Evidence for immunological cross-reactivity between smooth and skeletal muscle

In 1965 Johnson, Holborow & Glynn showed that some patients with chronic liver disease have antibodies which react with smooth muscle by indirect immunofluorescence. This work was rapidly confirmed and it was soon showed that the same serum may also react with renal glomeruli and other tissue components. Reactions with skeletal muscle were not demonstrated. In 1960 Strauss and co-workers deomonstrated that patients with myasthenia gravis may have antibodies which react with skeletal muscle. Subsequent work has suggested that these antibodies are specific for skeletal as opposed to smooth muscle. More recently smooth muscles antibodies (SMA) have been shown to react with a wide range of tissues and cells including neoplastic cells (Gabbiani et al,, 1973; Holborow et al., 1975). Throughout this work it has been assumed that such reactivity is due to the presence of smooth muscle contractile proteins. This conclusion was further supported by the demonstration that animals immunized with smooth muscle contractile proteins developed antibodies which produce similar patterns to those found with the naturally occurring antismooth muscle antibodies (Trenchev, Sneyd & Holborow, 1974). From these studies it appeared that there was very little if any cross reactivity between smooth and skeletal muscle, although Bray (1974) pointed to the need to re-examine this conclusion. In the course of screening human sera for autoantibodies we have been impressed by the occasional occurrence of sera which gave both smooth and skeletal muscle staining patterns. In this report we describe selected sera which react with antigens which appear specific for either smooth or striated muscle, and additional sera which react with antigens which appear common to both smooth and striated muscle. Immunization of rabbits with skeletal muscle contractile protein has provided further evidence for such cross reactivity,