Ultraviolet B irradiation selectively increases the production of interleukin-8 in human cord blood-derived mast cells

Abstract

UVB irradiation modulates immune responses in the skin and is a major cause of sunburn, during which neutrophils accumulate in the skin. Because of their abundance in skin and ability to produce a variety of proinflammatory mediators, we propose that mast cells may play a key role in ultraviolet B (UVB)-induced skin inflammation. Cord blood-derived human mast cells were treated in vitro with varying doses of UVB and production of multiple cytokines was measured in culture supernatants. UVB exposure significantly increased the release of interleukin (IL)-8 and modestly increased IL-1alpha production, but cytokines such as IL-2, IL-4, IL-6, IL-10, IL-12, IL-13, tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma were unaffected. Cycloheximide reduced the UVB-mediated induction of IL-8 by 30-40%, suggesting that new protein synthesis contributed to IL-8 production. In line with this, UVB treatment of mast cells significantly increased IL-8 mRNA. In contrast to its effect on IL-8 production, optimal doses of UVB did not provoke histamine or tryptase release, indicating little effect on degranulation. Our data suggest that mast cells may play a major role during UVB-induced acute inflammation by selectively inducing cytokines involved in neutrophil recruitment.

Fig. 1

Mast cell degranulatory products after ultraviolet B (UVB) irradiation. Degranulation of mast cells 1 h after UVB irradiation determined by histamine enzyme-linked immunosorbent assay (ELISA) (a) and Western blotting for tryptase (b) indicated no significant degranulation in response to various doses of UVB. (a) Each bar represents the mean ± standard error from three independent experiments.

Fig. 2

Induction of interleukin (IL)-8 by ultraviolet B (UVB) irradiation in mast cells. (a) Dose-dependent IL-8 production by mast cells after UVB irradiation showing significant increases at 8 h (solid squares) (*P < 0·05) (n = 3) but not at 1 h (open squares) (n = 2). (b) Time-dependent increase in IL-8 in response to 20 mJ/cm² UVB; significant increases in IL-8 occurred at each time-point (solid squares) compared to mock-irradiated control cells (solid trianges) (n = 7) (**P < 0·01, *P < 0·05).

Fig. 3

Ultraviolet B (UVB)-induced new synthesis of interleukin (IL)-8 by mast cells. (a) Partial inhibition of IL-8 synthesis by UVB-irradiated mast cells after treatment with various doses of cycloheximide (n = 3). (b) Expression of IL-8 mRNA and protein by mast cells 4 h after UVB-irradiation (n = 2). Histogram indicates real-time reverse transcription–polymerase chain reaction (RT–PCR) for IL-8 mRNA and line graph shows levels of IL-8 protein in supernatants of the same samples showing 10-fold increase in IL8 levels compared to control cells.

Fig. 4

Inhibition of ultraviolet B (UVB)-induced interleukin (IL)-8 production by mitogen-activated protein kinase (MAPK) inhibitors. Mast cells were pretreated with preoptimized dose of extracellular signal-regulated kinase (ERK) inhibitor (PD98059, 10 µM) or two p38 inhibitors (SB202190, 1 µM or SB203580, 1 µM) in duplicate for 1 h, then irradiated with 20 mJ/cm² of UVB. Levels of IL-8 in culture supernatants collected 24 h after irradiation were measured by enzyme-linked immunosorbent assay (ELISA) (n = 2). Data expressed as mean ± standard error of two independent experiments.