SPIB protein expression in selected human cell lines and normal hematolymphoid populations. (A) Western blot in selected human cell lines revealed overexpression of SPIB (clone 235 D/C7) in the Burkitt lymphoma and ABC-DLBCL cell lines DAUDI and OCILY-3, respectively. None of the other cell lines studied, including the GC-type DLBCL, T-cell lymphoma, or monocytic leukemia cell lines, showed positivity with SPIB mAb. (B) SPIB immunohistochemical expression in reactive lymph node hyperplasia. SPIB mAb stained the nuclei of mature B cells and plasmacytoid dendritic cells. The SPIB protein was expressed at low levels in mantle zone B cells and up-regulated in the GC reaction. In the GC, it stains centroblasts and centrocytes (see coexpression with BCL6 and GCET1); however, late centrocytes that enter the plasma cell differentiation program do not express SPIB (see double immunostains with Blimp1 and CD38). Normal plasmacytoid dendritic cells express SPIB intensely (see double immunostains with CD123). The intensity of the staining in this specific subpopulation was higher than that in the mature B-cell compartment. No expression was found in other subpopulations of the myelomonocytic cell lineage (ie, macrophages, follicular dendritic cells, and reticular and interdigitating cells).