Immunohistochemical staining for BCL10 protein expression.

(A) Reactive spleen with strong cytoplasmic BCL10 expression in the marginal zone and in the germinal center and absent to weak expression in the lymphocytic corona. Original magnification × 400. (B) High magnification of splenic reactive marginal zone cells, expressing BCL10 in the cytoplasm and not in the nucleus. Original magnification × 1000. (C) Cytoplasmic BCL10 expression in the tumor cells of case 20 (MALT-type lymphoma without the API2-MLT fusion). Original magnification × 1000. (D) Aberrant nuclear BCL10 expression in case 4 (MALT-type lymphoma with the API2-MLT fusion). Original magnification × 1000.