The immune response modifier resiquimod mimics CD40-induced B cell activation

In-vitro Modulation of mTOR-HIF-1α Axis by TLR7/8 Agonist (Resiquimod) in B-Chronic Lymphocytic Leukemia

Targeting toll-like receptors (TLRs), via TLR agonists, has been implicated in the regulation of immunometabolism. B-chronic lymphocytic leukemia (B-CLL) represents a suitable model for B-cell derived malignancies with shifted metabolic adaptations. Several signaling pathways have been found to be critical in metabolic reprogramming of CLL, including mechanistic target of rapamycin- hypoxia inducible factor-1α (mTOR- HIF-1α) pathway, the main metabolic regulator of glycolysis. Here, we investigated the effect of TLR7/8 agonist (Resiquimod) on the expression of mTOR and HIF-1α in patients with CLL. B cells were purified using Rosettesep Human B cell Enrichment Cocktail (Stem cell Technologies, Vancouver, BC, Canada#15,024) from peripheral venous blood of CLL patients (n = 20) and healthy individuals (n = 15). Isolated B cells were then cultured in both presence and absence of Resiquimod. Gene expression of mTOR and HIF-1α were assessed using qRT-PCR. Resiquimod significantly decreased mTOR and HIF-1α gene expression in both CLL (p < 0.001and p < 0.001, respectively) and Normal B cells (p = 0.004 and p = 0.001, respectively). Resiquimod may reprogram immunometabolism of malignant B-CLL cells via down-regulation of key glycolytic metabolic actors, mTOR and HIF-1α genes. Accordingly, Resiquimod may be an adjuvant as a therapeutic tool for CLL, which needs to be studied further.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-023-01649-y.

TLR7/TLR8 activation and susceptibility genes synergize to breach gut barrier in a mouse model of lupus

Background

Mounting evidence suggests that increased gut permeability, or leaky gut, and the resulting translocation of pathobionts or their metabolites contributes to the pathogenesis of Systemic Lupus Erythematosus. However, the mechanisms underlying the induction of gut leakage remain unclear. In this study, we examined the effect of a treatment with a TLR7/8 agonist in the B6.Sle1.Sle2.Sle3 triple congenic (TC) mouse, a spontaneous mouse model of lupus without gut leakage.

Materials and methods

Lupus-prone mice (TC), TC.Rag1-/- mice that lack B and T cells, and congenic B6 healthy controls were treated with R848. Gut barrier integrity was assessed by measuring FITC-dextran in the serum following oral gavage. Claudin-1 and PECAM1 expression as well as the extent of CD45+ immune cells, B220+ B cells, CD3+ T cells and CD11b+ myeloid cells were measured in the ileum by immunofluorescence. NKp46+ cells were measured in the ileum and colon by immunofluorescence. Immune cells in the ileum were also analyzed by flow cytometry.

Results

R848 decreased gut barrier integrity in TC but not in congenic control B6 mice. Immunofluorescence staining of the ileum showed a reduced expression of the tight junction protein Claudin-1, endothelial cell tight junction PECAM1, as well as an increased infiltration of immune cells, including B cells and CD11b+ cells, in R848-treated TC as compared to untreated control mice. However, NKp46+ cells which play critical role in maintaining gut barrier integrity, had a lower frequency in treated TC mice. Flow cytometry showed an increased frequency of plasma cells, dendritic cells and macrophages along with a decreased frequency of NK cells in R848 treated TC mice lamina propria. In addition, we showed that the R848 treatment did not induce gut leakage in TC.Rag1-/- mice that lack mature T and B cells.

Conclusions

These results demonstrate that TLR7/8 activation induces a leaky gut in lupus-prone mice, which is mediated by adaptive immune responses. TLR7/8 activation is however not sufficient to breach gut barrier integrity in non-autoimmune mice.

Role of B cells as antigen presenting cells

B cells have been long studied for their role and function in the humoral immune system. Apart from generating antibodies and an antibody-mediated memory response against pathogens, B cells are also capable of generating cell-mediated immunity. It has been demonstrated by several groups that B cells can activate antigen-specific CD4 and CD8 T cells, and can have regulatory and cytotoxic effects. The function of B cells as professional antigen presenting cells (APCs) to activate T cells has been largely understudied. This, however, requires attention as several recent reports have demonstrated the importance of B cells within the tumor microenvironment, and B cells are increasingly being evaluated as cellular therapies. Antigen presentation through B cells can be through antigen-specific (B cell receptor (BCR) dependent) or antigen non-specific (BCR independent) mechanisms and can be modulated by a variety of intrinsic and external factors. This review will discuss the pathways and mechanisms by which B cells present antigens, and how B cells differ from other professional APCs.

Evolution of Toll-like receptor 7/8 agonist therapeutics and their delivery approaches: From antiviral formulations to vaccine adjuvants

Imidazoquinoline derivatives (IMDs) and related compounds function as synthetic agonists of Toll-like receptors 7 and 8 (TLR7/8) and one is FDA approved for topical antiviral and skin cancer treatments. Nevertheless, these innate immune system-activating drugs have potentially much broader therapeutic utility; they have been pursued as antitumor immunomodulatory agents and more recently as candidate vaccine adjuvants for cancer and infectious disease. The broad expression profiles of TLR7/8, poor pharmacokinetic properties of IMDs, and toxicities associated with systemic administration, however, are formidable barriers to successful clinical translation. Herein, we review IMD formulations that have advanced to the clinic and discuss issues related to biodistribution and toxicity that have hampered the further development of these compounds. Recent strategies aimed at enhancing safety and efficacy, particularly through the use of bioconjugates and nanoparticle formulations that alter pharmacokinetics, biodistribution, and cellular targeting, are described. Finally, key aspects of the biology of TLR7 signaling, such as TLR7 tolerance, that may need to be considered in the development of new IMD therapeutics are discussed.

Sustained IL-4 priming of macrophages enhances the inflammatory response to TLR7/8 ligand R848

Macrophages (Mϕ) are highly plastic, and can acquire a variety of functional phenotypes depending on the presence of different stimuli in their local environment. Mφ stimulated by interleukin (IL)-4 induce an alternative activation state and function as anti-inflammatory cells and promote tissue repair. However, there is overwhelming evidence that IL-4 can play a role in promoting inflammation. In asthma and allergic inflammation, IL-4 mediates proinflammatory responses that lead to tissue damage. Thus the effect of IL-4 on the outcome of the immune responses is greatly influenced by other cofactors and cytokines present in the microenvironment. R848 (resiquimod), a TLR7/8 agonist is a novel vaccine adjuvant, triggering a strong Th1-skewed response but its efficacy as a vaccine adjuvant shows variable results. It is not currently known whether the presence of IL-4 can dampen or enhance immunity in response to TLR7 agonists. In the present study, we sought to investigate the impact of IL-4-induced Mφ polarization on the outcome of R848 stimulation. The activation marker expression and production of cytokines were measured in murine spleen-derived Mφ. Protein expression levels of innate recognition molecules and transcription factors involved, including retinoic-acid inducible gene I, mitochondrial antiviral signaling protein, stimulator of interferon genes (STING), and IFN regulatory factors were evaluated in activated Mφ. These play a crucial role in the control of viral replication and optimal CD8+ T cell priming. We report that sustained priming with IL-4 alone promotes an antiviral response in Mφ, and enhances proinflammatory responses to R848 treatment. This highlights the need for better understanding of IL-4 proinflammatory functions and its potential use as a broad-acting antiviral in combination with R848 may be used in combination with other therapies to target the innate arm of immunity against emerging infections.

R848 Is Involved in the Antibacterial Immune Response of Golden Pompano (Trachinotus ovatus) Through TLR7/8-MyD88-NF-κB-Signaling Pathway

R848 is an imidazoquinoline compound that is a specific activator of toll-like receptor (TLR) 7/8 and is often used in immunological research in mammals and teleosts. However, the immune responses initiated by R848 through the TLR7/8 pathway in response to bacterial infection remain largely unexplored in teleosts. In the current study, we investigated the antibacterial response and the participating signaling pathway initiated by R848 in golden pompano (Trachinotus ovatus). We found that R848 could stimulate the proliferation of head kidney lymphocytes (HKLs) in a dose-dependent manner, enhance the survival rate of HKLs, and inhibit the replication of bacteria in vivo. However, these effects induced by R848 were significantly reduced when chloroquine (CQ) was used to blocked endosomal acidification. Additionally, an in vivo study showed that R848 strengthened the antibacterial immunity of fish through a TLR7/8 and Myd88-dependent signaling pathway. A cellular experiment showed that Pepinh-MYD (a Myd88 inhibitor) significantly reduced the R848-mediated proliferation and survival of HKLs. Luciferase activity analysis showed that R848 enhanced the nuclear factor kappa B (NF-κB) activity, whereas this activity was reduced when CQ and Pepinh-MYD were present. Additionally, when an NF-κB inhibitor was present, the R848-mediated pro-proliferative and pro-survival effects on HKLs were significantly diminished. An in vivo study showed that knockdown of TLR7, TLR8, and Myd88 expression in golden pompano via siRNA following injection of R848 resulted in increased bacterial dissemination and colonization in fish tissues compared to that of fish injection of R848 alone, suggesting that R848-induced antibacterial immunity was significantly reduced. In conclusion, these results indicate that R848 plays an essential role in the antibacterial immunity of golden pompano via the TLR7/8-Myd88-NF-κB- signaling pathway.

TLR7 in B cells promotes renal inflammation and Gd-IgA1 synthesis in IgA nephropathy

TLR7 has been linked to the pathogenesis of glomerulonephritis, but its precise roles are not clear. In this study, we evaluated the roles of TLR7 in IgA nephropathy (IgAN). TLR7 proteins were abundant in CD19+ B cells infiltrated in the kidneys of patients with IgAN. The intensities of both intrarenal TLR7 and CD19 proteins were closely associated with kidney function (estimated glomerular filtration rate [eGFR] and serum creatinine concentration) and renal histopathology (tubular atrophy, leukocyte infiltration, tubulointerstitial fibrosis, and global glomerulosclerosis) in patients with IgAN. Meanwhile, TLR7 mRNA levels were significantly increased in peripheral blood B cells of patients with IgAN. TLR7+CD19+ B cells expressed inflammatory cytokines (IL-6 and IL-12) in kidneys and produced high levels of IgA1 and galactose deficient-IgA1 (Gd-IgA1) in peripheral blood of patients with IgAN. Mechanistically, TLR7 activated B cells to produce high levels of Gd-IgA1 via the TLR7-GALNT2 axis in IgAN. Protein levels of GALNT2 were increased by overexpression of TLR7, while they were reduced by TLR7 knockdown in B cells. GALNT2 overexpression augmented Gd-IgA1 production in B cells derived from patients with IgAN. Taken together, high TLR7 expression in B cells has dual roles in the development and progression of IgAN, by facilitating renal inflammation and Gd-IgA1 antibody synthesis.

Polymer-Coated Gold Nanospheres Do Not Impair the Innate Immune Function of Human B Lymphocytes in Vitro

Gold nanoparticles (GNPs) are intended for use within a variety of biomedical applications due to their physicochemical properties. Although, in general, biocompatibility of GNPs with immune cells such as macrophages and dendritic cells is well established, the impact of GNPs on B lymphocyte immune function remains to be determined. Since B lymphocytes play an important role in health and disease, the suitability of GNPs as a B cell-targeting tool is of high relevance. Thus, we provide information on the interactions of GNPs with B lymphocytes. Herein, we exposed freshly isolated human B lymphocytes to a set of well-characterized and biomedically relevant GNPs with distinct surface (polyethylene glycol (PEG), PEG/poly(vinyl alcohol) (PEG/PVA)) and shape (spheres, rods) characteristics. Polymer-coated GNPs poorly interacted with B lymphocytes, in contrast to uncoated GNPs. Importantly, none of the GNPs significantly affected cell viability, even at the highest concentration of 20 μg/mL over a 24 h suspension exposure period. Furthermore, none of the nanosphere formulations affected the expression of activation markers (CD69, CD86, MHC II) of the naive B lymphocytes, nor did they cause an increase in the secretion of pro-inflammatory cytokines ( i.e. , IL-6, IL-1β). However, the absence of polymer coating on the sphere GNPs and the rod shape caused a decrease in IL-6 cytokine production by activated B lymphocytes, suggesting a functional impairment. With these findings, the present study contributes imperative knowledge toward the safe-by-design approaches being conducted to benefit the development of nanomaterials, specifically those as theranostic tools.

Effective cancer immunotherapy in mice by polyIC-imiquimod complexes and engineered magnetic nanoparticles

Encouraging results are emerging from systems that exploit Toll like receptor (TLR) signaling, nanotechnology, checkpoint inhibition and molecular imaging for cancer immunotherapy. A major remaining challenge is developing effective, durable and tumour-specific immune responses without systemic toxicity. Here, we report a simple and versatile system based on synergistic activation of immune responses and direct cancer cell killing by combined TLR ligation using polyIC as TLR3 and imiquimod (R837) as TLR7 agonist, in combination with the model antigen ovalbumin (OVA) and phospholipid micelles loaded with zinc-doped iron oxide magnetic nanoparticles (MNPs). The combination of TLR agonists triggered a strong innate immune response in the lymph nodes (LNs) without systemic release of pro-inflammatory cytokines. The vaccines showed excellent efficacy against aggressive B16-F10 melanoma cells expressing OVA, which was improved with immune checkpoint abrogation of the immunosuppressive programmed death-ligand 1 (PD-L1) at the level of the cancer cells. By magnetic resonance (MR) and nuclear imaging we could track the vaccine migration from the site of injection to LNs and tumour. Overall, we show this synergistic TLR agonists and their combination with MNPs and immune checkpoint blockade to have considerable potential for preclinical and clinical development of vaccines for cancer immunotherapy.

Synergy of purine-scaffold TLR7 agonist with doxorubicin on systemic inhibition of lymphoma in mouse model

Chemo- and radio-therapy suffer from certain well-recognized drawbacks for lymphoma therapy. Passive immunotherapy with monoclonal antibody has improved outcome for patients with CD20⁺ B cell lymphoma, but not for T cell lymphoma. Therefore, novel treatment approaches are clearly required for T cell lymphoma. To date, the combined application targeting TLR7, 8 and 9 has established long-term antitumor immunity. We previously synthesized a purine-scaffold TLR7 agonist named GD5. Here, we report that the intratumoral administration of GD5 combined with doxorubicin (DOX), a conventional chemotherapeutic agent in T cell lymphoma. This combined treatment made mice to produce more cytokines in blood, and generate more potent cytotoxic T lymphocyte response, then result in effective eradication of both local and distant tumors in tumor-bearing mice. Our findings demonstrate the potential for enhancing the efficacy of the current standard DOX therapy through combination with TLR7 agonist GD5 to improve antitumor immune responses and provide durable remissions for T cell lymphoma.

TLR7 Signaling Regulates Th17 Cells and Autoimmunity: Novel Potential for Autoimmune Therapy

Innate regulation through TLR signaling has been shown to be important for promoting T cell subset development and function. However, limited information is known about whether differential TLR signaling can selectively inhibit Th17 and/or Th1 cells, which are important for controlling excessive inflammation and autoimmune responses. In this article, we demonstrate that activation of TLR7 signaling in T cells can inhibit Th17 cell differentiation from naive T cells and IL-17 production in established Th17 cells. We further report that downregulation of STAT3 signaling is responsible for TLR7-mediated inhibition of Th17 cells due to induction of suppressor of cytokine signaling 3 and 5. TLR7-mediated suppression of Th17 cells does not require dendritic cell involvement. In addition, we show that TLR7 signaling can suppress Th1 cell development and function through a mechanism different from Th17 cell suppression. Importantly, our complementary in vivo studies demonstrate that treatment with the TLR7 ligand imiquimod can inhibit Th1 and Th17 cells, resulting in the prevention of, and an immunotherapeutic reduction in, experimental autoimmune encephalomyelitis. These studies identify a new strategy to manipulate Th17/Th1 cells through TLR7 signaling, with important implications for successful immunotherapy against autoimmune and inflammatory diseases.

Degradation of acetalated dextran can be broadly tuned based on cyclic acetal coverage and molecular weight

Microparticles (MPs) derived from acid-sensitive biopolymers enable rapid degradation and cargo release under acidic conditions, such as at tumor microenvironments, within lysosomal/phagosomal compartments inside phagocytic cells, or at sites of inflammation. One such acid-sensitive biopolymer, acetalated dextran (Ace-DEX), has tunable degradation rates and pH-neutral degradation byproducts consisting of dextran, acetone, and ethanol. By studying the degradation profiles of Ace-DEX MPs with varying cyclic acetal coverage (CAC) and dextran molecular weight (MW), we concluded that MPs composed of low CAC or high MW polymer degraded the fastest at both pH 7.4 and 5.0. To further understand the properties of this unique polymer, we encapsulated a model drug resiquimod, which is a toll-like receptor (TLR) 7/8 agonist, into Ace-DEX MPs of different polymer CAC and dextran MW. It was observed that resiquimod was released faster from MPs of lower CAC or higher MW. By evaluating the activation of RAW macrophages cultured with different types of resiquimod-loaded Ace-DEX MPs, we found that MPs of lower CAC or higher MW promoted greater nitrite production and resulted in more robust cell activation. Our results indicate we can precisely control the degradation profile, release kinetics, and bioactivity of encapsulated cargos by altering CAC and MW, furthering Ace-DEX MPs' novelty as a drug carrier.

Adjuvants: Classification, Modus Operandi, and Licensing

Vaccination is one of the most efficient strategies for the prevention of infectious diseases. Although safer, subunit vaccines are poorly immunogenic and for this reason the use of adjuvants is strongly recommended. Since their discovery in the beginning of the 20th century, adjuvants have been used to improve immune responses that ultimately lead to protection against disease. The choice of the adjuvant is of utmost importance as it can stimulate protective immunity. Their mechanisms of action have now been revealed. Our increasing understanding of the immune system, and of correlates of protection, is helping in the development of new vaccine formulations for global infections. Nevertheless, few adjuvants are licensed for human vaccines and several formulations are now being evaluated in clinical trials. In this review, we briefly describe the most well known adjuvants used in experimental and clinical settings based on their main mechanisms of action and also highlight the requirements for licensing new vaccine formulations.

Interleukin 6 Accelerates Mortality by Promoting the Progression of the Systemic Lupus Erythematosus-Like Disease of BXSB.Yaa Mice

IL6 is a multifunctional cytokine that drives terminal B cell differentiation and secretion of immunoglobulins. IL6 also cooperates with IL21 to promote differentiation of CD4⁺ T follicular helper cells (T_FH). Elevated serum levels of IL6 correlate with disease flares in patients with systemic lupus erythematosus (SLE). We previously reported that IL21 produced by T_FH plays a critical role in the development of the SLE-like disease of BXSB.Yaa mice. To examine the possible contributions of IL6 to disease, we compared disease parameters in IL6-deficient and IL6-competent BXSB.Yaa mice. We report that survival of IL6-deficient BXSB.Yaa mice was significantly prolonged in association with significant reductions in a variety of autoimmune manifestations. Moreover, B cells stimulated by co-engagement of TLR7 and B cell receptor (BCR) produced high levels of IL6 that was further augmented by stimulation with Type I interferon (IFN1). Importantly, the frequencies of T_FH and serum levels of IL21 were significantly reduced in IL6-deficient mice. These findings suggest that high-level production of IL6 by B cells induced by integrated signaling from the IFN1 receptor, TLR7 and BCR promotes the differentiation of IL21-secreting T_FH in a signaling sequence that drives the lethal autoimmune disease of BXSB.Yaa mice.

Involvement of the cytoplasmic cysteine-238 of CD40 in its up-regulation of CD23 expression and its enhancement of TLR4-triggered responses

CD40, a member of the tumor necrosis factor receptor superfamily, plays a key role in both adaptive and innate immunity. Engagement of CD40 with its natural trimeric ligand or with cross-linked antibodies results in disulfide-linked CD40 (dl-CD40) homodimer formation, a process mediated by the cysteine-238 residues of the cytoplasmic tail of CD40. The present study was designed to elucidate the biological relevance of cysteine-238-mediated dl-CD40 homodimers to the expression of CD23 on B cells and to investigate its possible involvement in the innate response. Our results indicate that cysteine-238-mediated dl-CD40 homodimerization is required for CD40-induced activation of PI3-kinase/Akt signaling and the subsequent CD23 expression, as inhibition of dl-CD40 homodimer formation through a point mutation-approach specifically impairs these responses. Interestingly, cysteine-238-mediated dl-CD40 homodimers are also shown to play a crucial role in Toll-like receptor 4-induced CD23 expression, further validating the importance of this system in bridging innate and adaptive immune responses. This process also necessitates the activation of the PI3-kinase/Akt cascade. Thus, our results highlight new roles for CD40 and cysteine-238-mediated CD40 homodimers in cell biology and identify a potential new target for therapeutic strategies against CD40-associated chronic inflammatory diseases.

Toll-like receptors and B cells: functions and mechanisms

Numerous reports have described Toll-like receptor (TLR) functions in myeloid cells such as dendritic cells (DCs) and macrophages, but relatively fewer studies have examined TLR responses in B lymphocytes. B cells express a wide variety of TLRs and are highly activated after TLR ligation, leading to enhancements in B cell survival, surface molecule expression, cytokine and antibody production, and antigen presentation. During an immune response, B cells can receive signals through TLRs as well as the B cell antigen receptor (BCR) and/or CD40. TLR ligation synergizes with signals through these receptors and augments both innate and adaptive immune functions of B lymphocytes. Additionally, targeting B cell TLRs may provide new therapies against certain types of cancer as well as autoimmune diseases. Here, we summarize TLR expression and contributions to both normal and pathogenic functions in mouse and human B cells.

Immune effects of R848: evidences that suggest an essential role of TLR7/8-induced, Myd88- and NF-κB-dependent signaling in the antiviral immunity of Japanese flounder (Paralichthys olivaceus)

The imidazoquinoline compound R848 is a specific agonist of toll-like receptor (TLR) 7/TLR8 that has been used as an immunostimulant in humans against viral diseases. Although R848-induced immune response has been reported in teleost fish, the relevant mechanism is not clear. In this study, we investigated the antiviral potential and the signaling pathway of R848 in a model of Japanese flounder (Paralichthys olivaceus). We found that R848 was able to inhibit the replication of megalocytivirus, stimulated the proliferation of peripheral blood leukocytes (PBL), enhanced the expression of immune genes, and reduced apoptosis of PBL. When endosomal acidification was blocked by chloroquine (CQ), R848-mediated antiviral activity and immune response were significantly reduced. Likewise, inhibition of Myd88 activation markedly impaired the pro-proliferation and anti-apoptosis effect of R848. Cellular study showed that cultured founder cells treated with R848 exhibited augmented NF-κB activity, which, however, was dramatically reduced in the presence of CQ and Myd88 inhibitor. Furthermore, when NF-κB was inactivated, the effect of R848 on cell proliferation and apoptosis was significantly decreased. Taken together, these results indicate that R848 is an immunostimulant with antiviral property in a teleost species, and that the immune response of R848 is mediated by, most likely, TLR7/TLR8 signaling pathway, in which Myd88 and NK-κB play an essential role.

Electrospun acetalated dextran scaffolds for temporal release of therapeutics

Electrospun acetalated dextran (Ac-DEX) scaffolds were fabricated to encapsulate resiquimod, an immunomodulatory toll-like-receptor (TLR) agonist. Ac-DEX has been used to fabricate scaffolds for sustained and temporal delivery of therapeutics because it has tunable degradation rates that are dependent on its synthesis reaction time or the molecular weight of dextran. Additionally, as opposed to commonly electrospun polyesters that shift the local pH upon degradation, the degradation products of Ac-DEX are pH-neutral: dextran, an alcohol, and the metabolic byproduct acetone. Formulations of Ac-DEX with two different degradation rates were used in this study. The effects of electrospinning conditions on the scaffold size and morphology were examined as well as fibroblast adhesion as imaged with fluorescence microcopy and scanning electron microscopy. Macrophage (MΦ) viability further indicates that the scaffolds are cytocompatible. Also, the controlled release profiles of resiquimod from loaded scaffolds and nitric oxide (NO) production by MΦ incubated with these scaffolds show the potential for Ac-DEX scaffolds to be used to temporally and efficiently deliver therapeutics. Overall, we present a novel scaffold that can have tunable and unique drug release rates for tissue engineering, drug delivery, immunomodulation, and wound healing applications.

Type I IFN receptor and the B cell antigen receptor regulate TLR7 responses via distinct molecular mechanisms

Toll-like receptor 7 (TLR7) signals to B cells are critically involved in the innate immune response to microbes, as well as pathogenesis of autoimmune diseases, but the molecular mechanisms that normally regulate these responses are incompletely understood. We previously reported that repeated stimulation through TLR7 induces a state of hyporesponsiveness (TLR tolerance) in both human and mouse B cells, characterized by marked inhibition of particular signaling pathways. BCR signals prevent and overcome TLR7 tolerance. Because optimal responses to TLR7 in B cells require type I IFN, we investigated whether BCR-mediated effects on TLR7 tolerance are mediated by type I IFN receptor (IFNAR) signals. Surprisingly, although BCR-mediated reversal of TLR7 tolerance was IFNAR independent, IFNAR signals alone also blocked TLR7 tolerance, despite enhancing TLR7 expression. Both BCR and IFNAR signals restored the phosphorylation of the transcriptional regulator c-Jun, but only BCR signals blocked the tolerance-mediated inhibition of JNK. Both BCR and IFNAR-mediated regulation was dependent on activation of the PI3K/Akt/mammalian target of rapamycin signaling pathway, indicating a central role for this axis in integrating TLR7, BCR, and IFNAR signals in B cells. These new findings reveal distinct and overlapping signaling mechanisms used by BCR and IFNAR in the regulation of TLR7 tolerance and activation.

The Clinical Application of Ozonetherapy

The reader may be eager to examine in which diseases ozonetherapy can be proficiently used and she/he will be amazed by the versatility of this complementary approach (Table 9 1). The fact that the medical applications are numerous exposes the ozonetherapist to medical derision because superficial observers or sarcastic sceptics consider ozonetherapy as the modern panacea. This seems so because ozone, like oxygen, is a molecule able to act simultaneously on several blood components with different functions but, as we shall discuss, ozonetherapy is not a panacea. The ozone messengers ROS and LOPs can act either locally or systemically in practically all cells of an organism. In contrast to the dogma that “ozone is always toxic”, three decades of clinical experience, although mostly acquired in private clinics in millions of patients, have shown that ozone can act as a disinfectant, an oxygen donor, an immunomodulator, a paradoxical inducer of antioxidant enzymes, a metabolic enhancer, an inducer of endothelial nitric oxide synthase and possibly an activator of stem cells with consequent neovascularization and tissue reconstruction.

Antigen receptor signals rescue B cells from TLR tolerance

Interactions between innate and adaptive immune receptors are critical for an optimal immune response, but the role played by Ag receptors in modulating innate receptor functions is less clear. TLRs are a family of pattern recognition receptors that play crucial roles in detecting microbial pathogens and subsequent development of immune responses. However, chronic stimulation through TLRs renders immune cells hyporesponsive to subsequent stimulation with TLR ligands, a phenomenon known as TLR tolerance, well characterized in myeloid cells. However, it has not been studied in detail in B lymphocytes. In addition to the BCR, B cells express almost all known TLRs and respond robustly to many TLR ligands. Thus, B cells may receive signals through both TLRs and BCR during an infection and may respond differently to TLR stimulation than myeloid cells. We tested this possibility by stimulating repeatedly through either TLR alone or both TLR and BCR. Prestimulation through TLR7 resulted in reduced B cell proliferation, cytokine production, and IgM secretion upon subsequent TLR7 restimulation. The hyporesponsiveness to TLR7 restimulation was associated with reduced NF-kappaB and MAPK activation and defective c-Jun phosphorylation. However, simultaneous BCR signaling prevented or reversed TLR7 tolerance in both mouse and human B cells. Importantly, BCR signaling also rescued B cells from TLR7-mediated TLR9 tolerance. Additionally, the reversal of TLR7-mediated JNK activation was dependent on PI3K activation. Together these results present a novel mechanism to prevent and reverse TLR tolerance in B cells.

Modulation of the allergic asthma transcriptome following resiquimod treatment

Resiquimod is a compound belonging to the imidazoquinoline family of compounds known to signal through Toll-like receptor 7. Resiquimod treatment has been demonstrated to inhibit the development of allergen induced asthma in experimental models. The aim of the present study was to elucidate the molecular processes that were altered following resiquimod treatment and allergen challenge in a mouse model of allergic asthma. Employing microarray analysis, we have characterized the "asthmatic" transcriptome of the lungs of A/J and C57BL/6 mice and determined that it includes genes involved in the control of cell cycle progression, the complement and coagulation cascades, and chemokine signaling. Our results demonstrated that resiquimod treatment resulted in the normalization of the expression of genes involved with airway remodeling, and generally, chemokine signaling. Resiquimod treatment also altered the expression of cell adhesion molecules, and molecules involved in natural killer (NK) cell-mediated cytotoxicity. Furthermore, we have demonstrated that systemic resiquimod administration resulted in the recruitment of NK cells to the lungs and livers of the mice, although no causal relationship between NK cell recruitment and treatment efficacy was found. Overall, our findings identified several genes, important in the development of asthma pathology, that were normalized following resiquimod treatment, thus improving our understanding of the molecular consequences of resiquimod treatment in the lung milieu. The recruitment of NK cells to the lungs may also have application in the treatment of virally induced asthma exacerbations.

Triggering TLR7 in mice induces immune activation and lymphoid system disruption, resembling HIV-mediated pathology

Chronic immune activation is a major cause for progressive immunodeficiency in human immunodeficiency virus type-1 (HIV) infection. The underlying trigger, however, remains largely unknown. HIV single-stranded RNA is a potent immune activator by triggering Toll-like receptor (TLR) 7/8. Thus, we hypothesized that sustained TLR7 triggering induces chronic immune activation and thereby contributes to progressive immunodeficiency. We used the synthetic compound R848 or a mixture of uridine-rich HIV single-stranded (ss) RNA oligonucleotides--both are potent TLR7/8 agonists--to explore the effects of sustained TLR7 triggering on the murine lymphoid system. Sustained TLR7 triggering induced an immunopathology reminiscent of progressive lymphoid destruction in HIV disease; we observed lymphopenia, elevated proinflammatory cytokines, splenomegaly, contracted lymphoid subsets, and lymphoid microarchitecture alteration with reduced marginal zone B-lymphocytes. Upon exposure to inactivated vesiculo-stomatitis virus, antibody production was abolished, although splenic lymphocytes were activated and total IgG was elevated. Our data imply that HIV itself may directly contribute to immune activation and dysfunction by stimulating TLR7. Thus, manipulation of TLR7 signaling may be a potential strategy to reduce chronic hyper-immune activation and, thereby, disease progression in HIV infection.

Comparison of human B cell activation by TLR7 and TLR9 agonists

Background

Human B cells and plasmacytoid dendritic cells (pDC) are the only cells known to express both TLR7 and TLR9. Plasmacytoid dendritic cells are the primary IFN-α producing cells in response to TLR7 and TLR9 agonists. The direct effects of TLR7 stimulation on human B cells is less understood. The objective of this study was to compare the effects of TLR7 and TLR9 stimulation on human B cell function.

Results

Gene expression and protein production of cytokines, chemokines, various B cell activation markers, and immunoglobulins were evaluated. Purified human CD19⁺ B cells (99.9%, containing both naïve and memory populations) from peripheral blood were stimulated with a TLR7-selective agonist (852A), TLR7/8 agonist (3M-003), or TLR9 selective agonist CpG ODN (CpG2006). TLR7 and TLR9 agonists similarly modulated the expression of cytokine and chemokine genes (IL-6, MIP1 alpha, MIP1 beta, TNF alpha and LTA), co-stimulatory molecules (CD80, CD40 and CD58), Fc receptors (CD23, CD32), anti-apoptotic genes (BCL2L1), certain transcription factors (MYC, TCFL5), and genes critical for B cell proliferation and differentiation (CD72, IL21R). Both agonists also induced protein expression of the above cytokines and chemokines. Additionally, TLR7 and TLR9 agonists induced the production of IgM and IgG. A TLR8-selective agonist was comparatively ineffective at stimulating purified human B cells.

Conclusion

These results demonstrate that despite their molecular differences, the TLR7 and TLR9 agonists induce similar genes and proteins in purified human B cells.

A novel polymorphism of the human CD40 receptor with enhanced function

CD40 signaling is critical for innate and adaptive immunity against pathogens, and the cytoplasmic domain of CD40 is highly conserved both within and between species. A novel missense single nucleotide polymorphism (SNP) in the cytoplasmic domain of CD40 at position 227 (P227A) was identified, which resides on a conserved ancestral haplotype highly enriched in persons of Mexican and South American descent. Functional studies indicated that signaling via human (h) CD40-P227A stably expressed in several B-cell lines led to increased phosphorylation of c-Jun, increased secretion of the pro-inflammatory cytokines interleukin (IL)-6 and TNF-alpha, and increased Ig production, compared with wild-type hCD40. Cooperation between hCD40-P227A signaling and B-cell receptor (BCR)- or Toll-like receptor 9 (TLR9)-mediated signaling was also enhanced, resulting in elevated and synergistic production of IL-6 and Ig. We have thus identified a novel genetic variant of hCD40 with a gain-of-function immune phenotype.

Roles of TRAF molecules in B lymphocyte function

Tumor necrosis factor receptor associated factors (TRAFs) play a variety of interesting and important roles in the regulation of B lymphocyte function. They act both as cytoplasmic regulatory molecules, and as signal transducers for receptors involved in both innate and adaptive humoral immune responses. In this brief review, we highlight the current state of knowledge of the diverse roles of TRAF molecules in the functions of B lymphocytes.

Expression and function of Toll-like receptors on dendritic cells and other antigen presenting cells from non-human primates

Antigen presenting cells (APCs), especially dendritic cells (DCs), play a crucial role in immune responses against infections by sensing microbial invasion through Toll-like receptors (TLRs). In this regard, TLR ligands are attractive candidates for use in humans and animal models as vaccine adjuvants. So far, no studies have been performed on TLR expression in non-human primates such as rhesus macaques. Therefore, we studied the TLR expression patterns in different subsets of APC in rhesus macaques and compared them to similar APC subsets in human. Also, expression was compared with corresponding DC subsets from different organs from mice. Here we show by semi-quantitative RT-PCR, that blood DC subsets of rhesus macaque expressed the same sets of TLRs as those of human but substantially differed from mouse DC subsets. Macaque myeloid DCs (MDCs) expressed TLR3, 4, 7 and 8 whereas macaque plasmacytoid DCs (PDCs) expressed only TLR7 and 9. Additionally, TLR expression patterns in macaque monocyte-derived dendritic cells (mo-DCs) (i.e., TLR3, 4, 8 and 9), monocytes (i.e., TLR4, 7, and 8) and B cells (i.e., TLR4, 7, 8, and 9) were also similar to their human counterparts. However, the responsiveness of macaque APCs to certain TLR ligands partially differed from that of human in terms of phenotype differentiation and cytokine production. Strikingly, in contrast to human mo-DCs, no IL-12p70 production was observed when macaque mo-DCs were stimulated with TLR ligands. In addition, CD40 and CD86 phenotypic responses to TLR8 ligand (poly U) in mo-DCs of macaque were higher than that of human. Despite these functional differences, our results provide important information for a rational design of animal models in evaluating TLR ligands as adjuvant in vivo.

TLR7 and CD40 cooperate in IL-6 production via enhanced JNK and AP-1 activation

During vaccination or infection, adaptive and innate immune receptors of B cells are engaged by microbial antigens/ligands. A better understanding of how innate and adaptive signaling pathways interact could enlighten B lymphocyte biology as well as aid immunotherapy strategies and vaccine design. To address this goal, we examined the effects of TLR stimulation on BCR and CD40-induced B cell activation. Synergistic production of IL-6 was observed in both human and mouse primary B cells stimulated through B cell antigen receptors, CD40 and TLR7, and these two receptors also cooperated independently of BCR signals. The enhanced IL-6 production was dependent upon the activity of c-Jun kinase (JNK) and cFos. Dual stimulation through CD40 and TLR7 markedly enhanced JNK activity. The increased level of active JNK in dual-stimulated cells was accompanied by an increase in the level of active AP-1 monomers cJun and cFos. The stimulation of B cells through both CD40 and TLR7 therefore enhanced the production of cytokines through increased JNK signaling and AP-1 activity. In addition, the dual stimulation increased cFos/AP-1 species in stimulated cells, effectively expanding the repertoire of AP-1 dimers as compared to singly stimulated B cells.

Imiquimod: mode of action

OBJECTIVE

Since imiquimod, a nucleoside analogue of the imidazoquinoline family, has shown efficacy against many tumour entities, its mode of action has become a focus of scientific interest.

RESULTS

The major biologic effects of imiquimod are mediated through agonistic activity towards toll-like receptors (TLR) 7 and 8, and consecutively, activation of nuclear factor-kappa B (NF-kappaB). The result of this activity is the induction of pro-inflammatory cytokines, chemokines and other mediators leading to activation of antigen-presenting cells and other components of innate immunity and, eventually, the mounting of a profound T-helper (Th1)-weighted antitumoral cellular immune response. Several secondary effects on the molecular and cellular level may also be explained, at least in part, by the activation of NF-kappaB. Moreover, independent of TLR-7 and TLR-8, imiquimod appears to interfere with adenosine receptor signalling pathways, and the compound causes receptor-independent reduction of adenylyl cyclase activity. This novel mechanism may augment the pro-inflammatory activity of the compound through suppression of a negative regulatory feedback mechanism which normally limits inflammatory responses. Finally, imiquimod induces apoptosis of tumour cells at higher concentrations. The pro-apoptotic activity of imiquimod involves caspase activation and appears to depend on B cell lymphoma/leukemia protein (Bcl)-2 proteins.

CONCLUSIONS

Overall, imiquimod acts on several levels, which appear to synergistically underlie the profound antitumoral activity of the compound.

TLR7/8 ligand, R-848, inhibits IgE synthesis by acting directly on B lymphocytes

TLRs are involved in the regulation of immune responses. R-848, a TLR7/8 ligand, has potent anti-viral and anti-tumour properties and has been used as a new immune response modifier for enhancing Th1 immune response. In this study, we found that R-848 significantly inhibited IgE synthesis from murine B cells at the single cell levels by anti-CD40 plus IL-4-stimulated splenocytes, in which R-848 acted on the early stage of B cell differentiation to modulate IgE synthesis. This inhibitory effect of R-848 on IgE synthesis was not isotype specific as it also inhibited IgG1 synthesis. Moreover, R-848 had no significant effect on the production of IgG2a by anti-CD40 plus IL-4-stimulated splenocytes. Further studies showed that R-848 markedly promoted murine B cell activation induced by anti-CD40 plus IL-4 by up-regulating the expression of B cell activation markers CD25, CD69 and co-stimulatory molecule CD80. In contrast, R-848 inhibited the proliferation and division of murine B cells in anti-CD40 plus IL-4-stimulated splenocytes. R-848 promoted the production of IFN-gamma and IL-12 that were partially responsible for its inhibitory effect on IgE production by anti-CD40 plus IL-4 because the addition of anti-IFN-gamma or anti-IL-12 mAbs to the cultures could significantly restore IgE production by splenocytes. Importantly, R-848 had a direct effect on purified B cells to inhibit IgE production induced by anti-CD40 plus IL-4. Taken together, these results demonstrate that R-848 markedly inhibits IgE synthesis, and suggest that R-848 could be used to treat allergic diseases.

TLR7 and TLR8 as targets in cancer therapy

Small-molecule agonists at Toll-like receptor 7 (TLR7) and TLR8 have sparked a vivid interest in cancer research owing to their profound antitumoral activity. The lead compound of the imidazoquinoline family, imiquimod, is marketed as a topical formulation. It is efficacious against many primary skin tumors and cutaneous metastases. Using different imidazoquinoline species, distinct functions of TLR7 and TLR8 have been discovered. The predominant antitumoral mode of action of these agents is TLR7/8-mediated activation of the central transcription factor nuclear factor-kappaB, which leads to induction of proinflammatory cytokines and other mediators. Cutaneous dendritic cells are the primary responsive cell type and initiate a strong Th1-weighted antitumoral cellular immune response. Recent research has shown that dendritic cells themselves acquire direct antitumoral activity upon stimulation by imiquimod. In addition, there are a number of secondary effects on the molecular and cellular level that can be explained through the activation of TLR7/8. The proinflammatory activity of imiquimod, but not resiquimod, appears to be augmented by suppression of a regulatory mechanism, which normally limits inflammatory responses. This is achieved independently of TLR7/8 through interference with adenosine receptor signaling pathways. Finally, at higher concentrations imiquimod exerts Bcl-2- and caspase-dependent proapoptotic activity against tumor cells.

TLR7 imidazoquinoline ligand 3M-019 is a potent adjuvant for pure protein prototype vaccines

Cancer vaccines, while theoretically attractive, present difficult challenges that must be overcome to be effective. Cancer vaccines are often poorly immunogenic and may require augmentation of immunogenicity through the use of adjuvants and/or immune response modifiers. Toll-like receptor (TLR) ligands are a relatively new class of immune response modifiers that may have great potential in inducing and augmenting both cellular and humoral immunity to vaccines. TLR7 ligands produce strong cellular responses and specific IgG2a and IgG2b antibody responses to protein immunogens. This study shows that a new TLR7 ligand, 3M-019, in combination with liposomes produces very strong immune responses to a pure protein prototype vaccine in mice. Female C57BL/6 mice were immunized subcutaneously with ovalbumin (OVA, 0.1 mg/dose) weekly 4x. Some groups were immunized to OVA plus 3M-019 or to OVA plus 3M-019 encapsulated in liposomes. Both antibody and cellular immune responses against OVA were measured after either two or four immunizations. Anti-OVA IgG antibody responses were significantly increased after two immunizations and were substantially higher after four immunizations in mice immunized with OVA combined with 3M-019. Encapsulation in liposomes further augmented antibody responses. IgM responses, on the other hand, were lowered by 3M-019. OVA-specific IgG2a levels were increased 625-fold by 3M-019 in liposomes compared to OVA alone, while anti-OVA IgG2b levels were over 3,000 times higher. In both cases encapsulation of 3M-019 in liposomes was stronger than either liposomes alone or 3M-019 without liposomes. Cellular immune responses were likewise increased by 3M-019 but further enhanced when it was encapsulated in liposomes. The lack of toxicity also indicates that this combination may by safe, effective method to boost immune response to cancer vaccines.

Manipulation of the toll-like receptor 7 signaling pathway by Epstein-Barr virus

Epstein-Barr virus (EBV) infection of primary B cells causes B-cell activation and proliferation. Activation of B cells requires binding of antigen to the B-cell receptor and a survival signal from ligand-bound CD40, signals that are provided by the EBV LMP1 and LMP2A latency proteins. Recently, Toll-like receptor (TLR) signaling has been reported to provide a third B-cell activation stimulus. The interaction between the EBV and TLR pathways was therefore investigated. Both UV-inactivated and untreated EBV upregulated the expression of TLR7 and downregulated the expression of TLR9 in naive B cells. UV-inactivated virus transiently stimulated naive B-cell proliferation in the presence of the TLR7 ligand R837, while addition of the TLR7 antagonist IRS 661 impaired cell growth induced by untreated EBV. Interferon regulatory factor 5 (IRF-5) is a downstream mediator of TLR7 signaling. IRF-5 was induced following EBV infection, and IRF-5 was expressed in B-cell lines with type III latency. Expression of IRF-5 in this setting is surprising since IRF-5 has tumor suppressor and antiviral properties. B-cell proliferation assays provided evidence that EBV modulates TLR7 signaling responses. Examination of IRF-5 transcripts identified a novel splice variant, V12, that was induced by EBV infection, was constitutively nuclear, and acted as a dominant negative form in IRF-5 reporter assays. IRF-4 negatively regulates IRF-5 activation, and IRF-4 was also present in type III latently infected cells. EBV therefore initially uses TLR7 signaling to enhance B-cell proliferation and subsequently modifies the pathway to regulate IRF-5 activity.

Fatos e mitos sobre imunomoduladores

O objetivo deste artigo é discutir alguns fatos dos imunomoduladores modernos que podem ser úteis para o dermatologista clínico. Outro objetivo importante é o de dissipar mitos que possam ter impacto negativo no uso dessas drogas pelo clínico. O foco inicial está em imunomoduladores estimuladores que podem conduzir à acentuação da resposta normal das células imunocompetentes. Para tanto, diversos aspectos associados à regulação do sistema imune e às vias regulatórias das células do sistema imune são mencionados. Discutem-se a regulação aberrante e seu impacto no sistema imune e examina-se a classe de drogas imunossupressoras que têm sua função bem estabelecida. Diversas drogas não foram mencionadas. A razão para isso é o foco do artigo que pretende cobrir os fatos bem estabelecidos ou os mitos que as novas evidências científicas modificaram. Com esse padrão em mente, é provável que exista uma quantidade considerável de similaridade nos conceitos, uma vez que descrevem drogas imunomoduladoras. Nesse contexto, a intenção de fornecer novas perspectivas de como o sistema imune pode ser modulado por essas drogas supera esse problema.

Toll-like receptors mediate proliferation and survival of multiple myeloma cells

Multiple myeloma (MM) is an incurable B-cell malignancy characterized by accumulation of malignant plasma cells in bone marrow (BM) and recurrent or persistent infections. Toll-like receptors (TLRs) are essential in the host defense against infections and today 10 human TLRs (TLR1-TLR10) and one TLR-homolog (RP105) have been characterized. B cells express several TLRs (mainly TLR1, 6, 7, 9, 10 and RP105) and TLR-initiated responses in B cells include proliferation, anti-apoptosis effect and plasma cell (PC) differentiation. The present study was designed to analyze the role of TLRs in MM. We show that frequent expressions of TLRs were detected in cell lines from MM patients (minimum six TLRs in each). In comparison, only few TLRs (mainly TLR1 and or RP105) were found expressed in PCs from BM of healthy donors. In addition, TLR-specific ligands induce increased proliferation and survival of the MM cell lines, partially due to an autocrine interleukin-6 production. Importantly, we demonstrate that also PC from MM patients proliferates in response to TLR-specific ligands. In conclusion, TLR-ligands may contribute to increased growth and survival of MM cells in MM patients.

Immune response modifiers--mode of action

The innate immune system governs the interconnecting pathways of microbial recognition, inflammation, microbial clearance, and cell death. A family of evolutionarily conserved receptors, known as the Toll-like receptors (TLRs), is crucial in early host defense against invading pathogens. Upon TLR stimulation, nuclear factor-kappaB activation and the interferon (IFN)-regulatory factor 3 pathway initiate production of pro-inflammatory cytokines, such as interleukin-1 and tumor necrosis factor-alpha, and production of type I IFNs (IFN-alpha and IFN-beta), respectively. The innate immunity thereby offers diverse targets for highly selective therapeutics, such as small molecular synthetic compounds that modify innate immune responses. The notion that activation of the innate immune system is a prerequisite for the induction of acquired immunity raised interest in these immune response modifiers as potential therapeutics for viral infections and various tumors. A scenario of dermal events following skin cancer treatment with imiquimod presumably comprises (i) an initial low amount of pro-inflammatory cytokine secretion by macrophages and dermal dendritic cells (DCs), thereby (ii) attracting an increasing number type I IFN-producing plasmacytoid DCs (pDCs) from the blood; (iii) Langerhans cells migrate into draining lymph nodes, leading to an increased presentation of tumor antigen in the draining lymph node, and (iv) consequently an increased generation of tumor-specific T cells and finally (v) an accumulation of tumoricidal effector cells in the treated skin area. The induction of predominately T helper (Th)1-type cytokine profiles by TLR agonists such as imiquimod might have further benefits by shifting the dominant Th2-type response in atopic diseases such as asthma and atopic dermatitis to a more potent Th1 response.

Topical imiquimod is a potent adjuvant to a weakly-immunogenic protein prototype vaccine

A major challenge in the development of more effective vaccines for cancer and other diseases is the development of potent adjuvants that can strongly, simply and safely enhance vaccine immunogenicity. Adjuvants that preferentially enhance Th1 type of responses are particularly desirable, as these responses are believed to play the major role in immune resistance to cancer. This study describes the ability of topical application of imiquimod to act as a potent, safe and simple vaccine adjuvant in mice. Groups of C57BL/6 mice were immunized subcutaneously with ovalbumin (OVA, 0.1mg/dose) weekly x 4. Imiquimod in a 5% cream formulation was rubbed into the skin over the injection site for 15s to give a dose of approximately 1mg/treatment following each immunization. Control mice were immunized with OVA alone, with irradiated E.G7-OVA cells (that express ovalbumin), with OVA encapsulated in liposomes, or to PBS. Topical imiquimod enhanced anti-OVA antibody responses 100-fold and markedly increased cellular responses compared to mice not given imiquimod. The responses were shifted towards a Th1 phenotype, with marked enhancement of IgG2a, IgG2b, and CD8+ T cell responses and concomitant suppression of IgM and IgG1 responses. More frequent topical applications of imiquimod further enhanced both antibody and cellular responses. There was no detectable local or systemic toxicity associated with treatment. These results indicate that topical imiquimod can safely and strongly enhance both antibody and CD8+ T cell response to OVA immunization, and suggest that it may provide a simple, safe and effective way to enhance the immunogenicity of vaccines in general.

Systemic administration of a TLR7 ligand leads to transient immune incompetence due to peripheral-blood leukocyte depletion

Toll-like receptor (TLR) ligands lead to the induction of proinflammatory cytokines and are potent enhancers of specific immune responses. We show here that a single systemic dose of R-848, a ligand for TLR7, potently enhanced hapten sensitization during the induction of contact hypersensitivity (CHS). However, R-848 administration also resulted in a rapid and almost complete depletion of leukocytes from the blood. This effect was transient and was associated with general induction of endothelial adhesiveness. In response to R-848, endothelial cells up-regulated adhesion molecules in vitro and in vivo and leukocytes exhibited increased rolling on endothelia in R-848-treated animals. Adhesion molecule induction appeared to be a direct effect, because endothelial cells expressed TLR7 in vitro and in vivo. After R-848 treatment, the tissue residence time of leukocytes was markedly prolonged in all major peripheral organs. The resulting transiently reduced availability of peripheral-blood leukocytes (PBLs) (TRAP) significantly inhibited otherwise potent CHS responses until the effector cells returned. Thus, although TLR7 ligands are effective adjuvants for the induction of cell-mediated immunity, they can transiently inhibit the elicitation of localized immune responses, possibly due to a systemic endothelial activation throughout the vasculature.

The Mucosal Adjuvant Macrophage-Activating Lipopeptide-2 Directly Stimulates B Lymphocytes via the TLR2 without the Need of Accessory Cells

The macrophage-activating lipopeptide-2 (MALP-2) is an agonist of the TLR heterodimer 2/6, which exhibits potent activity as mucosal adjuvant, promoting strong humoral and cellular responses. Although B cells expressing TLR2/6 are potential targets, very little is known about the effect of MALP-2 on B cells. Studies were performed using total spleen cells or purified B cells from WT mice or animals deficient in TLR2, T cells, B cells, or specific subpopulations of B cells. They demonstrated that MALP-2 promotes a T cell-independent activation and maturation of B cells (mainly follicular but also B-1a and marginal zone B cells) via TLR2. MALP-2 also increased the frequency of IgM- and IgG-secreting cells, but bystander cells were required for IgA secretion. Activated B cells exhibited increased expression of activation markers and ligands that are critical for cross-talk with T cells (CD19, CD25, CD80, CD86, MHC I, MHC II, and CD40). Immunization of mice lacking T cells showed that MALP-2-mediated stimulation of TLR2/6 was unable to circumvent the need of T cell help for efficient Ag-specific B cell activation. Immunization of mice lacking B cells demonstrated that B cells are critical for MALP-2-dependent improvement of T cell responses. The knowledge emerging from this work suggests that MALP-2-mediated activation of B cells through TLR2/6 is critical for adjuvanticity. B cell stimulation by pattern recognition receptors seems to be a basic mechanism that can be exploited to improve the immunogenicity of vaccine formulations.

Plasmacytoid Dendritic Cells Control TLR7 Sensitivity of Naive B Cells via Type I IFN

Detailed information of human B cell activation via TLR may lead to a better understanding of B cell involvement in autoimmunity and malignancy. In this study we identified a fundamental difference in the regulation of TLR7- and TLR9-mediated B cell stimulation: whereas the induction of polyclonal naive B cell proliferation by the TLR7 ligands resiquimod (R848) and loxoribine required the presence of plasmacytoid dendritic cells (PDCs), activation via the TLR9 ligand CpG was independent of PDCs. We found that PDC-derived type I IFN enhanced TLR7 sensitivity of B cells by selectively up-regulating TLR7 expression. In contrast the expression levels of TLR9 and of other TLRs studied remained unchanged. In the presence of type I IFN, TLR7 ligation triggered polyclonal B cell expansion and B cell differentiation toward Ig-producing plasma cells; notably, this occurred independently of T cell help and B cell Ag. Human B cells did not respond to ligands of other TLRs including TLR2, TLR4 and TLR6 with and without type I IFN. In conclusion, our results reveal a distinct regulation of TLR7 and TLR9 function in human B cells and highlight TLR7 and TLR9 as unique targets for therapeutic intervention in B cell-mediated immunity and disease.

Resiquimod, a new immune response modifier from the family of imidazoquinolinamines, inhibits allergen-induced Th2 responses, airway inflammation and airway hyper-reactivity in mice

BACKGROUND

Allergen-induced sensitization and airway disease are the results of adverse immune reactions against environmental antigens that may be prevented or inhibited by immune modifying strategies.

OBJECTIVE

To investigate the effects of the novel immune response modifier resiquimod (R-848), from the family of imidazol-derivates, in a murine model of allergen-mediated Th2-immune responses and concomitant airway inflammation and airway hyper-reactivity.

METHODS

BALB/c mice were systemically sensitized with ovalbumin (OVA) on days 1 and 14 and challenged with OVA aerosol on days 28 and 29. R-848 was applied intranasally to sensitized animals once prior to the first allergen airway challenge, on day 27.

RESULTS

A single application of R-848 significantly reduced numbers of eosinophils and lymphocytes in bronchoalveolar lavage fluid and inhibited mucus gland hyperplasia, compared with sensitized and challenged controls. Associated with the decrease in airway inflammation, single intranasal treatment with R-848 abolished the development of airway hyper-reactivity after allergen sensitization and airway challenges. Additionally, Th2-cytokine production in lung tissues from sensitized and R-848-treated animals was reduced, whereas IL-12 and IFN-gamma production was increased, compared with non-treated sensitized mice.

CONCLUSION

These data indicate that R-848 effectively inhibits allergen-induced airway inflammation and hyper-reactivity by modulation of increased Th2-immune responses.

The multifaceted roles of TRAFs in the regulation of B-cell function

Tumour-necrosis factor receptor (TNFR)-associated factors (TRAFs) are cytoplasmic adaptor proteins that are important in lymphocyte activation and apoptosis. Many studies of TRAFs have used models of exogenous overexpression by non-lymphoid cells. However, the actions of TRAFs present at normal levels in lymphoid cells often differ considerably from those that have been established in non-lymphocyte overexpression models. As I discuss here, information obtained from studying these molecules in physiological settings in B cells reveals that they have several roles, which are both unique and overlapping. These include activation of kinases and transcription factors, and interactions with other signalling proteins, culminating in the induction or inhibition of biological functions.

Imiquimod and resiquimod in a mouse model: adjuvants for DNA vaccination by particle-mediated immunotherapeutic delivery

Imiquimod, an immune response modifier and inducer of cytokines in vitro and in vivo, has been shown to have potent antiviral and antitumour activity and to act as an adjuvant for protein vaccination. We have undertaken studies in mice to investigate the potential of imiquimod and resiquimod to adjuvant DNA vaccination. These imidazoquinolines were administered by subcutaneous injection at the vaccination site immediately after particle-mediated immunotherapeutic delivery of plasmid DNA using a gene gun. Imiquimod was found to increase the number and maturation status of dendritic cells in draining lymph nodes, and to enhance antigen-specific CD4(+) and CD8(+) T cell responses, as assessed by analyses of clonal expansion, and the quantity and kinetics of cytokine production from these cells in lymph nodes and spleens collected after vaccination. A more substantial increase in IFN-gamma-producing, compared with IL-4-producing CD4(+) T cells suggested that imiquimod biased the immune response towards a predominance of Th1 cells. The analogue resiquimod was found to be to produce a similar Th1 biased immune response with a 10-fold reduced dose compared with imiquimod. Collectively, these studies suggest that both imiquimod and resiquimod may be suitable adjuvants for therapeutic DNA vaccines requiring induction of potent cytotoxic T cell responses.

Induction of apoptosis by Toll-like receptor-7 agonist in tissue cultures

Toll-like receptor (TLR)-7 agonists represent a new group of immune response modifiers, which include imiquimod and resiquimod (R-848). Topically applied imiquimod is used for the treatment of both external and perianal genital warts, and benign and malignant epithelial lesions. Based on the induction of interferons and other cytokines in vitro and in vivo, regression of epithelial lesions probably depends on induction of both innate and cellular immune responses. As clinical remission is not always associated with inflammation, other mechanisms may also be involved. Using two different assays for detection of apoptosis (TUNEL test and gel analysis of DNA fragmentation), we observed induction of apoptosis by imiquimod in human epithelial cell lines (HeLa S3) and keratinocytes (HaCaT, A431 cells), as well as in mouse fibroblasts (McCoy cells). These findings suggest that the mode of action of imiquimod to eliminate virus-infected, dysplastic or neoplastic epithelial cells may also include the induction of apoptotic processes.

The CD40-CD154 interaction in B cell-T cell liaisons

The CD40 receptor is expressed constitutively on B lymphocytes, for which it provides important signals regulating clonal expansion, antibody production and isotype switching, as well as the development of humoral memory. The major source of CD154, the ligand for CD40, is activated T lymphocytes. Interactions between CD40 and CD154 provide a number of signals that play important roles in regulating the complex and multifactorial interactions between these two major cell types of the adaptive immune response. Understanding both the biological effects of this receptor-ligand interaction, as well as how CD40 signaling pathways are controlled, adds to our detailed picture of the complex interplay between B and T cells.