Expression of HLA ABC and DR antigens in thyroid neoplasia and correlation with mononuclear leukocyte infiltration.

The rejection of tumor cells by the immune system depends on the production of tumor-associated antigens and the expression of HLA antigens on these cells. We therefore studied the expression of HLA ABC and DR antigens in malignant and benign thyroid disorders and correlated it with the types and extent of mononuclear cell infiltration. In the normal thyroid, HLA ABC expression was weak and focal, while it was diffusely present in benign disorders and in most but not all malignancies. HLA DR antigens, while absent or infrequently expressed in normal thyroid, were strongly but often focally expressed in all cases of autoimmune thyroid disease (AITD), as well as in most cases of malignant tumors and benign epithelium surrounding these tumors, and colloid nodule disease. There was a T cell predominance in all disorders, and the CD4+/CD8+ ratio was greater than 1 in most benign and malignant specimens. There was a direct correlation between the high expression of HLA antigens and dense inflammatory infiltration in AITD but not in most tumor specimens. Lack of such correlation suggests that the expression of HLA antigens is an autonomous event in tumors, independent of cellular infiltrate.