Ultraviolet B induces mast cell apoptosis: a hypothetical mechanism of ultraviolet B treatment for uraemic pruritus

Abstract

The pathogenesis of uraemic pruritus is unclear, although there is some evidence that an increased number of skin-infiltrating mast cells may play a role. Ultraviolet B reduces itchy sensation of uraemic patients by leading to depletion of cutaneous mast cells. This study presents data that both broad-band and narrow-band ultraviolet B irradiation are able to induce apoptosis in transformed mast cells (murine mastocytoma cell line P815) in a dose-dependent manner at a time point of 24 hours. The positive apoptotic rates were as follows: sham-exposed cells (controls) – 13.3%±0.6%; with broad-band ultraviolet B irradiation −24.5%±1.1% with 10mJ/cm2, 57.9%±4.6% with 20mJ/cm2 and 70.9%±4.5% with 30mJ/cm2; with narrow-band ultraviolet B irradiation – 29.6%±2.3% with 100mJ/cm2, 57.3%±4.1% with 200mJ/cm2 and 81.5%±1.9% with 300mJ/cm2. The difference between the number of apoptotic cells in all groups of ultraviolet B-irradiated cells and sham-exposed cells was highly significant (P<0.001). Based on these findings, it is hypothesized that ultraviolet B induced mast cell apoptosis could be an important factor in phototherapy for the diseases dependent on increased number of cutaneous mast cells, including uraemic pruritus.