Evaluation of CD23 expression in paraffin-embedded gastric lymphomas of mucosa-associated lymphoid tissue

The CD23 antigen is expressed in a normal subset of B lymphocytes and in some non-Hodgkin's lymphomas. Reactivity for anti-CD23 (BU38) is present in paraffin-embedded tissue in the large majority of nodal small lymphocytic lymphomas, as well as in follicular center cell lymphomas. Most studies of gastric lymphomas of mucosa-associated lymphoid tissue (MALT) reported a lack of CD23, but these studies were performed on frozen tissue. We evaluated CD23 staining in paraffin-embedded tissue in a large series of gastric MALT lymphomas, as well as in cases of chronic gastritis. We assayed 49 well-characterized gastric lymphomas (9 high-grade non-MALT and 40 MALT [20 low grade, 13 mixed low and high grade, and 7 high grade]). High-grade MALT lymphomas without a low-grade component were distinguished from high-grade non-MALT lymphomas by the presence of lymphoepithelial lesions composed of large cells. In addition, we studies nine cases of chronic gastritis containing B-cell aggregates. We used anti-CD23 (BU38) in formalin-fixed, paraffin-embedded tissue. All of our low-grade gastric MALT lymphomas lacked CD23 immunoreactivity. One of the 13 mixed low-grade and high-grade lesions showed CD23 expression in the high-grade component. All of the high-grade MALT and high-grade non-MALT lesions lacked CD23. All of the nine cases of chronic gastritis lacked CD23. CD23 highlighted residual follicular dendritic cells and gastric epithelium. We concluded that gastric MALT lymphomas lacked CD23 (BU38) in paraffin-embedded tissue, with rare exceptions. This lack of CD23 expression might represent a useful feature in small or partially crushed biopsy specimens, particularly in the differential diagnosis with follicular small cleaved cell lymphoma presenting in the gastrointestinal tract.