Lymphocyte subpopulations in sensitization and specific immunotherapy in an experiment. Lymphocyte subpopulations in sensitization to staphylococci, Artemisia pollen and their combinations

The distribution of T- and B-lymphocytes in the body of guinea pigs was studied in different groups of the animals. As shown in this study, in delayed hypersensitivity to staphylococci the number of PE- and E-rosette-forming cells increased in the blood, the spleen, and the lymph nodes and decreased in the thymus; the number of EA- and EAC-rosette-forming cells decreased in the bone marrow and the spleen, the number of T gamma-suppressors decreased in the bone marrow and the distant lymph node. Immediate hypersensitivity to tarragon pollen induced the general increase of the content of T- and B-lymphocytes; the number of T gamma-cells decreased in the thymus, the bone marrow, and the lymph nodes and increased in the spleen. The characteristic features of combined microbial-pollen sensitization were the high content of B-cells in all lymphoid organs (except the thymus), a low level of T-lymphocytes in the blood and the peripheral lymphoid organs, the decreased number of T gamma-cells in most of the immunogenetic organs.     

Properties and kinetics of a population of B-lymphocytes during rat ontogenesis]

Cells bearing surface immunoglobulins (Ig+-cells) detected by the indirect immunofluorescent method and cells forming rosettes (RFC) with sheep erythrocytes coated with antibody and complement (EAC rosettes) were found in the liver and the spleen on the 15th and the 20th days of prenatal life of rats. The percentage of Ig+-cells and RFC in the liver was high and remained unchanged and at about the same level during the whole postnatal life. The spleen and the bone marrow displayed an increase of the Ig+-cells and RFC increased throughout the 1st month of postnatal life with the maximum at the 30th day after birth; a sharp decrease occurred in old animals. In the thymus the Ig+-cells and the RFC were either absent or present in very small amounts only at some periods of study. Ig+-cells with "capping" were discovered in the spleen and bone marrow on the 5th--10th days of postnatal life; their count increased considerably in 30-day and adult rats. Such cells were absent in the lymphoid tissues of old 40-month rats.     

Immunohistochemical localization of xenogeneic antibodies against Iak lymphocytes on B cells and reticular cells

Rabbit antiserum against B10.AQR mouse spleen and lymph node cells (RAQR), after appropriate absorption, reacted with Ia^k-positive spleen and lymph node cells in cytotoxic and complement-fixing indicator systems. It reacted neither with Ia^k-positive thymocytes nor Ia^k-negative thymocytes, spleen, and lymph node cells. Cryostat sections of tissue from Ia^k-positive and Ia^k-negative mice were incubated with RAQR and either rabbit anti-mouse Ig or rabbit anti-T cell globulin. With the unlabeled antibody enzyme method, RAQR-stained lymphocytes were concentrated in the B-cell regions of spleen and lymph nodes of Ia^k-positive CBA mice. The tissues of mice bearingI-region haplotypes different fromk were negative. Reticular cells of the T cell-supporting network were also positive in Ia^k mice, but liver, gall bladder, and testicular cells were not. Macrophages of both Ia^k-positive and -negative mice were stained by RAQR and also by heat-aggregated, peroxidase-labeled Ig. Ia^k-positive reticular cells survived 900 R total body irradiation and persisted after grafting with Ia^k-negative bone marrow. The reticular cells were also seen in a thymus which was depleted of cortisone-sensitive lymphocytes.Abbreviations used in this paper are as follows RAQR rabbit anti-mouse-B10.AQR globulin - RAMTG rabbit anti-mouse T-cell globulin - RAMIG rabbit anti-mouse Ig - SARIG sheep anti-rabbit Ig - agg-HIg aggregated human Ig - PAP anti-peroxidase-peroxidase-complex     

Migratory patterns of B lymphocytes. IV. Effect of anti-Ig on follicular localization of radioactively labeled murine spleen and bone marrow cells.

A study was made of the localization of nylon-wool-adherent (AD) and nonadherent (NA) murine spleen cells in lymphoid tissue of irradiated syngeneic recipients. Cells were labeled in vitro with [³H]uridine or ⁵¹Cr and injected intravenously. Localization in recipient tissues was expressed as percent of injected radioactivity. NA and AD [³H]uridine labeled cells gave spleen to lymph node (S:LN) ratios of 1.0 and 2.7, respectively. After treatment of AD cells with rabbit anti-mouse Fab + C at 37 °C, localization in S decreased markedly.NA cells primarily localized in LN paracortex and splenic periarteriolar sheaths. Untreated and NRS-treated AD cells localized in lymphoid follicles, whereas anti-Fab-treated AD cells did not. When ⁵¹Cr-labeled AD cells were treated with anti-Fab at 4 °C without C, there was a transient decrease in splenic localization at 24 hr followed by a recovery to the normal pattern at 48 hr after transfer. [³H]uridine-labeled bone marrow (BM) cells showed less localization in lymphoid tissue than did S cells. Some BM cells were seen in LN follicles, particularly at 48 hr after transfer, but this localization was not affected by prior treatment with anti-Fab + C. The possible role of surface Ig in the determination of follicular localization of B lymphocytes is discussed.     

Differences in the repertoire expressed by peritoneal and splenic Ly-1 (CD5)+ B cells.

Purified populations of B cells expressing the Ly-1 and/or Mac-1 surface Ag were isolated from normal unmanipulated mice by cell sorting. The number of lymphocytes in each population secreting antibodies reactive with DNA, bromelain-treated mouse RBC, phosphorylcholine and TNP-keyhole limpet hemocyanin was quantitated by ELISA spot assay. The proportion of B cells secreting Ig in vivo and the repertoire of antibodies they produced varied as a function of B cell phenotype and location. Among peritoneal lymphocytes, those that were Ly-1+ or Ly-1- Mac-1+ secreted Ig 10 times more frequently that Mac-1- Ly-1- B cells from the same location. In addition, the former populations expressed repertoires that were significantly skewed toward the production of antibodies reactive with bromelain-treated mouse RBC (p less than 0.001). In contrast, splenic B cells expressing the Ly-1 surface Ag did not differ significantly from splenic Ly-1- B cells in their expressed repertoire or frequency of Ig production. B cells isolated from the spleen and peritoneum tended to differ in antibody specificity from bone marrow and lymph node-derived lymphocytes. For example, B cells from the spleen secreted anti-DNA antibodies two to four times more frequently than B cells from other organs. These results demonstrate that phenotype and microenvironment influence the repertoire of antibodies expressed by B cells in vivo.     

Correction or transfer of immunodeficiency due to TNF-LT alpha deletion by bone marrow transplantation.

BACKGROUND: Mice with inactivated tumor necrosis factor (TNF) and lymphotoxin alpha (LT alpha) genes have profound abnormalities of the immune system including lymphocytosis, lack of lymph nodes, undifferentiated spleen, hypoimmunoglobulinaemia, and defective Ig class switch. Here, we asked whether this phenotype is due to incompetent lymphohemopoietic progenitors or to a defective environment. MATERIALS AND METHODS: Lethally irradiated TNF-LT alpha-deficient and wild-type mice received bone marrow cells from either TNF-LT alpha-deficient or wild-type mice. The reconstitution and transfer of the phenotype was followed by morphological and functional analyses. RESULTS: Bone marrow cells from wild-type mice restored the synthesis of TNF and LT alpha, corrected the splenic microarchitecture, normalized the lymphocyte counts in the circulation, and repopulated the lamina propria with IgA-producing plasma cells of TNF-LT alpha-deficient mice. Furthermore, the formation of germinal centers in the spleen and the defective Ig class switch in response to a T-cell dependent antigen was corrected, while no lymph nodes were formed. Conversely, the TNF-LT alpha phenotype could be transferred to wild-type mice by bone marrow transplantation after lethal irradiation. CONCLUSIONS: These data demonstrate that most TNF- and LT alpha-producing cells are bone marrow derived and radiosensitive, and that the immunodeficiency due to TNF-LT alpha deletion can be corrected to a large extent by normal bone marrow cell transplantation. The genotype of the donor bone marrow cells determines the functional and structural phenotype of the TNF-LT alpha-deficient adult murine host, with the exception of lymph node formation. These findings may have therapeutic implications for the restoration of genetically defined immunodeficiencies in humans.     

"Lymph node" form of graft-versus-host reaction in mice]

Local type of the graft-versus-host reaction was induced in adult hybrid mice (CBA X C57BL) F1 by the transfer of splenic, thymus and bone marrow CBA cells subcutaneously into the right hind footpad.The weight gain of the regional knee lymph node and blast accumulation in it 7 days later were used as indices of the graft-versus-host activity. After the transfer of 5 and 20 x 10(6) splenic cells the absolute weight of the regional lymph node was 8-10 times higher than that of the contralateral control; it was also significantly greater in comparison with controls which received live syngeneic or semiallogeneic dead cells from the same source. Contrary to controls, in case of the live cells a direct dose-effect dependency could be seen. The lymph node weight gain was accompanied by a regular immunoblast accumulation. The effect of the thymus and the bone marrow cells was less pronounced than that of the splenic cells.     

Studies of the T-lymphocytes resident in the spleens of thymectomized, irradiated, bone marrow-reconstituted (TXB) mice.

The T-lymphocytes resident in the spleens of thymectomized, lethally irradiated mice that had been reconstituted with syngeneic bone marrow (TXB) were characterized. Both recently reconstituted N-TXB, (approximately 3 weeks after bone marrow injection) and aged (>6 months after reconstitution) A-TXB animals were studied. The T-lymphocytes from spleens of recently reconstituted N-TXB donors did not respond to PHA but did react significantly to Concanavalin A (Con A). The lack of PHA sensitivity was not due to dilution of reactive cells by other cell types. Removal of adherent cells, likewise, did not restore N-TXB spleen cell PHA responsiveness. N-TXB splenic T-cells were cortisone resistant. N-TXB spleen cells by themselves did not cause a graft vs host response. However, N-TXB spleen cells amplified the graft vs host response of normal lymph node cells but not N-TXB lymph node cells. Addition of cyclic GMP enhanced [³H]thymidine uptake of N-TXB spleen cells caused by Con A. N-TXB spleen cells were exclusively spleen seeking. The Con A reactive cell within N-TXB spleens was demonstrated to be of donor origin. Fetal liver as well as syngeneic bone marrow contained cells capable of reconstituting the Con A response. Spleen cells from aged. (>6 months) A-TXB were found to be PHA sensitive. Competitive inhibition assays measuring θ expression in A-TXB spleen cells indicate a significant increase in the θ positive lymphocyte population occurred with time. The data indicate that considerable reconstitution of θ positive cells had occurred in A-TXB donors. The results also suggest that the T-lymphocyte population of the TXB spleen may be a unique subpopulation of T-lymphocytes that resides exclusively in spleen and bone marrow.     

Failure of ovalbumin associated with allogeneic spleen ceels to stimulate proliferation of lymph node cells of immune mice.

Ovalbumin-pulsed spleen cells were found to stimulate thymidine uptake of lymph node cells of syngeneic mice immunized with ovalbumin in complete Freund's adjuvant after treatment of spleen cells with Mitomycin C but not after heating the spleen cells at 56degrees for 30 min. Ovalbumin-pulsed spleen cells of allogeneic mice failed to stimulate the immune lymph node cells more than unpulsed cells, although a net increase in the thymidine uptake above the allogeneic stimulation was observed when free ovalbumin was added to the mixed culture. To eliminate the high background of the mixed lymphocyte reaction, F1 mice were made chimeric with bone marrow of one of the parental strains. Using lymph node cells of the immunized chimeras, the stimulation by pulsed spleen cells was much greater when antigen was presented on cells of the parental strain used for bone marrow injection than when presented on cells of the other parental strain.     

Peripheral tolerance induced in lymph nodes by syngeneic spleen cells inhibits generation of CTLs to hapten-altered self antigens but not to alloantigens.

The immunological tolerance that is induced in lymph nodes that have been exposed to syngeneic spleen cells has been examined. Development of cytotoxic T lymphocytes was used to assess the immunological status of the lymph node cells. The tolerance was studied from the viewpoint of its induction, its activation, and its specificity. We had already reported that injecting either T or B cells of splenic origin into a regional lymph node environment a week prior to immunization for CTL to hapten-altered self antigens prevents development of the CTL. Here, we confirm that syngeneic splenic cells but not lymph node cells will induce the suppression provided that spleen cells are not coupled with hapten. We now report that splenic cells that cannot replicate or synthesize and secrete protein are capable of inducing the suppression. The data suggest a preformed surface marker peculiar to spleen cells and perhaps on cells that traverse the thymus induces local tolerance that is mediated by suppressor cells. Triggering the induced suppressor T cells (previously identified as CD8-) was achieved by syngeneic spleen cells as well as by H-2-compatible, Mls-disparate spleen cells but not by syngeneic lymph node cells or apparently by allogeneic spleen cells. Furthermore, triggering suppression was achieved by hapten-coupled syngeneic spleen cells whereas such cells would not induce the suppression. Thus, activating the suppressor cells requires reexposure to splenic cells of the proper MHC haplotype, unaltered or coupled with either TNP or FITC. Once triggered, the suppression was manifested toward CTL generation against hapten-coupled syngeneic antigens on either spleen or lymph node cells but not against allogeneic antigens. Thus, the specificity of the tolerance was directed to altered self antigens despite its induction by unaltered spleen antigen. Furthermore, for suppression to be seen the spleen antigen was not required to be on the hapten-coupled syngeneic cells used for the CTL immunization. The relationship of the splenic cell "antigen" to hapten-altered self antigens and to other surface markers and its site of acquisition within the body and its significance for cell homing have become intriguing questions of importance. This information has been discussed from the viewpoint of its applicability to autoimmune diseases as well as to cessation of inflammatory reactions that may be mediated by lymph node cells.     

Cell cooperation in abolition of tolerance of xenogeneic tumor.

Thymectomized, lethally irradiated mice reconstituted with syngeneic bone marrow cells are tolerant to xenogeneic Yoshida ascites sarcoma (YAS). The tolerance was abolished by an injection of syngeneic normal spleen, thymus, or lymph node cells given simultaneously with YAS. Allogeneic and semiallogeneic spleen cells were ineffective. The YAS-rejecting mice produced specific anti-tumor antibodies. The serum of these mice transferred to tolerant T-cell-deficient mice protected the latter from inoculated YAS cells. These serum-protected mice were not able to resist the reinoculum of the tumor cells as the mice restored with lymphoid cells did. The latter mice rejected the YAS at the time when donor cells were practically absent in their lymphoid tissue. The low effective ratio of injected syngeneic lymphoid to tumor cells, efficiency of injected thymus cells, and other data led to the conclusion that transferred lymphoid cells did not act directly on tumor cells but through cooperation with host lymphoid cells. The cooperation of donor T- and host B-lymphocytes enabled the activation of the latter, and YAS cells were rejected.     

Formation of spleen colonies by CFU-S from long-term culture of bone marrow and embryonic liver in the presence of thymocytes

The syngeneic thymocytes increase the efficiency of spleen colony formation and proliferative activity of CFU-S derived from fetal liver on 13th-16th day of gestation and CFU-S from long term bone marrow culture. The thymocytes effect spleen colony cells. These data indicate that T-cell-CFU-S interaction in spleen colony formation have a physiological character.     

Administration of IL-7 to mice with cyclophosphamide-induced lymphopenia accelerates lymphocyte repopulation

Lymphopenia was induced in mice by a single injection of cyclophosphamide. IL-7 or a control protein were administered to the mice twice daily and the cellularity and composition of the spleen, lymph node, bone marrow, and thymus were determined at various time points thereafter. In comparison to the control cyclophosphamide-treated mice, animals receiving cyclophosphamide and IL-7 had an accelerated regeneration of splenic and lymph node cellularity. There was no significant difference in the rate of recovery of the bone marrow and thymus of the control and IL-7-treated mice. Assessment of the pre-B cell compartment revealed a dramatic increase in total pre-B cell numbers in the spleen and bone marrow of the IL-7-treated mice as measured by both flow microfluorimetry and a pre-B cell colony-forming assay. This was followed in a few days by a significant increase in surface IgM+B cell numbers to levels above normal values in both the spleen and lymph node. IL-7 administration to cyclophosphamide-treated mice also resulted in an accelerated recovery of peripheral CD4+ and CD8+ cell numbers in the spleen and lymph node. The numbers of CD8+ cells were increased by twofold over normal levels in cyclophosphamide-treated mice receiving IL-7. Myeloid recovery was determined in cyclophosphamide treated mice by assessing the numbers of CFU-granulocyte-macrophage and Mac 1+ cells. There was no significant difference in myeloid recovery between cyclophosphamide-treated mice receiving IL-7 or control protein. These results suggest that administration of IL-7 after chemical-induced lymphopenia may have therapeutic benefits in shortening the period required to achieve normal lymphoid cellularity.     

Effect of mononuclear phagocytes on the differentiation of syngeneic, allogeneic and xenogeneic hematopoietic stem cells

The colony formation in spleen of lethally irradiated syngeneic or hybrid recipients was studied after transplantation of bone marrow cells, with or without macrophages from lymph nodules or from peritoneal cavity of mice, cells of macrophage-like cell line J-774, and monocytes from peripheral blood of healthy donors. The direction of stem cell differentiations in the presence of all the types of mononuclear phagocytes was seen to change from mainly erythroid to mainly myeloid one. The ratio of erythroid to myeloid colonies became equal to 0.5-0.9 instead of 2.0, when bone marrow cells were injected with equivalent quantity of mononuclear phagocytes. This new regulatory function of mononuclear phagocytes is discussed.     

Comparative migration of B- and T-Lymphocytes in the rat spleen and lymph nodes.

B-lymphocytes were obtained either by thoracic duct cannulation of thymectomized, irradiated rats or by isolation of complement-receptor-bearing lymphocytes from normal rats. They were labeled in vitro with [³H]-leucine and injected iv into syngeneic recipients from which samples of spleen and lymph node were taken at intervals from 15 min to 48 hr after injection. The sites of initial localisation of B- and T-lymphocytes were identical suggesting that the cells migrated into both organs by a common entrance. The two cell types remained closely associated for several hours in the paracortex of lymph nodes and at the periphery of the periarteriolar lymphoid sheath of the spleen. After 1–6 hr, B-cells segregated from T-cells by moving on into the adjacent part of the lymphocyte corona in the follicular area. By 24 hr, B-cells were evenly distributed throughout the corona. A definite minority of B-cells but no T-cells were seen within the germinal centres. In the spleen, T-cells moved into the central area of the periarteriolar sheath before returning to the blood. The immunological significance of the routes of B- and T-cell migration is discussed.     

A novel alloantigen on rat macrophages and granulocytes

Previous studies have shown that immunization of MAXX rats with spleen and lymph node cells from the MHC-identical BN strain results in the formation of antibodies that react with the renal endothelial alloantigen Eag-1. In the present study, the reactivity of MAXX anti-BN sera was further characterized. No reactivity of the antisera was detected with unseparated spleen, lymph node, thymus and bone marrow cell suspensions, peripheral blood, or cells obtained from lung lavages. The antisera did, however, react with splenic macrophages, as well as with peritoneal granulocytes and macrophages from BN, BMA, BN.1L, and PVG rats. Genetic studies revealed that the antigen, provisionally designated Pag-1, segregates independently of Eag-1, the RT1 complex, sex, and the hooded and albino traits. Pag-1 appears to be absent in the kidney, since absorption of MAXX anti-BN sera with BN kidney homogenates did not remove the reactivity against Pag-1, and antisera raised against BN peritoneal cells did not bind with the renal endothelium. Pag-1 is expressed on bone marrow-derived cells, since peritoneal cells from lethally irradiated MAXX rats that were reconstituted with bone marrow cells from BN donors reacted with MAXX anti-BN sera, whereas peritoneal cells from BN rats reconstituted with MAXX bone marrow did not.Abbreviations used in this paper BSA bovine serum albumin - CDC complement-dependent microcytotoxicity - MHC major histocompatibility complex - PBS phosphate-buffered saline     

Role of immune RNA in the interaction of T- AND B-lymphocytes]

"Immune" RNA preparations were obtained from the total population and also from the T- and B-lymphocytes of the spleens of the QBA line. Intact bone marrow cells or splenic cells activated with antigen served as target cells for the "immune" RNA. Investigations were carried out in the system of syngenic transfer. To study the target cells in the activated population of the spleen elimination of T-or B-lymphocytes was realized immediately after the incubation of the suspension of the splenic cells with the RNA preparations with the aid of anti-theta-or anti-B-antilymphocytic sera. T-lymphocytes served as the source of the biologically active RNA in the total preparation. B-lymphocytes of the spleen and the bone marrow served as target cells for the RNA of the cells of thymus origin. However, to detect the inducing action of the RNA simultaneous presence in the population of T- and B-lymphocytes is necessary.     

A membrane antigen of rabbit thymus cells

Rabbit cells, bearing a thymus-specific antigen, which we call rabbit thymus lymphocyte antigen (RTLA), could be detected with a suitably absorbed heterologous antiserum (goat). In the presence of complement, the RTLA antiserum lysed more than 95% of thymus cells, 70 ± 6% of lymph node cells, 46 ± 10% of spleen cells and 12 ± 7% of bone marrow cells. The number of direct or indirect hemolytic spleen plaques was not reduced by treatment with RTLA antiserum and complement, but was greatly diminished by an unabsorbed thymus antiserum which killed more than 90% of bone marrow cells. RTLA-bearing subpopulations of spleen cells were characterized by velocity sedimentation analysis and were distinguished from Ig receptor bearing subpopulations. The antiserum concentration could be so adjusted that the cytotoxicity against bone marrow was not manifested, while the cytotoxicity against other cell populations remained unchanged. The latter were identified by thymidine incorporation induced by treatment with antibody directed against rabbit light chain allotype. A small subpopulation of thymus cells did not have RTLA antigen and sedimented with a velocity distinct from that of the peak of RTLA-bearing cells.     

The effect of colony stimulating factor on the synthesis of ribonucleic acid by mouse bone marrow cells in vitro.

The effect of granulocyte-macrophage colony stimulating factor (GM-CSF) on the synthesis of RNA in liquid cultures of mouse bone marrow, spleen, thymus, peritoneal, peripheral blood leukocytes and lymph node cells was investigated. GM-CSF appeared to stimulate RNA-synthesis in syngeneic bone marrow cells within ten minutes of adding it to the culture. In the presence of GM-CSF bone marrow cultures maintained their initial rate of RNA synthesis for approximately ten hours. GM-CSF had no apparent effect on the uptake of 3H-uridine into bone marrow cells. This stimulation was still observed in the presence of puromycin and cycloheximide, but was abrogated by actinomycin D. The magnitude of the stimulation was not affected by the density of cells between 1 and 20 x 10(6) cells/ml but was slightly smaller at 0.1 and 40 x 10(6) cells/ml. Increasing concentration of GM-CSF (up to 2 X 105 units per ml) led to increased stimulation of RNA synthesis in bone marrow cells, but a significant stimulation could be detected at concentrations as low as 800 units/ml. GM-CSF did not significantly stimulate RNA synthesis in spleen, thymus, mesenteric or subcutaneous lymph node cells. However a small stimulation was observed in peripheral blood leukocytes and peritoneal cells. Autoradiographic studies showed that GM-CSF stimulated RNA synthesis in blast cells, myelocytes, metamyelocytes and polymorphs. Nucleated erythroid cells showed no increased labeling with GM-CFS. Labeling in lymphoid-like cells was highly variable but the level of labeling did not appear to be influenced by GM-CSF.     

Effects of neonatal anti-delta antibody treatment on the murine immune system. I. Suppression of development of surface IgD+ B cells and expansion of a surface IgM+ IgD- B lymphocyte population

Lymphocytes that bear surface (s) IgD make up the majority of B cells in mature mice and are the precursors of most antibody secreting cells in primary immune responses made by these mice. In order to study the functional capabilities of the minority sIgD- B lymphocyte population and to gain insight into the possible roles of sIgD, we attempted to abort the development of sigD+ B cells and to expand the sigM+IgD- B cell population by treating mice from birth with affinity-purified rabbit antibodies specific for mouse IgD (RaM delta). RaM delta-suppressed mice had no detectable sIgD+ spleen, lymph node, or bone marrow cells and, on average, only 20% as many sIgM+Ia+ splenic B cells as control mice but had normal numbers of splenic T cells. Lymph nodes from anti-delta suppressed mice were even more depleted of B cells than were spleens from these mice, whereas the percentage of bone marrow B cells in these mice was relatively normal. Germinal centers of anti-delta suppressed mice were fairly normal in appearance, whereas follicular mantle layers, the locus of most sIgD+ B cells in normal mice, were greatly depleted. In addition to their lack of sIgD, splenic B cells of anti-delta suppressed mice differed from those found in control mice in that they bore, on average, twice as much sIgM as control cells, and in that they included an increased percentage of large, DNA synthesizing cells as compared with spleen cells from control mice. However, most sIgM+IgD- splenic B cells from anti-delta suppressed mice were small, nonproliferating cells. B cells from anti-delta suppressed mice insert little or no sIgD into their cell membranes since they continued to bear no detectable sIgD 2 days after in vivo neutralization of RaM delta and since, unlike B cells from control mice, they failed to be activated by a single in vitro injection of a goat anti-mouse delta antibody. Despite their lack of sIgD+ B cells, anti-delta suppressed mice had relatively normal levels of serum IgG as well as normal to increased levels of serum IgM. Thus, sIgM+IgD- B cells appear to have the potential of differentiating into Ig secreting cells in vivo without acquiring sIgD.