Cell differentiation and bone protein synthesis in the lungs of sheep with spontaneous calcinosis.

The lungs of three sheep with spontaneous enzootic calcinosis induced by the calcinogenic plant Nierembergia veitchii (Nv) were examined electron microscopically and immunohistochemically. The main ultrastructural changes were activation of fibroblasts and modified smooth muscle cells (SMCs) in the pulmonary interstitium, with an increase in extracellular matrix and precipitation of calcium, either in a laminated pattern or as amorphous aggregates. Macrophages and multinucleated giant cells, some with calcium crystals in the cytoplasm, were found in areas of increased extracellular matrix. Thickening and replication of the basal lamina of capillaries were prominent. The bone proteins osteocalcin, osteopontin and osteonectin were detected immunohistochemically in the cytoplasm of activated fibroblasts, in modified SMCs and in the extracellular matrix. It is suggested that 1,25-dihydroxyvitamin D(3)in Nv induces cellular differentiation and the synthesis of a calcifiable matrix.