Mast cells and mast cell VDR expression are required to limit pathology induced by chronic low-dose UVB irradiation of ear skin. Cross sections of ears obtained from WBB6F₁-Kit^+/+ (WT) mice (A–C), WBB6F₁-Kit^W/W-v (Kit^W/W-v) mice (D–F), WT BMCMC→Kit^W/W-v mice (G–I), or VDR^−/− BMCMC→Kit^W/W-v mice (J–L) at 24 h after the final exposure to 2 kJ/m² UVB (15 exposures, 2 d apart; B, C, E, F, H, I, K, and L); sections stained with H&E (A, B, D, E, G, H, J, and K), or Toluidine blue (C, F, I, and L). Mice that did not receive UVB irradiation were also killed for analysis of skin histology at the end of the experiment (A, D, G, and J). C*, cartilage. Double-headed arrows indicate thickness of dermis (D) or epidermis (Ep). Red arrowheads indicate mast cells (C, F, I, and L). Bars: 100 µm (inset in A; for A–L); 1,000 µm (A; for insets in A, B, D, E, G, H, J, and L); 10 µm (C and I insets). Results are representative of those obtained in the three different experiments performed, each with three to four mice analyzed per group.