An extractable nuclear antigen not attaching to tannic acid-treated erythrocytes

One of the antigens present in isotonic phosphate buffer extract of calf thymus nuclei against which antibodies are produced in collagen diseases, was shown not to attach to tanned sheep erythrocytes. It is, however, well exposed on slides coated with smears of ENA-extract and fixed with methanol-acetone. Reactions with the antigen can be demonstrated by the mixed haemadsorption technique. Preliminary results suggest that it may be a ribonucloprotein closely related to the 'soluble ribonucleoprotein" (sRNP) attachable to tanned erythrocytes. It may also have a similar relationship to clinical symptoms.