Phenotypic heterogeneity of the OKM1-positive lymphocyte population: Reactivity of OKM1 monoclonal antibody with a subset of the suppressor/cytotoxic T-cell population

Upon analysis on a fluorescence-activated cell sorter, about 20% of E-rosette-positive cells from normal donors were found to stain with OKM1, a monoclonal antibody reacting primarily with cells of myelomonocytic origin. These OKM1(+) cells are not monocytes since they have small light scatter and are peroxidase negative. They also stain with OKT11 and antibody 9.6, two monoclonal antibodies against an antigen identical to or related to the E receptor. In two-color immunofluorescence experiments, the existence of an OKM1(+) OKT8(+) cell was demonstrated. This was also confirmed with additive staining experiments. This cell type constitutes ~10% of the E-rosette(+) cell population. OKM1 reacts with approximately 33% of OKT8(+) cells. Conversely, 48% of OKM1(+) E-rosette(+) cells are also OKT8(+). The same overlap was found between Leu 2a and OKM1 while no overlap between OKT4 and OKT8 staining cells, or between OKT4 and OKM1 staining cells was detected. The OKM1(+) lymphocyte population was isolated by removing OKT3(+) cells from nylon wool-nonadherent cells: 43 ± 13% of these cells also reacted with Ab 9.6 and 33 ± 10% with OKT8. At least three subpopulations of OKM1(+) lymphoid cells can therefore be identified: one without any T cell marker, one that is E-receptor positive, and one that has, in addition to the E receptor, a definite T-cell marker (OKT8). In addition, OKT8(+) cells can be separated into OKT8(+) OKT3(+) and OKT8(+) OKT3(-) populations. Only the OKT8(+) OKT3(+) population suppresses Ig synthesis in pokeweed mitogen-stimulated cultures.