Context: In comparison to alphabeta T cells, little is known about the immunophenotype of healthy peripheral blood gammadelta 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 gammadelta 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 gammadelta T cells comprised either more than 5% of the total lymphocytes or had an absolute count of more than 200 cells per muL or both, were studied further. Clinical data were available from 36 cases.
Results: The gammadelta T cells often had an immunophenotype distinct from the alphabeta 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 gammadelta 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 gammadelta T cells are immunophenotypically distinct from alphabeta 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 gammadelta T cells can exhibit distinctive immunophenotypic features that are also encountered in neoplastic conditions, such as T-cell large granular lymphocytic leukemia.