IgD-receptor-positive human T lymphocytes. II. Identification and partial characterization of human IgD-binding factor.
Membrane receptors specific for IgD (IgD-R) have been identified on murine CD4+ and human CD4+ and CD8+ T lymphocytes. Up-regulation of these IgD-specific receptors can be achieved by exposure of such T cells to various stimuli, including oligomeric or Ag cross-linked IgD, IL-2, IL-4, and T cell mitogens, such as PHA. Previous studies with murine IgD-R+ splenic T cells and IgD-R+ T hybridoma cells have demonstrated the existence of soluble IgD-binding factors (IgD-BF) that are shed or released into the medium in which these cells are grown. In our study, human peripheral blood T cells and IgD-R+ T hybridoma cells were examined for their ability to produce human IgD-BF. PHA stimulation of peripheral blood T cells results in their release of an IgD-specific factor with an apparent Mr of 70 kDa. IgD- Sepharose-purified IgD-BF was able to competitively inhibit rosetting of IgD-R+ T cells with IgD-coated RBC. Immunoblot assays in which alkaline phosphatase-conjugated human IgD myeloma protein was used as a probe, confirmed the IgD specificity of IgD-BF. An IgD-BF-specific mAb (LTB9) that also reacts with membrane IgD-R was produced after immunization of BALB/c mice with this factor. LTB9 was able to detect IgD-BF in the supernatants derived from human IgD-R+, tetanus toxoid-specific T hybridoma cells, H9-CEM1, and to stain membrane IgD-R by indirect immunofluorescence. Stimulation of H9-CEM1 cells with immobilized IgD resulted in up-regulation of membrane IgD-R expression, as measured cytofluorometrically with LTB9-stained cells, and potentiated release of IgD-BF from these cells. Finally, LTB9 as well as IgD-Sepharose, immunoprecipitated a 70-kDa protein from the lysates of biosynthetically labeled H9-CEM1 cells. Similar immunoprecipitation results were obtained with H9-CEM1-derived supernatants containing IgD-BF. Taken together, these results support the hypothesis that human T cell membrane IgD-R are released as soluble IgD-BF.
Tamma
S M
SM
Department of Microbiology, City University of New York Medical School, NY 10031.
Coico
R F
RF
D000911:Antibodies, Monoclonal / Q000276:immunology; D006801:Humans; D006825:Hybridomas / Q000276:immunology; D007072:Immunoglobulin D / Q000378:metabolism*; D008222:Lymphokines / Q000032:analysis*; D010835:Phytohemagglutinins; D029584:Prostatic Secretory Proteins; D011961:Receptors, Fc; D011971:Receptors, Immunologic / Q000032:analysis*; D013601:T-Lymphocytes / Q000737:chemistry*
D000911:Antibodies, Monoclonal; D007072:Immunoglobulin D; D008222:Lymphokines; D010835:Phytohemagglutinins; D029584:Prostatic Secretory Proteins; D011961:Receptors, Fc; D011971:Receptors, Immunologic; C043076:beta-microseminoprotein; C050855:immunoglobulin D receptor; C013059:immunoglobulin-binding factors