Complement-mediated muscle cell lysis: A possible mechanism of myonecrosis in anti-SRP associated necrotizing myopathy (ASANM)

- Anti-SRP positive sera are myotoxic in vitro in the presence of complement
- Surface staining for SRP, C3c and C5b-9 in anti-SRP treated myoblasts
- Sarcolemmal staining for SRP, C3c and C5b-9 in anti-SRP myopathy biopsies
- Complement-dependent antibody-mediated mechanism of injury in anti-SRP myopathy

The mechanism of necrotizing myopathy associated with antibodies to signal recognition particle (SRP) remains unclear. We investigated the effect of anti-SRP + serum and complement on cell viability in myoblast cultures. Cell viability was only slightly reduced by incubation with anti-SRP + serum compared with control serum. However, the addition of fresh complement resulted in a marked reduction in cell survival. Surface immunostaining for SRP, C3c and C5b-9 was demonstrated in cultures pre-incubated with anti-SRP + serum and complement, and in muscle biopsies from patients with myopathy. These findings provide further support for a complement-dependent antibody-mediated mechanism in anti-SRP associated myopathy.