Defective expression of MHC class I antigens is frequent in B-cell lymphomas of high-grade malignancy

An unselected series of 66 immunohistologically proven B-cell lymphomas was examined for the expression of MHC class I antigens with monoclonal antibodies directed against non-polymorphic determinants of HLA-A,B,C heavy chain and beta 2-microglobulin. The tumors were classified according to the Kiel classification. No significant differences were observed in the reaction for HLA-A,B,C and beta 2m which may be indicative of a coordinate expression in our lymphoma series. In 37 cases (56%), all tumor cells exhibited strong staining for class I antigens as observed in normal B cells. The remaining 29 cases (44%) showed abnormally low or undetectable class I expression in varying tumor cell subsets; 13 cases were completely devoid of HLA-A,B,C. Twenty-two out of 30 lymphomas of high-grade malignancy but only 7/36 lymphomas of low-grade malignancy presented defective class I expression. This difference in proportion is highly significant (p less than 0.00002). Eleven of the 13 class I-negative lymphomas belonged to the group of high-grade malignancy. Centrocytic lymphoma, which has the poorest prognosis among the B-cell lymphomas of low-grade malignancy, was defective in 40% of the cases examined. The lymphoblastic type represented an exception within the lymphomas of high-grade malignancy as no defective expression was observed. In addition to the correlation between the high-grade malignancy and defective class I expression, defects occurred more frequently in lymphomas with an extra-nodal primary manifestation (p less than 0.05). The grade of malignancy, however, was not correlated with the primary site of the lymphoma.