been fully characterized. We sought to define the cutaneous response at 24 hours following narrowband UVB (NB-UVB, 312-nm peak), a therapeutically relevant source of UVB, using transcriptional profiling, immunohistochemistry, and immunofluorescence. There were 1,522 unique differentially regulated genes, including upregulated genes encoding antimicrobial peptides (AMPs) (S100A7, S100A12, human beta-defensin 2, and elafin), as well as neutrophil and monocyte/dendritic cell (DC) chemoattractants (IL-8, CXCL1, CCL20, CCL2). Ingenuity pathway analysis demonstrated activation of innate defense and early adaptive immune pathways. Immunohistochemistry confirmed increased epidermal staining for AMPs (S100A7, S100A12, human beta-defensin 2, and elafin). Inflammatory myeloid CD11c(+)BDCA1(-) DCs were increased in irradiated skin, which were immature as shown by minimal colocalization with DC-LAMP, and coexpressed inflammatory markers tumor necrosis factor (TNF) and TNF-related apoptosis-inducing ligand in irradiated skin. There were increased BDCA3(+) DCs, a cross-presenting DC subtype with immunosuppressive functions, and these cells have not been previously characterized as part of the response to UVB. These results show that the acute response of human skin to erythemogenic doses of NB-UVB includes activation of innate defense mechanisms, as well as early infiltration of multiple subtypes of inflammatory DCs, which could serve as a link between innate and adaptive immunity.

Ultraviolet light and resistance to infectious diseases

Exposure to ultraviolet (UV) radiation, as in sunlight, can modulate immune responses in animals and humans. This immunomodulation can lead to positive health effects especially with respect to certain autoimmune diseases and allergies. However, UV-induced immunomodulation has also been shown to be deleterious. Experimental animal studies have revealed that UV exposure can impair the resistance to many infectious agents, such as bacteria, parasites, viruses, and fungi. Importantly, these effects are not restricted to skin-associated infections, but also concern systemic infections. UV radiation induces a multistep process, locally in the skin as well as systemically, that ultimately leads to immunosuppression. The first event is the absorption of "UV" photons by chromophores, or so-called photoreceptors, such as DNA and urocanic acid (UCA) in the upper cell layers of the skin. Upon absorption of UV radiation, trans-UCA isomerizes to the cis-isomer. Cis-UCA is likely the most important mediator of UV-induced immunosuppression, as this compound has been shown to modulate the induction of contact type hypersensitivity and delayed type hypersensitivity, allograft rejection, and the functions of monocytes and T-lymphocytes as well as natural killer cells. The real consequences of UV-induced immunomodulation on resistance to infectious diseases for humans are not fully known. Risk estimations have been performed through extrapolation of animal data, obtained from infection models, to the human situation. This estimation indicated that UV doses relevant to outdoor exposure can impair the human immune system sufficiently to have effects on resistance to infections, but also indicated that human data are necessary to further quantify and validate this risk estimation. Further information has been obtained from vaccination studies in human volunteers as ethical reasons prohibit studies with infectious agents. Studies in mice and human volunteers on the effects of prior UVB exposure on hepatitis B vaccination responses revealed suppressed cellular and humoral immune responses in mice but not in human volunteers. However, subgroups within the performed human volunteer study made by determination of cytokine polymorphisms or UVB-induced mediators, revealed that some individuals have suppressed hepatitis B vaccination responses after UVB exposure. Thus, it might be concluded that the human immune system can be affected by UVB exposure, and decreased resistance to infectious diseases can be expected after sun exposure.

The Use of In Vitro Systems for Evaluating Immunotoxicity: The Report and Recommendations of an ECVAM Workshop

This is the report of a workshop organised by the European Centre for the Validation of Alternative Methods (ECVAM). ECVAM's main goal, as defined in 1993 by its Scientific Advisory Committee, is to promote the scientific and regulatory acceptance of alternative methods that are of importance to the biosciences and which replace, reduce or refine the use of laboratory animals. One of the first priorities set by ECVAM was the implementation of procedures that would enable it to become well informed about the state-of-the-art of non-animal test development and validation, and the potential for the possible incorporation of alternative tests into regulatory procedures. It was decided that this would be best achieved by the organization of ECVAM workshops on specific topics, at which small groups of invited experts would review the current status of various types of in vitro tests and their potential uses, and make recommendations about the best ways forward (Anonymous, 1994). The workshop on "The use of in vitro systems for evaluating Immunotoxicity" was held at ECVAM (Ispra), Italy, on 24th-26th November 2003. The participants represented academia, national organizations, international regulatory bodies and industry. The aim of the workshop was to review the state-of-the-art in the field of in vitro immunotoxicology, and to develop strategies towards the replacement of in vivo testing. At the end of this report are listed the recommendations that should be considered for prevalidation and validation of relevant and reliable procedures, that could replace the use of animals in chemical and cosmetics toxicity testing.

The challenges of UV-induced immunomodulation for children's health

Exposure to solar ultraviolet radiation (UVR) is recognised to have both beneficial and harmful effects on human health. With regard to immune responses, it can lead to suppression of immunity and to the synthesis of vitamin D, a hormone that can alter both innate and adaptive immunity. The consequences in children of such UV-induced changes are considerable: first there are positive outcomes including protection against some photoallergic (for example polymorphic light eruption) and T cell-mediated autoimmune diseases (for example multiple sclerosis) and asthma, and secondly there are negative outcomes including an increased risk of skin cancer (squamous cell carcinoma, basal cell carcinoma and cutaneous malignant melanoma) and less effective control of several infectious diseases. Many uncertainties remain regarding the amount of sun exposure that would provide children with the most effective responses against the variety of immunological challenges that they are likely to experience.

The consequences of UV-induced immunosuppression for human health

Exposure to UV radiation can cause suppression of specific immune responses. The pathways leading to the down-regulation are complex, starting from the absorption of UV photons by chromophores in the skin and ending with local and systemic changes in immune mediators, the generation of T and B regulatory cells and inhibition of effector and memory T cell activation. The consequences for human health are thought to be both beneficial and adverse. The former are illustrated by protection against polymorphic light eruption, and possible protection against T cell-mediated autoimmune diseases and asthma. The latter are illustrated by skin cancer, cutaneous lupus erythematosus and infectious diseases including vaccination. Many outstanding questions remain in this rapidly developing and controversial area, not least what advice to give the general public regarding their sun exposure. While considerable advances have been made in the development of strategies that preserve the health benefits of sunlight exposure and decrease its detrimental effects, further research is required before optimal levels of protection are achieved.

UV-induced immunosuppression and the efficacy of vaccination

Exposure to ultraviolet radiation (UVR) suppresses immunity by complex pathways, initiated by chromophores located in the skin and ending with the generation of specific subsets of T and B regulatory cells. The primary and memory (recall) immune response to a wide variety of antigens, including microorganisms, can be reduced by UVR, leading to the possibility that the efficacy of vaccination could be similarly reduced. A limited number of animal models of vaccination demonstrate that this may indeed be the case. The situation in human subjects has not been rigorously assessed but there are indications from a variety of sources that UVR adversely affects the immune responses to several vaccines. These studies are reviewed and the implications for vaccine administration discussed. As vaccination represents a major public health measure world-wide for the control of an increasing number of common infections, it is important to maximise its efficacy; therefore further evaluation of UVR in the context of vaccination is required and warranted.

Preliminary assessment of the risks associated with solar ultraviolet-A exposure

An approach is proposed to assess the periods of human skin exposure to solar ultraviolet-A (UV-A, 315-400 nm) irradiance in natural conditions that are able to yield doses found to trigger carcinogenesis in laboratory experiments. Weighting functions, adopted to perform such estimate are constructed, allowing for a comparison between environmental and laboratory doses. Furthermore, the impact of stratum corneum (SC) thickness on the studied environmental doses was investigated. Based on laboratory studies, it was found that exposure periods of less than a month, at mid-latitudes, could provide irradiance doses capable of causing tumor formation. The duration of these exposure periods closely depends on the exposure regime, atmospheric conditions and SC thickness. It is believed that the presented evaluations could provide a useful preliminary estimation of the risk associated with environmental UV-A exposure prior to the formulation of the corresponding action spectra and determination of the threshold doses.

Multiple sclerosis and solar exposure before the age of 15 years: case-control study in Cuba, Martinique and Sicily

Few studies report a protective role of childhood solar exposure to multiple sclerosis. Our objective was to confirm the protective role of childhood solar exposure in multiple sclerosis in Cuba, Martinique and Sicily. This was a matched case- control study, and cases met Poser criteria for clinically, laboratory (definite, probable) multiple sclerosis. Controls were resident population, without neurological disorder, living close to cases (within 100 km), matched for sex, age (+/-5 years), residence before age 15. We recruited 551 subjects during a 1-year period (193 cases, Cuba n = 95, Sicily n = 50, Martinique n = 48; 358 controls). Some (89%) met definite clinical multiple sclerosis criteria (relapsing remitting form (with and without sequel) (74%), secondary progressive (21%), primary progressive (5%)). Odds ratios in a uni-variate analysis were: family history of multiple sclerosis (5.1) and autoimmune disorder (4.0); wearing shirt (3.5), hat (2.7), pants (2.4); sun exposure causing sunburn (1.8); sun exposure duration (1 h more/day; weekends 0.91, weekdays 0.86); bare-chested (0.6); water sports (0.2). Independent factors in the multivariate analysis were family history of multiple sclerosis (4.8 (1.50-15.10)), wearing pants under sunlight (1.9 (1.10-3.20)), sun exposure duration (1 h more/ day, weekdays 0.90 (0.85-0.98), weekends 0.93 (0.87-0.99)), water sports (0.23 (0.13-0.40)). We conclude that outdoor leisure activities in addition to sun exposure reports are associated with a reduced multiple sclerosis risk, with evidence of dose response.

The dark and the sunny sides of UVR-induced immunosuppression: photoimmunology revisited

Immunosuppression induced by solar UVR is regarded as one of the major negative impacts of sunlight on human health. Despite this immunosuppression, bacterial superinfections are rarely observed after UVR exposure. A possible explanation for this seeming paradox may be that although it suppresses T-cell-mediated immune reactions, UVR induces the release of cutaneous antimicrobial peptides--an essential component of the innate immune system. The "sunshine vitamin," vitamin D, also appears to be involved, as UVR suppresses the adaptive but induces the innate immune response. T cells in the skin are the critical cellular mediators of the vast majority of inflammatory dermatoses, and thus probably more harmful than beneficial. Hence, it is tempting to speculate that a certain and constant level of immunosuppression by physiological UVR doses might be beneficial, taming overshooting immune reactions. At the same time, by inducing antimicrobial peptides, these low UVR doses may foster the antibacterial defense. Thus, suppression of the adaptive and induction of the innate immune system by UVR may be components of a physiological protection process. These insights might have effect on the future recommendations for daily sun protection.

Alterations of immune functions induced by 12C6+ ion irradiation in mice

PURPOSE

To estimate the biological risks to the immune system of the type of space radiation, 12C6+, encountered by cosmonauts during long-term travel in space.

MATERIALS AND METHODS

The Kun-Ming strain mice were whole-body irradiated by 12C6+ ion with 0, 0.01, 0.05, 0.075, 0.2, 0.3, 0.5, 0.75, 1 or 2 Gy, at a dose rate of 1 Gy/min. At 35 days after irradiation, the thymus and spleen weights were measured, the natural killer (NK) cells activity of spleen was determined by 3-(4, 5-dimethylthiazol-2-yl)- 2, 5-diphenyl tetrazolium bromide (MTT), and the interferon-gamma (IFN-gamma) levels in serum and thymus were detected with enzyme-linked immunosorbent assays (ELISA).

RESULTS

The results showed that the thymus weight, IFN-gamma levels in serum and the activity of splenic NK-cells had significantly increased at a dose of 0.05 Gy. With further dose increase, the weight of spleen continued to increase but the weight of thymus, IFN-gamma level and NK-cells activity declined.

CONCLUSIONS

These results suggest that the dose of 0.05 Gy irradiation has a stimulatory effect on mouse immunity; this effect declined with increasing dose.

Seasonality in flares and months of births of patients with ulcerative colitis in a Chinese population

BACKGROUND AND AIMS

Reports on seasonality in flares or months of births of inflammatory bowel disease patients have been inconsistent, but little data are available in a Chinese population. The aim of this study was to determine whether symptom flares and births of ulcerative colitis (UC) patients follow a seasonal pattern.

METHODS

Patients with a diagnosis of UC established between January 1990 and December 2007 were investigated according to the occurrence of flares of symptoms and months of births. The expected flares or births were calculated on a monthly basis over the study period, taking into consideration the difference in the number of days in the month in each year.

RESULTS

A total of 409 UC patients were included in the study, and 1030 flares of symptoms were determined. The peak number of flares occurred during the spring and summer, especially in June, while the nadir occurred in the winter, especially in January (chi(2) ((11 df))=32.74304, P<0.005). The symptom flares also occurred more frequently in the spring-summer period than in the autumn-winter period (chi(2) ((3 df))=22.1269, P<0.001). There was no statistical difference in birth distribution on a monthly or seasonal (spring, summer, autumn, winter) basis. However, the births of UC patients occurred more frequently in the autumn-winter period than in the spring-summer period when the data were merged into these two seasonal components (chi(2) ((1 df))=5.255607, P<0.025).

CONCLUSIONS

The data indicate that the symptom flares of UC occurred more frequently in the spring and summer, while the births of UC patients occurred more often in the autumn and winter. Environmental recurring factors may be associated with the symptom flares of UC, and these factors during pregnancy or postpartum may be associated with susceptibility to UC later in life.

DNA damage, apoptosis and langerhans cells--Activators of UV-induced immune tolerance

Solar UVR is highly mutagenic but is only partially absorbed by the outer stratum corneum of the epidermis. UVR can penetrate into the deeper layers of the epidermis, depending on melanin content, where it induces DNA damage and apoptosis in epidermal cells, including those in the germinative basal layer. The cellular decision to initiate either cellular repair or undergo apoptosis has evolved to balance the acute need to maintain skin barrier function with the long-term risk of retaining precancerous cells. Langerhans cells (LCs) are positioned suprabasally, where they may sense UV damage directly, or indirectly through recognition of apoptotic vesicles and soluble mediators derived from surrounding keratinocytes. Apoptotic vesicles will contain UV-induced altered proteins that may be presented to the immune system as foreign. The observation that UVR induces immune tolerance to skin-associated antigens suggests that this photodamage response has evolved to preserve the skin barrier by protecting it from autoimmune attack. LC involvement in this process is not clear and controversial. We will highlight some basic concepts of photobiology and review recent advances pertaining to UV-induced DNA damage, apoptosis regulation, novel immunomodulatory mechanisms and the role of LCs in generating antigen-specific regulatory T cells.

Does solar exposure, as indicated by the non-melanoma skin cancers, protect from solid cancers: vitamin D as a possible explanation

BACKGROUND

Skin cancers are known to be associated with sun exposure, whereas sunlight through the production of vitamin D may protect against some cancers. The aim of this study was to assess whether patients with skin cancer have an altered risk of developing other cancers.

METHODS

The study cohort consisted of 416,134 cases of skin cancer and 3,776,501 cases of non-skin cancer as a first cancer extracted from 13 cancer registries. 10,886 melanoma and 35,620 non-melanoma skin cancer cases had second cancers. The observed numbers (O) of 46 types of second primary cancer after skin melanoma, basal cell carcinoma or non-basal cell carcinoma, and of skin cancers following non-skin cancers were compared to the expected numbers (E) derived from the age, sex and calendar period specific cancer incidence rates in each of the cancer registries (O/E=SIR, standardised incidence ratios). Rates from cancer registries classified to sunny countries (Australia, Singapore and Spain) and less sunny countries (Canada, Denmark, Finland, Iceland, Norway, Scotland, Slovenia and Sweden) were compared to each other.

RESULTS

SIR of all second solid primary cancers (except skin and lip) after skin melanoma were significantly lower for the sunny countries (SIR(S)=1.03; 95% CI 0.99-1.08) than in the less sunny countries (SIR(L)=1.14; 95%CI 1.11-1.17). The difference was more obvious after non-melanoma skin cancers: after basal cell carcinoma SIR(S)/SIR(L)=0.65 (95%CI=0.58-0.72); after non-basal cell carcinoma SIR(S)/SIR(L)=0.58 (95%CI=0.50-0.67). In sunny countries, the risk of second primary cancer after non-melanoma skin cancers was lower for most of the cancers except for lip, mouth and non-Hodgkin lymphoma.

CONCLUSIONS

Vitamin D production in the skin seems to decrease the risk of several solid cancers (especially stomach, colorectal, liver and gallbladder, pancreas, lung, female breast, prostate, bladder and kidney cancers). The apparently protective effect of sun exposure against second primary cancer is more pronounced after non-melanoma skin cancers than melanoma, which is consistent with earlier reports that non-melanoma skin cancers reflect cumulative sun exposure, whereas melanoma is more related to sunburn.

Epidemic influenza and vitamin D

In 1981, R. Edgar Hope-Simpson proposed that a 'seasonal stimulus' intimately associated with solar radiation explained the remarkable seasonality of epidemic influenza. Solar radiation triggers robust seasonal vitamin D production in the skin; vitamin D deficiency is common in the winter, and activated vitamin D, 1,25(OH)2D, a steroid hormone, has profound effects on human immunity. 1,25(OH)2D acts as an immune system modulator, preventing excessive expression of inflammatory cytokines and increasing the 'oxidative burst' potential of macrophages. Perhaps most importantly, it dramatically stimulates the expression of potent anti-microbial peptides, which exist in neutrophils, monocytes, natural killer cells, and in epithelial cells lining the respiratory tract where they play a major role in protecting the lung from infection. Volunteers inoculated with live attenuated influenza virus are more likely to develop fever and serological evidence of an immune response in the winter. Vitamin D deficiency predisposes children to respiratory infections. Ultraviolet radiation (either from artificial sources or from sunlight) reduces the incidence of viral respiratory infections, as does cod liver oil (which contains vitamin D). An interventional study showed that vitamin D reduces the incidence of respiratory infections in children. We conclude that vitamin D, or lack of it, may be Hope-Simpson's 'seasonal stimulus'.

Narrowband filter radiometer for ground-based measurements of global ultraviolet solar irradiance and total ozone

The ultraviolet narrowband filter radiometer (UV-RAD) designed by the authors to take ground-based measurements of UV solar irradiance, total ozone, and biological dose rate is described, together with the main characteristics of the seven blocked filters mounted on it, all of which have full widths at half maxima that range 0.67 to 0.98 nm. We have analyzed the causes of cosine response and calibration errors carefully to define the corresponding correction terms, paying particular attention to those that are due to the spectral displacements of the filter transmittance peaks from the integer wavelength values. The influence of the ozone profile on the retrieved ozone at large solar zenith angles has also been examined by means of field measurements. The opportunity of carrying out nearly monochromatic irradiance measurements offered by the UV-RAD allowed us to improve the procedure usually followed to reconstruct the solar spectrum at the surface by fitting the computed results, using radiative transfer models with field measurements of irradiance. Two long-term comparison campaigns took place, showing that a mean discrepancy of +0.3% exists between the UV-RAD total ozone values and those given by the Brewer #63 spectroradiometer and that mean differences of +0.3% and -0.9% exist between the erythemal dose rates determined with the UV-RAD and those obtained with the Brewer #63 and the Brewer #104 spectroradiometers, respectively.

Seasonal variations in onset of symptoms in Crohn's disease

BACKGROUND

Seasonal variations in onset of symptoms have been reported in ulcerative colitis but not in Crohn's disease. AIM.: To investigate whether our inflammatory bowel diseases patients presented seasonal variations in onset of symptoms.

PATIENTS AND METHODS

Patients with a diagnosis of inflammatory bowel diseases established between 1995 and May 2004, and consecutively observed from June 2003 to May 2004, were included in the study. Onset of symptoms (year, season and month) was recorded. Expected onsets with a uniform distribution during the year were calculated and compared to observed onsets.

STATISTICAL ANALYSIS

chi-square test, odds ratio (95% confidence interval).

RESULTS

Overall 425 inflammatory bowel diseases patients were enrolled. Onset of symptoms (year and season) was established in 353/425 patients (83%; 150 Crohn's disease; 203 ulcerative colitis). Onset of symptoms in inflammatory bowel diseases patients as a whole occurred more frequently in spring-summer compared to autumn-winter (odds ratio 1.39; 95% confidence interval 1.03-1.87; p<0.03). This variation was observed in Crohn's disease (odds ratio 1.59; 95% confidence interval 1.00-2.51; p<0.05) and a similar trend, although not significant, was observed in ulcerative colitis (odds ratio 1.27; 95% confidence interval 0.86-1.88; p=0.27).

CONCLUSIONS

These data indicate that onset of Crohn's disease symptoms occurred more frequently during spring-summer. A similar trend was observed in ulcerative colitis. Environmental factors, such as associated infections, smoking, use of drugs and seasonal changes in immune function may be responsible for triggering the clinical onset of inflammatory bowel diseases.

Combined dermal exposure to permethrin and cis-urocanic acid suppresses the contact hypersensitivity response in C57BL/6N mice in an additive manner

Cutaneous exposure to the pyrethroid insecticide permethrin significantly suppresses contact hypersensitivity (CH) response to oxazolone in C57BL/6N mice. Additionally, cis-urocanic acid (cUCA), an endogenous cutaneous chromophore isomerized to its active form following exposure to ultraviolet radiation, modulates cell-mediated cutaneous immune responses. This study describes cutaneous immune alterations following combined topical permethrin and intradermal cUCA exposure. Female C57BL/6N mice were administered 5, 50 or 100 microg cUCA daily for 5 consecutive days. CH was then evaluated by the mouse ear swelling test (MEST) response to oxazolone. Decreased responses of 52.3%, 76.3% and 76.3%, respectively, as compared to controls were observed. Then, mice were co-exposed to 5 microg cUCA daily for 5 days and 1.5, 5, 15, or 25 microL permethrin, on either day 1, 3 or 5 of the cUCA treatment to evaluate combined immunomodulatory effects of the two chemicals, or cUCA daily for 5 days followed by permethrin on day 3, 5, or 7 after the last cUCA injection to demonstrate prolonged immunosuppressive effects. Two days after final treatment, mice were sensitized with oxazolone and MEST was performed. Mice receiving five cUCA injections and permethrin topically on cUCA injection day 1 showed up to 93.3% suppression of MEST compared to vehicle control. CH was suppressed by 87.5%, 86.6% and 74.2% in mice treated with 25 muL permethrin on days 3, 5 and 7 after cUCA, respectively, compared to vehicle control. Taken together, these data indicate co-exposure to cUCA and permethrin profoundly suppresses cell-mediated cutaneous immunity.

Sunlight exposure and (sero)prevalence of epidermodysplasia verruciformis-associated human papillomavirus

Ultraviolet radiation (UVR) is associated with an increased risk of squamous cell carcinoma (SCC), which is in part due to immunomodulation. In addition, human papilloma virus (HPV), especially the epidermodysplasia verruciformis (EV)-associated types, may be involved. In view of the capacity of UVR to impair host resistance to infections, we investigated the relationship between solar exposure and the prevalence of cutaneous HPV. In a case-control study on skin cancer (320 controls and 156 patients) a lifetime-retrospective questionnaire on sun exposure was administered. The presence of DNA of HPV types 5, 8, 15, 20, 24, and 38 in plucked eyebrow hair and type-specific seroreactivity were assessed and analyzed in relation to estimated exposure. Sunburn episodes in the past, especially at age 13-20 y, appeared to be associated with an enhanced risk of EV-HPV DNA positivity. In contrast, a higher lifetime sun exposure was associated with a lower risk of HPV infection. These results indicate that UVR at erythematogenic doses increases the risk of EV-HPV infection, possibly due to impaired host resistance to HPV and/or a direct effect of UVR on viral replication. The favorable association between lifetime sun exposure and HPV prevalence, however, underscores the enigmatic role of HPV in skin carcinogenesis.

Molecular mechanisms of cis-urocanic acid and permethrin-induced alterations in cutaneous immunity

BACKGROUND/PURPOSE

Cutaneous cis-urocanic acid (cUCA) or ultraviolet B exposure has been shown to cause diminished cutaneous contact hypersensitivity (CH) and to induce systemic tolerance (increased regulatory T lymphocytes) in mice. Permethrin is also a known CH inhibitor, but the molecular mechanisms are currently poorly understood. In this study, CH was evaluated in four strains of mice: an immunosensitive strain (C57BL/6N), an immunoresistant strain (SvImJ), a strain developed from C57BL/6N mice but genetically altered at both the tumor necrosis factor-alpha receptors (TNFalphap55R and p75R), and a strain developed from C57BL/6N but genetically deleted at the interferon-gamma (IFNgamma) locus.

METHODS

CH was evaluated in each group via oxazolone challenge following a 5-day exposure to intradermal (ID) cUCA or a single exposure to topical permethrin, or co-exposure to both chemicals in 5-week-old female C57BL/6N, SvImJ, and C57BL/6N mice genetically altered at the TNFalpha or IFNgamma locus.

RESULTS

A 5-day exposure to ID cUCA or a single exposure to topical permethrin resulted in diminished CH response in C57BL/6N mice, and this effect was exacerbated with concurrent exposure to both chemicals. CH in SvImJ was both cUCA- and permethrin-resistant relative to C57BL/6N mice, as 5-day cUCA or a single exposure to permethrin did not diminish CH, nor did concurrent exposure to cUCA and permethrin. Mice deleted at both TNFalphaR loci displayed similar but somewhat blunted diminished CH responses to cUCA or permethrin. This trend became significant with combined chemical exposure. IFNgamma knockout mice displayed similar diminished CH responses to cUCA or permethrin alone. Unlike C57BL/6N mice, the IFNgamma knockout mice did not show a further reduction in CH with combined chemical exposure.

CONCLUSIONS

These results suggest the following: (1)Mouse strains show variable susceptibility to permethrin- and cUCA-induced immunomodulation. (2)TNFalpha may be involved in the immunomodulatory effects of cUCA and permethrin. (3)IFNgamma may be required for the more than additive depression of CH caused by cUCA+permethrin.

What does epidemiology tell us about risk factors for herpes zoster?

Reactivation of latent varicella zoster virus as herpes zoster is thought to result from waning of specific cell-mediated immunity, but little is known about its determinants in individuals with no underlying immunosuppression. We systematically reviewed studies of zoster epidemiology in adults and analysed data from a large morbidity study to identify factors that might be modulated to reduce the risk of zoster. Annual zoster incidence in population-based studies varied from 3.6-14.2/10(3) in the oldest individuals. Risk factors identified in analytical studies that could explain this variation included age, sex, ethnicity, genetic susceptibility, exogenous boosting of immunity from varicella contacts, underlying cell-mediated immune disorders, mechanical trauma, psychological stress, and immunotoxin exposure. Our review highlights the lack of information about risk factors for zoster. We suggest areas of research that could lead to interventions to limit the incidence of zoster. Such research might also help to identify risk factors for age-related immune decline.

Ultraviolet radiation, resistance to infectious diseases, and vaccination responses

Exposure to ultraviolet (UV) radiation, as in sunlight, can modulate immune responses in animals and humans. This immunomodulation can lead to positive health effects especially with respect to certain autoimmune diseases and allergies. However, UV-induced immunomodulation has also been shown to be deleterious. Experimental animal studies have revealed that UV exposure can impair resistance to many infectious agents, such as bacteria, parasites, viruses, and fungi. Importantly, these effects are not restricted to skin-associated infections, but also concern systemic infections. The real consequences of UV-induced immunomodulation on resistance to infectious diseases are not known for humans. Risk estimations have been performed through extrapolation of animal data, obtained from infection models, to the human situation. This estimation indicated that UV doses relevant to outdoor exposure can impair the human immune system sufficiently to have effects on resistance to infections. To further quantify and validate this risk estimation, data, e.g., from human volunteer studies, are necessary. Infection models in humans are not allowed for ethical reasons. However, vaccination against an infectious disease evokes a similar immune response as the pathogen and thereby provides an opportunity to measure the effect of UV radiation on the immune system and an estimate of the possible consequences of altered resistance to infectious agents. Effects of controlled UVB exposure on immune responses after hepatitis B vaccination have been established in mice and human volunteers. In mice, cellular and Th1-associated humoral immune responses to hepatitis B were significantly impaired, whereas in human volunteers no significant effect of UVB on these responses could be found. Preliminary data indicate that cytokine polymorphisms might be, at least in part, responsible for interindividual differences in immune responses and in susceptibility to UVB-induced immunomodulation. In addition, adaptation to UV exposure needs to be considered as a possible explanation for the difference between mice and humans that was observed in the hepatitis B vaccination model.

Seasonal influences on immunological parameters in HIV-infected homosexual men: searching for the immunomodulating effects of sunlight

In view of the capacity of ultraviolet radiation (UVR) to induce suppression of various immunological parameters and to enhance the viral replication of HIV, we investigated whether seasonal influences on immunological parameters that are relevant for HIV infection could be identified. As the sunny season is associated with high levels of ambient UVR, a decline of immunological parameters and an increase of the HIV viral load during the summer months might ensue. We analysed the immunological data of the HIV-infected homosexual men who participated in the Amsterdam Cohort Study on HIV infection and AIDS (1984-1996; n = 556). The effect of season on the individual development of various immunological parameters in time was examined by means of a random effects model for repeated measurements. Lower levels in the mean number of CD4+ T cells and the mean CD4+/CD8+ ratio were found during summer and spring, respectively (P = 0.0001/0.0001). For the CD8+ T cells, high mean values were observed both in April and September (P = 0.0001). The highest T-cell reactivity values were found during the summer (P = 0.0001). No effect of season on the viral load was established. The seasonal effect on CD4+ T cells seemed to be more pronounced at a more advanced stage of the HIV infection. It is concluded that the lower CD4+ T-cell counts during summer support the notion that solar UVR may have a suppressive effect on the cellular immunity of HIV-infected persons. However, whether this observation can be attributed to the effect of ambient UVR solely is questionable, as the other immunological parameters follow different seasonal courses and other reports suggest that both internal and environmental factors influence immunological parameters.