Sporadic inclusion body myositis (sIBM) and polymyositis (PM) are characterized 
by muscle inflammation, with sIBM showing additional degenerative alterations. 
In this study we investigated human beta defensins and associated TLRs to 
elucidate the role of the innate immune system in idiopathic inflammatory 
myopathies (IIM), and its association with inflammatory and degenerative 
alterations. Expression levels of human beta-defensin (HBD)-1, HBD-2, HBD-3 and 
TLR2, 3, 4, 7 and 9 were analysed by quantitative real-time PCR in skeletal 
muscle tissue. Localization of HBD-3, collagen 6, dystrophin, CD8-positive 
T-cells, CD-68-positive macrophages, β-amyloid, the autophagy marker LC3, and 
TLR3 were detected by immunofluorescence and co-localization was quantified. 
HBD-3 and all TLRs except for TLR9 were overexpressed in both IIM with 
significant overexpression of TLR3 in sIBM. HBD-3 showed characteristic 
intracellular accumulations near deposits of β-amyloid, LC3 and TLR3 in sIBM, 
and was detected in inflammatory infiltrations and macrophages invading necrotic 
muscle fibres in both IIM. The characteristic intracellular localization of 
HBD-3 near markers of degeneration and autophagy, and overexpression of 
endosomal TLR3 in sIBM hint at different pathogenetic mechanisms in sIBM 
compared with PM. This descriptive study serves as a first approach to the role 
of the innate immune system in sIBM and PM.