Interleukin-1 expression in normal motor endplates and muscle fibers showing neurogenic changes

Histological features of neurogenic muscle involvement include type grouping, muscle fiber atrophy and target fibers. In zidovudine-induced myopathy and dermatomyositis, immunoreactivity for interleukin (IL)-1 has been reported in diseased muscle fibers involving myofibrillar breakdown and atrophy. Since IL-1 is a signal for muscle proteolysis, we studied myofiber expression of IL-1 in neurogenic muscle involvement, specially in atrophic myofibers and target fibers which are associated with myofilament breakdown. Muscle biopsy samples from patients with normal (5 cases) or neurogenic muscle involvement (25 cases) were studied by enzyme histochemistry and immunohistochemistry. In normal muscles, immunoreactivity for IL-1beta was restricted to the postsynaptic domain of motor endplates and that for IL-1alpha had a similar localization but was faint. Immunoreactivity for IL-1alpha and -beta was observed, respectively, in 42.5% and 75.5% of target fibers, in 8.5% and 10.4% of dark angulated fibers, in 0% and 0.3% of non-atrophic type-grouped fibers, in 14.2% and 16.5% of moderately atrophic fibers, and in 65% and 20.9% of severely atrophic fibers. Immunoblot study showed the presence of both proIL-1 (31 kDa) and mature IL-1 (17.5 kDa). From this study, we conclude that IL-1 is normally expressed in the muscular domain of neuromuscular junctions; that IL-1 is mainly expressed in neurogenic target fibers; and that IL-1 expression by muscle fibers in pathological conditions seems to be associated with myofibrillar protein breakdown and regeneration.