Ultraviolet light and resistance to infectious diseases

Radiobiological effects and medical applications of non-ionizing radiation

Radiation is used in medicine to diagnose and treat diseases but it can also cause harm to the body by burning or mutation. This depends on whether the radiation is ionizing or nonionizing. Despite its vast applications in surgery, dermatology and cosmetics, little is taught and thus known about non-ionizing radiation. This review article discusses the fundamentals of non-ionizing electromagnetic radiations. The main aim is to extensively explain the different types of non-ionizing radiation. This will equip students and medical personnel with knowledge on different medical applications and expose them to a variety of specializations in medicine that utilize non-ionizing radiation. The article discusses the physics, hazard, means of protection and medical application of each type of radiation: ultraviolet radiation, light (both visible light and LASER), infrared radiation, microwaves and extremely low frequency radiation separately. It presents these terms in a simple manner that avoids rigors mathematics and physics, which makes them comprehensible for medical students. The development of new diagnostic and therapeutic approaches could also lead to increased hazards to the body unless they are treated with precaution. If not adequately monitored, a significant health risk may be posed to potentially exposed employees. Hence proper dosage should be used for non-ionizing radiation. This is only possible through understanding of the risks/benefits of these radiations by studying the physics and radiobiological effects of each individual radiation.

Exposure to Solar UVR Suppresses Cell-Mediated Immunization Responses in Humans: The Australian Ultraviolet Radiation and Immunity Study

Animal and human studies show that exposure to solar-simulated UVR is immunomodulatory. Human studies that used natural sun exposure and controlled for confounding are rare. We immunized 217 healthy adults (age range = 18-40 years) with a T-cell-dependent antigen, keyhole limpet hemocyanin, and measured personal clothing-adjusted UVR exposure (for 5 days before and after immunization), lifetime cumulative UVR exposure, serum 25-hydroxyvitamin D concentration at immunization, and potential confounding factors. We tested cellular and humoral immune responses in relation to UVR exposure. The delayed-type hypersensitivity response to keyhole limpet hemocyanin recall challenge was lower in individuals with higher personal clothing-adjusted UVR exposure on the day before immunization (P = 0.015) and during intervals spanning the day before to 2-3 days after immunization. There was an incremental increase in T helper type 17 cells (as a proportion of CD4⁺ T cells) from preimmunization to postimmunization in the high, compared with the low, personal clothing-adjusted UVR exposure group (0.31% vs. -0.39%, P = 0.004). Keyhole limpet hemocyanin-specific antibody titers were not associated with acute or cumulative UVR exposure or serum 25-hydroxyvitamin D levels. Higher UVR exposure at antigen sensitization was associated with a reduced delayed-type hypersensitivity response and altered T helper type 17 kinetics. This has implications for the effectiveness of vaccinations and susceptibility to infections that rely on cell-mediated immune responses.

Exploring the link between ultraviolet B radiation and immune function in amphibians: implications for emerging infectious diseases

Amphibian populations the world over are under threat of extinction, with as many as 40% of assessed species listed as threatened under IUCN Red List criteria (a significantly higher proportion than other vertebrate group). Amongst the key threats to amphibian species is the emergence of novel infectious diseases, which have been implicated in the catastrophic amphibian population declines and extinctions seen in many parts of the world. The recent emergence of these diseases coincides with increased ambient levels of ultraviolet B radiation (UVBR) due to anthropogenic thinning of the Earth's protective ozone layer, raising questions about potential interactions between UVBR exposure and disease in amphibians. While reasonably well documented in other vertebrate groups (particularly mammals), the immunosuppressive capacity of UVBR and the potential for it to influence disease outcomes has been largely overlooked in amphibians. Herein, we review the evidence for UVBR-associated immune system disruption in amphibians and identify a number of direct and indirect pathways through which UVBR may influence immune function and disease susceptibility in amphibians. By exploring the physiological mechanisms through which UVBR may affect host immune function, we demonstrate how ambient UVBR could increase amphibian susceptibility to disease. We conclude by discussing the potential implications of elevated UVBR for inter and intraspecific differences in disease dynamics and discuss how future research in this field may be directed to improve our understanding of the role that UVBR plays in amphibian immune function.

"Let there be light": the role of vitamin D in the immune response to vaccines

Vitamin D's non-skeletal actions, including immunomodulatory role, have been increasingly recognized. Of significance, many immune cells are able to synthesize a biologically active form of vitamin D from circulating 25-hydroxyvitamin D with subsequent intracrine actions, and the vitamin D receptor is broadly distributed. In this review, we discuss vitamin D's potent role in innate and adaptive immune responses and published studies evaluating the impact of serum vitamin D, vitamin D gene pathway polymorphisms or empiric vitamin D supplementation on vaccine immunogenicity. We highlight existing knowledge gaps and propose the steps needed to advance the science and answer the question of whether vitamin D may prove valuable as a vaccine adjuvant for certain vaccines against infectious diseases.

A review of the consequences of global climate change on human health

The impact of climate change has been significant enough to endanger human health both directly and indirectly via heat stress, degraded air quality, rising sea levels, food and water security, extreme weather events (e.g., floods, droughts, earthquakes, volcano eruptions, tsunamis, hurricanes, etc.), vulnerable shelter, and population migration. The deterioration of environmental conditions may facilitate the transmission of diarrhea, vector-borne and infectious diseases, cardiovascular and respiratory illnesses, malnutrition, etc. Indirect effects of climate change such as mental health problems due to stress, loss of homes, economic instability, and forced migration are also unignorably important. Children, the elderly, and communities living in poverty are among the most vulnerable of the harmful effects due to climate change. In this article, we have reviewed the scientific evidence for the human health impact of climate change and analyzed the various diseases in association with changes in the atmospheric environment and climate conditions.

Sunshine, rainfall, humidity and child pneumonia in the tropics: time-series analyses

Few studies have formally examined the relationship between meteorological factors and the incidence of child pneumonia in the tropics, despite the fact that most child pneumonia deaths occur there. We examined the association between four meteorological exposures (rainy days, sunshine, relative humidity, temperature) and the incidence of clinical pneumonia in young children in the Philippines using three time-series methods: correlation of seasonal patterns, distributed lag regression, and case-crossover. Lack of sunshine was most strongly associated with pneumonia in both lagged regression [overall relative risk over the following 60 days for a 1-h increase in sunshine per day was 0·67 (95% confidence interval (CI) 0·51-0·87)] and case-crossover analysis [odds ratio for a 1-h increase in mean daily sunshine 8-14 days earlier was 0·95 (95% CI 0·91-1·00)]. This association is well known in temperate settings but has not been noted previously in the tropics. Further research to assess causality is needed.

New insights about infant and toddler skin: implications for sun protection

The skin is increasingly recognized as a component of the innate immune response, in addition to its role as a physical barrier. Although the deleterious effects of solar ultraviolet radiation (UVR), including immunosuppression and cutaneous tumorigenesis, are widely acknowledged, most studies to date have concentrated on adult skin. Despite the more sensitive nature of infant and toddler skin, little is known about its responses to UVR exposure, whether acute or long-term. Accumulating evidence suggests not only that the skin's barrier protection remains immature throughout at least the first 2 years of life but also that accumulation of UVR-induced changes in the skin may begin as early as the first summer of life. Such evidence not only affirms the importance of sun protection during the infant and toddler years but underscores the need for more research to establish evidence-based standards of care in this area. In this article we review recent studies in which differences between the skin properties of infants and young children and those of adults were compared, and we discuss the implications of these differences for sun-protection practices.

Sun-induced changes in stratum corneum function are gender and dose dependent in a Chinese population

Previous studies have demonstrated that UVB radiation changes the epidermal permeability barrier and stratum corneum (SC) hydration. It is well known that sun exposure causes erythema, sunburn and melanoma. However, whether daily sun exposure alters SC integrity and epidermal permeability barrier function is largely unknown, especially in Chinese subjects. In the present study, we assess the SC integrity, SC hydration and epidermal permeability barrier function following various doses of sun exposure. A total of 258 subjects (124 males and 134 females) aged 18-50 years were enrolled. A multifunctional skin physiology monitor (Courage & Khazaka MPA5) was used to measure SC hydration and transepidermal water loss (TEWL) on the forearms. In males, basal TEWL was higher with higher doses of sun exposure than with lower doses and control, whereas in females, basal TEWL was higher with lower doses of sun exposure than with higher doses and control. In the group with higher doses of sun exposure, TEWL in females was significantly lower than that in males. The barrier recovery was faster in females than in males in both control and lower-dose groups. In both males and females, barrier recovery was delayed with higher doses of sun exposure. In males, sun exposure did not alter SC hydration, while in females SC hydration was lower with lower doses of sun exposure as compared with control and higher doses of sun exposure. These results demonstrated that sun-induced changes in SC function and SC hydration vary with gender and the extent of sun exposure.