[Expression and tissue and species specificity of P25 protein in patients with myasthenia gravis].

OBJECTIVES: To confirm the specific decrease of P25 protein, a novel myasthenia gravis (MG) associated protein, in myasthenia gravis (MG) patients and to study the tissue and species specificity of its expression. METHODS: Samples of great pectoral muscle were taken from 28 MG patients, 17 males and 11 females, 10 of which being complicated with thymoma and 18 with hyperplasia of thymus, during thymectomy, and 24 wounded persons as normal controls, 14 males and 10 females, during thoracic surgery. Ten samples of skeletal muscle were taken from 10 patients with other muscular disorders (OMD) during skeletal muscle biopsy. Six samples of normal skeletal muscle, smooth muscle, brain, lung, kidney, and skin were taken from persons who died of accident. Two samples of normal cardiac muscle and thymus gland were taken from a patient undergoing cardiac valve replacement. Eight samples of animal skeletal muscle were taken from the thighs of pig, cattle, dog, rabbit, rat, mouse, chicken, and frog. Immunohistochemistry was used to examine the expression of P25 protein in the samples from the MG patients and the normal controls. Western blotting was used to detect the expression of P25 in the samples from MG patients, normal controls, OMD patients, 8 samples of different human tissues, and skeletal muscle samples from 8 different animals. RESULTS: Immunohistochemistry showed that the staining intensity of P25 protein in skeletal muscle of MG patients was much lower than that of the normal controls. Western blotting showed that the relative density value of P25 protein in MG patients was 1.04 +/- 0.18, significantly lower than those in the normal controls and OM patients (1.27 +/- 0.21 and 1.21 +/- 0.15 respectively. P < 0.01 and P < 0.05). No statistically significant difference in expression of P25 protein was found among different clinical and pathological types of MG patients. Among the 8 human tissues P25 protein was expressed only in skeletal muscle and among the 8 animal samples of skeletal muscle P25 protein expression was found only in swine skeletal muscle. CONCLUSION: The expression of P25 protein is significantly decreased in skeletal muscle of MG patients. The expression of P25 protein is tissue- and species specific.