NORMAL SPLENIC LYMPHOID SUBSETS MIMIC ABERRANT ANTIGEN EXPRESSION.
Nidhi Aggarwal, Jason Fischer, Fiona E. Craig
University of Pittsburgh School of Medicine, Department of Pathology
Background: Flow cytometry (FC) assists in the diagnosis of lymphoma through identification of aberrant antigen expression. However, normal lymphoid subsets with less well-recognized phenotypes can mimic lymphoma. This study characterizes lymphoid subsets in normal spleen using 8-color FC.
Design: 20 spleens removed for traumatic rupture, with cell viability >50%, were analyzed within 24 hrs with the following FC combinations: CD16&57/CD7/CD4/CD2/CD56/CD3/CD5/CD8; K//CD5/CD19/CD10/CD38/CD20/CD45;TCRab/TCRgd/CD3/CD25 and CD14/CD13&33/CD45/CD34.
Results: This study reveals the normal variation in splenic lymphoid subsets and demonstrates some subsets with phenotypes that have been associated with lymphoid neoplasms. Well recognized lymphoma-associated phenotypes identified in this study include CD5+ B-cells (20 of 20 specimens), CD7- T-cells (20 of 20), and CD3 bright gamma-delta T-cells (16 of 20). In addition, less well-recognized lymphoid subsets were identified that resemble those described in lymphoma: CD5- T-cells (20 of 20) (Figure 1a), CD2- NK-cells (20 of 20) and CD7dim+ NK-cells (20 of 20) (Figure 1b).The latter two NK-cell phenotypes were seen more often in the mature subtype (p<0.01).
Conclusion: 8-color FC analysis of normal spleen demonstrates lymphoid phenotypes that may resemble those described in subtypes of lymphoma, such as LGL leukemia, hepatosplenic lymphoma, and chronic NK-cell lymphoproliferative disorders. Familiarity with these normal phenotypes can help prevent misinterpretation. Furthermore, these findings support that these neoplastic phenotypes reflect expanded normal subsets rather than aberrant antigen expression.