Immunological Tolerance to the Thymus-Independent Antigen Dextran can be Abrogated by Thymus-Dependent Dextran Conjugates: Evidence against Clonal Deletion as the Mechanism of Tolerance Induction

Tolerance to the alpha1--6 epitope of native dextran B512 was found to be very stable and could not be broken by the injection of dextran conjugated to several substances, such as protein A, keyhole limpet haemocyanin, edistin, concanvalin A or Staphylococcus bacteria, strain Cowan. However, when tolerant mice were injected with dextranase, all the above conjugates induced a strong anti-alpha1--6 immune response. In contrast, native dextran itself never induced a response in tolerant, dextranase-treated mice. It was concluded that tolerance only affects the specific B-cell subpopulation that can respond to the polyclonal B-cell-activating (PBA) property of dextran, whereas other specific B cells having PBA receptors for, e.g., signals delivered by collaborating T cells remain in a resting state. These B cells can respond in a specific immune response against the tolerogen after removal of the antigen, which blocks the Ig receptors and therefore prevents them from passively focusing the antigen. Thus, immunological tolerance is not caused by clonal elimination of the antigen-specific clone, but only affects a small subfraction of cells with Ig receptors against the tolerogen.     

Mechanism of B-Cell Activation and Paralysis by Thymus-Independent Antigens

Normal spleen cells showed a bell-shaped dose response profile when stimulated in vitro with die thymus independent antigen (4 -hydroxy-3,5 dinitiophenyl)acetyl (NNP)-lipopolysaccharide (LPS) with regard to the development of high-avidity plaque-forming cells to NNP The addition of suboptimal concentrations of LPS to cultures stimulated by suboptimal concentrations of NNP LPS resulted in optimal induction of B cells in that affinity fraction Addition of LPS to cultures optimally stimulated by NNP-LPS resulted in paralysis of the specific cells These results are interpreted in terms of the additive effects between the mitogenicity LPS and the mitogenicity of NNP LPS the latter being selectively focused on the specific cells, thus providing further evidence for the 'one nonspecific signal' hypothesis for immune activation of B cells     

Rise in Inulin-Sensitive B Cells During Ontogeny Can Be Prematurely Stimulated by Thymus-Dependent and Thymus-Independent Antigens

We have shown that the delayed acquisition of competence in expression of an anti-inulin (IN) response by neonatal BALB/c mice is preceded by a natural increase in the frequency of IN-sensitive B cells between 3 to 5 weeks of life. Up until 3 weeks of age, BALB/c mice resemble adult germfree mice in their low frequency of IN-sensitive B cells (1 to 2/10(6) B cells). Thereafter, the population of IN-reactive B cells rises about 10-fold to the young adult level, without deliberate immunization. This naturally expanded population of IN-reactive cells has an isotype profile resembling populations arising after intentional priming with other antigens in that it contained a large proportion of cells which generated clones expressing immunoglobulin G and immunoglobulin A isotypes, often without detectable immunoglobulin M. The late rise in frequency of IN-sensitive precursors could be induced prematurely by deliberate priming at 3 days of age with either the thymus-dependent antigen IN-hemocyanin or the thymus-independent bacterial levan. However, no circulating anti-IN could be detected following this early administration of antigen. Thus, the delayed expression of anti-IN does not reflect an absence of B cells of the appropriate specificity which can be stimulated to divide by antigen but rather other events occurring subsequent to perinatal generation of antigen-sensitive cells. Our observations support a role for the beta2 --> 1 fructosyl group as an environmental determinant which selectively expands out preexisting antigen-sensitive B cells at 3 to 5 weeks of age and these include clonotypes which express the predominant anti-IN idiotypes.     

Thymus-Independent B-Cell Activation: Passively Incorporated Membrane Antibodies Serve to Focus the Antigen but Cannot Transmit Activation Signals

We have activated B cells with membrane-incorporated monoclonal antibodies against the hapten trinitrophenyl (TNP) using various concentrations of the polyclonal activator lipopolysaccharide (LPS) haptenated with TNP. We found that anti-TNP-decorated B cells were polyclonally activated by 1000-fold lower concentrations of TNP-LPS than untreated B cells or B cells decorated with antibodies of other specificities. In order to test whether the passively incorporated anti-TNP monoclonals could mediate activation signals or only served to focus the polyclonal activator TNP-LPS to the B cells, we compared the response of anti-TNP-decorated B cells from normal C3H/He mice and from the LPS-unresponsive strain C3H/HeJ. We found that B cells from C3H/HeJ mice could not be activated to polyclonal antibody synthesis, in contrast to B cells from the LPS-responsive strain C3H/He. Thus, contrary to what was previously suggested, the incorporated anti-TNP antibodies could not mediate activation signals, but only served to passively bind and concentrate TNP-LPS to the membrane of the B cells, thereby increasing the concentration of the polyclonal B-cell activator LPS to the B cells.     

Lymphocyte Subpopulations in Man: B-Cell Stimulation Induced by Pokeweed Mitogen and Irradiated T Cells

The enhanced stimulation of human B lymphocytes by pokeweed mitogen in the presence of irradiated T helper lymphocytes has been studied, revealing that the proliferative responses measured by incorporation of thymidine in cultures of B lymphocytes and irradiated T lymphocytes in a 1:2 or 1:4 ratio is mostly a function of the B cells. Only a minimal number, if any, of the T cells contaminating the B cell suspensions is stimulated to proliferation. This is in contrast to stimulation of the B-cell suspensions without addition of irradiated T cells, where both B cells and T cells proliferate. The irradiated T helper cells have no FcR for antigen-bound IgG, and as well allogeneic as autologous T cells exhibit helper capacity of equal strength. The test system described makes it possible selectively to test one B-cell function and the corresponding T helper capacity.     

Potentiation of the PFC Response to Thymus-Independent Antigens by Heterologous Erythrocytes

Immunization with horse erythrocytes (HRBC) and a thymus-independent (TI) antigen of the TI-2 category, such as a native dextran, dinitrophenyl-dextran (DNP-dextran), or DNP-Ficoll, resulted in a three- to four-fold enhancement of the plaque-forming cell response to the TI antigen. The effect was found to be T-cell associated, since cyclosporin A abrogated enhancement. The T cells of T-cell factor involved were elicited early in the response to HRBC and acted on the initial stages of the TI response. The HRBC-induced potentiation affected only B cells activated by the TI antigen; it could not induce a TI response when TI-2 antigen was given under nonresponsive conditions; and it had only a slight effect on the response to a thymus-dependent (TD) antigen. A soluble TD antigen, bovine serum albumin-coupled dextran (BSA-dextran), did not have potentiating ability equivalent to that of the particulate HRBC. It was concluded that non-specific T-cell help can influence TI-2 responses when they are present simultaneously.     

Stimulation of Interleukin 6-Like B-Cell Differentiation Factor Production in Human Adherent Synovial Cells by Recombinant Interleukin 1

Abnormal production of immunoglobulin in the joint space is frequently observed in patients with rheumatoid arthritis (RA). We have previously demonstrated that adherent synovial cells (ASC) from patients with RA are involved in B-cell differentiation by their spontaneous production of B-cell differentiation factor (BCDF). The regulation of the production of this factor, however, has not yet been described. We investigated the effects of recombinant interleukin 1 alpha and beta (rIL-1 alpha and rIL-1 beta) on the production of BCDF in ASC. Increased production of BCDF was observed with increased rIL-1 concentration. Production of BCDF was detected 3 h after exposure of ASC to rIL-1 and increased throughout a 48-h culture. This BCDF, assayed on SKW6-CL4 cells, was found to share a common active site with interleukin 6. The effect of rIL-1 was almost neutralized by anti-IL-1 antibody and the addition of polymyxin B did not diminish the effect of rIL-1, indicating that rIL-1 itself stimulates ASC in vitro. These results suggest that IL-1 may play a regulatory role in the production of BCDF in synovial tissue.     

A Trypanosoma cruzi Alkaline Antigen Induces Polyclonal B-Cell Activation of Normal Murine Spleen Cells by T-Cell-Independent, BCR-Directed Stimulation

We have previously reported that a cytosolic alkaline fraction (FI) obtained from epimastigotes of Trypanosoma cruzi promotes the activation, proliferation and differentiation of normal murine B cells into antibody-secreting plasmocytes. Neither the mechanism nor the cells involved in the FI-induced polyclonal B-cell activation were established. In this work we report that accessory cells are required for FI-induced polyclonal B-cell activation as no proliferative responses were obtained following treatment of normal spleen mononuclear cells (NSMC) with L-leucine methyl ester. Furthermore, FI did not induce the expression of CD25 on T cells and it promoted the proliferation of a T-cell-depleted population, indicating that it acts in a T-independent manner. We observed that NSMC were stimulated in vitro by FI-released cytokines, such as interleukin (IL)-4, IL-6 and IL-10, which are involved in B-cell proliferation and differentiation. Interestingly, while significant amounts of interferon-gamma (IFN-gamma) were found in culture supernatants we did not observe detectable levels of IL-2. Additionally, we found that B-cell receptor (BCR) and major histocompatibility complex (MHC) class II antigens were involved in the proliferative response induced by FI because antibodies directed against cell-surface immunoglobulin M (IgM), CD45 and MHC class II molecules inhibited the FI-induced B-cell proliferation. CD40 ligand (CD40L) did not participate in such a phenomenon.     

Independent Segregation of Two Functional Markers Expressed on the Same B-Cell Subset in the Mouse: The Mls Determinants and LPS Receptors

Mice of the C3H/Tif strain display a mixed leukocyte reaction (MLR) with all H-2k strains carrying any of the known alleles of the Mls locus. In particular, C3H/Tif is incompatible with the related substrain C3H/HeJ, from which it also differs at the locus responsible for the recognition of lipopolysaccharides (LPS) as B-cell mitogens, and at the Mod-1 locus. Our genetic analysis indicates that the MLR incompatibility between these strains is not H-2-linked and segregates as controlled by a single locus, most probably identical to Mls, for which the C3H/Tif strain expresses a previously unidentified allele, Mlse. Moreover, segregation data show that this locus assorts independently of LPS responsiveness and that neither marker is closely linked to the Mod-1 locus in linkage group II.     

Alterations of the B-Cell Response by HIV-1 Replication

While the hallmark of HIV-1 infection is the progressive depletion of CD4(+) T cells, extensive B-cell dysfunction ensues that impairs the quality of the humoral response. HIV-1 infection causes hypergammaglobulinemia, polyclonal activation, loss of memory B-cell subsets, B-cell exhaustion, aberrant B-cell surface markers, and impaired humoral responses against infections and vaccinations. The totality of the mechanisms that contribute to B-cell dysfunction in vivo is unknown, although roles for HIV proteins (Env, Tat, and Nef) and virions binding to CD21 on B cells have been identified. Recent studies suggest that early antiretroviral therapy, that minimizes virus replication, can profoundly preserve the early B-cell response to HIV-1. Thus, it is clear that there is an intricate interplay between HIV replication and stimulation of the host B-cell response to infection. A better understanding of how HIV-1 subverts a productive B-cell response is needed to inform vaccine strategies that aim to elicit long-lived plasma cells and memory B-cell responses that can act quickly upon antigen stimulation.     

Therapeutic Efficacy and Hepatotoxicity of a Composition of Isoniazid and Dialdehyde Dextran Obtained by Radiochemical Oxidation of Dextran

Tuberculous granulomas were found in all parenchymal organs of mice infected with mycobacteria of BCG vaccine. The number and size of hepatic granulomas decreased, while the count of degenerated and necrobiotic hepatocytes in infected animals increased 3 months after the start of therapy with a composition of isoniazid and dialdehyde dextran. The composition of isoniazid and dialdehyde dextran obtained by radiochemical oxidation of dextran had greater therapeutic efficacy and lower hepatotoxicity. Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Suppl. 1, pp. 73–75, 2008     

Stimulation of Glucose Metabolism in Rat Mast Cells by Antigen,Dextran and Compound 48/80, Used as Histamine Releasing Agents

Histamine release in aerobic medium from rat peritoneal mast cells by anaphylactic reaction, dextran and compound 48/80 was associated with a stimulation of exogenous glucose metabolism as determined by carbon dioxide and lactate production. There was generally a correlation between the amount of histamine released and the degree of metabolic stimulation. In anaerobic medium a stimulation of lactate production was observed in most of the experiments when histamine was released by anaphylactic reaction and dextran. Compound 48/80-induced histamine release in presence of oligomycin was not, however, associated with any appreciable change in lactate production. Galactose and fructose were metabolized by rat mast cells to CO2 and lactate, but the rate of CO2 production was only 18 % and 29 %, respectively, and that of lactate production (aerobic) 5 % and 3.6 %, respectively, as compared to the metabolism of glucose to these products under the same conditions. 80 mM galactose could partially reverse the cyanide inhibition of histamine release while the same concentration of fructose was ineffective.     

Human Complement Activation by Polygeline and Dextran 70

The complement cascade is activated during cardiopulmonary bypass (CPB) and in trauma victims. In order to study whether plasma expanders may contribute to complement activation in these settings, fresh human serum was incubated with dextran 70 and polygetine. C3-activation products and the terminal complement complex (TCC) were quantified in enzyme immunoassays. At 37 C, dextran caused immediate, dose-dependent C3 activation and TCC formation with decline later in the rate of TCC formation relative to serum-saline controls. High doses of polygeline caused slight activation after 15–30 min. The authors tested also the activation under conditions comparable to those found during clinical CPB. Activation induced by dextran and polygeline was increased by dilution of the serum. Furthermore, the plasma expanders counteracted the well-known inhibitory effects of heparin (4 IU/ml) and moderate hypothermia (30°C) on complement activation. The authors conclude that dextran, and to a lesser extent polygeline. may contribute to complement activation during CPB and other clinical settings such as shock treatment.     

右旋糖酐40、70对红细胞与内皮细胞粘附的影响

采用流室显微观察系统，定量研究右旋糖酐４０（ＤＸ４０）和右旋糖酐７０（ＤＸ７０）对红细胞与内皮细胞动态粘附特性的影响。统计分析处理数据，得到反映切应力与细胞间动态粘附数关系的经验公式及粘附特征常数ａ，ｂ值。ａ值反映红细胞的初始粘附数，ｂ值反映随切应力增大，粘附数减小的速率。ＤＸ７０实验组的ａ值大于ＤＸ４０组的，而ｂ值的情况相反。故结果显示切应力越大，粘附的红细胞越少；ＤＸ４０使红细胞的粘附明显减少；ＤＸ７０使红细胞粘附显著增加。由此提示不同长度的细胞桥接分子对红细胞的粘附影响不同，且临床上选用ＤＸ４０作血浆扩容剂较ＤＸ７０优越得多     

Inhibition of B-Cell Function by Concanavalin-A-Induced Suppressor Cells

The in vitro immune response of normal spleen cells to the thymus-independent antigen dinitrophenylated levan (DNP-LE) was found to be inhibited by suppressor cells induced previously by concanavalin A (Con A) in vitro. At various suppressor to target cell ratios, the level of suppression observed was comparable to that seen in anti-sheep erythrocyte (SRBC) responses. Consequently, it is suggested that B cells constitute a direct target for Con-A-induced suppressor cell activity.     

Specific Antibodies are Responsible for the Low Dose Suppression of the Immune Response to Thymus-Independent Antigens

Animals primed to the thymus-independent antigen native dextran B512 could not respond to the FITC hapten after immunization with native FITC-dextran. The degree of suppression of the anti-FITC response paralleled the increase of the anti-α1-6 PFC after priming with different doses of dextran. Suppression could be passively transferred with serum from dextran primed animals. Young animals that are very low- or non-responders to the α1-6 epitope of dextran B512, failed to suppress the anti FITC PFC response after priming with native dextran. We conclude that antibodies against the dextran carrier were responsible for the suppressed response to the FITC epitope in FITC-dextran immunized animals that had been primed with low doses of the dextran carrier.     

B-Cell Receptor Signaling Inhibitors for Treatment of Autoimmune Inflammatory Diseases and B-Cell Malignancies

B-cell receptor (BCR) signaling is essential for normal B-cell development, selection, survival, proliferation, and differentiation into antibody-secreting cells. Similarly, this pathway plays a key role in the pathogenesis of multiple B-cell malignancies. Genetic and pharmacological approaches have established an important role for the spleen tyrosine kinase (Syk), Bruton's tyrosine kinase (Btk), and phosphatidylinositol 3-kinase isoform p110delta (PI3Kδ) in coupling the BCR and other receptors on B cells to B-cell survival, migration, and activation. In the past few years, several small-molecule inhibitory drugs that target PI3Kδ, Btk, and Syk have been developed and shown to have efficacy in clinical trials for the treatment of several types of B-cell malignancies and inflammatory diseases. Emerging preclinical and clinical data have also shown a critical role of BCR signaling in the activation and function of self-reactive B cells that contribute to autoimmune diseases. Because BCR signaling plays a major role in both B-cell-mediated autoimmune inflammation and B-cell malignancies, inhibition of this pathway may represent a promising new strategy for treating these diseases. This review summarizes recent achievements in understanding the mechanism of action, pharmacological properties, and clinical activity and toxicity of these BCR signaling inhibitors, with a focus on their emerging role in treating lymphoid malignancies and autoimmune disorders.     

In Vitro Induction of Specific T Cells Able to Help in the Generation of Delayed-Type Hypersensitivity by Thymus-Dependent and Type-II 'Thymus-Independent' Antigens

An in vitro system is described which supports the primary induction of T cells able to help in the induction of delayed-type hypersensitivity. This system is used to demonstrate that hapten-Ficoll conjugates induce potent hapten-specific T cells with this function. These type-II 'thymus-independent' antigens are thus able to induce specific regulatory T cells. These helper T cells are similar to those induced by classical thymus-dependent antigens in that they are specific for antigen rather than idiotype and act by a linked mechanism.     

刺激作用下大规模神经元群的随机非线性演化模型及动态神经编码

在前期研究工作的基础上，我们考虑外刺激作用下神经振子群对信息的处理及神经编码的动态演化。通过对模型的数值分析，得到了在三维空间用于描述神经元群内神经元放电过程时的数密度随时间演化的图像，即神经编码的动态演化。数值分析的结果表明该模型能够用来描述大量相互作用神经元在刺激下神经编码的演化过程，研究证明只有在适当的刺激强度下神经元之间的耦合强度与耦合结构才能发生改变，从而体现了神经元的可塑性变化。