The multifaceted character of lymphotoxin β in inflammatory myopathies and muscular dystrophies

Lymphotoxin beta (LTβ) regulates some inflammatory mechanisms that could be operative in idiopathic inflammatory myopathies (IM). We studied LTβ and LTβR in inflammatory myopathies, normal and disease controls with immunohistochemistry, Western blotting and in situ hybridisation. LTβ occurs in myonuclei of normal controls, implying its role in normal muscle physiology. LTβ is strongly upregulated in regenerating muscle fibres in all myopathies, but not in denervated myofibres. Normal-appearing myofibres in inflammatory myopathies and muscular dystrophies express LTβ possibly reflecting early myofibre damage, representing a hitherto undescribed pathologic hallmark. Furthermore, we visualised LTβ in several inflammatory cell types in inflammatory myopathies, suggesting its involvement in the different inflammatory mechanisms underlying inflammatory myopathy subgroups.