Immunohistochemical and histochemical profile of Aschoff bodies in rheumatic carditis in excised left atrial appendages: an immunoperoxidase study in fresh and paraffin-embedded tissue.

We have evaluated the nature of Aschoff cells within Aschoff bodies seen in 35 of 100 excised left atrial appendages from cases of rheumatic mitral stenosis who underwent closed mitral valvotomy. These were tested using a panel of monoclonal and polyclonal antisera by the indirect immunoperoxidase staining for leucocyte common antigen, macrophage, desmin, vimentin, alpha-1-antitrypsin, alpha-1-antichymotrypsin, lysozyme, acid phosphatase and nonspecific esterase. The Aschoff cell gave strong reactivity with monoclonal antisera to vimentin, macrophage and variable reaction with polyclonal antisera known to recognise macrophages/histiocytes in tissues, namely alpha-1-antitrypsin, alpha-1-antichymotrypsin and lysozyme. These were also strongly positive for acid phosphatase and nonspecific esterase. The Aschoff cell lacked affinity for desmin and only an occasional cell in 4 out of 20 and 6 out of 35 cases showed a weak reaction with myoglobin and leucocyte common antigen, respectively. Intense consistent reactivity with several histiocytic markers affirms the genesis of these cells from macrophages/histiocytes and not muscle cells; a controversy which must be laid to rest!