Coexpression of CD43 by benign B cells in the terminal ileum.

Expression of CD43 by B cells is often used as a diagnostic criterion in favor of a B-cell lymphoproliferative disorder, including small lymphocytic lymphoma/chronic lymphocytic leukemia, mantle cell lymphoma, Burkitt lymphoma, precursor B-lymphoblastic lymphoma, and a subset of marginal zone B-cell lymphomas. Benign B cells generally do not coexpress CD43. The authors analyzed 20 biopsies of the terminal ileum for nonneoplastic disease for expression of CD43 and compared them with other sites and with CD20, CD138, and CD3 reactivity. The majority of cases (85%) showed strong coexpression of CD43 by benign perifollicular B cells. The presence of CD43 coexpression in B-cell populations of the terminal ileum, including those of Peyer's patches, should not be used as a diagnostic parameter to differentiate extranodal marginal zone B-cell lymphoma of MALT type from reactive processes.