Themed collection Commemorative issue in honour of Jan van der Leun

Welcome to this Photochemical & Photobiological Sciences special issue dedicated to Jan van der Leun.

Cutaneous T-cell lymphomas (CTCL) are a heterogenous group of non-Hodgkin lymphomas arising in the skin. Phototherapy with ultraviolet radiation, introduced in 1976, is still a mainstay of treatment. Depending on CTCL variant and stage psoralen and ultraviolet A, narrow-band ultraviolet B, or photopheresis are used and can provide effective palliation for many patients.

Drug photosensitivity is a relatively common occurrence and a range of mechanisms may be involved.

This paper illustrates the independent and interactive role of genetic and environmental factors in the etiology of melanoma.

Solar ultraviolet (UV) radiation generates bulky photodimers at di-pyrimidine sites that pose stress to cells and organisms by hindering DNA replication and transcription.

Based on the polη-dependent TLS across deaminated CPDs, the wavelength dependence of UVR mutations can be explained by different photochemistries of CPD formation, the singlet/triplet and collective excitations that cause UV-signature and UVA-signature mutations, respectively.

UV-induced DNA damage plays a key role in the initiation phase of skin cancer. Their yield and chemical structure strongly depend on the wavelength.

Major steps in the pathway leading to the increased risk of skin cancer by the immunosuppression induced by UVR exposure.

Kidney transplant recipients with the lowest wintertime vitamin D levels appear to run the highest risk of internal malignancies. The effect was strongest in women.

The increase in ambient temperature due to climate change is expected to affect the carcinogenicity of squamous cell carcinoma (SCC) and basal cell carcinoma (BCC).

Many microorganisms are alive while suspended in the atmosphere, but are exposed to solar ultraviolet (UV) radiation from all directions. Geographic and seasonal patterns of DNA-damaging UV doses can be estimated from observations as well as modeling.

At UVI < 3, sun protection is not recommended, but UVA irradiance may be high; even short exposures may incur health risks. Duration of exposure must be considered with UVI for risks and benefits of sun exposure.

Humans have been exposed to solar UV radiation since their appearance on Earth and evolution has enabled most individuals to adapt to this exposure, to some degree.

The earliest contribution made by Jan van der Leun to the field of photobiology was studying the mechanism of UV-induced erythema in human skin – a subject he chose for his PhD in the 1960s.