Calcification of cultured urticaria pigmentosa skin. An electron optical study of the calcium-apatite deposition.

Mast cells participate in experimental calcinosis. Skin from patients with urticaria pigmentosa (cutaneous mastocytosis) calcifies in vitro. In the present report, the nature of the calcium deposit was studied by electron optical techniques. The cultured mast cells of urticaria pigmentosa skin were surrounded by a large number of round bodies with an average diameter of 200-300 nm. Most of the round bodies were membrane bounded, while a few contained lamellar structures. These bodies may represent matrix vesicles as seen in calcifying hard tissues and/or may be remnants of mast cell granules. The calcified deposits were located on the round bodies, collagen fibrils and elastic matrix. Electron diffraction and X-ray microanalysis demonstrated that the deposits consisted of crystalline calcium apatite.