B lymphocyte regulation of the immune system. I. In vivo biologic activity of the novel lymphokine, B cell-derived enhancing factor (BEF)

B cell-derived enhancing factor (BEF) is a lymphokine of B cell origin which was originally identified and characterized by its ability to enhance in vitro antibody responses, an effect shown to be due to the ability of BEF to reduce the activation of suppressor T cells. The present study was undertaken to determine whether BEF could also be active in modulating antibody responses in vivo. The data presented here demonstrate that BEF is biologically active in vivo, as manifested by significantly enhanced primary IgM and IgG antibody responses in mice that were either injected with BEF prepared exogenously or implanted with growing BEF-secreting cells of a B cell line. Moreover, BEF was shown to enhance subsequent development of immunologic memory in mice pretreated with BEF at the time of primary immunization; these mice then displayed enhanced secondary responses when challenged with the same antigen some weeks later. The mechanism by which BEF exerts biologic activities to positively modulate in vivo antibody responses and immunologic memory reflects the ability of BEF to modulate one or more T cell functions, as evidenced by the following findings. 1) Transient in vitro exposure to BEF of T cells, but not of B cells, endowed such cells with the capacity to adoptively transfer enhanced primary antibody responses to irradiated recipients. 2) Utilizing adoptive in vivo antibody responses, in which fractionated B cell or T cell populations were obtained from BEF-pretreated mice, revealed that one effect of BEF which results in enhanced immunologic memory is related to its activity on T cells during the priming phase of the immune response. Finally, the existence of this B cell-derived lymphokine and the demonstration of its in vivo regulatory effects on the immune system provide yet another example of the emerging biologic importance of B lymphocytes in the overall regulation of the immune system.     

FcR epsilon+ lymphocytes and regulation of the IgE antibody system. II. FcR epsilon+ B lymphocytes initiate a cascade of cellular and molecular interactions that control FcR epsilon expression and IgE production

This study additionally explores the orderly sequence of events concerning the induction of Fc receptors for IgE (FcR epsilon) that are initiated by IgE and mediated by IgE-induced regulants (EIR). Thus, lymphoid cells exposed to monomeric IgE displayed an early phase of exclusive B cell FcR epsilon expression, followed by the progressive appearance of FcR epsilon+ T cells, ultimately resulting in equal proportions of FcR epsilon+ B cells and T cells. Parallel cultures of lymphoid cells stimulated with EIR derived from unfractionated lymphoid cells (EIRT) also manifested rapid induction of FcR epsilon+ cells, but these FcR epsilon+ cells were predominantly T cells from the outset. Data presented here demonstrate that IgE-induced FcR epsilon expression by B cells ultimately results in the production of EIRT, which then induces FcR epsilon expression by T cells. The existence of EIRT that selectively induce T cell FcR epsilon expression prompted us to search for an EIRB that is selectively active in inducing FcR epsilon+ B cells. Indeed, IgE-stimulated, T cell-depleted lymphoid cells produce an EIRB that selectively induces FcR epsilon expression by B cells. This EIRB, but not EIRT, can also be generated by IgE stimulation of Lyt-2+ cell-blocked lymphoid cells, indicating that Lyt-1+ cells are not inhibitory to EIRB production and that production of EIRT is dependent upon functionally competent Lyt-2+ cells. Similar to IgE, EIRB induces rapid FcR epsilon expression, first by B cells and then by T cells, so that by 16 hr post induction equal proportions of FcR epsilon+ B and T cells were observed. Although complete T cell depletion does not affect IgE-induced FcR epsilon expression, selective blocking of Lyt-1+ cells markedly diminishes such responses, suggesting that Lyt-2+ cells are antagonistic to the induction of FcR epsilon+ B cells. Studies involving sequential T cell subset depletion clearly demonstrated that in the absence of functionally competent Lyt-1+ cells, Lyt-2+ cells exert an inhibitory influence on IgE-induced FcR epsilon expression by B cells. Stimulation of Lyt-1+ cell-blocked cultures with EIRT, and to a lesser degree with IgE, resulted in the elaboration of an EIR (EIRI), which lacks direct FcR epsilon-inductive properties, but conversely, directly inhibits IgE-induced FcR epsilon expression in fresh B cell cultures.     

Regulatory function of Thy-1- cells. IV. Biologic and Biochemical characterization of B cell clone-derived lymphokine (BEF)

Studies were made on the immunoregulatory activity of a lymphokine produced by a B cell clone that does not express immunoglobulin heavy or light chains. The B factor (BEF; B cell-derived enhancing factor), was effective in augmenting the primary and the anamnestic response to SRBC and/or in prolonging the IgG anamnestic response to SRBC and the response to DNP-LE, provided it was added at early stages of culture. The BEF seems to act mainly by preventing the activation of T suppressor cells rather than by counteracting the activity of already activated suppressor cells. Indeed, thymocytes and virgin T cells, but not Con A-activated thymocytes, Con A-activated T cells or B cells, express acceptors for the BEF. The biochemical properties of the BEF were also reported. The apparent m.w. of the factor was 450,000 to 500,000 by gel chromatography. The BEF was sensitive to digestion by papain, trypsin, and subtilisin, indicating that it was protein in nature. The regulatory activity was precipitated by 50% (NH4)2SO4 and was destroyed by heating at 70 degrees C for 30 min or by exposure to pH 2.2 for 6 hr.     

Feedback regulation of immune responses by immune complexes; possible involvement of a suppressive lymphokine by FcR gamma-bearing B cell

Inoculations of antigen-antibody complexes (immune complexes) with the intact Fc portion generates suppressor cells in vivo by binding to FcR gamma on B cells via Fc portions. The cell type responsible for the suppression appears to be B cells bearing FcR gamma. Neither T cells nor macrophages participate in both the inductive and effective phases of this type of regulation. The suppression caused by splenic B cells, previously stimulated with immune complexes in vivo, is mediated by humoral factor(s) released from them. The suppressive factor(s) have H-2 gene product(s) coded by the right-hand side of the H-2 gene complex, but not for FcR gamma themselves or immunoglobulins. It has shared component(s) with suppressive B cell factor (SBF) released from FcR gamma + B cells stimulated with immune complexes in vitro, and it resembles SBF in its mode of action. These findings indicate that immune complexes, the final products of antibody responses, control the immune responses by stimulating surface FcR gamma on B cells. It is of interest that this type of regulation functions in vivo.     

Cell surface expression of cytotoxic T lymphocyte-defined, AKR/Gross leukemia virus-associated tumor antigens by normal AKR.H-2b splenic B cells

We previously described a system in which H-2Kb-restricted C57BL/6 (B6) cytotoxic T lymphocytes (CTL) could be raised that were specific for tumors, such as the thymic lymphoma AKR.H-2b SL1, that were induced by endogenous AKR/Gross murine leukemia virus and that expressed the Gross cell surface antigen. In this study, certain normal lymphoid cells from AKR.H-2b mice were also found to express target antigens defined by such anti-AKR/Gross virus CTL. AKR.H-2b spleen, but surprisingly not thymus, cells stimulated the production of anti-AKR/Gross virus CTL when employed at either the in vivo priming phase or the in vitro restimulation phase of anti-viral CTL induction. This selective stimulation by spleen vs thymus cells was not dependent on the age of the mice over the range (3 to 28 wk) tested. Both AKR.H-2b spleen and thymus cells, however, were able to stimulate the generation of H-2-restricted B6 anti-AKR minor histocompatibility (H) antigen-specific CTL. Thus, AKR.H-2b spleen cells appeared to display the same sets (minor H and virus-associated) of cell surface antigens recognized by CTL as the AKR.H-2b SL1 tumor, whereas AKR.H-2b thymocytes were selectively missing the virus-associated target antigens, a situation analogous to that of cl. 18-5, a variant subclone of AKR.H-2b SL1 insusceptible to anti-AKR/Gross virus CTL. Like AKR.H-2b thymocytes, neither AKR spleen cells or thymocytes nor B6.GIX + thymocytes were able to stimulate the generation of anti-AKR/Gross virus CTL from primed B6 responder cell populations. In contrast, both T cell-enriched and B cell-enriched preparations derived from AKR.H-2b spleen cells were able to stimulate at the in vitro phase of induction, although B cell-enriched preparations were considerably more efficient. The discordant results obtained with AKR.H-2b spleen cells vs thymocytes were confirmed and extended in experiments in which these cells were employed as target cells to directly assess the cell surface expression of virus-associated, CTL-defined antigens. Thus, AKR.H-2b spleen cells, but not thymocytes, were recognized by anti-AKR/Gross virus CTL when fresh normal cells were tested as unlabeled competitive inhibitors, or when mitogen blasts were tested as labeled targets. Fresh or lipopolysaccharide-stimulated B cell-enriched spleen cells were as efficiently recognized as unseparated spleen cell preparations. Unexpectedly, fresh or Lens culinaris hemagglutinin-stimulated T cell-enriched spleen cell preparations, although susceptible to anti-minor H CTL, were almost as poor as targets for anti-viral CTL as were thymocytes. Together, these results demonstrate the H-2-restricted expression of CTL-defined, endogenous, AKR/Gross virus-associated target antigens by normal AKR.H-2b splenic B cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

In vitro and in vivo activation of murine gamma/delta T cells induces the expression of IgA, IgM, and IgG Fc receptors.

The present studies examined resting and activated murine gamma/delta T lymphocytes, in vitro and in vivo, for surface expression of FcR. Polyclonal gamma/delta TCR+ lymphocytes selectively grown from the spleen and intestine of normal mice did not express FcR when the cells were in a resting state, but when cells were activated with anti-CD3 antibody virtually all of the splenic gamma/delta lymphocytes and a large subpopulation of the intestinal gamma/delta lymphocytes expressed IgA and IgM FcR. This was confirmed by using transgenic mice. Resting gamma/delta TCR+ lymphocytes from the spleen, thymus, lymph node, and blood of gamma/delta TCR transgenic mice did not express FcR for any of the five major classes of Ig H chains. Activation of the gamma/delta TCR+ cells via the CD3/TCR complex induced high levels of IgM and IgA FcR and low levels of IgG FcR. Finally, in hepatic granulomas of schistosome-infected mice, activated gamma/delta TCR+ cells are present and express high levels of IgA and IgM FcR and low levels of IgG FcR. These investigations establish that transition of gamma/delta TCR+ lymphocytes from a resting to an activated state (triggered via the T3Ti TCR complex) is accompanied by the induction of surface membrane receptors specific for Ig H chain isotypes. The activation-linked expression of FcR on gamma/delta TCR+ lymphocytes provides potential mechanisms for coupling the functional activities of gamma/delta T lymphocytes with immune mechanisms that involve Ig molecules, such as antibody-dependent cellular cytotoxicity.     

An in vitro system for the generation of suppressor cells and the requirement for B cells in their induction

An in vitro method for the generation of effector suppressor cells (Ts3) was developed. By utilizing this protocol, it was possible to investigate both the cellular and genetic requirements for suppressor cell induction. It was determined that populations containing Ts3 cells can be induced after a 4-day culture of spleen cells and antigen. These Ts3 cells are similar to Ts3 cells generated by in vivo immunization. Both populations are I-J+, bind NP hapten, bind NP hapten, bear receptors which share NPb idiotypic determinants with anti-NP antibodies, function during the effector phase of the immune response, and require activation with Ts2 cells. Generation of Ts3-containing populations required both nylon wool-nonadherent T cells and a nylon-adherent, B cell-enriched population from an Igh-identical donor. T cells cultured with antigen alone or with syngeneic macrophages and antigen did not develop suppressive activity. Lytic treatment of the nylon-adherent population with a B cell-specific monoclonal antibody (J11d) removed the ability to generate suppressor cells. These results imply that the induction of suppressor T cells requires B lymphocytes, and that this induction process is dependent on Igh-linked gene products.     

Human natural killer cells analyzed by B73.1, a monoclonal antibody blocking Fc receptor functions. II. Studies of B73.1 antibody-antigen interaction on the lymphocyte membrane

In this paper, we characterize the antigen recognized by the monoclonal antibody B73.1 and the modification occurring at the membrane of the positive cells after interaction with the antibody. The B73.1-defined antigen is a protein of 50,000 to 72,000 daltons that is sensitive to pronase but not to trypsin treatment. B73.1 antibody, and its F(ab')2 fragment, directly block, at high concentrations, the binding of IgG antibody-sensitized erythrocytes to the Fc receptors (FcR) of a subpopulation of lymphocytes and neutrophils. B73.1 antibody dissociates rapidly from the positive cells, but concomitant modulation of both B73.1 antigen and FcR is induced when cells are incubated in the continuous presence of antibody or when B73.1 antibody is cross-linked at the cell membrane with an anti-mouse immunoglobulin antiserum. Reaction of lymphocytes with immune complexes also induces modulation of both FcR and B73.1 antigen, without affecting the expression of other antigens on the positive cells. The possibility that the antigen is internalized and digested by the cell after reaction with the antibody is discussed. B73.1 antibody inhibits antibody-dependent cytotoxicity mediated by lymphocytes (K cells) and neutrophils, whereas it does not affect spontaneous cytotoxicity of NK cells. These results suggest the B73.1-defined antigen might be the FcR or a structure closely related to it on K/NK cells.     

Human peripheral blood T helper cell-induced B cell activation results in B cell surface expression of the CD23 (BLAST-2) antigen

We have developed an in vitro system to assess the early stages of B cell activation induced by peripheral blood T helper cells. Peripheral blood mononuclear cells are cultured for 16 hr with anti-CD3 monoclonal antibody (mAb), T lymphocytes are then removed by sheep red blood cell rosette depletion, and expression of the B cell surface activation antigen CD23 (BLAST-2) is assessed by indirect immunofluorescence. Anti-CD3 mAb, but not a control anti-CD5 mAb, stimulates the expression of CD23 on 20-50% of peripheral blood B cells cultured with autologous T cells. T cell subset depletion studies show that the CD4+ T cell subset is responsible for anti-CD3-mediated induction of CD23 on autologous B cells. Anti-CD3-induced, T helper cell-dependent CD23 expression is not MHC-restricted, as allogeneic combinations of T and non-T cells, cultured in the presence of anti-CD3 antibody, also result in the expression of B cell CD23. Individuals whose monocyte Fc receptors bind murine IgG1 mAb poorly fail to trigger T cell proliferation in response to murine IgG1 anti-CD3 mAb and also fail to express B cell CD23 following culture of PBMC with IgG1 anti-CD3 mAb, while the usual expression of CD23 is seen after culture with IgG2a anti-CD3 mAb. The mechanism of anti-CD3-induced B cell activation was addressed in experiments using a two-chamber culture system. While little IL-4 activity was detected in anti-CD3-stimulated culture supernatants, optimal induction of CD23 was observed when T and B cells were cultured together in a single chamber. This suggests that under physiologic conditions, in which quantities of lymphokine may be limiting, close physical contact between the anti-CD3-activated Th cell and B cell may be required for CD23 expression. The anti-CD3-induced BLAST-2 assay will facilitate the analysis of Th cell-mediated B cell activation in any individual and should permit us to separately evaluate the roles of Th cells and B cells in the impaired immunoregulation characteristic of autoimmune disorders.     

Polyclonal activation of murine B lymphocytes by Fc fragments. I. The requirement for two signals in the generation of the polyclonal antibody response induced by Fc fragments

Fc fragments derived from human IgG1 induce murine splenic B lymphocytes to undergo proliferation and differentiation to antibody-secreting cells. The polyclonal antibody response was found to require both the presence of macrophages and T cells. Spleen cell cultures from nude mice or T cell-depleted normal mice proliferate to the level of untreated control mice but do not produce polyclonal antibody unless T cells are added. Regulation of the Fc fragment induced B cell differentiation to antibody synthesis apparently occurs through two distinct signals. One signal is provided by Fc fragments for proliferation and the other by T cells for differentiation. This suggestion is supported by the observation that spleen cell preparations, devoid of T cells, are capable of proliferation to the level of normal spleen cell cultures in response to Fc fragments, but are incapable of making a polyclonal antibody response. The cell population that responds to the differentiation signal also responds to the proliferative signal. "Hot pulse" experiments demonstrated that proliferation precedes polyclonal activation.     

Inhibitory activity of interleukin B on the suppressor T cell hybrid T2D4

Interleukin B (IL-B), a product of unstimulated B cells, is defined by its ability to selectively prevent the differentiation of suppressor T lymphocytes from precursors into effectors. The present study was undertaken to determine whether IL-B could also be active in modulating the activity of the T cell hybrid T2D4, which produces immunoglobulin-binding suppressor factors. T2D4 cells can be selectively induced by incubation with various isotypes of antibody to express isotype-specific Fc receptors and to release soluble factors that suppress production of the corresponding isotype. The data presented here demonstrate that IL-B is greatly effective in inhibiting T2D4 activities. Either pretreatment with IL-B or continuous exposure to IL-B prevents isotype activation of T2D4. As a result, T2D4 cells do not express isotype receptors and do not produce detectable amounts of isotype-specific suppressor factors. This IL-B regulatory activity on T2D4 is temperature dependent and is inhibited by cytochalasin B. These findings provide new insights on the mechanism by which IL-B enhances antibody responses, and they offer a conceptual framework for analyzing IL-B activity on suppressor T cells.     

Immune dysfunction in mice with plasmacytomas. I. Evidence that transforming growth factor-beta contributes to the altered expression of activation receptors on host B lymphocytes.

Plasmacytoma-bearing mice (PC-mice) develop a polyclonal B cell immunodeficiency syndrome characterized by marked impairment of: a) primary antibody responses and b) proliferative responses to B cell mitogens. The present investigations used two-color flow cytometry to examine B lymphocytes from the spleens and lymph nodes of PC-mice and found decreased surface membrane expression of surface IgM (sIgM), transferrin receptors (TfR) and IgE FcR (CD23), increased expression of class II MHC, but normal expression of B220, Mel-14, Fc gamma RII, and Fc mu R. These changes were not related to the H chain class or the amount of Ig produced by the plasmacytoma. When cultured with IL-4, B lymphocytes from PC-mice increased their expression of sIgM and class II MHC, but not of CD23. Several findings implicate transforming growth factor-beta 1 (TGF-beta 1) in the mechanism that modulates receptor expression on B lymphocytes in PC-mice: a) ascites fluid from PC-mice contains large quantities of TGF-beta 1; b) supernatants of cultured spleen cells from PC mice contain up to eightfold more TGF-beta than is found with normal spleen cells; c) cloned plasmacytoma cells produce TGF-beta in vitro; and d) the abnormal phenotype of B cells from PC-mice, i.e., decreased CD23, sIgM, and TfR, and increased class II MHC, is induced on normal B cells cultured in the presence of TGF-beta 1. Because sIgM, TfR, class II MHC, and CD23 are molecules that play fundamental roles in the activation of normal B cells, their modulation by TGF-beta 1: a) identifies molecular mechanisms that could account for some of the known immunosuppressive properties of TGF-beta 1 and b) implicates TGF-beta in the pathogenesis of the polyclonal B cell immunodeficiency that is characteristic of plasma cell tumors.     

Isotype Specificity and Heterogeneity of Fcγ-Receptors on Guinea Pig Splenic B and T Lymphocytes

The isotype specificity of Fc-receptors for IgG (Fcγ-Rs) on normal guinea pig splenic B and T cells was determined by a rosette assay using sheep erythrocytes sensitized with either homologous IgG1 or IgG2 anti-sheep erythrocyte antibody [EA(IgG1) or EA(IgG2)]. Approximately 70% of the lymphocytes in the highly purified B-cell fraction could form rosettes with EA(IgG2), and 55% of the cells with EA(IgG1). Inhibition experiments with soluble complexes of IgG1 or IgG2 antibody with ovalbumin demonstrated that approximately 20% of the EA(IgG2) rosette-forming B cells bore the Fcγ-R monospecific for IgG2, whereas 80% of the cells had two distinct Fcγ-Rs simultaneously; one monospecific for IgG2 and the other bispecific for IgG1 and IgG2. The existence of a B cell bearing the Fcγ-R monospecific for IgG1 was not definitively demonstrated in the B-cell fraction. In the T cell-enriched fraction, approximately 40% of the cells could form rosettes with EA(IgG2). The EA(IgG1)rosette-forming cells, however, comprised only 6% of the total cells, indicating that most of the EA(IgG2) rosette-forming T cells bear essentially the Fcγ-R monspecific for IgG2 alone. The results obtained revealed that guinea pig splenic lymphocytes bear two distinct Fcγ-Rs, which are not equally distributed on the B- and T-cell populations and also on their respective subsets.     

Mechanism of the suppressive effect of interferon on antibody synthesis in vivo.

Mouse interferon preparations significantly suppress the in vivo antibody response to sheep red blood cells (SRBC), a thymus-dependent antigen, and to Salmonella typhimurium lipopolysaccharide (LPS), a thymus-independent antigen. It is also possible to effect the late responses of antigen sensitive "memory" cells observed during secondary immunization by administration of interferon prior to primary immunization. The immunosuppressive activity of interferon was time- and dose-dependent. Maximum suppression was produced when animals were given 1.5 times 10-5 units of interferon between 4 and 48 hr before antigenic stimulation. These findings suggested that interferon affects some early event(s) in the process of antibody synthesis which might be related to the general inhibitory effect of interferon on rapidly dividing cells and viral m-RNA translation. In addition, the use of nonadherent spleen cell cultures from interferon-treated mice, immunized in vitro with a thymus-independent antigen, indicated that in this situation the inhibitory effect of interferon was due to an action on B lymphocytes. A variety of soluble "suppressive" factors are secreted by T cells as a consequence of activation by mitogens or specific antigens in vitro. Since T cells are recognized as one of the sources of interferon, it is suggested that interferon should be investigated as a suppressor T cell-produced lymphokine which can regulate B cell expression.     

The immunoregulatory role of bone marrow. II. Characterization of a suppressor cell inhibiting the in vitro antibody response.

The addition of bone marrow cells (BMC) to spleen cell cultures suppressed the antibody response in a dose-dependent manner. This suppression required viable cells. Treatment of BMC with anti-thymocyte serum did not affect the suppressive activity and BMC, but not spleen cells, from nude mice inhibited the antibody response to the same degree as marrow from normal littermates. BMC which had been depleted of macrophages with antimacrophage serum or carbonyl iron showed increased suppressor activity. Furthermore, fractionation of BMC by velocity sedimentation and resetting revealed the suppressor cell to be a medium-to-large Fc receptor-positive lymphocyte. Absence of detectable B or T cell markers on the suppressor cell indicates this cell to be an Fc-positive null lymphocyte, possibly a precursor cell, which inhibits the response of mature lymphocytes     

Production of BSF-1 during an in vivo, T-dependent immune response

BSF-1, a cytokine produced by some T lymphocyte tumors, has been shown to act with anti-Ig antibodies to stimulate B lymphocyte proliferation, to independently induce resting B lymphocytes to increase their expression of surface Ia antigen, and to induce some activated B lymphocytes to differentiate into IgG1- or IgE-secreting cells. To determine whether BSF-1 might be secreted by normal lymphoid cells in the course of a physiologic immune response, BALB/c mice were injected with an affinity-purified goat antibody to mouse IgD (GaM delta), which induces the generation of a large, polyclonal T-dependent IgG1 response; 4-hr culture supernatants of spleen cells from these mice were prepared, and these supernatants were assayed for BSF-1 activity by analyzing their ability to induce BALB/c nu/nu spleen cells to increase their expression of cell surface Ia in vitro. Culture supernatants of unfractionated spleen cells removed from mice 4 to 8 days after GaM delta antibody injection induced substantial increases in B lymphocyte surface Ia expression; these increases were blocked by a monoclonal anti-BSF-1 antibody. Culture supernatants of spleen cells from untreated BALB/c mice or from untreated or GaM delta antibody-treated BALB/c nu/nu mice induced small to moderate increases in B cell surface Ia expression, and GaM delta antibody itself induced large increases in B cell surface Ia expression; however, these increases were not significantly blocked by a monoclonal anti-BSF-1 antibody. A culture supernatant of T cell-enriched spleen cells from untreated mice induced small increases in B cell surface Ia expression that were inhibited by anti-BSF-1 antibody, as was the larger increase in B cell Ia expression induced by a culture supernatant of T cell-enriched spleen cells from mice sacrificed 3 days after GaM delta injection. On the other hand, T cell-depleted spleen cells from BALB/c mice injected with GaM delta antibody 7 days before sacrifice failed to generate culture supernatants with BSF-1 activity. Supernatants prepared from spleen cells taken from untreated mice or mice treated with GaM delta antibody 1 to 3 days before sacrifice did not block the ability of purified BSF-1 to induce an increase in B cell surface Ia expression, and thus did not contain inhibitors of BSF-1 activity.(ABSTRACT TRUNCATED AT 400 WORDS)     

No direct association between Ia antigens and Fc receptors on the B cell membrane.

The capping of Ia antigens does not induce redistribution of Fc receptors (FcR) on B lymphocytes. This rules out the possibility of a unidirectional association between Ia and FcR such as has been reported to link Ig and FcR. Ia-capping was achieved with hapten-sandwich antibodies devoid of Fc regions: hapten-conjugated Fab anti-Ia followed by (Fab')2 anti-hapten antibody. Three different immune complex systems were used to label FcR. With fluorescent double labeling, Ia and FcR were readily distinguished. The independent labeling and surface mobility of Ia and FcR are considered in connection with reports of the inhibition of FcR by anti-Ia antibodies.     

In vivo and in vitro regulation of IgE production in murine hybridomas

Normal BALB/c mice injected i.p. with the IgE-secreting hybridomas B53 (epsilon, kappa anti-DNP), SE1.3 (epsilon, kappa, anti-arsonate) or A3B1 (epsilon, kappa, anti-TNP) were monitored for serum IgE concentrations and frequencies of splenic T lymphocytes with surface membrane receptors for the Fc portion of IgE (Fc epsilon R+ T lymphocytes). Mice with B53 or SE1.3 hybridomas initially developed high concentrations of IgE and CD8+ Fc epsilon R+ T lymphocytes, followed by a progressive decline in both serum IgE and expression of cytoplasmic epsilon-chains in the hybridoma cells. Serum IgE concentrations in mice with A3B1 hybridomas progressively increased without development of Fc epsilon R+ T lymphocytes nor a subsequent decline in IgE or change in cytoplasmic epsilon-chain expression in the A3B1 cells. An in vitro system in which the IgE-secreting hybridoma cells were cocultured with spleen cells harvested from mice with established B53 tumors was used to investigate the mechanisms involved in the inhibition of IgE production by the hybridoma cells. The results of these studies indicate that: 1) the induction/upregulation of Fc epsilon R on CD8+ T lymphocytes in vivo requires factors in addition to high serum IgE concentrations; 2) in addition to CD8+ Fc epsilon R+ T lymphocytes and monocytes, another, as yet unidentified, splenic cell component appears to contribute to the process by which epsilon-chain expression in IgE-secreting hybridoma cells is suppressed, and 3) a hybridoma (A3B1) that fails to induce CD8+, Fc epsilon R+ T lymphocytes in vivo and is not inhibited in IgE expression in vivo, nonetheless is inhibited in IgE expression in vitro when cocultured with spleen cells from mice with B53 tumors.     

The control of autoreactivity. I. Lack of autoreactivity in murine spleens is due to concomitant presence of suppressor and autocytotoxic lymphocytes.

To determine if autocytotoxic lymphocytes were naturally occurring in murine spleens, C57BL/6 spleen cells were fractionated on discontinuous BSA gradients. Autocytotoxicity was assessed in vitro (cytotoxicity of C57BL/6 fibroblasts) and in vivo (splenomegaly and popliteal node enlargement in C57BL/6 mice). A medium density subpopulation of lymphocytes was shown to be autocytotoxic and to be similar to autoreactive lymphocytes produced by the in vitro "sensitization" of splenic lymphocytes on syngeneic fibroblasts monolayers. The naturally occurring autocytotoxic lymphocytes express no detectable theta antigen, did not adhere to nylon, but did have an Fc receptor. In recombination experiments, BSA-fractionated lymphocytes were incubated with autocytotoxic and "sensitized" lymphocytes. A light density subpopulation was shown to suppress both autoreactive lymphocyte subpopulations at a 1:50 ratio. The suppressor cells were nylon nonadherent T lymphocytes. The lack of autoreactivity of unfractionated murine spleen cells is due to the concomitant presence of autocytotoxic and suppressor lymphocytes. If suppressor lymphocytes are selectively removed in vitro, the reactivity of autocytotoxic lymphocytes can be detected.     

Increased expression of the B lymphocyte receptor for transferrin is stimulated by in vivo crosslinking of cell surface IgD

Expression of a receptor for the serum protein transferrin has been shown to be a characteristic of several cell lineages and increased transferrin receptor (TFR) expression to reflect cellular activation. In vitro studies of human B lymphocytes stimulated with antibodies to IgM have demonstrated that these cells have the ability to express TFR and that increased B-cell TFR expression is seen first sometime after these cells enter the G1 phase of the cell cycle. It also has been shown that TFR expression is necessary for proliferation to occur and may be regulated by a factor produced by mitogen-activated T lymphocytes. To examine expression of TFR by activated B lymphocytes in vivo, and to determine the kinetics of induction of TFR expression, we have studied the effects of injecting mice with an affinity-purified goat antibody to mouse IgD (GaM delta) on TFR expression. This antibody previously has been shown to activate polyclonally mouse splenic B cells in vivo in a T-independent fashion. Results show that there is a small but definite quantity of TFR on resting splenocytes, at 24 hr after injection nearly all B cells but not T cells express increased amounts of TFR, TFR is increased to nearly the same extent in congenitally athymic BALB/c nu/nu mice as in their normal nu/+ littermates and therefore GaM delta-induced increased B lymphocyte TFR expression is relatively T independent, TFR expression increases as early as 3 hr after injection of 800 micrograms of GaM delta and increases steadily until it peaks 24-48 hr later, and TFR expression in GaM delta-injected mice increases concomitantly with surface Ia antigen and cell size.