Ultrastructural observations on epithelioid cell granulomas induced by zirconium in the guinea-pig.

An ultrastructural study has been made of the allergic-type nodular granulomas that can be induced in guinea-pigs sensitised to sodium zirconium lactate. Lesions taken at the peak of granuloma development 7 days after skin testing contained epithelioid cells which could be recognised particularly by their content of rough endoplasmic reticulum, fimbriated cell membrane and typical nuclear appearance. Multinucleate giant cells were also seen. These cells were characterised by their large number of lysosome-like dense bodies and phagocytic structures. Both epithelioid cells and multinucleate giant cells were similar to those described in zirconium granulomas in man. However, these cells differed in a number of respects from similar cells observed in human sarcoidosis. A constant feature of the guinea-pig lesions was the presence of large numbers of apparently active fibroblasts.