Prostaglandin E2 promotes IL-4-induced IgE and IgG1 synthesis

PG of the E series are generally known to suppress immune responses, however, we have found that PGE synergizes with IL-4 to induce IgE and IgG1 production in LPS-stimulated murine B lymphocytes. PGE2 and PGE1 (10(-6) to 10(-8) M) significantly increase IgE and IgG1 production (up to 26-fold) at all concentrations of IL-4 tested. In addition to its effects on IgE and IgG1, PGE also causes a significant decrease in IgM and IgG3 synthesis, suggesting that PGE may promote IL-4-induced class switching. The specificity of the E series PG effect is demonstrated by the fact that PGF2 alpha (10(-6) M) does not alter production of any of these isotypes. Because PGE can mediate its effects through cAMP in some cases, we investigated the importance of cAMP levels in regulation of isotype expression. Other agents that increase intracellular cAMP levels (cholera toxin and dibutyryl cAMP) were assessed for their ability to regulate isotype differentiation. Cholera toxin (100 pg/ml) and dibutyryl cAMP (100 microM) significantly enhanced IgE and IgG1 production and diminished IgM and IgG3 synthesis. We also show that PGE and cholera toxin elevate intracellular cAMP in B lymphocytes in a dose-dependent manner. In contrast, PGF2 alpha (10(-6) M) and the B subunit of cholera toxin (100 pg/ml) did not increase cAMP and did not regulate the isotype of Ig produced, reiterating the importance of cAMP in enhancing isotype differentiation. Although PGE is known to inhibit a number of immune responses, our data show that it is not always inhibitory. PGE may play a role in atopy in vivo where PGE-secreting cells such as macrophages, follicular dendritic cells, and fibroblasts can promote IgE synthesis. This research emphasizes the importance of PGE in regulation of the humoral immune response and adds a new stimulatory action to the repertoire of known PGE effects.     

IL-4 is required for the IgE and IgG1 increase and IgG1 autoantibody formation in mice treated with mercuric chloride

Previous studies have established that in susceptible mouse strains, such as A.SW (H-2s), repeated injections of subtoxic doses of HgCl2 induce increased serum levels of total IgE and IgG1, high serum titers of antinuclear autoantibodies (ANo1A), and immune-complex glomerulonephritis. Moreover, it has been shown that susceptibility is determined by H-2As and that Th cells are required for the induction of these immunopathologic alterations by HgCl2. In the present study we showed that treatment in vivo with anti-IL-4 mAb completely abrogated the HgCl2-induced increase in total IgE and partially inhibited the increase in IgG1, but failed to suppress the increase in IgG2A. Furthermore, we showed that IL-4 influences the pattern of IgG subclass distribution among ANo1A of HgCl2-treated mice. Whereas treatment with anti-IL-4 mAb significantly reduced the titers of IgG1 ANolA, it increased those of IgG2A, IgG2B, and IgG3 ANolA. Thus, these results show that IL-4 contributes to the optimal formation in vivo of murine IgG1 and that it is involved in the autoantibody formation of a systemic autoimmune disease. The available evidence suggests that HgCl2 induces an increased production of IL-4 by Th2 cells. If this is correct, it implies that MHC class II alleles determine whether the preferential response to HgCl2 is made by Th1 or Th2 cells and, hence, the type of immunopathologic alterations ensuing.     

T help requirements for the generation of an in vivo IgE response: a late acting form of T cell help other than IL-4 is required for IgE but not for IgG1 production

To further define requirements for T cell help in the stimulation of an in vivo IgE response, we studied a system in which the injection of mice with a goat antibody to mouse IgD (GaMD) stimulates large polyclonal IgG1 and IgE responses. In this system, both responses are blocked by anti-CD4 antibody, but only the IgE response is blocked by (anti-IL-4) antibody. Anti-CD4 antibody, if injected 5 days after GaMD, was found to inhibit the GaMD-induced IgE response to a much greater extent than the IgG1 response, even though both responses occur simultaneously and are inhibited to an equal extent by optimal or suboptimal doses of anti-CD4 antibody administered 2 days after GaMD. Even a suboptimal, 50-micrograms dose of anti-CD4 antibody, when injected 5 days after GaMD, inhibited the IgE response to a much greater extent than did an optimal 10-mg dose of anti-IL-4 antibody injected at the same time, even though 10 mg of anti-IL-4 antibody more completely inhibited GaMD-induced IgE production than did 50 micrograms of anti-CD4 antibody when injected 2 days after GaMD. These observations provide evidence that a late acting form of T cell help other than IL-4 is important for the generation of an IgE response but not an IgG1 response in GaMD-immunized mice.     

IL-4 and T cells are required for the generation of IgG1 isotype antibodies against cardiolipin

Infection with Mycobacterium tuberculosis induces Abs against a vast array of mycobacterial lipids and glycolipids. One of the most prominent lipid Ags recognized is cardiolipin (CL). The kinetics of the generation of anti-CL Abs during infection reveals that IgM titers to CL increase over time. Interestingly, at day 30 postinfection CL-specific IgG1 appears, an isotype usually dependent on T cell help. Using an immunization schedule with CL/anti-CL Ab complexes, which induces antiphospholipid syndrome in mice, we show that the generation of IgG1 to CL requires IL-4 and that optimal production is T cell dependent. IgG1 production to CL was impaired in nude (nu/nu) mice devoid in conventional T cells, but was not affected in mice deficient for either alphabeta TCR(+), gammadelta TCR(+), CD4(+), CD8(+), or NK1.1(+) T cells. We conclude that IgG1 production to CL depends on T cell help and IL-4, which can be provided by different T cell populations. This is the first report that IL-4 is indispensable for the induction of IgG1 Abs to lipid Ags.     

IL-5-Induced Eosinophils Suppress the Growth of Leishmania amazonensis In Vivo and Kill Promastigotes In Vitro in Response to Either IL-4 or IFN-gamma

In IL-5 transgenic mice (C3H/HeN-TgN(IL-5)-Imeg), in which 50% of peripheral blood leukocytes are eosinophils, the development of infection by Leishmania amazonensis was clearly suppressed. To determine mechanistically how this protozoan parasite is killed, we performed in vitro killing experiments. Either IL-4 or IFN-gamma effectively stimulated eosinophils to kill Leishmania amazonensis promastigotes, and most of the killing was inhibited by catalase but not by the NO inhibitor L-N5-(1-iminoethyl)-ornithine, suggesting that hydrogen peroxide is responsible for the killing of L. amazonensis by eosinophils. There was no significant degranulation of eosinophils in the culture, because eosinophil peroxidase was not detected in culture supernatants when L. amazonensis promastigotes were killed by activated eosinophils. Such resistance was also observed in BALB/c mice, which are highly susceptible to L. amazonensis. Expression plasmids for IL-4, IL-5, and IFN-gamma were transferred into muscle by electroporation in vivo starting 1 week before infection. Expression plasmid for IL-5 was most effective in slowing the development of infection among three expression plasmids. Expression plasmid for IL-4 was slightly effective and that for IFN-gamma had no effect on the progress of disease. These results suggest that IL-5 gene transfer into muscle by electroporation is useful as a supplementary protection method against L. amazonensis infection.     

Mutagenesis of the Aquaporin 4 Extracellular Domains Defines Restricted Binding Patterns of Pathogenic Neuromyelitis Optica IgG

Neuromyelitis optica-immunoglobulin G (NMO-IgG) binds to aquaporin-4 (AQP4) water channels in the central nervous system leading to immune-mediated injury. We have previously demonstrated that a high proportion of CSF plasma cells of NMO patients produce antibody to the extracellular domains of the AQP4 protein and that recombinant IgG (rAb) derived from these cells recapitulate pathogenic features of disease. We performed a comprehensive mutational analysis of the three extracellular loops of the M23 isoform of human AQP4 using both serial and single point mutations, and we evaluated the effects on binding of NMO AQP4-reactive rAbs by quantitative immunofluorescence. Whereas all NMO rAbs required conserved loop C (¹³⁷TP¹³⁸ and Val¹⁵⁰) and loop E (²³⁰HW²³¹) amino acids for binding, two broad patterns of NMO-IgG recognition could be distinguished based on differential sensitivity to loop A amino acid changes. Pattern 1 NMO rAbs were insensitive to loop A mutations and could be further discriminated by differential sensitivity to amino acid changes in loop C (¹⁴⁸TM¹⁴⁹ and His¹⁵¹) and loop E (Asn²²⁶ and Glu²²⁸). Alternatively, pattern 2 NMO rAbs showed significantly reduced binding following amino acid changes in loop A (⁶³EKP⁶⁵ and Asp⁶⁹) and loop C (Val¹⁴¹, His¹⁵¹, and Leu¹⁵⁴). Amino acid substitutions at ¹³⁷TP¹³⁸ altered loop C conformation and abolished the binding of all NMO rAbs and NMO-IgG, indicating the global importance of loop C conformation to the recognition of AQP4 by pathogenic NMO Abs. The generation of human NMO rAbs has allowed the first high resolution mapping of extracellular loop amino acids critical for NMO-IgG binding and identified regions of AQP4 extracellular structure that may represent prime targets for drug therapy.     

IL-4 induces co-expression of intrinsic membrane IgG1 and IgE by murine B cells stimulated with lipopolysaccharide

IL-4 promotes IgG1 and IgE secretion by murine B cells stimulated with bacterial LPS. We show that stimulation of unprimed resting splenic B cells with LPS and 10(4) U/ml rIL-4 results in the expression of membrane (m) IgG1 and mIgE on 40 to 50% and 15 to 25% of the total B cell population, respectively, on day 4 of culture. The possibility of a significant contribution to cell surface staining by cytophilic, secreted Ig isotypes was eliminated by either the addition of anti-Fc gamma or anti-Fc epsilon R mAb during the culture or by acid treatment before staining. A similar proportion of IgE-expressing B cells are also found, after stimulation with LPS and 10(4) U/ml IL-4, by cytoplasmic staining using fluorescence microscopy. Cell sorting analysis further indicates that B cell populations that express mIgG1 and mIgE secrete these respective Ig isotypes. In addition, such cells show striking diminution in IgM secretion compared to mIgG1- or mIgE- sorted B cells. Stimulation with LPS and IL-4 (10(4) U/ml) induces co-expression of mIgG1 and mIgE on LPS-stimulated B cells; up to 75% of mIgE+ B cells co-express mIgG1 and up to 19% of mIgG1+ B cells express mIgE. This striking co-expression of mIgG1 and mIgE is mirrored by the co-expression of mIgG1 with mIgG3 and mIgG2b by B cells stimulated with LPS and 200 U/ml IL-4. Cell sorting analysis demonstrates that the B cell population that co-expresses mIgG1 and mIgE secretes both IgG1 and IgE. However, "two-color" cytoplasmic staining fails to demonstrate any B cells that simultaneously secrete both IgG1 and IgE.     

The Extracellular Domain of Lrp5/6 Inhibits Noncanonical Wnt Signaling In Vivo

Lrp5/6 are crucial coreceptors for Wnt/β-catenin signaling, a pathway biochemically distinct from noncanonical Wnt signaling pathways. Here, we examined the possible participation of Lrp5/6 in noncanonical Wnt signaling. We found that Lrp6 physically interacts with Wnt5a, but that this does not lead to phosphorylation of Lrp6 or activation of the Wnt/β-catenin pathway. Overexpression of Lrp6 blocks activation of the Wnt5a downstream target Rac1, and this effect is dependent on intact Lrp6 extracellular domains. These results suggested that the extracellular domain of Lrp6 inhibits noncanonical Wnt signaling in vitro. In vivo, Lrp6−/− mice exhibited exencephaly and a heart phenotype. Surprisingly, these defects were rescued by deletion of Wnt5a, indicating that the phenotypes resulted from noncanonical Wnt gain-of-function. Similarly, Lrp5 and Lrp6 antisense morpholino-treated Xenopus embryos exhibited convergent extension and heart phenotypes that were rescued by knockdown of noncanonical XWnt5a and XWnt11. Thus, we provide evidence that the extracellular domains of Lrp5/6 behave as physiologically relevant inhibitors of noncanonical Wnt signaling during Xenopus and mouse development in vivo.     

Down-Regulation of Neuregulin1/ErbB4 Signaling in the Hippocampus Is Critical for Learning and Memory

Hippocampal function is important for learning and memory, and dysfunction of the hippocampus has been linked to the pathophysiology of neuropsychiatric diseases such as schizophrenia. Neuregulin1 (NRG1) and ErbB4, two susceptibility genes for schizophrenia, reportedly modulate long-term potentiation (LTP) at hippocampal Schaffer collateral (SC)-CA1 synapses. However, little is known regarding the contribution of hippocampal NRG1/ErbB4 signaling to learning and memory function. Here, quantitative real-time PCR and Western blotting were used to assess the mRNA and protein levels of NRG1 and ErbB4. Pharmacological and genetic approaches were used to manipulate NRG1/ErbB4 signaling, following which learning and memory behaviors were evaluated using the Morris water maze, Y-maze test, and the novel object recognition test. Spatial learning was found to reduce hippocampal NRG1 and ErbB4 expression. The blockade of NRG1/ErbB4 signaling in hippocampal CA1, either by neutralizing endogenous NRG1 or inhibiting/ablating ErbB4 receptor activity, enhanced hippocampus-dependent spatial learning, spatial working memory, and novel object recognition memory. Accordingly, administration of exogenous NRG1 impaired those functions. More importantly, the specific ablation of ErbB4 in parvalbumin interneurons also improved learning and memory performance. The manipulation of NRG1/ErbB4 signaling in the present study revealed that NRG1/ErbB4 activity in the hippocampus is critical for learning and memory. These findings might provide novel insights on the pathophysiological mechanisms of schizophrenia and a new target for the treatment of Alzheimer’s disease, which is characterized by a progressive decline in cognitive function.     

IL-2 Inhibited the Generation of CD4+ Memory T Cells

The survival of T cells at different stages of development is dependent on extrinsic signals. IL-7 is necessary for the development of memory T cells. IL-7 could induce and maintain the differentiation, survival, and proliferation of CD4⁺ memory T cells, and the roles of IL-2 and IL-15 in the generation of CD4⁺ memory T cells were still unclear. A CD4⁺ memory T cells in vitro generated system by adding IL-7. The phenotype of CD4⁺ memory T cells was identified by FACS. The cells proliferation was analyzed by CFSE staining. The involved signal pathways were analyzed by Western blot. We found that IL-2, not IL-15, could inhibit CD4⁺ memory T cells generation. Western blot showed that IL-7 up-regulated the P-STAT5A expression and down-regulated Bax expression, IL-2 reduced the effect of IL-7. Besides, IL-2-combined IL-7 up-regulated the P-AKT and Foxo3a expression a little. In conclusion, our data revealed the inhibitory role of IL-2 in CD4⁺ memory T cells generation and indicated that PI3K/AKT signal pathway was involved.     

The activity of soluble VCAM-1 in angiogenesis stimulated by IL-4 and IL-13

IL-13 is a multifunctional lymphokine sharing a number of biological properties with IL-4. We previously observed that IL-4 shows angiogenic activities in vitro as well as in vivo. In this study we examined the effect of IL-13 on angiogenesis in vitro and in vivo and also the underlying mechanisms. Human IL-13 significantly stimulated the formation of tube-like structures in collagen gels by human microvascular endothelial cells and bovine aortic endothelial cells by about 3-fold over the controls in the absence of the cytokines. Administration of murine IL-13 led to neovascularization when implanted in the rat cornea. Coadministration of neutralizing mAb to the IL-4R inhibited both tubular morphogenesis in vitro and activation of STAT6 induced by IL-4 or IL-13. Both IL-4 and IL-13 markedly increased mRNA levels of VCAM-1 in vascular endothelial cells, and the production of the soluble form of VCAM-1 was also stimulated in response to IL-4 or IL-13. Administration of anti-VCAM-1 Ab in vitro blocked tubular morphogenesis induced by IL-4 and IL-13. Angiogenesis induced in vivo in rat cornea by IL-4 and IL-13 was also inhibited by Ab against the rat alpha4 integrin subunit. These findings suggest that angiogenesis dependent on IL-4 and IL-13 is mainly mediated through a soluble VCAM-1/alpha4 integrin pathway.     

T regulatory-1 cells induce IgG4 production by B cells: role of IL-10

The study was aimed to find out whether T cells with a regulatory profile could regulate the secretion of IgG4. Using tetanus Ag we found that PBMC of healthy human donors responded to exogenous IL-10 by down-regulating IgG1 and increasing IgG4 secretion. IgE was not affected. To investigate the direct effect of IL-10-producing T cells on B cells, we generated T cell clones (TCC) with two different cytokine profiles: first, IL-10high, IL-2low, IL-4low TCC, and second, IL-10low, IL-2high, IL-4high. The T cell-dependent Ab secretion was measured by coculturing purified CD19+ B cells and the TCC. Interestingly, we found that IgG4 production in the coculture correlated with the TCC production of IL-10 (r2 = 0.352, p = 0.0001), but not with IL-2, IL-4, nor IFN-gamma. IgE showed only a trend with regard to IL-4. Further, there was decreased Ab secretion in the absence of T-B cell contact. IL-10 also induced IgG4 when added to a Th1 TCC-B cell coculture system. The present study thus shows that in T-B cell coculture, IL-10, if induced by the TCC or added to the system, down-regulates the immune response by inducing IgG4 secretion. This establishes a direct implication of IL-10 in humoral hyporesponsiveness, particularly in compartments where the T-B cell interplay determines the subsequent immune response. The correlation between IgG4 and IL-10 (r2 = 0.352) indicates that IL-10 is an important but not the only factor for IgG4 induction.     

Production of Polyclonal Antisera that Recognize and Distinguish Between the Extracellular Domains of Neuronal Nicotinic Acetylcholine Receptor Subunits

Abstract: Ligand-gated ion channels are oligomeric transmembrane proteins that usually contain more than one kind of monomer. The variety of monomers available to participate in oligomer formation and the apparent latitude in acceptable monomer combinations allows considerable diversity. Mechanisms for identifying the monomers comprising specific receptors are needed. We have generated affinity-purified polyclonal antisera that recognize the extracellular domain of nine neuronal nicotinic acetylcholine receptor (nAChR) subunits and distinguish between them. We prepared these antisera by immunizing rabbits with bacterially expressed recombinant protein representing the N-terminal extracellular domain of each neuronal nAChR subunit followed by affinity purification of antibodies against synthetic peptides corresponding to residues 68–81 of the α1 subunit. We demonstrate subunit specificity of each affinity-purified antisera by western blots of the bacterially expressed protein and immunoblot against peptide. We further used these antibodies to demonstrate expression of neuronal nAChR subunits on the surface of transiently transfected simian kidney (COS-7) cells.