Autoantibodies to cardiac conducting tissue and their characterization by immunofluorescence.

(1) A new antibody has been found by immunofluorescence which reacts with cardiac conducting tissue using ox heart false tendons. It was detected in eight out of ninety-three cases of idiopathic heart block (8-6%), in one out of twenty-two cases of secondary heart block (4-5%) and in seven of 165 normal controls (4.2%), in titres varying from 1:10 to 1:40. Previous authors had indicated that this tissue might contain unique antigens. (2) Sera reacting with type I fibres in skeletal muscle (red zebra) were found to be of two varieties, one of which stained conducting fibres diffusely while it gave minimal staining of cardiac muscle; the other reacting with myofibrils in Purkinje cells and heart. (3) Some sera with high titre smooth muscle antibodies (SMA) reacted with conducting tissue together with skeletal and cardiac muscle, suggesting that the four tissues have at least one antigen in common. (4) Known non-organ specific antibodies behaved as expected on beef conducting fibres: striational fluorescence of myasthenia gravis sera reacted with the same patterns on Purkinje myofibrils; AMA and ANA produced IFL in expected locations; ribosomal antibodies reacted strongly, while LKM and reticulin antibodies showed no reactivity. (5) Although the incidence of specific Purkinje fibre antibodies was not significantly raised in idiopathic heart block, the clinical associations suggest that some cases might be related to autoimmunity possibly involving cell-mediated mechanisms as in polymyositis.