Studies on the mechanism of polyclonal B cell stimulation by TH2 cells

Recently, it has been shown that cloned L1/1 T helper cells of type 2 (TH2-cells), when stimulated with antigen, are able to induce polyclonal B cell proliferation. Here we present evidence that this process is dependent on direct cell-cell interaction between T and B cells, which in the effector phase, i.e., during stimulation of the B cells by activated T cells, can be mediated by a mechanism other than cognate interaction. This conclusion is derived from experiments in which highly purified, small B cells of high density were polyclonally stimulated by L1/1 T cells triggered by an anti-T3 monoclonal antibody in the absence of antigen. The triggering process was independent of the presence of the Fc part of the antibody and occurred in cultures devoid of macrophages. Thus, the well-established cognate recognition does not appear to be the only mechanism of B cell induction by T helper cells.     

Evidence for polyclonal B cell activation as the mechanism for LCMV-induced autoimmune hemolytic anemia.

A docile substrain of lymphocytic choriomeningitis virus (LCMV) causes a persistent infection in adult C3HeB mice and induces a severe autoimmune hemolytic anemia (AIHA) which is maximal around three weeks post infection (PI). Evaluations of serum immunoglobulin levels of these mice demonstrated grossly elevated IgG2a levels along with increased IgG1 and IgG2b levels, suggesting that these animals also develop polyclonal B cell activation (PBA). Interestingly, LCMV-infected B10.BR mice did not demonstrate a marked hypogammaglobulinemia nor did they experience a severe hemolytic anemia. Although evaluations of the hematocrits indicated that these animals endure a mild anemia 21 days PI, a below normal reticulocyte count until day 18 PI suggests that there was a prolonged suppression in hematopoiesis. It is clear from RBC survival studies that there is not an accelerated rate of RBC elimination, as seen in infected C3H mice, demonstrating that the anemia in B10.BR mice is not due to a hemolytic process. These results imply a correlation between the development of PBA and AIHA, suggesting a cause and effect relationship.     

Dependence of lymphocyte surface Ig on continuous polyclonal activation.

We have previously shown that most rabbit splenic B cells cultured in a medium supplemented with 5% autologous serum require continuous polyclonal stimulation to maintain detectable amounts of surface Ig. In the absence of this stimulation B cells shed but do not replace their surface Ig. Here, we investigated the mechanism responsible for the loss or maintenance of surface Ig. We showed that the addition of inhibitors of mRNA and protein synthesis to the cell cultures completely abolished the Ig maintenance effect provided by the mitogen thereby suggesting that it did not act by 'freezing' the membrane Ig but rather by continuously stimulating resynthesis. Moreover, by labelling the surface Ig with 125I-labelled Fab anti-allotype antibody we showed that the maintenance of surface Ig by mitogen stimulation was due to the turnover of surface Ig. The cells shed and replaced their surface Ig with a half-life of about 2 h only when mitogen was present but shed without replacing the surface Ig in the absence of mitogen. Also, the B-cell mitogens, SM and LPS, were able to maintain surface Ig even at extremely small concentrations while the T-cell mitogens, Con A and PHA, failed to do so at any concentration, suggesting that direct stimulation of B cells was needed to maintain surface Ig. When spleen cells were cultured in 'crowded' conditions in the absence of mitogen they did not lose their surface Ig; under these conditions it appeared that a factor associated with the macroglobulin fraction is induced and acts in the same manner as a B-cell polyclonal activator to maintain the turnover of surface Ig. Such a factor may actually function in vivo since lymphocytes are in very close contact in the lymphoid organs. We concluded that rabbit B lymphocytes shed and replace their surface Ig with a half-life of about 2 h and that the replacement, but not the shedding of surface Ig, is dependent on continuous exogenous or endogenous polyclonal activation.     

Studies on the mechanism whereby cyclosporin A inhibits T-lymphocyte activation

The immunosuppressive drug Cyclosporin A (CyA) inhibited the ConA-induced DNA synthesis in C57B1/6 spleen cells at a concentration of 40 ng/ml totally; this inhibition could not be overcome by the addition of highly purified interleukin-1. ConA-induced RNA synthesis was also inhibited by concentrations of 40 or 200 ng/ml CyA, although total inhibition could not be achieved. In contrast, lipopolysaccharide-induced proliferation could not be inhibited. CyA at a concentration of 40 ng/ml also inhibited the ConA-induced production of interleukin-2 by mouse spleen cells, this inhibition was not due to a toxic mechanism. On the contrary, the proliferative response of T cell blasts from a long-term T cell line (M2) to interleukin-2 containing supernatants was not inhibited by concentrations of 40 or 200 ng/ml CyA; only at 20-100-fold higher concentrations partial inhibition could be observed. One of the earliest events in the course of lymphocyte activation, the enhanced incorporation of unsaturated fatty acids into the lymphocyte plasma membranes; was also inhibited by concentrations of CyA, which abrogated the ConA-induced DNA synthesis. The inhibition of the enhanced incorporation of 14C-oleic acid and 14C-linoleic acid, which are incorporated by the membrane-bound lysolecithin-acyltransferase, thus suggests a molecular site of action for CyA.     

Correlation between ribosylation of pertussis toxin substrates and inhibition of peptidoglycan-, muramyl dipeptide- and lipopolysaccharide-induced mitogenic stimulation in B lymphocytes

Selective inhibition by pertussis toxin (PT) of mitogenic activation of mouse B lymphocytes by bacterial mitogens (peptidoglycan and lipopolysaccharide) and muramyl dipeptide (a synthetic analog of peptidoglycan fragment) was demonstrated. Mitogenic activation of B cells by protein kinase C activators and ionomycin was insensitive to PT. Also PT did not inhibit peptidoglycan- and lipopolysaccharide-induced differentiation of B cells into Ig-secreting cells, when it was added to the cultures after the proliferative stage of the response. B lymphocyte membranes contained two major PT substrates (40 and 41 kDa). The extent of PT-mediated ADP ribosylation of these substrates correlated with the degree of PT-mediated inhibition of mitogenic stimulation of B cells. B cell stimulation by all mitogens tested was not inhibited by cholera toxin at nontoxic concentrations that are known to cause maximal increase in cAMP in B cells. Since the only known substrates for PT-mediated ADP ribosylation in mammalian cells are the alpha subunits of some G proteins, our data suggest that G proteins are present in B cell membranes and that they are involved in B cell activation induced by bacterial mitogens.     

Amplification of the polyclonal activation of human T cells. I. Null-cell products promote the polyclonal proliferation of T cells.

Synergy can be observed in the proliferative response to mitogens of cultures containing human T and Null cells when compared with those containing only highly purified cells of those two types. This synergy was analysed (i) by evaluation of the proliferative response at each step of the purification process leading to separation of T and Null cells; (ii) by back-mixing T and Nul cells at different rations; and (iii) by evaluation of the proliferative response of free suspension cultures of T cells overlaying a semi-solid layer containing Null cells, or of free suspension cultures of Null cells over a semi-solid culture layer of T cells. The following conclusions were reached: (i) purified Null cells are unresponsive to mitogen when cultured alone or in the presence of diffusible T-cell products; (ii) the T cells are less responsive when cultured alone than in the presence of Null cells or diffusible Null cell products. Thus the synergistic effect observed between T and Null cells is not due to the promotion of Null-cell proliferation by T -cell products but can be accounted for by diffusible Null-cell products enhancing the process of T lymphocyte activation by mitogens.     

Modulation of polyclonal activation by plasma fibronectin and fibronectin fragments.

Modulation of activation of polyclonal IgM, IgG and IgM anti-DNA antibodies by plasma fibronectin (Fn) was studied because in some autoimmune diseases there appears to be a correlation between the increased level of Fn in the affected tissues and increased polyclonal B-cell activation. Fn caused a dose-dependent polyclonal activation of IgM, IgG and IgM anti-DNA antibody-secreting cells in cultures of mouse splenocytes. Fn significantly inhibited the generation of polyclonal antibodies by Fn-binding stimulants and did not significantly change the generation of polyclonal antibodies by the stimulants that do not bind Fn. Plasmin or trypsin digestion of Fn abolished both the polyclonal activating properties of Fn and the inhibitory effects of Fn that were selective for the Fn-binding polyclonal activators. Digestion of Fn with trypsin also generated immunosuppressive Fn fragments that inhibited polyclonal activation by both Fn-binding and non-binding bacteria. Under our culture conditions Fn or Fn digests were not mitogenic and had no effect on the mitogenicity of Fn-binding and non-binding stimulants. These results indicate that Fn can act as a polyclonal activator and that it can also modulate lymphocyte activation induced by other activators.     

槲皮素对LPS诱导中性粒细胞活性化效应的抑制作用

目的研究槲皮素(Quercetin,Que)对细菌脂多糖(Lipopolysaccharide,LPS)诱导的中性粒细胞(Polymorphonuclear,PMN)活化效应的影响。方法运用免疫荧光法和流式细胞术,对接受1h LPS刺激的PMN表面黏附分子(CD62L,CD11b／CD18)的表达进行测定,同时应用MTT法对不同状态下的PMN活性进行测定。结果Que对LPS诱导的中性粒细胞活化效应有明显抑制作用,表现为抑制细胞表面黏附分子CD62L的表达和促进CD11b／CD18的表达,同时Que对LPS增加细胞活性的效应有抑制作用。结论槲皮素通过对抗LPS对PMN黏附分子CD62L,CD11b／CD18的表达的影响,抑制LPS诱导的中性粒细胞活化效应,从而阻止PMN对血管内皮细胞的黏附,减少炎症细胞向炎症局灶的浸润,这可能是槲皮素发挥抗炎作用的一个重要机制。     

Monocyte suppression of Fusobacterium nucleatum-induced human polyclonal B-lymphocyte activation.

Previous studies reported that Fusobacterium nucleatum induced polyclonal B-lymphocyte activation (PBA) as determined by immunoglobulin M production in cultures of human peripheral blood mononuclear cells. However, the PBA response was greatly enhanced when the cells were depleted of esterase-positive, adherent cells (i.e., monocytes). The purpose of this study was to confirm and further examine the suppression of F. nucleatum-induced PBA (F. nucleatum-PBA) by blood monocytes. For comparison, PBA induced by pokeweed mitogen (PWM-PBA), which is enhanced by monocytes, was assessed in some experiments. We found the removal of monocytes from unfractionated cells by (i) Sephadex G-10, (ii) anti-monocyte specific OM-1 monoclonal antibody plus complement, or (iii) L-leucine methyl ester, a compound which selectively kills lysosome-rich cells, resulted in a population of cells responsive to F. nucleatum-PBA and unresponsive to PWM-PBA. The addition of double adherence-purified monocytes (greater than 85% esterase-positive cells), particularly in concentrations of greater than 10%, to lymphocytes depleted of monocytes by G-10, OM-1, or L-leucine methyl ester treatments, suppressed F. nucleatum-PBA and enhanced PWM-PBA. Monocytes also suppressed a mixture of isolated T and B cells combined in a T/B cell ratio of 3:1, which is an optimal ratio for F. nucleatum-PBA. Allogeneic monocytes suppressed F. nucleatum-PBA, although at low numbers these cells were not as suppressive as autologous monocytes. Heating at 56 degrees C for 15 min, sonicating, or freeze-thawing the monocyte preparations resulted in an abrogation of monocyte-induced suppression of F. nucleatum-PBA. Kinetic studies in which fresh monocytes were added daily to lymphocytes stimulated with F. nucleatum or PWM showed that the monocytes must be added within the first 2 days of culture to suppress F. nucleatum-PBA or enhance PWM-PBA. Monocytes incubated with F. nucleatum for 48 h released into the culture medium a soluble factor that suppressed F. nucleatum-PBA. The results from this study demonstrate a potent mechanism by which the host might prevent exaggerated nonspecific immunoglobulin responses when exposed to PBA-inducing concentrations of F. nucleatum. On the other hand, the induction of suppressive monocytes (or monocyte-mediated suppressive factors) by interaction with F. nucleatum might result in the inhibition of host protective immune reactions.     

Studies on the mechanism of hyaluronate lyase action.

Hyaluronate lyase from streptococci group A was purified by chromatography on DEAE-Sephadex A-50 and on Biogel P-150, thereby enriching it about 1,000-fold and separating it into two enzyme fractions with the same amino acid composition. The photooxidation of hyaluronate lyase in the presence of methylene blue results in rapid inactivation of the enzyme. The histidine content of the enzyme is decreased considerably, but also the content of methionine, tyrosine, and lysine is lowered. The enzyme is inhibited, but incompletely so, by N-tosyl-L-phenyl-alanine-chloromethyl ketone (TPCK) and N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK). Hyaluronic acid methyl ester, prepared form hyaluronic acid and diazomethane, is not split by hyaluronate lyase (EC 4.2.2.1.). Hyaluronic acid methyl ester is not a competitive inhibitor of hyaluronate lyase. For the mechanism of the enzymatic elimination reaction a proton transfer between histidine of the enzyme and the carboxylate group of hyaluronate is proposed.     

Neutralization of T-replacing factor by T8-positive lymphocytes: an important suppressor mechanism operating in the regulation of polyclonal B-cell activation.

Pokeweed mitogen (PWM)-induced B-cell activation was entirely abrogated by pre-treating peripheral mononuclear cells (PBM) with T4 (anti-T-helper-inducer subset) or T11 (anti-sheep erythrocyte receptor, ie. anti-pan-T-cell) monoclonal antibody plus complement. Immunoglobulin secretion was restored in T11- but not T4- cultures by adding the culture supernatant from PWM-stimulated PBM (T-replacing factor, TRF). Since T8+ (T-suppressor-cytotoxic subset) cells were present in high concentrations in T4- but absent from T11- cultures, it appeared that these cells could inhibit B-cell activation by PWM plus TRF and that suppression could occur in the absence of T4+ cells. Incubation of TRF with purified, unstimulated T8+ cells prior to addition to T11- cultures abrogated subsequent PWM-induced B-cell activation, whereas T8- PBM had no effect on TRF. T8+ cells did not secrete suppressor factors during incubation with TRF. Absorption of one or more of the factors required for B-cell growth and differentiation by T8+ cells appears to be an important suppressor mechanism operating in the PWM system.     

三七皂苷Rg1抑制脂多糖诱导的小胶质细胞激活

目的 探讨三七皂苷Rg1(Rg1)对脂多糖(LPS)诱导的小胶质细胞系BV-2细胞炎性因子释放的抑制作用.方法 用LPS刺激BV-2细胞构建炎症模型,采用四甲基偶氮唑盐比色法检测Rg1对BV-2细胞活力的影响,免疫荧光染色和反转录PCR方法检测不同浓度Rg1(10、20、40μmol/L)对细胞炎性蛋白酶诱导型一氧化氮合酶(iNOS)和环氧合酶-2 (COX-2)、细胞炎性因子肿瘤坏死因子-α(TNF-α)和白细胞介素-1β(IL-1β)、炎性信号分子NF-κB蛋白与mRNA的表达变化.结果 不同浓度的Rg1在转录水平和翻译水平上明显抑制了LPS诱导的细胞炎性蛋白酶iNOS和COX-2、细胞炎性因子TNF-α和IL-1β与炎性信号分子NF-κB的上调,并且iNOS、COX-2和NF-κB的表达呈剂量依赖性.结论 Rg1可通过调控LPS诱导的小胶质细胞系BV-2细胞炎性因子释放从而抑制小胶质细胞激活,发挥抗神经炎症的作用.     

Maternal aggression persists following lipopolysaccharide-induced activation of the immune system

Lactating females direct aggressive behaviors towards intruders presumably to reduce the likelihood of infanticide of their pups. Infected animals display a constellation of responses that include lethargy, anorexia, and decreased social interactions. This suite of responses is referred to as sickness behavior, and is putatively part of an adaptive strategy to aid the organism in recovery from infection. Previous work has suggested that animals can suppress the behavioral symptoms of sickness in order to engage in adaptive behaviors. To test whether adaptive nest defense is affected by illness, dams received a peripheral injection of either saline or lipopolysaccharide (LPS [50, 400, or 1000 microg/kg]), a non-replicating component of bacterial cell walls that activates the immune system. Simulated infection with LPS reduced body mass and food intake in dams and interfered with litter growth in a dose-dependent manner. Generally, nest defense was unaffected by LPS; the proportion of dams displaying maternal aggression against a male intruder, as well as the latency and duration of aggressive encounters were only suppressed at the highest LPS dose tested. Further, LPS treatment also altered non-agonistic behavior during the aggression test as indicated by reduced social investigation of the intruder and an increased time spent immobile during the session. LPS administration also significantly increased serum corticosterone concentrations in lactating females. These findings suggest that maternal aggression is not suppressed by LPS-evoked immune activation at doses that attenuate other aspects of maternal and social behavior.     

辣椒素对脂多糖诱导血管内皮细胞活化的影响及机制

 目的:探讨辣椒素对脂多糖（LPS）刺激后小鼠主动脉内皮细胞活化的影响,并探讨其可能机制。方法:（1）体外分离培养小鼠主动脉内皮细胞,免疫荧光鉴定内皮细胞特异性标志。（2）以100 μg/L LPS作用于血管内皮细胞后,以不同浓度的辣椒素（50 μmol/L、100 μmol/L和200 μmol/L）进行干预,分别于12、24和48 h收集主动脉血管内皮细胞及细胞上清液。采用ELISA法检测各组细胞上清液中的可溶性细胞间黏附分子 1（sICAM-1）、可溶性血管细胞黏附分子 1（sVCAM-1）和可溶性P-选择素(sP-selectin)水平,Western blotting法检测各组主动脉血管内皮细胞核内NF-κB p65水平和胞浆p-IκBα、IκBα水平。结果:与对照组相比,LPS组细胞上清液中sP-selectin、sICAM-1和sVCAM-1含量显著升高（P<0.05）, LPS能够时间依赖性上调sICAM-1和sVCAM-1的含量。与同时点的LPS组相比,辣椒素能够剂量依赖性下调sP-selectin、sICAM-1和sVCAM-1水平。与对照组相比,LPS作用24 h后, 细胞核内NF-κB p65和胞浆p-IκBα蛋白水平显著升高（P<0.05）,胞浆IκBα蛋白水平显著降低（P<0.05）。与同时点LPS组相比,辣椒素能够剂量依赖性下调细胞核内NF-κB p65和胞浆p-IκBα蛋白的水平（P<0.05）,剂量依赖性上调胞浆IκBα蛋白水平（P<0.05）。结论: 辣椒素能够显著抑制LPS作用后血管内皮细胞活化水平,该效应可能是通过下调IκBα降解和NF-κB p65胞核内转位而实现的。     

Loss of surface IgD by human B lymphocytes during polyclonal activation.

Surface and cytoplasmic immunoglobulins were studied by direct immunofluorescence in pokeweed mitogen-stimulated cultures of human blood lymphocytes. The results compared to those of studies of unstimulated cultures and of fresh normal lymphocytes showed a striking decrease in surface IgD during terminal maturation of B lymphocytes into plasma cells. The number of cells which expressed IgG Fe receptor also decreased, although to a lesser extent.     

Schistosoma mansoni: autoantibodies and polyclonal B cell activation in infected mice.

The appearance of autoantibodies was investigated during the course of Schistosoma mansoni infection in C57Bl/6 mice. Anti-liver autoantibodies or lymphocyte-reactive alloantibodies were detected respectively without cell-mediated immunity against liver antigen or lymphocytotoxic activity. Anti-liver, anti-DNA, anti-Ig and anti-lymphocyte antibodies were shown 6-7 weeks after the beginning of the infection concomitantly with the increase of immunoglobulin levels and circulating immune complexes. At this period, the antibody response to polyvinylpyrrolidone (PVP) was increased and the injection of spleen cells from day-45-infected mice to uninfected recipients increased the anti-PVP antibody response. Conversely, the injection of spleen cells from uninfected to infected mice did not modify the anti-PVP Ab response. After 6 weeks of infection, the basal thymidine incorporation of spleen cells was increased contrasting with the marked inhibition of spleen cell response to PHA. The present data are consistent with the induction of a polyclonal non-specific B cell activation by S. mansoni.     

Effect of cell division inhibitors on polyclonal activation can vary according to the target cell used.

The effects of inhibitors of cell division on polyclonal stimulation induced either by bacterial lipopolysaccharide (LPS) or by a synthetic adjuvant, MDP, were compared, using different target cells. Doses of colchicine that prevented 3H-thymidine incorporation also prevented the induction of antibodies against TNP and against an altered self antigen: bromelain-treated mouse red blood cells (br-MRBC). Under identical conditions, incubation with cytosine arabinoside (CA) strongly prevented the induction of anti-TNP PFC and to a lesser degree anti-SRBC PFC. However, the number of anti br-MRBC PFC was unchanged even when a dose of CA which inhibits totally the incorporation of 3H-thymidine was used. Our findings indicate that the general term "polyclonal stimulation" may concern at least two different types of cell populations and therefore we strongly stress the importance of choosing similar targets in comparative experiments.     

尼古丁抑制脂多糖诱导的原代多巴胺能神经元变性及相关机制

目的: 观察尼古丁对脂多糖(LPS)诱导的胎鼠中脑小胶质细胞激活的影响及对其白介素6(IL-6)分泌的影响,以探讨尼古丁对中脑多巴胺(DA)能神经元的保护机制.方法: 取孕14d SD大鼠,胎鼠中脑腹侧区组织,混合培养中脑神经元-胶质细胞,Elisa检测细胞不同时间点分泌IL-6的水平;免疫细胞化学术检测小胶质细胞特异的钙结合蛋白(Iba1)和标记DA能细胞的酪氨酸羟化酶(TH)的阳性细胞数.结果: 经LPS激活的小胶质细胞胞体增大,活化标记物Ibal表达上调;DA能细胞的数目减少,突起受损.Elisa方法测定显示10ng/ml LPS致小胶质细胞在8、24和72h分泌IL-6的量均增高;在尼古丁(100μmol/L)预处理组,小胶质细胞的激活被抑制,TH免疫阳性的多巴胺能神经元的数量增加,LPS+尼古丁组分泌IL-6的量减少,在不同时间点(8、24和72h)与LPS组比较差异均有统计学意义.结论: 尼古丁可抑制小胶质细胞的激活,保护多巴胺能神经元,抑制小胶质细胞炎性因子的释放可能是其主要保护机制.