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The staining pattern of anti-actin sera on various cells smeared on glass was compared to the relative amount of cellular actin estimated by SDS-polyacrylamide-gel electrophoresis with subsequent scanning of the gel. Although the cells showed a varying stainability the actin content was fairly constant. Thus, the staining differences reflected changes in the organization of cellular actin rather than actual differences in the amount of actin. [ABSTRACT FROM AUTHOR]

Thirty sera reacting by IFL. technique in titres⩾ 100 with smooth muscle fibres of rat stomach, rat renal glomeruli, and with the membrane region of thyroid cells were randomly chosen among sera .sent in for routine testing of tissue antibodies. All sera but one were found to be derived from patients with chronic active hepatitis. The smooth muscle and other relevant cell staining were abolished after absorption of sera with actin, prepared from rabbit skeletal muscle and found to be homogeneous by SDS gel-electrophoresis and by electron microscopy. The actin antibodies were purified by precipitation of sera with K-actin and elution of the precipitates at acid pH. The purified antibodies stained all tissues in the same way as the original sera. In double immunudirtusion tests all thirty .sera gave precipitation with actin. Thus, it was concluded that these broad-reacting SMA are directed against actin. The finding of high-titred S.MA is of diagnostic value and supports the clinical diagnosis of active chronic hepatitis. In addition, anti-actin antibodies eluted from buman sera are a suitable tool for studying actin-containing cellular structures. [ABSTRACT FROM AUTHOR]