Smooth-muscle antibodies in children with neuroblastoma

Smooth-muscle antibodies (SMA) were detected in 16 of 18 (89%) children with neuroblastoma and in 43 of 172 (25%) pediatric hospital patients without malignancies. The SMA were mainly of the IgG class. The most common immunofluorescence pattern was SMA-V (vessel) and titers did not exceed 1:160. Absorption and immunodiffusion tests with action (from rabbit skeletal muscle) showed that the SMA associated with neuroblastoma are mainly directed against actin, although different antigen specificities (myosin, meromyosin) are probably involved in some cases. In both chronic active hepatitis and neuroblastoma, SMA would represent a specific response to intracellular contractile proteins (mainly actin) induced by tissue damage. A feedback role in controlling cellular proliferation has been postulated for experimentally raised SMA. This would be relevant in cases of malignancy.