title: Characterization of a non-T, non-B human lymphocyte (L cell) with use of monoclonal antibodies. Its regulatory role in B lymphocyte function.
abstract: These studies investigate the role of L lymphocytes in regulating terminal B lymphocyte differentiation. L cells have abundant Fc IgG receptors and comprise 10--15% of human peripheral blood mononuclear cells (PBMC). L cells lack the conventional markers of B and T lymphocytes and in culture, do not develop into B cells, T cells, or macrophages. Additionally, use of monoclonal antibodies failed to detect on L cells, surface antigens specific for B cells, T cells, and macrophages. In these studies, purified L cell subpopulations depleted of macrophages were co-cultured with autologous PBMC in the presence of pokeweed mitogen and at the end of 8 d, development of intracytoplasmic immunoglobulin (Ig) was determined. L cells were depleted of B and T cells by rosetting techniques and, in addition, by cytotoxicity techniques using monoclonal-specific antisera to T cells. In 14 individuals, L cells when co-cultured with PBMC, enhanced Ig synthesis by 83% +/- 62 SD, and also enhanced cell proliferation. Radiated L cells lost enhancing properties. To study the role of their high density Fc IgG receptors, L cells pretreated with IgG antibody-sensitized erythrocytes were used (i.e., after lysis of rosettes). Such L cells significantly inhibited Ig synthesis (by greater than 50%) despite promoting cell proliferation. Antibody-sensitized erythrocyte-rosetted macrophages did not inhibited Ig synthesis. Thus, positive and negative influences can be mediated by the same cell, depending on the state of Fc-receptor stimulation. Such cells may play a more prominent role in "feed-back" regulation of Ig synthesis by virtue of having abundant Fc IgG receptors.
mesh_terms: D000917:Antibody Formation / Q000187:drug effects; D000936:Antigen-Antibody Complex; D000954:Antigens, Surface / Q000032:analysis; D001402:B-Lymphocytes / Q000276:immunology*; D002999:Clone Cells / Q000276:immunology; D003208:Concanavalin A / Q000494:pharmacology; D006801:Humans; D006822:Hybrid Cells / Q000276:immunology; D008213:Lymphocyte Activation / Q000187:drug effects; D008211:Lymphocyte Cooperation / Q000187:drug effects; D008214:Lymphocytes / Q000145:classification / Q000276:immunology*; D011961:Receptors, Fc / Q000032:analysis
chemical_list: D000936:Antigen-Antibody Complex; D000954:Antigens, Surface; D011961:Receptors, Fc; D003208:Concanavalin A