ALPHA(1)-ANTITRYPSIN EXPRESSION IN HUMAN THYROID PAPILLARY CARCINOMA

Alpha(1)-antitrypsin is a plasma serine protease inhibitor originally used as a marker for tumors of histiocytic origin. Our casual finding of immunoreactive (a)lpha(1)-antitrypsin in one case of thyroid papill ary carcinoma led us to investigate its presence in 10 thyroid papilla ry carcinomas by applying immunocytochemical and immunochemical techni ques to tissue sections and Western blots of tissue homogenates prepar ed from neoplastic tissue and from uninvolved normal areas in the vici nity of each tumor. The immunocytochemical study was performed in both thyroid tissue and metastatic regional lymph nodes. This analysis rev ealed immunoreactivity for alpha(1)-antitrypsin in nine of the 10 case s studied. Immunoreactivity was intense in some of the cells forming t he papillar and follicular structures. These cells were intermingled w ith completely unstained tumoral cells. In contrast to neoplastic tiss ue, the normal thyroid tissue present in the vicinity of each tumor sh owed no staining for alpha(1)-antitrypsin. The electrophoretic analysi s performed on homogenates prepared from both tumoral and normal thyro id tissue revealed a drastic reduction in the band corresponding to th yroglobulin in the tumoral tissue compared with normal thyroid extract s, where it represented the major protein. Western blotting and immuno printing with a polyclonal alpha(1)-antitrypsin antibody confirmed the results obtained with immunocytochemistry about the presence of this protease inhibitor in neoplastic thyroid tissue. Immunoprinting with t he anti-alpha(1)-antitrypsin antibody revealed an intense immunoreacti ve band of 53 kDa in the extracts prepared from tumoral tissue. This b and had exactly the same apparent molecular mass previously described by others for alpha(1)-antitrypsin purified from plasma and was identi cal to the molecular mass of the purified commercial standard employed .