SHP-1 expression by malignant small B-cell lymphomas reflects the maturation stage of their normal B-cell counterparts

SHP-1 is a protein phosphotyrosine phosphatase that plays an important role in modulating intracellular signaling, which regulates cell activation, pr oliferation, differentiation, and migration. It is a negative regulator of signal transduction induced by a number of cell receptors. Our immunohistoc hemical examination of paraffin-embedded reactive lymph nodes and lymphoid tissues revealed that B lymphocytes in follicle germinal centers do not exp ress SHP-1. A weak staining of the B cells in the germinal center light zon es was detected when an ultrasensitive amplification system was used. In co ntrast, normal B cells in mantle and marginal zones as well as interfollicu lar B lymphocytes and plasma cells displayed strong immunoreactivity. This pattern of SHP-1 expression was repealed in small B-cell lymphomas. All cas es of mantle cell lymphoma (12 of 12), marginal zone lymphoma (10 of 10), a nd chronic lymphocytic leukemia/small lymphocytic lymphoma (13 of 13) expre ssed SHP-1 protein. However, only 1 of 30 cases of grade 1 follicle center cell lymphoma expressed SHP-1. Our observations highlight the biologic func tions of SHP-1 and demonstrate that the SHP-1 expression pattern by small B -cell lymphomas reflects the maturation stage of their normal cell counterp arts. These results indicate that determination of SHP-1 expression may hel p in the differential diagnosis of small B-cell lymphomas.