Reactivity of monoclonal antibodies Leu 1 and OKT1 with malignant human lymphoid cells. Correlation with conventional cell markers.

This study delineated the distribution of reactivity of malignant human lymphoid cells with monoclonal antibodies Leu 1 and OKT1, and correlated this expression with that of conventional lymphoid cell markers. The presence of Leu 1 on benign lymph nodal T-cells and its absence from benign lymph nodal B-cells was confirmed. Twenty-two T-cell neoplasms, expressing a variety of intrathymic and mature peripheral phenotypes, expressed Leu 1, but this expression was heterogeneous with respect to percent-positive cells and antigenic density, and appeared to correlate with stages of T-cell differentiation. This study demonstrated the expression of Leu 1 by 33 of 36 cases of B-CLL, by 10 of 15 cases of the closely allied small lymphocytic cell lymphoma, and by 9 of 29 follicular center-cell lymphomas. This included B-cell malignancies of each surface immunoglobulin isotype, and some cases associated with a monoclonal protein spike. Leu 1 was not expressed by myeloma plasma cells, and was absent from non-B, non-T acute lymphoblastic leukemia cells in each of 15 cases studied. Finally, Leu 1 and OKT1 were expressed in parallel, with respect to percent-positive cells and staining intensity, on benign and malignant T-cells, and on malignant B-cells, wherever studied. Possible explanations for this shared antigen are the existence of a minor Leu 1+ B-cell subset, a transformation-associated event, or glycosylation.