The rat basophilic leukemia (RBL) cell lines were cloned and the various sublines compared for their chromosome number, IgE-mediated histamine release and for IgE surface receptors. It was found that cell lines started from tumors at different times vary in both their chromosome number and their ability to release histamine by an IgE-mediated reaction. RBL-I and III have approximately 44 chromosomes and did not respond to an IgE-mediated reaction. RBL-II and RBL-IV have 68-73 chromosomes and showed moderate levels of histamine release (percent release mean = 5 +/- 2 and 10 +/- 4, respectively). The cloning of the RBL-IV line resulted in some sublines which were excellent histamine releasers (range 39-100%) and some which were relatively refractory (less than 10%) to IgE-mediated histamine release. These clones did not differ significantly in chromosome number. Recloning the releasing lines gave rise to poor releasers, whereas the recloning of poor releasers did not produce good releasers indicating that the mutational drift in culture is toward loss of histamine-releasing capacity. The number of IgE receptors and the rate of IgE association and dissociation were similar for the different cell lines. The study failed to disclose significant molecular weight differences in the IgE receptor from the various clones and sublines indicating that the failure to release probably does not reside in the receptor. The various cloned sublines are phenotypically stable, and the isolation of excellent histamine-releasing sublines are useful for studies of the complex phenomenon of the histamine release.

No abstract

No abstract

B lymphocytes originate from pluripotent hematopoietic stem cells and differentiate into antibody-secreting cells through multistep differentiation stages, such as pre-B cells, immature B cells with surface IgM, and mature B cells with surface IgM and IgD . A number of human B cell antigens have been defined by in Abs (I-10) . However, most B cell-specific mAbs, except for antibodies against plasma cells (5) and activated B cells (9,10), are known to recognize cells of the B lineage at a wide range of differentiation stages from pre-B cells to mature B cells . It has therefore been difficult to identify B cells at a specific differentiation stage by using such B cell-specific mAbs.Several previous studies (11)(12)(13)(14) have shown the expression of FcER on a certain percentage (1-5%) of circulating B or T cells using the rosette method with IgE-conjugated ox red blood cells (ORBC).t Our previous study (15) with FcER-specific mAbs with several different epitope specificities showed that >50% of circulating B cells express FcER on their surface, while T cells do not display this receptor, even with T cells from patients with hyper-IgE syndrome . The discrepancy in the results may be due to the difference in the sensitivity of the assay system and the antibodies used. In the present study, the distribution of FcER + cells was studied in various lymphoid tissues, and the results show that FcER is a B cell-specific phenotype marker, the expression of which is strictly correlated with the differentiation stage of B cells, especially with the isotype switching in B cells . Materials and MethodsAntibodies . Human IgE(PS) was the same preparation as described previously (16 1456Fce RECEPTOR AND ISOTYPE SWITCHING F(ab)' 2 fragment of goat anti-human IgD and FITC-F(ab)' 2 fragment of goat anti-human IgA were purchased from Tago Inc . (Burlingame, CA). FITC-anti-B1 was from Coulter Immunology (Hialeah, FL) . An anti-human IgM mAb was a kind gift from Dr. M . Sugi (Yamasa Shoyu Co., Ltd, Tokyo, Japan) . An anti-human IgE mAb was the same preparation as described previously (17). The anti-FcER mAbs 1-7, 3-5, and 8-30, which are of IgG2b, IgG 1, and IgM, respectively, were produced by hybridization ofP3U 1 myeloma with spleen cells from BALB/c mice immunized with RPMI-8866 cells (15). Two antibodies (1-7 and 8-30) recognized the epitope close to IgE-binding site of Fc(R and blocked IgE binding to 8866 lymphoblastoid cells . The antibody 3-5 recognized a different epitope on FccR, and could not block IgE binding to 8866 cells . These antibodies precipitated 25,000 and 46,000 Mr polypeptides under reducing and nonreducing conditions . The mAbs were purified from ascites by 50% saturated ammonium sulfate precipitation followed by gel filtration using Sepharose 6 B (Pharmacia Fine Chemicals, Uppsala, Sweden) for IgM class, or by ion-exchange chromatography using QAE-Sephadex (Pharmacia Fine Chemicals) for IgGI and IgG2b classes . Some of the antibodies were conjugated with biotin or FITC as described (18,19) . Some of the antib...