Immunophenotypic attributes of benign peripheral blood γδ T cells and conditions associated with their increase

Context. - In comparison to αβ T cells, little is known about the immunophenotype of healthy peripheral blood γδ T cells or about conditions associated with expansion of this usually minor T-cell subset. Objective. - To study the immunophenotype of increased nonneoplastic peripheral blood γδ T cells and to determine clinical conditions associated with this laboratory finding. Design. - Flow cytometric T-cell phenotyping studies performed on 352 consecutive peripheral blood specimens were reviewed, and 62 cases (18%) in which γδ T cells comprised either more than 5% of the total lymphocytes or had an absolute count of more than 200 cells per μL or both, were studied further. Clinical data were available from 36 cases. Results. - The γδ T cells often had an immunophenotype distinct from the αβ T cells, with differences in CD5 expression as the most common (n = 17), followed by differences in CD3 (n = 6) and CD7 (n = 3). CD16 coexpression by the γδ T cells was also frequent (n = 20). In 28 (78%) of 36 cases, there were one or more associated conditions: infection/inflammatory disease (n = 18), autoimmune disease (n = 9), lymphoproliferative disorder (n = 6), and splenectomy (n = 3). Conclusions. - Circulating γδ T cells are immunophenotypically distinct from αβ T cells, and mild increases in these cells are not uncommon and may be associated with immune system activation and splenectomy. Recognition of this phenomenon is important because reactive γδ T cells can exhibit distinctive immunophenotypic features that are also encountered in neoplastic conditions, such as T-cell large granular lymphocytic leukemia.