Ultrastructural evidence for lack of tissue damage in a local immune complex reaction: a study of a mild passive Arthus reaction.

An electron microscopic study of a mild reversed passive Arthus reaction (RPAR) was performed using a horeradish peroxidase (HRP)-anti-HRP system to demonstrate the biological usefulness of the process which exists to clear tissue of immune complexes. To disclose the antigen, HRP, the biopsy material was subjected to a peroxidase reaction. HRP was mainly detected within irregular electron-dense precipitates which were considered insoluable HRP-anti-HRP immune complexes. Neutrophils were found to phagocytose and digest the deposited immune complexes in a similar way as described previously. But there was no vascular and other tissue damage. This study provides morphological evidence that the process of clearing tissues of immune complexes need not be harmful to the host.