Screening of new KL-6-associated mucins useful in clinical diagnosis of interstitial pneumonitis

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Screening of murine monoclonal antibodies which react with novel antigenic deternlinants on KL-6 molecules was performed last year.EK-7 monoclonal antibody was finally selected for the purpose this year.EK-7 antibody was IgM and reacted with an antigenic determinant different from the determinant recognized with KL-6 antibody. The antigenic determinant was peptide portion of KL-6 molecules.The PEP-76 molecule in serum which was detected by a sandwich type of enzyme immunoasssay using EK-7 antibody as a catcher and KL-6 antibody as a tracer was designated as PEP-76. The method using 96-well EIA plates was similar to that for the measurement of KL-6.Study population was 51 healthy individuals, 13 patients with idiopathic interstitial pneumonia and 12 patients with sarcoidosis.PEP-76 level was 0.9 (0.9-3.9) U/ml [median (range)] in healthy individuals, 54 (0.9-580) U/ml in idiopathic interstitial pneumonia, and 1 (0.9-13) U/ml in sarcoidosis. Both the levels in idiopathic interstitial pneumonia and sarcoidosis were statistically higher than that in healthy individuals. when the cut-off level of PEP-76 was determined at 2.7 U/ml from the distribution of the levels of healthy individuals, the positive rate was 92% in idiopathic interstitial pneumonia and 33% in sarcoidosis. The sensitivity of PEP-76 was higher than that of KL-6 in same sera from patients with interstitial pneumonitis.These observations indicate that PEP-76 is a novel serum marker for the diagnosis of interstitial pneumonitis.