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

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Abstract
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 β2‐microglobulin. The tumors were classified according to the Kiel classification. No significant differences were observed in the reaction for HLA‐A,B,C and β2m 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 < 0.00002). Eleven of the 13 class l‐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 < 0.05). The grade of malignancy, however, was not correlated with the primary site of the lymphoma.
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