Mathematical model of B lymphocyte replacement kinetics: its application to the recovery from tolerance in adult mice

In a previous paper a simple mathematical model was developed, describing the induction of B cell tolerance by direct inactivation of immunocompetent cells by antigen, and the escape from tolerance due to spontaneous differentiation of stem cells. The model was compared with experiments on newly hatched chickens whose reactivity with antigens increases with age, and this causes difficulties with the simple model. In this paper the model is compared with experiments on adult mice using sheep erythrocytes and human gamma globulin as antigens. The rates of elimination of these two antigens from circulation differ markedly, and the escape from tolerance in these experiments correlates with the rates of elimination. Our model, which is based on this fact, agrees reasonably well with experimental results.     

Increased growth of RSV-induced tumors in chickens partially tolerant to MHC alloantigens

Chickens withB ² B ² MHC genotypes were made partially tolerant to B₅ MHC cell-surface antigens and the fate of their Rous-sarcoma-virus (RSV)-induced tumors was determined.B ² B ² chickens partially tolerant to viable or lysed white blood cells (WBC) or viable red blood cells (RBC) fromB ⁵ B ⁵ chickens had a significantly higher incidence of tumor progression than untreated, PBS-treated, orB ² B ² chickens inoculated with WBC from otherB ² B ² chickens. The criteria for tolerance were absence of antibody titer to the cell type inoculated and acceptance of allografts fromB ⁵ B ⁵ donors byB ² B ² chickens. Graft-vs-host reactions occurred only inB ² B ² chickens inoculated with viable WBC fromB ⁵ B ⁵ chickens. It appears thatB ² B ² chickens partially tolerant to B₅ antigens failed to mount a successful immune response to RSV-induced tumors partly because a B₅ MHC antigen(s) cross-reacted with a tumor associated antigen(s) thereby severely limitingB ² B ² host recognition of the tumor as foreign. Since WBC and RBC cell-surface antigens appear to contribute similarly to the effect, theB-F- region of the MHC may be involved.     

A mathematical model of B lymphocyte differentiation: Control by antigen

A mathematical model of B lymphocyte differentiation, based on experimental results, has been developed. The model focuses on the role of antigen in initiating and regulating B cell differentiation while other mechanisms, acting in concert with antigen but the functioning of which can be circumvented under appropriate conditions, are not considered. The importance of presence of antigen at individual stages of B cell differentiation was studied in experiments with an easily metabolizable antigen. Immunocompetent cells (ICC), arising by antigen-independent differentiation of stem cells, are activated by antigen (they become immunologically activated cells — IAC). Excess of antigen drives IAC into the terminal stage (antibody-forming cells — AFC) thereby restricting proliferation. Exhaustive terminal differentiation results in tolerance. A low primary dose permits IAC to escape antigen; IAC proliferate and later give rise to resting memory cells (MC) which are amenable to reactivation. MC have higher avidity for antigen (due to higher affinity, number and density of receptors) and the effect of different doses of antigen on MC is diverse. A very low secondary dose induces tolerance, a medium dose secondary response, and the administration of a high dose of antigen also brings about tolerance. The model suggests that the fate of memory cells is controlled by the ratio RAg, of the number of immunoglobulin receptors on B cells (R) to the number of available antigenic molecules (Ag), low values of RAg favouring stimulation to differentiation while high values of RAg favouring inactivation. A nonlinear system of ordinary differential equations, describing the development of the populations involved in antigen driven B cell differentiation, was used to simulate experiments and good qualitative agreement was achieved.     

AT-1.1: A thymus-specific alloantigen of chickens

A thymocyte-specific alloantigen, designated AT (avian thymus) –1.1, has been detected in Cornell C strain (CS) and Obese strain (OS) chickens, the latter being a strain derived from CS which develops a spontaneous form of autoimmune thyroiditis (SAT). Antisera specific for this antigen were developed first in a turkey immunized with thymocytes from an OS chicken and, later, in AT-1.1-negative CS chickens immunized with AT-1.1-positive thymocytes. AT-1.1 was detected in 50–70% of cells in a thymus cell suspension, but was not seen on peripheral blood lymphocytes, erythrocytes, or cells from bursa, spleen, kidney, liver, or brain. It was present on thymocytes of chickens at all ages tested, from 1 day to 6 months of age. AT-1.1 was not detected in six chicken lymphoid tumor cell lines tested, and birds expressing it were found to be negative for the presence of Marek's disease viral antigens. Pedigree studies on 287 (OS × CS)F₂ chickens demonstrated that AT-1.1 is expressed in a dominant or codominant manner, and the gene coding for this antigen was not linked to the B (major histocompatibility) complex. The genetics and tissue distributions of AT-1.1 indicate that it differs from thymus cell surface antigens, avian or mammalian, previously described.     

Restricted expression of an MHC alloantigen in cells of the erythroid series: A specific marker for erythroid differentiation

The spectrum of reactivity with various types of cells of a monoclonal antibody (CH-4) which detects a private MHC antigen of chickens was analysed. CH-4 agglutinates only RBCs that possess the B² (MHC) haplotype. A new rosetteforming cell (RFC) assay was devised to detect individual cells (excluding RBCs) that possess the CH-4 specificity on their cell surfaces. RBCs that have CH-4 chemically coupled to their surfaces attach to, and form rosettes with, B² antigen-bearing cells. Most non-RBC RFC were detected in active erythropoietic organs (adult bone marrow and embryonic spleen), and none were found in organs where erythropoiesis does not occur: adult thymus and bursa. Preincubation of bone marrow cells with CH-4 plus complement almost completely inhibits their capacity to form CFU-E without affecting their ability to form GM-CFU. In addition, CH-4 plus complement does not inhibit the capacity of B²/B² lymphocytes to induce a graft-versus-host reaction under conditions where anti-B² lymphocyte alloantisera are completely inhibitory. Our results strongly suggest that CH-4 monoclonal antibodies detect a private specificity on a gene product of the B-G locus whose expression is restricted to erythroid stem cells and erythrocytes.     

A three-locus model for the chicken major histocompatibility complex

The major histocompatibility complexes (B complexes) of chickens of various origins have been studied by serological and biochemical methods. TwoB complexes are of particular interest:B ^R1, a recombinant haplotype derived from theB complexes of the inbred CB and CC strains, andB ^G-B1 , theB haplotype of the G-B1 strain. TheB ^R1 haplotype differs detectably from theB ^CB haplotype only at a locus controlling the synthesis of an antigen, B-G, which (in peripheral blood) is present only on red cells. Anti-B-G sera precipitate, from¹²⁵I-labeled red cell lysates, two chains of apparent molecular weights 42,000 and 31,000 (measured under reducing conditions); the smaller is perhaps derived by proteolysis from the larger. TheB ^G-B1 haplotype differs detectably from theB ^CC haplotype only at a locus controlling the synthesis of an antigen whose tissue distribution and biochemical and biological properties are identical to those of B-G. The chicken major histocompatibility complex therefore contains at least three loci—those controlling synthesis of the B-G, and of the previously defined B and B-L antigens.The following abbreviations are used in this paper MHC major histocompatibility complex - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis - MLR mixed leukocyte reaction - GVH graft-versus-host reaction     

Cross-reactivity between RSV-induced tumor antigen and B5 MHC alloantigen in the chicken

Lymphocytes from chickens homozygous (B ² B ²) at the major histocompatibility complex (MHC) were tested for cytotoxic activity against five types of target chicken embryo fibroblasts (CEF). Lymphocytes from B²B² chickens bearing RSV-induced tumors lysed in vitro targets of B ² B ² and B ⁵ B ⁵ RSV-infected CEF and B ⁵ B ⁵ normal CEF, but did not lyse B ² B ² and B ²⁴ B ²⁴ normal CEF. Lymphocytes from normal B ² B ² chickens did not lyse any of the five types of CEF targets. Alloantisera absorption studies showed that both RSV-infected and uninfected CEF shared alloantigens, in particular B-F alloantigens, with syngeneic erythrocytes. Absorption with B ² B ² RSV-infected CEF significantly lowered the titer of B ² B ² anti-B ⁵ B ⁵ alloantisera. Cross-reactivity between B ₅ antigen(s) and tumor-associated antigen was suggested and the nature of the cross-reactivity was discussed. It is hypothesized that this cross-reactivity prevents B ⁵ B ⁵ chickens from recognizing RSV-induced tumors as foreign, enhances tumor growth and leads to death of the host.     

Transfer of agammaglobulinemia in the chicken. I. Generation of suppressor activity by injection of bursa cells

Spleen cells from adult agammaglobulinemic (bursectomized) chickens taken 1 to 3 weeks after an injection of histocompatible bursa cells can inhibit the adoptive antibody response to B. abortus of normal spleen or bursa cells in irradiated recipients. Spleen cells from Aγ chickens not injected with bursa cells generally do not. Moreover, bursectomized chickens which have been reconstituted with spleen cells within the first week after hatching do not respond with suppressor cell formation upon bursa cell injection. This apparent “autoimmunization” with bursa cells induces suppressor T cells which are only minimally sensitive to treatment with mitomycin C or to 5000 R γ irradiation. The suppressor activity is neither induced nor potentiated by concanavalin A in vivo. It is much stronger in spleen than in thymus cells and appears to be macrophage independent and to require intact cells. The cell component which stimulates the suppressor activity is more pronounced on bursa than on spleen cells, and is at most present to a very limited extent on bone marrow, thymus, or peritoneal exudate cells. It is better represented in comparable cell numbers of Day 17 than of Day 14 embryonic bursa. The inducing cell component is present in the membrane fraction of disrupted bursa cells. Immunization with bursa cells from B locus histoincompatible chickens leads to suppressor activity against histocompatible bursa cells. Although the removal of Ig-bearing cells from bursa greatly diminishes its immunizing capacity, injection of serum IgM and IgG does not induce suppressor cells. It is suggested that tolerance to a B-cell antigen is lacking in adult Aγ chickens, resulting in an autoimmune response upon exposure to B cells. The B-cell antigen may be a cell surface-specific form of Ig, a complex of Ig and a membrane component, or a differentiation antigen which appears simultaneously with Ig during ontogeny.     

The <Emphasis Type="Italic">ABI2</Emphasis>-dependent abscisic acid signalling controls HrpN-induced drought tolerance in <Emphasis Type="Italic">Arabidopsis</Emphasis>

HrpN, a protein produced by the plant pathogenic bacterium Erwinia amylovora, has been shown to stimulate plant growth and resistance to pathogens and insects. Here we report that HrpN activates abscisic acid (ABA) signalling to induce drought tolerance (DT) in Arabidopsis thaliana L. plants grown with water stress. Spraying wild-type plants with HrpN-promoted stomatal closure decreased leaf transpiration rate, increased moisture and proline levels in leaves, and alleviated extents of damage to cell membranes and plant drought symptoms caused by water deficiency. In plants treated with HrpN, ABA levels increased; expression of several ABA-signalling regulatory genes and the important effector gene rd29B was induced or enhanced. Induced expression of rd29B, promotion of stomatal closure, and reduction in drought severity were observed in the abi1-1 mutant, which has a defect in the phosphatase ABI1, after HrpN was applied. In contrast, HrpN failed to induce these responses in the abi2-1 mutant, which is impaired in the phosphatase ABI2. Inhibiting wild-type plants to synthesize ABA eliminated the role of HrpN in promoting stomatal closure and reducing drought severity. Moreover, resistance to Pseudomonas syringae developed in abi2-1 as in wild-type plants following treatment with HrpN. Thus, an ABI2-dependent ABA signalling pathway is responsible for the induction of DT but does not affect pathogen defence under the circumstances of this study.Hong-Ping Dong and Haiqin Yu contributed equally to this study and are regarded as joint first authors.     

滑液囊支原体不同感染途径的致病力比较

【背景】自2010年以来,我国鸡群中滑液囊支原体(Mycoplasma synoviae,MS)的感染率不断增高,目前MS已广泛存在于我国不同的鸡群中,包括蛋鸡、种鸡、白羽肉鸡和地方品种鸡等,其血清阳性率已超过40%,严重危害我国养鸡业,并造成了严重的经济损失。【目的】系统比较MS以不同感染途径对56日龄无特定病原体(Specific Pathogen Free,SPF)鸡的致病力。【方法】采用MS强毒FZ株以点眼、爪垫注射、胸部皮下注射、单次气管注射、连续3次气管注射等不同途径感染56日龄SPF鸡,观察感染后临床症状和解剖病理变化,检测感染后血清中的MS抗体,并且对气管组织进行病原再分离和组织病理学观察。【结果】MS的FZ株以不同途径感染SPF鸡后临床表现和发病率差异较大,爪垫注射和胸部皮下注射可导致100%的鸡发生爪垫肿大或胸部囊肿,而单次或连续3次气管注射可引起33%-50%的鸡发生严重气囊炎,点眼感染途径基本不能引起临床病理变化;爪垫肿大主要为肉芽组织增生和出现大量的黄色干酪样块状物质,胸部囊肿在囊肿部位有大量的血红色样液体和黄色干酪样块状物质;组织病理学结果显示连续3次气管注射方式感染更易对气管造成损伤,表现为气管黏膜固有层/黏膜下层发生轻微至轻度灶性炎细胞浸润,而爪垫肿大和胸部囊肿组织有大量的纤维组织和血管增生,同时伴有大量炎性细胞浸润;点眼和气管注射途径的气管MS病原再分离率可达100%,而胸部皮下注射或脚垫注射也可从气管中分离到MS病原;爪垫注射途径更易引起MS抗体转阳。【结论】系统比较了MS以不同感染途径对56日龄SPF鸡的致病性,并筛选出了相应的评价指征,成功建立了MS人工感染8周龄SPF鸡的发病模型,其中点眼感染途径和气管注射途径以气管病原再分离作为主要指征,辅以气囊炎进行评价,而胸部皮下注射和爪垫注射途径分别以胸部囊肿和爪垫肿胀作为主要病理指征进行评价。     

siRNA介导的ERA1表达下调对拟南芥抗旱性的影响

ERA1是控制植物气孔开闭的一个重要基因,根据其保守域构建RNA干扰(RNAi)载体并转化拟南芥,考察转基因植株的生长、气孔导度、离体叶片失水率以及ERA1和相关基因表达,探讨siRNA介导的ERA1表达下调对拟南芥抗旱性的影响。结果表明:转基因拟南芥株系中ERA1的表达受到明显抑制,其离体叶片失水率低于野生型,但并未出现ERA1缺失突变体的负面生长表型;转基因株系对ABA处理比野生型更敏感,其ABA处理株的根长显著变短,气孔孔径更小;转基因株ABI1、ABI2、ATHB6的表达量降低,而RAB18、RD29B、ADH1的表达量升高,siRNA介导的ERA1表达下调可能会激活RAB18、RD29B等逆境响应元件。研究发现,采用RNAi技术可以有效下调ERA1表达,在没有过多负面生长表型的前提下提高拟南芥的抗旱性,且ERA1表达下调可能通过ABA途径正面影响拟南芥的抗旱性。     

The distinct effects of a butanol fraction of <Emphasis Type="Italic">Bidens pilosa</Emphasis> plant extract on the development of Th1-mediated diabetes and Th2-mediated airway inflammation in mice

Bidens pilosa is claimed to be useful for immune or anti-inflammatory disorders; however, little scientific evidence has been published concerning its function. In this paper, immune disease mouse models were used to study the function of a butanol fraction of B.pilosa. We demonstrated treatment with the butanol fraction of B.pilosa ameliorated Th1 cell-mediated autoimmune diabetes in nonobese diabetic (NOD) mice but caused deterioration of Th2 cell-mediated airway inflammation induced by ovalbumin (OVA) in BALB/c mice. We next showed that Th2 cytokines (IL-4 and/or IL-5) increased but Th1 cytokine (IFN-) decreased following injections with the butanol fraction of B.pilosa in both mouse strains. Accordingly, Th2 cytokine-regulated IgE production in mouse serum increased following treatment with this fraction. Finally, we found that the butanol fraction of B.pilosa inhibited Th1 cell differentiation but promoted Th2 cell differentiation. Taken together, the butanol fraction of B.pilosa has a dichotomous effect on helper T cell-mediated immune disorders, plausibly via modulation of T cell differentiation.     

T cell tolerance in the chicken. I. Parameters affecting tolerance induction to human gamma-globulin in agammaglobulinemic and normal chickens.

T cell-mediated delayed hypersensitivity (DH) to human gamma-globulin (HGG) can be induced in chickens by subcutaneous injection of the antigen in complete Freund's adjuvant (CFA). In the present work, it has been demonstrated that specific tolerance of the cells mediating this DH can readily be induced in both normal and bursectomized (BX) FP strain chickens by simple i.v. injection of soluble antigen, regardless of the presence of antibody production to the tolerogen. A significant degree of tolerance at the DH and helper T cell levels could be generated in BX birds by injection of as little as 0.5 mg of HGG; such a dose only induced tolerance in normal birds when it had been previously deagregated by ultracentrifugation. Regular, nondeaggregated antigen could produce tolerance in normal animals, but only at doses of greater than 5 mg. The tolerizing injection induced a primary antibody response in normal birds in all cases, but a secondary response could not be obtained in animals rendered tolerant at the T cell level. Establishment of tolerance appeared to be very rapid, and animals remained refractory to induction of DH for at least 3 weeks after the tolerizing injection. The mode in which the antigen was presented to the animals appeared to be crucial in determining whether tolerance or sensitivity would be established.     

A predictive model for the growth rate of Bacillus cereus in broth by response surface methodology

A response surface methodology (RSM) was developed for predicting the growth rate of Bacillus cereus in a tryptic soy broth medium as a function of temperature (10 to 40°C), pH (5.5 to 8.5), and the NaCl concentration (0 to 8%). The primary model showed a good fit (r² = 0.920 to 0.999) to a Gompertz equation to obtain growth rates each condition. The quadratic polynomial model was found to be significant (p < 0.0001) and predicted values were found to be in good agreement with experimental values (R² value of 0.9486). The evaluation of RSM for describing the growth rate of B. cereus used the bias factor (B_f) and the accuracy factor (A_f). Both the B_f value (1.11) and the A_f value (1.50) were within acceptable ranges. This model was provided an efficient and accurate method for predicting the growth of B. cereus as a function of the controlling factors.     

Immunosuppression in experimental cryptococcosis in rats

Using a rat model, we have previously demonstrated that infection with Cryptococcus neoformans can trigger the production of a series of suppressor cells that specifically inhibit the cell-mediated immune response to a non-related antigen, human serum albumin (HSA), that has been injected 7 days after the infection. We previously determined that the cryptococcal infection induces afferent suppressor or suppressor induction cells (Ts₁) to HSA. The primary objective of the present study was to investigate the suppressor cells involved in the efferent phase of delayed-type hypersensitivity (DTH) response to HSA in rats infected with C. neoformans and immunized with the non-related antigen and determine the role that the Ts₁ cell plays in the induction of that cell. For this purpose, the spleen mononuclear (SpM) cells containing the Ts₁ or SpM cells from immunized non-infected rats (used as donor controls) were transferred to two groups of syngeneic naive recipients (first recipients). Later, the SpM cells from both groups of animals were transferred to rats immunized with HSA (second recipients). The efferent limb of the DTH response to HSA was suppressed in the recipients that received SpM cells from donors injected with Ts₁ cells. Additional HSA antigen was not required for induction of these efferent suppressor cells. Furthermore, we here show that these cells are resistant to treatment with cyclophosphamide (Cy), and that they can activate another suppressor population. The latter are Cy sensitive and are present in the immune recipient.     

Protective effect of nicotinamide on neuronal cells under oxygen and glucose deprivation and hypoxia/reoxygenation

Nicotinamide (vitamin B₃) reduces the infarct volume following focal cerebral ischemia in rats; however, its mechanism of action has not been reported. After cerebral ischemia and/or reperfusion, reactive oxygen species (ROS) and reactive nitrogen species may be generated by inflammatory cells through several cellular pathways, which can lead to intracellular calcium influx and cell damage. Therefore, we investigated the mechanisms of action of nicotinamide in neuroprotection under conditions of hypoxia/reoxygenation. Results showed that nicotinamide significantly protected rat primary cortical cells from hypoxia by reducing lactate dehydrogenase release with 1 h of oxygen-glucose deprivation (OGD) stress. ROS production and calcium influx in neuronal cells during OGD were dose-dependently diminished by up to 10 mM nicotinamide (p<0.01). This effect was further examined with OGD/reoxygenation (H/R). Cells were stained with the fluorescent dye 4,6-diamidino-2-phenylindole (DAPI) or antibodies against anti-microtubule-associated protein-2 and cleaved caspase-3. Apoptotic cells were studied using Western blotting of cytochrome c and cleaved caspase-3. Results showed that vitamin B₃ reduced cell injury, caspase-3 cleavage and nuclear condensation (DAPI staining) in neuronal cells under H/R. In addition, nicotinamide diminished c-fos andzif268 immediate-early gene expressions following OGD. Taken together, these results indicate that the neuroprotective effect of nicotinamide might occur through these mechanisms in this in vitro ischemia/reperfusion model.     

High tolerance to abiotic stressors and invasion success of the slow growing freshwater snail, Melanoides tuberculatus

Considerable research has been conducted to determine traits common to invasive species with the goal of predicting, preventing, or managing invasions. The importance of physiological tolerance to abiotic stressors in the ability of invasive species to establish and displace native species has been hypothesized to be important although there are few actual tests of the hypothesis in the literature. In freshwater molluscs it has been suggested that high fecundity is the most important trait for invasion success and that physiological tolerance to abiotic conditions is unlikely to play a significant role. We examined the tolerance to abiotic stressors using a known invasive snail species (Melanoides tuberculatus) that has a much slower growth rate and fecundity than a native species it has displaced (Biomphalaria glabrata). We tested the hypothesis that M. tuberculatus would have significantly greater tolerance to natural and anthropogenic abiotic stressors (cadmium, malathion, temperature extremes, and desiccation) which may provide a mechanism for displacement of B. glabrata. A time-to-event analysis was used to determine relative tolerance between species. M. tuberculatus was significantly more tolerant to the tested abiotic stressors than B. glabrata with the exception of low temperature (5°C). Stress tolerance may partly explain the ability of M. tuberculatus to displace B. glabrata despite having a much lower growth rate and fecundity. These results also suggest that M. tuberculatus is likely to have a strong advantage in disturbed or polluted habitats. Identifying those traits most important for the invasion success of particular species could be used to better inform removal strategies and may allow for improved predictions of invasion potential.     

Effect of copper nanoparticles administered in ovo on the activity of proliferating cells and on the resistance of femoral bones in broiler chickens

The objective of this study was to evaluate bone resistance after in ovo administration of copper nanoparticles (NanoCu) and to determine the number of cells positive for proliferating cell nuclear antigen (PCNA) in the femoral bones of broiler chickens (n = 12 per group). The study demonstrated that femoral bones from the NanoCu group were characterised by a higher weight and volume and by significantly greater resistance to fractures compared to the Control group. NanoCu promoted the proliferation of PCNA-positive cells in the long bones of chickens. A significantly higher number of PCNA-positive cells in the bones of birds in the NanoCu group compared with the Control group (137 and 122, respectively) indicate a stimulatory effect during embryogenesis. Considering the improvement in bone resistance to fractures and the effect of NanoCu on the number of PCNA-positive cells in femoral bones, NanoCu may be an alternative agent to minimise the ever-present problem of weak bones in broiler chickens.     

Vitamin B12 transport in Escherichia coli K12 does not require the btuE gene of the btuCED operon

Summary Transport of vitamin B₁₂ across the cytoplamic membrane ofEscherichia coli requires the products ofbtuC andbtuD, two genes in thebtuCED operon. The role ofbtuE, the central gene of this operon, was examined. Deletions withinbtuE were constructed by removal of internal restriction fragments and were crossed onto the chromosome by allelic replacement. In-frame deletions that removed 20% or 82% of thebtuE coding region did not affect expression of the distalbtuD gene. These nonpolar deletions had little effect on vitamin B₁₂ binding (whole cells or periplasmic fraction) and transport. They did not affect the utilization of vitamin B₁₂ or other cobalamins for methionine biosynthesis, even in strains with decreased outer membrane transport of vitamin B₁₂. ThebtuE mutations did not impair adenosyl-cobalamin dependent catabolism of ethanolamine or repression ofbtuB expression. Thus, despite its genetic location in the transport operon, thebtuE product plays no essential role in vitamin B₁₂ transport.