Flow cytometric and immunohistochemical characterization of the gamma/delta T-lymphocyte population in normal human lymphoid tissue and peripheral blood.

We determined the quantitative and topographic distribution of gamma/delta lymphocytes in normal human lymphoid tissue and peripheral blood using a monoclonal antibody that detects a framework determinant on delta molecules and delineated the immunophenotypic characteristics of the gamma/delta lymphocyte population by one- and/or two-color immunohistochemical and two- and/or three-color flow cytometric analysis. Variable, but generally small, numbers of gamma/delta lymphocytes are present in peripheral blood and in all lymphoid tissues. The vast majority, greater than or equal to 90%, of lymphoid tissue delta lymphocytes reside in interfollicular (T-cell) zones. Approximately 90% of delta thymocytes are present in the thymic medulla. The percentage of CD3-positive T cells that express delta are: spleen 12.5 +/- 8.1%, peripheral blood 4.0 +/- 3.1%, appendix 2.9 +/- 1%, lymph node 2.2 +/- 1%, thymus 1.4 +/- 0.5%, and tonsil 0.7 +/- 0.5%. We further demonstrated that 1) gamma/delta-thymocytes and gamma/delta peripheral lymphocytes express T-cell lineage restricted antigens CD3 and CD2 but only a variable subset, 30% to 90%, express T-cell lineage associated antigens CD5 and/or CD8; (2) approximately 60% of gamma/delta thymocytes express low-density CD4 while all gamma/delta peripheral lymphocytes lack detectable CD4; 3) gamma/delta lymphocytes lack natural killer (NK), macrophage, and B-cell associated antigens CD16, CD14, and CD20, respectively, but greater than or equal to 70% of gamma/delta T lymphocytes express CD11b, Leu7, and NKH-1, antigens, which are also expressed by suppressor/cytotoxic and NK cells; and 4) a large subpopulation, approximately 25%, of gamma/delta thymocytes are in S1-G2 phase, while greater than or equal to 98% of gamma/delta peripheral lymphocytes are small lymphocytes in G0-G1 phase and lack activation/proliferation markers. Together these results indicate that gamma/delta lymphocytes are resting, mature T cells that probably play a primary role in suppressor/cytotoxic phenomena. They also indicate that gamma/delta lymphocytes variably express multiple-cell surface antigens associated with various cell lineages, suggesting that gamma/delta lymphocytes represent a considerably more heterogeneous cell population than previously appreciated and that they may actually subserve multiple functions.