Elevated immunosuppressive acidic protein in patients with subacute thyroiditis

Abstract

Immunosuppressive acidic protein (IAP) has been reported to be found in the sera of not only cancer patients but also collagen diseases such as SLE and rheumatoid arthritis and certain inflammatory diseases such as liver abcess and pyothorax. IAP is proved to be one of the heterogeneity of human serum α1 -acid glycoprotein and to suppress both phytohemagglutinin-induced lymphocyte blast formation and mixed-lymphocyte reaction in vitro (Cancer Research, 41 : 3244, 1981).In the present study, we measured IAP by the single radial immunodiffusion methods in patients with various thyroid diseases.The IAP concentration in patients with subacute thyroiditis was 956 ± 256μg/ml (mean ± S.D., n=32), which is significantly higher than that in hyperthyroidism (267 ± 64μg/ml, n=10), hypothyroidism (328 ± 81μg/ml, n=9), chronic thyroiditis (366 ± 120 μg/ml, n=24) and destructive thyroiditis (352 ± 34μg/ml, n=4), respectively. The normal value of IAP concentration is below 500μg/ml.After therapeutic administration of prednisolone or salicylate to patients with subacute thyroiditis, IAP rapidly decreased to normal levels in association with the recovery of elevated erythrocyte sedimentation rate (ESR) and serum thyroxine (T4) and triiodothyronine (T3).In the densitometric tracing of IAP separated by thin-layer isoelectric focusing at a pH range of 2.5 to 5, the major acidic protein had an isoelectric point (pI) of 3.0 in patients with subacute thyroiditis during the active phase as well as in one patient with gastric cancer. Furthermore, the acidic protein at pI 3.0 decreased and the one at pI 3.1, which is the major protein observed in normal serum, became prominent during the recovery phase in patients with subacute thyroiditis. The major acidic protein also had a pI of 3.1 in the sera of patients with hyperthyroidism, hypothyroidism and chronic thyroiditis.IAP remained within the normal range in a patient with destructive thyroiditis who showed thyrotoxic symptoms and then became hypothyroid.It is suggested that the determination of IAP is useful in the clinical diagnosis of subacute thyroiditis. Further analysis of IAP might be helpful for the clarification of the pathogenesis of subacute thyroiditis.