Role of antigen-specific T cell help in the generation of in vivo antibody responses. I. Antigen-specific T cell help is required to generate a polyclonal IgG1 response in anti-IgD antibody-injected mice.

A system in which injection of mice with an antibody to mouse IgD that they recognize as foreign stimulates a large, T cell-dependent IgG response was used to study whether Ag-specific T cell help is required to stimulate polyclonal (non-Ag-specific) IgG production in vivo. Igha x Ighb allotype heterozygous mice were injected with a conjugate of a foreign Ag coupled to a mAb specific for one of the two IgD allotypes expressed in these mice. This conjugate cross-links mIgD on B cells that express the recognized allotype. These cells process the conjugate and present the foreign Ag to Ag-specific T lymphocytes, which become activated. Thus, B cells of the recognized allotype can be stimulated by cross-linking of their mIgD, Ag-specific T cell help, non-Ag-specific cytokines, and non-Ag-specific contact with activated T cells. In contrast, B cells that express the Igh allotype not recognized by the Ag-anti-IgD antibody conjugate (bystander B cells) can be stimulated in this system only by non-Ag-specific cytokines and non-Ag-specific contact with activated T cells. Although both recognized and bystander B cells in conjugate-injected mice demonstrated substantial increases in size and Ia expression, only the recognized B cells were induced to synthesize DNA and to make a substantial polyclonal Ig response. Bystander B cells still failed to secrete IgG when mice were injected with an anti-IgD-Ag conjugate specific for the other Igh allotype as well as a mAb that cross-linked IgD of the bystander B cell allotype. These observations demonstrate that although non-Ag-specific cytokine and contact-mediated T cell help are sufficient to induce B cells to increase in size and Ia expression in anti-IgD antibody-injected mice, Ag-specific T cell help is required to stimulate the generation of an IgG response in these mice.     

Characterization of an antigen expressed on activated human T cells and platelets

We have identified a protein complex on the surface of activated human T cells and platelets. This Ag, detected by the murine mAb 1B3, is not expressed on resting human T cells or platelets or on other hematopoeitic cells. The majority of T cells express the Ag after stimulation with PHA, Con A, or allogeneic cells. Platelets express the Ag after activation with 1 U/ml thrombin. Immunoprecipitation of 125I-labeled activated T cells with antibody 1B3 shows a heterodimer of 180,000 and 155,000 Mr. An additional protein of 130,000 Mr is very faintly seen depending on the cell type. On platelets, the 180,000 Mr protein is the predominant protein immunoprecipitated under both nonreducing and reducing conditions. Antibody 1B3 may prove useful in identification of activated T cells and platelets as well as definition of specific mechanisms of T cell and platelet activation.     

Subpopulations of B cells in germinal centers. III. HJ6, a monoclonal antibody, binds globoside and a subpopulation of germinal center B cells.

To identify surface Ag uniquely expressed on human germinal center B cells, we produced a mouse mAb, HJ6. When tonsillar lymphocytes were examined, HJ6 did not label T cells and labeled only about half of PNA+ B cells that were HK23-. HJ6 did not label mononuclear cells from peripheral blood, splenocytes, and any of 29 cell lines including 23 B cell lines. This binding pattern of HJ6 was very similar to that of a mAb named 5B5. It was shown previously that 5B5 bound a glycolipid named CTH (CD77) and its Ag was expressed on HK23- PNA+ tonsillar lymphocytes and Burkitt's lymphoma cell lines. Despite the similarity, HJ6 differed from 5B5: HJ6 did not stain Burkitt's lymphoma cell lines and stained PNA+ tonsillar lymphocytes in the presence of a large concentration of galactose. When its binding to isolated glycolipids was studied, HJ6 was found to bind globoside and Forssman Ag and not to other glycolipids including CTH. When its binding to neutral glycolipids extracted from tonsillar lymphocytes was studied, HJ6 bound only globoside; Forssman Ag was not detected in tonsillar lymphocytes. Taken together, we conclude that globoside is a B cell Ag expressed on a subpopulation of germinal center B cells.     

Artificial T cell:B cell conjugation. A unique approach to analyze weak cell-cell interactions

An antibody response against a thymic-dependent Ag requires cognate recognition of the Ag by B and T cells. Functional T-B cell (T-B) interaction involves binding of Ag by B cell surface Ig, internalization and processing of Ag, expression of an Ag fragment in the context of Ia, binding of Ag/Ia by the TCR and binding of T cell-derived lymphokines by B cell lymphokine receptors. It is becoming increasingly evident that B and T cell accessory molecules also are involved in T-B interactions. To determine the role of accessory molecules in T-B collaboration, we have designed a system in which T-B interaction was artificially induced in the absence of carrier protein. TNP-modified, turkey gamma-globulin-specific, Th cells were allowed to form conjugates with TNP-specific B cells in the absence of hapten-carrier complex. Both B and T cells were induced to proliferate and B cells partially differentiated into antibody-secreting cells when B cells were cultured with TNP-modified but not unmodified T cells. The activation of B cells by TNP-modified T cells was not MHC restricted but was blocked by anti-Ia antibodies, suggesting a role for Ia distinct from Ag presentation. Furthermore, B cell proliferation was also inhibited by antibodies to L3T4 and LFA-1, suggesting a functional accessory role for these molecules in induction of B cell proliferation/differentiation.     

A novel functional cell surface dimer (Kp43) expressed by natural killer cells and T cell receptor-gamma/delta+ T lymphocytes. I. Inhibition of the IL-2-dependent proliferation by anti-Kp43 monoclonal antibody.

In the present study we describe a novel functional cell surface molecule, designated as Kp43, which is expressed among leukocytes by NK cells, TCR-gamma/delta + T lymphocytes, and some CD8+ CD56+TCR-alpha/beta + T cell clones. The Kp43 Ag is a 70-kDa disulfide-linked dimer, which migrates in SDS-PAGE under reducing conditions as a single 43-kDa band. Two-color immunofluorescence staining of fresh PBL revealed that only a fraction of CD16+, and of TCR-gamma/delta + T lymphocytes expressed the Ag. The analysis of TCR-alpha/beta + T cell clones showed that a small proportion (2 out of 20) weakly expressed Kp43 together with the CD8 and CD56 molecules. By immunoperoxidase staining of different tissues the anti-Kp43, reactivity was detected exclusively in lymphoid organs, where a minority of scattered cells was stained, and in some liver sinusoidal cells. Essentially all NK cells acquired Kp43 when stimulated with a B lymphoblastoid cell line. By contrast, the pattern of distribution of Kp43 remained stable upon in vitro culture of T-gamma/delta lymphocytes, thus delineating two subsets according to its expression. In lymphokine-activated killer populations, obtained by culturing either PBL or NK cells with high concentration of IL-2, most CD16+ and CD56+ cells became Kp43+. The Kp43-specific mAb inhibited the IL-2-dependent proliferative response of cultured NK and TCR-gamma/delta + T cells without affecting their non-MHC-restricted cytotoxicity. The partial inhibitory effect, which was mediated as well by pepsin digested F(ab')2 fragments, was lost upon reduction to Fab. The anti-Kp43 mAb did not interfere with the specific binding of IL-2 to its surface receptors. Altogether the data point out that the Kp43 dimer is involved in the regulation of the IL-2-dependent proliferative response of NK cells and a subset of TCR-gamma/delta + T lymphocytes.     

Cross-linking of human T cell receptor proteins: association between the T cell idiotype beta subunit and the T3 glycoprotein heavy subunit

Bifunctional cross-linking reagents DSP, DSS, and BSOCOES were used to cross-link 125I-surface-labeled viable T lymphocytes. The cross-linked cells were solubilized in Nonidet-P40, immunoprecipitated with anti-Ti (monoclonal antibody T40/25) or anti-T3 (monoclonal antibodies UCHT-1 or OKT3), and analyzed by SDS-PAGE. With all three cross-linkers, the intact cross-linked products obtained with monoclonal antibody T40/25 from HPB-ALL cells were 20-30 kd heavier than the Ti dimer (Mr 80,000). When the DSP cross-linked product was isolated using either anti-Ti or anti-T3 monoclonal antibodies and then cleaved, bands having molecular weights identical with both the Ti and T3 subunits were obtained. The two-dimensional SDS-PAGE analysis (nonreducing followed by reducing conditions) of the DSS and BSOCOES cross-linked products revealed the specifically cross-linked bands to have Mr 40,000 and Mr 28,000. These data indicate that the Ti molecule and the T3 molecule are spatially associated on the cell surface and suggest the predominant association is between the Ti beta subunit (Mr 40,000) and the T3 heavy subunit (Mr 28,000).     

Adherent Ia+ murine cell lines with characteristics of dendritic cells. II. Characteristics of I region-restricted antigen presentation

The ability of an adherent Ia+, interleukin 1+ (IL-1) tumor cell line (P388AD) to present turkey gamma-globulin (TGG) to primed T lymphocytes was demonstrated and compared with normal antigen-presenting cells (APC) found in mouse spleen. P388AD tumor cells presented TGG to long-term cultures of TGG-reactive T cells (LTTC) and to lymph node-derived T cells which were enriched on nylon wool columns and subsequently depleted of endogenous antigen-presenting cells with anti-Ia antisera and complement. MHC-restricted antigen presentation by P388AD was observed when long-term cultures of TGG-reactive T cells were used as the responding T-cell population. Furthermore, antisera directed against I-region determinants expressed on the P388AD tumor cells inhibited TGG-specific T-cell proliferation in a dose-related fashion, suggesting a functional role for the tumor cell-associated Ia molecules. The kinetics of antigen presentation to LTTC by P388AD were similar to the kinetics observed for splenic APC, although the magnitude of the proliferative response to LTTC to TGG was generally lower when antigen (Ag) was presented by the tumor cells compared to splenic antigen-presenting cells (APC). However, the magnitude of T-cell proliferation of immune lymph node (LN) T cells was comparable when Ag was presented on tumor cells or splenic APC. Several experiments suggested that Ag uptake and/or processing may be less effective in P388AD tumor cells as compared to normal splenic APC. A nonadherent Ia+, IL-1- tumor cell line (P388NA), which was isolated from the same parental tumor as P388AD, was also tested for the ability to present Ag to primed T lymphocytes and Ag-reactive LTTC. In contrast, to P388AD, the nonadherent tumor cell failed to present TGG under identical culture conditions even though Ia molecules were expressed on the tumor cells and Ag uptake had occurred. However, the defect in Ag presentation by P388NA could be corrected if an exogenous source of purified interleukin 1 was supplied to the cultures. A unique opportunity thus exists with both the P388AD and P388NA tumor cell lines to decipher some of the molecular interactions leading to T-cell proliferation during antigen presentation.     

Two roles for Ia in antigen-specific T cell activation. II. Toward a Velcro model of antigen recognition

It has been previously reported that Ia Ag on APC seems to be involved in Ag-specific T cell activation in at least two different ways: one is to associate with foreign Ag to form a neoantigenic determinant (the Ag-specific Ia function), and the second is to interact with T cells in a non-Ag-specific manner. Both Ia functions are required for T cell activation. In the present study we examined whether the T cell structures responsible for the non-Ag-specific Ia interaction were separable from the Ag-specific alpha/beta TCR. Purified protein derivative of tuberculin (PPD)-specific murine hybridoma T cells and polyclonal lymph node T cells were stimulated for IL-2 production by APC pulsed with PPD, glutaraldehyde fixed, and anti-Ia antibody treated, to provide the antigenic PPD/Ia determinant, in the presence of glutaraldehyde-fixed non-Ag-pulsed APC, to provide the non-Ag-specific Ia interactions. However, in several different approaches the T cell structures or activation signals responsible for the Ag-specific recognition and non-Ag-specific Ia interactions seemed to be associated with each other in this experimental system. First, the Ag-specific and non-Ag-specific Ia interactions with T cells were both required simultaneously to initiate T cell activation, and it was not possible to activate T cells by providing either Ia signal subsequent to the other. Second, the T cell structures responsible for the non-Ag-specific Ia interactions appeared to be clonally distributed in PPD-specific lymph node T cells. Third, another T cell hybridoma specific for bovine insulin also showed dual Ia interactions, but the specificity of the non-Ag-specific Ia function was different than that for the PPD-specific T cell response. Fourth, all subclones of PPD-specific T hybridomas that had lost Ag-specific responsiveness also lost functional non-Ag-specific Ia interactions. Taken together, these observations suggest that a single species of TCR may mediate both the Ag-specific and non-Ag-specific Ia interactions. In addition, the non-Ag-specific Ia interaction with T cells augmented the Ag-specific Ia interaction for T cell activation, indicating that both types of interactions may be involved in some T cell responses. Based on these observations, a Velcromodel depicting the synergy between the two Ia functions is proposed in which a matrix of interactions consisting of higher affinity Ag binding and lower affinity Ia-TCR associations provides cooperative sets of signals necessary for cellular activation.     

Long-term-cultured mouse B-lymphocyte line. II. Modulation of Ia-antigen expression on B-lymphocyte line

Mouse B-cell line, established by culturing anti-Thy-1 and complement-treated splenic B cells with concanavalin A-stimulated conditioned medium, expressed immunoglobulins and Ia antigens on its surface. The long-term-cultured B-cell line was split in two and maintained with or without 3300 R X-irradiated T-cell-depleted syngeneic splenic adherent cells (SAC). Interestingly, the B-cell line cultured without SAC lost its Ia antigen but not its Ig expression, whereas the cell line with SAC maintained both Ia and Ig expression. The ability to express Ia antigens was restored by culturing them only in the presence of Ia-positive feeder cells. Neither recombinant interferon-gamma or lectin-stimulated conditioned medium nor cell-free culture supernatant SAC had the ability to restore Ia antigen expression on the B-cell line. Incubation of Ia-negative B-cell line with phorbol esters restored the Ia expression. It is suggested that the expression of Ia antigen on B lymphocytes was controlled differently from that on macrophage lineage. The B-cell line expressing Ia antigens acts as stimulator cells for alloantigen-activated T lymphocytes and as antigen-presenting cells on the KLH-specific Ia-restricted proliferative T-cell clone in the presence of a specific antigen.     

Modeling of T cell contact-dependent B cell activation. IL-4 and antigen receptor ligation primes quiescent B cells to mobilize calcium in response to Ia cross-linking.

The generation of antibody secretory cells from resting B lymphocytes after immunization with most protein Ag requires B cell signaling by Ag, direct Th cell contact and lymphokines. Previous studies suggest that cell contact-mediated signals may be transduced by Ia after Ia binding by alpha beta TCR and/or CD4. Seemingly inconsistent with this concept are findings that cross-linking of Ia molecules on quiescent B cells leads to cAMP generation that is antagonistic for B cell mitogenesis. Here we show that ligand binding to IL-4 and Ag receptors on quiescent B cells induce transition of these cells into a competent state in which Ia molecules transduce signals via a distinct mechanism. This mechanism involves the tyrosine kinase-dependent activation of phospholipase C leading to Ca2+ mobilization from intracellular stores and the extracellular space. This competence, which is seen within 4 h of priming, is not simply a function of increased Ia expression by the B cell because the response can be induced by cross-linking of less than 5% of cell surface Ia molecules on primed cells. Finally, cross-linking of Ia molecules leads to more than fivefold greater increase in [Ca2+]i than is induced by membrane Ig ligation. These findings are consistent with alpha beta TCR/CD4 delivery via Ia of proliferative signals mediated by tyrosine kinase activation, phosphoinositide hydrolysis and Ca2+ mobilization.     

Identification of Ia on a subpopulation of human T lymphocytes that stimulate in a mixed lymphocyte reaction

The delineation of discrete subpopulations of human T lymphocytes has permitted preliminary analyses of the complex cellular network regulating the immune response in man. We previously showed that a subset of T lymphocytes, designated as theophylline-sensitive because of their inability to bind sheep red blood cells in the presence of the drug, are responsible for antigen-specific suppression or regulation in an in vitro plaque-forming cell assay. We now show that 25 to 45% of these theophylline-sensitive T cells were Ia-positive by immunofluorescence with a rabbit antiserum raised against purified B lymphoblast surface antigenic material. These data suggested that 4 to 7% of peripheral blood T cells carry Ia determinants. The presence of Ia determinants on this T cell subset was confirmed by gel analysis of radioiodinated surface material. Furthermore, in mixed lymphocyte culture, the theophylline-sensitive cells demonstrated HLA-D determinants and were 10-fold more potent stimulators than equal numbers of B lymphocytes. The presence of Ia determinants on these T cells indicates the expression of major histocompatibility complex-related regulatory gene products on a specific human T lymphocyte subpopulation.     

Detection of HLA-DRw (Ia-like) antigens on human T lymphocytes grown in tissue culture.

Human T lymphocytes that proliferate in the presence of conditioned medium from PHA-stimulated allogeneic peripheral blood cells were shown to express IPA antigens after the 8th culture day. Ia antigens as detected by xenogeneic antisera were present on 80 to 90% of the cultured cells which were also strongly reactive with xenogeneic antisera defining a human T cell antigen and formed E rosettes. Control cultures with PHA or no conditioned medium expressed T cell but not Ia antigens. These cultured T cells also express the same HLA-DRw determinants as the B cells of the donor they were derived from. Absorption of xenogeneic Ia, and HLA-DRw alloantisera with cultured T cells completely removed the reactivity of these sera for enriched peripheral blood B lymphocytes from normal donors.     

The role of antigen-presenting B cells in T cell priming in vivo. Studies of B cell-deficient mice

Mice rendered B cell deficient by treatment with rabbit anti-mouse IgM (anti-mu) antibodies from birth fail to respond when primed with soluble protein antigens in CFA, as measured by T cell proliferation when challenged with antigen in vitro. The role of B cells in T cell priming in vivo was examined by adoptively transferring hapten-specific B cells into anti-mu mice, followed by immunization with haptenated Ag in CFA. The T cell proliferative response to OVA of anti-mu BALB/c mice was partially restored by the administration of TNP or FITC-specific B cells and immunization with TNP-OVA or FITC-OVA, respectively. This reconstitution was Ag-specific, inasmuch as hapten-binding B cells restored the T cell responses to OVA in mice immunized with the same hapten coupled to OVA. The mechanism of B cell reconstitution of T cell priming in anti-mu mice was addressed using parental to F1 B cell transfers. The Ia restriction pattern of the activated T cells from these mice indicated that both direct presentation of Ag by transferred B cells and antibody-mediated enhancement of Ag presentation by non-B, host Ag-presenting cells occurred. Thus, Ag-specific B lymphocytes play a critical role in priming of T cells in vivo.     

Effect of gamma radiation on resting B lymphocytes. II. Functional characterization of the antigen-presentation defect

The effect of radiation on three discrete Ag-presentation functions in resting B cells was examined: 1) Ag uptake and processing, 2) expression of processed Ag in the context of functional class II molecules, and 3) provision of necessary co-stimulatory, or "second," signals. Analysis of radiation's effect on B cell presentation of intact vs fragmented Ag or its effect on presentation by Ag-pulsed B cells indicated that damage to Ag uptake and processing could not account for the bulk of the radiation-induced Ag-presentation defect. Experiments with phosphatidylinositol hydrolysis as an indirect measure of TCR occupancy suggested that irradiation caused a fairly rapid (within 1 to 2 h) decrease in the ability of the B cell APC to display a stimulatory combination of Ag and class II molecule. Ag dose-response analyses demonstrated that when presenting a fragment of the Ag pigeon cytochrome c to a T cell clone, 3000 rad-treated B cell APC were able to stimulate approximately 50% as much phosphatidylinositol turnover as unirradiated B cells. It was also found that, in contrast to their inability to initiate T cell proliferation, and similarly to chemically cross-linked splenocytes, heavily irradiated resting B cells plus Ag induced a state of Ag hyporesponsiveness in T cell clones. This effect on T cells had the same Ag- and MHC-specificity as did receptor occupancy required for proliferation, indicating that heavily irradiated resting B cells bear functional class II molecules. Co-culture of T cells with allogeneic B cells and syngeneic heavily irradiated B cells or chemically cross-linked splenic APC plus Ag resulted in T cell proliferation and interfered with the induction of the hyporesponsive state. This co-stimulatory function was radiosensitive in resting allogeneic B cells. Together, these data support the hypothesis that the major functional consequences of radiation to resting B cell APC are a reduction in the effective display of Ag plus class II molecules and, probably what is more important, a loss in the ability to provide APC-derived co-stimulatory signals.     

The Ia.2 epitope defines a subset of lipid raft-resident MHC class II molecules crucial to effective antigen presentation

Previous work established that binding of the 11-5.2 anti-I-A(k) mAb, which recognizes the Ia.2 epitope on I-A(k) class II molecules, elicits MHC class II signaling, whereas binding of two other anti-I-A(k) mAbs that recognize the Ia.17 epitope fail to elicit signaling. Using a biochemical approach, we establish that the Ia.2 epitope recognized by the widely used 11-5.2 mAb defines a subset of cell surface I-A(k) molecules predominantly found within membrane lipid rafts. Functional studies demonstrate that the Ia.2-bearing subset of I-A(k) class II molecules is critically necessary for effective B cell-T cell interactions, especially at low Ag doses, a finding consistent with published studies on the role of raft-resident class II molecules in CD4 T cell activation. Interestingly, B cells expressing recombinant I-A(k) class II molecules possessing a β-chain-tethered hen egg lysosome peptide lack the Ia.2 epitope and fail to partition into lipid rafts. Moreover, cells expressing Ia.2(-) tethered peptide-class II molecules are severely impaired in their ability to present both tethered peptide or peptide derived from exogenous Ag to CD4 T cells. These results establish the Ia.2 epitope as defining a lipid raft-resident MHC class II conformer vital to the initiation of MHC class II-restricted B cell-T cell interactions.     

Activation of rat B lymphocytes. I. Characterization of anti-immunoglobulin responses and isotype density of rat B cells

Spleen cells of two rat strains, Lewis and Brown Norway (BN), have been activated by lectins and by antibodies specific for immunoglobulin isotypes embedded in their cell membranes. Optimal concentrations of antibodies specific for mu, gamma, or delta-chains of rat augments in vitro incorporation of 3H-TdR 5 to 18-fold in Lewis B lymphocytes and 1.5 to 4-fold in BN B lymphocytes. In addition, F(ab')2 fragments of anti-Ig reagents induced Lewis splenic B cells but not BN B cells to incorporate 3H-TdR. Responses to LPS and dextran sulfate, B lymphocyte mitogens, measured by radioactive uptake, were five to 10 times greater in Lewis B cell populations than in BN B cell populations. Density of surface Ig isotypes and capping kinetics were similar in the two rat strains, although the percentage of T cells, T cell subsets, B cells, and Ia+ B cells differed in the spleens of these strains of rats. Both T lymphocytes and macrophages were needed in culture to effect an optimal response. IL-2 restored the response in B cell cultures depleted of T cells and macrophages, and enhanced 3H-TdR uptake in whole spleen cells of Lewis but not BN rats. The strain-dependent responsiveness of B cells to specific anti-Ig reagents or B cell mitogens appears to be associated with inherent (genetic) defects in T cells and B cells or defects in T cell to B cell cooperation in BN rats.     

Genetic control of experimental autoimmune myasthenia gravis in mice. III. Ia molecules mediate cellular immune responsiveness to acetylcholine receptors

When MHC congenic and recombinant mice are inoculated with Torpedo acetylcholine receptors (AChR) with adjuvants, the magnitude of autoantibody responses to muscle AChR and the defect of neuromuscular transmission closely parallel in vitro lymphocyte proliferative responses to Torpedo AChR. All of these responses are controlled by gene(s) at the I-A subregion of the H-2 complex. Data presented in this report confirm in back-cross mice that T lymphocyte proliferative responses to AChR are controlled by a Mendelian dominant gene linked to H-2, at the I-A subregion. Lymphocyte responses were eliminated by blocking Ia antigens on lymph node cell surfaces with appropriate anti-I-A alloantisera and by removal of adherent cells. A spontaneous mutation at the I-A subregion in the B6 strain, which resulted in structural alteration of the A beta chain of Ia, converted high responsiveness to AChR to a state of low responsiveness. These data implicate a macrophage-associated Ia molecule in induction of autoimmune responses to AchR, probably in the presentation of AChR to helper T lymphocytes that thereby help B lymphocytes to differentiate into anti-AChR antibody-forming cells.     

Respiratory burst in human B lymphocytes. Triggering of surface Ig receptors induces modulation of chemiluminescence signal.

B lymphocytes have been shown to proliferate and release oxygen metabolites when surface Ig is cross-linked and when stimulated with phorbol ester. Biochemical evidence has been provided for the presence of a superoxide generating system in B cells, which seems to be identical to the well-characterized NADPH-oxidase of phagocytes. In this report, we show that normal and EBV-transformed B cells produce superoxide anions after stimulation with phorbol ester and when surface Ig was cross-linked, as detected by lucigenin-dependent chemiluminescence. Anti-surface IgG antibodies induced a significant respiratory burst whereas those directed against surface IgM had no effect on B cell oxidative metabolism. Prestimulated B lymphocytes responded to further triggering by the same or another ligand. Pretreatment with Staphlococcus aureus Cowan I strain (SAC) or anti-IgM antibodies resulted in complete unresponsiveness to subsequent SAC or anti-IgG stimulation, but it did not affect PMA- and ionomycin-mediated B cell chemiluminescence. In contrast to preincubation with anti-IgM antibodies, the pretreatment of B cells with SAC induced a transient inhibitory effect on B cell signaling. In fact, SAC-pretreated B lymphocytes could be restimulated with the same ligand when blast cells were isolated. Furthermore, a 24-h incubation of the pretreated B cells in the absence of SAC completely restored the SAC-mediated respiratory burst. These results suggest that two distinct mechanisms may account for SAC- and anti-IgM-induced inhibition: a transient and reversible modulation of surface Ig, induced by SAC, and a long-lasting desensitization of the surface Ig receptors, respectively. These findings may have interesting implications for understanding the transduction of negative signals in B lymphocytes.     

Murine interstitial nephritis. IX. Induction of the nephritogenic effector T cell repertoire with an antigen-specific T cell cytokine

The experiments presented in this report describe the biochemical and functional characteristics of a soluble Th cell factor (ThF) which can induce a nephritogenic effector T cell repertoire producing autoimmune interstitial nephritis. The ThF is Ag-specific, I-A-restricted, and comprises two chains noncovalently linked as a heterodimer. One chain at approximately 78,000 Mr is related to the TCR/Id and expresses a framework determinant (14-30) common to Ag-binding factors, and the other chain at approximately 82,000 Mr is I-A+. Together these chains can replace their parent cell by providing cognate help to precursor effector T lymphocytes in the presence of accessory cells, tubular Ag, and IL-2.