Functional and biochemical characteristics of human "null" lymphoid cells

Human peripheral null cells (non-T and non-B lymphocytes) were isolated by removing B lymphocytes and monocytes on nylon-wool columns and by E rosette-forming cells depletion. The null cell population contained less than 1% of SIg-bearing cells, cells with complement receptors (EAC+), and E mouse rosette-forming cells, but was contaminated by about 5% of T lymphocytes and 10% of monocytes. High affinity Fc receptors were present on 12% of the null cells. No intracytoplasmic immunoglobulins (CIgs) were detected by immunofluorescence. Culture of these null cells for 2 to 6 days did not modify their surface receptors. Null cells were not stimulated to undergo blastogenesis by the following mitogenic agents: concanavalin A (Con A), phytohemagglutinin-L (PHA-L), lentil lectin, wheat germ agglutinin, pokeweed mitogen (PWM), peanut agglutinin, and neuraminidase-galactose oxidase. PWM did not induce the transformation of null cells into B lymphocytes and no SIg, CIg, and production of Ig were detected by immunofluorescence and by measuring the incorporation of 3H-leucine. However the antibody-dependent cellular cytotoxicity of these null cells was very active compared to unpurified lymphocytes. Analysis of the lectin-binding surface glycoproteins, after labeling of the cells, by polyacrylamide gel electrophoresis (PAGE), showed that the 27,000- to 33,000-dalton component (Ia-like antigen) present in large amounts on B lymphocytes and monocytes was absent in null cells. These results are in agreement with the hypothesis that null cells consist of one or several populations different from the other lymphocytes and that they are not direct precursors or immature T and B lymphocytes.