HLA class II expression in well differentiated thyroid carcinoma: correlation with clinicopathological features.

ABSTRACT

Lymphocytic infiltration and aberrant expression of HLA class II antigens on malignant thyroid epithelial cells are assumed to play a relevant role in the immune response against thyroid cancer. Aberrant expression of the HLA class II alpha and beta chains as well as number and distribution of tumor infiltrating lymphocytes were investigated in primary tumors (n = 54) and metastases (n = 4) of well differentiated thyroid carcinomas (follicular carcinoma n = 26, papillary carcinoma n = 28). The immunohistochemical findings were correlated with clinicopathological features. An aberrant HLA class II beta chain expression was detected in 9 (28%) papillary carcinomas and 4 (15%) follicular carcinomas. Three HLA class II beta chain positive papillary carcinomas and all follicular carcinomas were negative for the HLA class II alpha chain. All lymph node and distant metastases were negative for both HLA class II alpha and beta chain. Number and distribution of CD45R0+ lymphocytes significantly (p < 0.05, Fisher test) correlated with the aberrant HLA II antigen expression on tumor cells. There was also a significant correlation (p < 0.05, Fisher test) between an aberrant HLA II antigen expression and invasion of the vessels. No correlation was found between aberrant HLA class II expression and the occurrence of lymph nodes or distant metastases. Our findings indicate that the expression of HLA class II antigens on thyroid carcinoma cells is high in the step of invasive growth and that the local immune response towards the HLA class II antigens appears to prevent metastatic spread of HLA II positive tumor cells. There is evidence of different expression of HLA class II chains in follicular and in papillary thyroid carcinomas, which could be a further indicator that in these two subgroups of thyroid carcinomas different changes in the regulatory mechanisms of HLA class II antigen expression occur.