2017 年 33 巻 6 号 p. 633-637
Immune–mediated necrotizing myopathy (IMNM), characterized by necrosis and regeneration of muscle fibers in the absence of prominent inflammatory cells, is one of inflammatory myopathies. Autoantibodies against signal recognition particle (SRP) or 3–hydroxy–3–methylglutaryl–coenzyme A reductase (HMGCR) are regarded as serological markers for IMNM. SRP is a cytoplasmic ribonucleoprotein consisting of six proteins and 7S RNA. Recently, anti–SRP antibodies have been observed to entail a broad variety of neuromuscular phenotypes, collected under the heading “anti–SRP myopathy”. RNA immunoprecipitation is an original detection method for anti–SRP antibodies. One disadvantage is that RNA immunoprecipitation requires a complicated technique and is performed at only a limited number of facilities. Other conventional detection assays including enzyme–linked immunosorbent assay (ELISA) and line blot assay using a recombinant SRP protein are typically used. In contrast, Mammen et al. identified autoantibodies to HMGCR in patients with statin–induced myopathy. Although anti–HMGCR antibodies were originally identified by protein immunoprecipitation assay using radiolabeled culture cell extracts, many researchers agree that ELISA is a preferred standard method. Anti–SRP and anti–HMGCR antibody studies are not used in routine clinical practice because there is no convenient, widely accepted assay. Our goal was to establish accurate quantitative assays for IMNM–associated autoantibodies. We have developed new ELISAs for anti–SRP and anti–HMGCR with some modifications of previous studies. The advantage of ELISAs is its ability to provide quantitative results, which may be useful in evaluating disease activity. In addition, ELISAs can be performed easily and quickly and are particularly suitable for screening large numbers of sera. We believe that our ELISAs can substitute for an immunoprecipitation assay in the clinical settings.
