Jan C. van der Leun

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Some improvements are reported of a relatively unknown method for measuring the thickness of the epidermis in vivo. The excursion of a microscope tube is measured when focussing respectively on the summits of the dermal capillary loops and on the epidermal surface. With this method values may be produced with a standard deviation in the order of 10 µm.(More)
An animal experiment is presented in which three groups of albino hairless mice (Skh-hr 1) were exposed to daily doses of either UV-B or UV-A to study carcinogenesis. The UV-A was filtered carefully so as to eliminate contaminating UV-B. The doses required for acute effects (erythema and edema) were also determined for the two radiation modalities. In order(More)
An animal experiment is presented in which two groups of pigmented hairless mice were exposed daily to suberythemal doses of UVA to study tumourigenesis. The aim of the study was to estimate the carcinogenic risks of tanning by UVA. The pigmented hairless mice, Skh-hr2, were separated by selective breeding into two groups, the “browns” and the “blacks”.(More)
The development of skin tumors (mainly squamous cell carcinomas) in hairless Skh-HRl mice after discontinuation of a course of daily UV irradiations (wavelengths, 280-370 nm) is compared to that when the daily irradiations are continued. Under conditions of continued daily exposures 50% of 22 animals contracted tumors with diameters of at least 4 mm in 135(More)
Information on the variation in carcinugcnicity with wavelength is crucial in risk assessments for skin cancers induced hy 1 \ radiation. I ntil recently the wavelength (A) dependencies of other detrimental I'V elTects. such as sunburn, have been used as suhstitutes. Direct information on the A dependency can only be obtained from animal experiments. To(More)
We have proposed that c e l l u l a r senescence is cont ro l led by normal genes that are act ivated or whose funct ions become manifest at the end of the l i f e span of a ce l l . Defects in these genes al low ce l l s to escape senescence and become immortal. Senescence genes have been mapped to spec i f ic human chromosomes ( I , 4 and X) using somatic(More)
In the usual protocols for the PUVA-therapy, an interval of 2 h is taken between the oral administration of the psoralen and the exposure of the patient to UV-A (Parrish et al. 1974). The most suitable time for the exposure appears to be the time when the sensitivity of the skin to UV-A is maximal. In preparing an investigation to compare the effectiveness(More)
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