Suppression of TH2-type allergic reactions by helminth infection

There is no immunological mechanism to adequately explain the sudden epidemic in allergies noted in the last 30 years in developed countries. The reduction in the development of allergic disorders observed in individuals infected with parasitic helminths, however, supports a possible role for worms in suppressing allergies. Helminths regulate the immunity of the host to ensure a mutually beneficial environment for the survival of both the parasite and the host. This interplay between helminths and allergic responses raises fundamental questions in immunobiology. Harnessing current mechanistic studies for translational research into helminth infections and atopy might have potential for the identification of novel biomarkers, and even therapeutics, in allergic diseases.     

The role of IL-10 in crossregulation of TH1 and TH2 responses

The identification of helper T (T_H)-cell subsets has greatly improved understanding of the regulation of immune effector functions. In addition to controlling humoral and delayed-type hypersensitivity responses, these subsets crossregulate by secreting mutually inhibitory cytokines. In this review, Tim Mosmann and Kevin Moore examine these phenomena and in particular the role of interleukin 10, a cytokine secreted by T_H2 cells that inhibits T_H1-cell function.     

Critical role for the AIM2 inflammasome during acute CNS bacterial infection

Interleukin‐1β (IL‐1β) is essential for eliciting protective immunity during the acute phase of Staphylococcus aureus (S. aureus) infection in the central nervous system (CNS). We previously demonstrated that microglial IL‐1β production in response to live S. aureus is mediated through the Nod‐like receptor protein 3 (NLRP3) inflammasome, including the adapter protein ASC (apoptosis‐associated speck‐like protein containing a caspase‐1 recruitment domain), and pro‐caspase 1. Here, we utilized NLRP3, ASC, and caspase 1/11 knockout (KO) mice to demonstrate the functional significance of inflammasome activity during CNS S. aureus infection. ASC and caspase 1/11 KO animals were exquisitely sensitive, with approximately 50% of mice succumbing to infection within 24 h. Unexpectedly, the survival of NLRP3 KO mice was similar to wild‐type animals, suggesting the involvement of an alternative upstream sensor, which was later identified as absent in melanoma 2 (AIM2) based on the similar disease patterns between AIM2 and ASC KO mice. Besides IL‐1β, other key inflammatory mediators, including IL‐6, CXCL1, CXCL10, and CCL2 were significantly reduced in the CNS of AIM2 and ASC KO mice, implicating autocrine/paracrine actions of IL‐1β, as these mediators do not require inflammasome processing for secretion. These studies demonstrate a novel role for the AIM2 inflammasome as a critical molecular platform for regulating IL‐1β release and survival during acute CNS S. aureus infection.

     

Trypanosoma cruzi: the role of PGE2 in immune response during the acute phase of experimental infection

Chagas disease is characterized by cardiac lesions and a high level of PGE2. Our objective was to investigate the role of PGE2 in cardiac lesions. BALB/c mice were infected with Trypanosoma cruzi (1x10(3) trypomastigote forms) and were treated daily with PBS, meloxicam (0.5 mg/kg) or etoricoxib (0.6 mg/kg). The animals were sacrificed on the 21st day of infection and we collected the cardiac tissue and spleen cells for tissue culture. We observed that treatment with COX-2 inhibitors was able to decrease synthesis of PGE2 by spleen cells. This reduction was accompanied by reduction of the inflammatory infiltrate, parasite nets, cardiac fibrosis and fewer COX-2 positive cells in cardiac tissue obtained from these animals. In conclusion, treatment with COX-2 inhibitors, and consequent inhibition of PGE2 synthesis, was able to reduce the cardiac damage observed during the acute phase of experimental Chagas disease, thus demonstrating the involvement of this mediator in the cardiac lesion.     

CD154 is essential for protective immunity in experimental salmonella infection: evidence for a dual role in innate and adaptive immune responses

CD40-CD154 interactions are of central importance in the induction of humoral and cellular immune responses. In the present study, CD154-deficient (CD154-/-) mice were used to assess the role of CD40-CD154 interactions in regulating the immune response to a systemic Salmonella infection. Compared with C57BL/6 (CD154+/+) controls, CD154-/- mice were hypersusceptible to infection by an attenuated strain of Salmonella enterica serovar Typhimurium (S. typhimurium), as evidenced by decreased survival rate and mean time to death, which correlated with increased bacterial burden and persistence in target organs. CD154-/- mice exhibited a defect both in the production of IL-12, IFN-gamma, and NO during the acute phase of the disease and in the generation of Salmonella-specific Ab responses and Ig isotype switching. Furthermore, when CD154-/- animals were administered a sublethal dose of attenuated S. typhimurium and subsequently challenged with a virulent homologous strain, all mice succumbed to an overwhelming infection. Similar treatment of CD154+/+ mice consistently resulted in > or =90% protection. The lack of protective immunity in CD154-/- mice correlated with a decreased T cell recall response to Salmonella Ags. Significant protection against virulent challenge was conferred to presensitized CD154-/- mice by transfer of serum or T cells from immunized CD154+/+ mice. For best protection, however, a combination of immune serum and T cells was required. We conclude that intercellular communications via the CD40-CD154 pathway play a critical role in the induction of type 1 cytokine responses, memory T cell generation, Ab formation, and protection against primary as well as secondary Salmonella infections.     

The essential role of the intestinal microbiota in facilitating acute inflammatory responses

The restoration of blood flow, i.e., reperfusion, is the treatment of choice to save viable tissue following acute ischemia of a vascular territory. Nevertheless, reperfusion can be accompanied by significant inflammatory events that limit the beneficial effects of blood flow restoration. To evaluate the potential role of the intestinal microbiota in facilitating the development of tissue injury and systemic inflammation, germ-free and conventional mice were compared in their ability to respond to ischemia and reperfusion injury. In conventional mice, there was marked local (intestine) and remote (lung) edema formation, neutrophil influx, hemorrhage, and production of TNF-alpha, KC, MIP-2, and MCP-1. Moreover, there was an increase in the concentration of serum TNF-alpha and 100% lethality. In germ-free mice, there was no local, remote, or systemic inflammatory response or lethality after intestinal ischemia and reperfusion and, in contrast to conventional mice, germ-free animals produced greater amounts of IL-10. Similar results were obtained after administration of LPS, i.e., little production of TNF-alpha or lethality and production of IL-10 after LPS in germ-free mice. Blockade of IL-10 with Abs induced marked inflammation and lethality in germ-free mice after ischemia and reperfusion or LPS administration, demonstrating that the ability of these mice to produce IL-10 was largely responsible for their "no inflammation" phenotype. This was consistent with the prevention of reperfusion-associated injury by the exogenous administration of IL-10 to conventional mice. Thus, the lack of intestinal microbiota is accompanied by a state of active IL-10-mediated inflammatory hyporesponsiveness.     

PCR detection of Anaplasma platys in blood and tissue of dogs during acute phase of experimental infection

Four dogs were experimentally infected with Anaplasma platys to determine changes in real-time TaqMan PCR detection in blood and tissue, microscopically detectable parasitemia, and platelet concentrations during the first 28 days of infection. Buffy-coat blood cells were PCR positive for A. platys DNA at 4 days after inoculation and remained positive in all dogs until day 14. Marked thrombocytopenia and low parasitemia occurred in dogs during that initial period. During 17 and 28 days post-inoculation, the PCR results on buffy-coat blood cells were intermittently negative in each dog with marked thrombocytopenia and no microscopic evidence of parasitemia. Bone marrow and splenic aspirates collected from the A. platys-infected dogs were tested by real-time TaqMan PCR. Two dogs were PCR positive in spleen and marrow at 28 days post-inoculation, when PCR results for buffy-coat blood cells were negative. Spleen and/or bone marrow samples should be considered as additional samples for PCR testing of dogs, particularly when blood samples are PCR negative during the acute phase of A. platys infection.     

An essential role for talin during alpha(M)beta(2)-mediated phagocytosis

The cytoskeletal, actin-binding protein talin has been previously implicated in phagocytosis in Dictyostelium discoideum and mammalian phagocytes. However, its mechanism of action during internalization is not understood. Our data confirm that endogenous talin can occasionally be found at phagosomes forming around IgG- and C3bi-opsonized red blood cells in macrophages. Remarkably, talin knockdown specifically abrogates uptake through complement receptor 3 (CR3, CD11b/CD18, alpha(M)beta(2) integrin) and not through the Fc gamma receptor. We show that talin physically interacts with CR3/alpha(M)beta(2) and that this interaction involves the talin head domain and residues W747 and F754 in the beta(2) integrin cytoplasmic domain. The CR3/alpha(M)beta(2)-talin head interaction controls not only talin recruitment to forming phagosomes but also CR3/alpha(M)beta(2) binding activity, both in macrophages and transfected fibroblasts. However, the talin head domain alone cannot support phagocytosis. Our results establish for the first time at least two distinct roles for talin during CR3/alpha(M)beta(2)-mediated phagocytosis, most noticeably activation of the CR3/alpha(M)beta(2) receptor and phagocytic uptake.     

An essential role for IL-18 in CD8 T cell-mediated suppression of IgE responses

The ability of CD8 T cells to suppress IgE responses is well established. Previously, we demonstrated that CD8 T cells inhibit IgE responses via the induction of IL-12, which promotes Th1 and suppresses Th2 responses. In this study, we show that IL-18 also plays an essential role in IgE suppression. In vitro, IL-18 synergized with IL-12 to promote Th1/T cytotoxic 1 and inhibit Th2/T cytotoxic 2 differentiation. OVA-specific TCR transgenic (OT-I) CD8 cells induced both IL-12 and IL-18 when cultured with OVA(257-264) peptide-pulsed dendritic cells. In vivo, IL-18(-/-) mice exhibited higher IgE and IgG1 levels compared with wild-type mice after immunization with OVA/alum. Furthermore, adoptive transfer of CD8 T cells from OVA-primed mice suppressed IgE responses in OVA/alum-immunized mice, but not in IL-18(-/-) mice. IgE suppression in IL-18(-/-) mice was restored if CD8 T cells were coadoptively transferred with IL-18-competent wild-type bone marrow dendritic cell progenitors, demonstrating an essential role of IL-18 in CD8 T cell-mediated suppression of IgE responses. The data suggest that CD8 T cells induce IL-18 production during a cognate interaction with APCs that synergizes with IL-12 to promote immune deviation away from the allergic phenotype. Our data identify IL-18 induction as a potentially useful target in immunotherapy of allergic disease.     

An essential role for Grk2 in Hedgehog signalling downstream of Smoothened

The G‐protein‐coupled receptor kinase 2 (adrbk2/GRK2) has been implicated in vertebrate Hedgehog (Hh) signalling based on the effects of its transient knock‐down in mammalian cells and zebrafish embryos. Here, we show that the response to Hh signalling is effectively abolished in the absence of Grk2 activity. Zebrafish embryos lacking all Grk2 activity are refractory to both Sonic hedgehog (Shh) and oncogenic Smoothened (Smo) activity, but remain responsive to inhibition of cAMP‐dependent protein kinase (PKA) activity. Mutation of the kinase domain abrogates the rescuing activity of grk2 mRNA, suggesting that Grk2 acts in a kinase‐dependent manner to regulate the response to Hh. Previous studies have suggested that Grk2 potentiates Smo activity by phosphorylating its C‐terminal tail (CTT). In the zebrafish embryo, however, phosphomimetic Smo does not display constitutive activity, whereas phospho‐null mutants retain activity, implying phosphorylation is neither sufficient nor necessary for Smo function. Since Grk2 rescuing activity requires the integrity of domains essential for its interaction with GPCRs, we speculate that Grk2 may regulate Hh pathway activity by downregulation of a GPCR.     

An essential role for putrescine biosynthesis during meiotic maturation of amphibian oocytes

The objective of this study was to investigate the role of polyamines during meiotic maturation of Xenopus oocytes. The results indicate a rapid and significant increase in the activity of ornithine decarboxylase (ODC), the rate-limiting enzyme in the polyamine biosynthetic pathway, during the meiotic maturation induced by either progesterone or human chorionic gonadotropin (HCG). This increase in the enzyme activity was followed by an accumulation of putrescine without any effect on the levels of spermidine or spermine. The inhibition of ODC activity and the accumulation of putrescine levels by α-difluoromethyl ornithine (DFMO), a catalytic irreversible inhibitor of ODC, also resulted in the inhibition of maturation mediated by progesterone in Xenopus oocytes. DFMO caused an inhibition of both maturation and ovulation induced by HCG in ovarian fragments. This inhibition was readily reversible by exogenous supply of putrescine to the medium. These observations suggest that putrescine plays an important role during the meiotic maturation of amphibian oocytes.     

TH cells primed during influenza virus infection provide help for qualitatively distinct antibody responses to subsequent immunization.

The quality of the primary Ab-forming cell (AFC) response in cervical lymph nodes and mediastinal lymph nodes of mice to intranasal influenza virus was strongly influenced by viral replicative capacity. IgA secretors were prominent in the early AFC response to infectious virus in mediastinal lymph nodes, while IgG expression was more frequent among isotypically switched AFC in cervical lymph nodes of the same mice; this pattern was reversed in the response to inactivated virus. Influenza viruses A/Puerto Rico/8/34 (A/PR8) and A/X-31 share six of eight genome segments, differing only in hemagglutinin (H1 in A/PR8, H3 in A/X-31) and neuraminidase (N1 in A/PR8, N2 in A/X-31) genes. These viruses therefore elicit extensively cross-reactive TH populations, though their glycoproteins are serologically unrelated. Mice recovered from an A/X-31 infection thus mount a primary B cell response against A/PR8 glycoproteins, when challenged with the latter virus, though this response can call upon memory TH cells. To assess the impact of memory TH populations on a primary Ab response, we compared the AFC response to inactivated A/PR8 in naive mice and mice that had cleared an A/X-31 infection. A/X-31 immune mice mounted a more vigorous AFC response against A/PR8 H1 and N1 glycoproteins than naive animals, when immunized intranasally with inactivated A/PR8. However the distribution of isotypes among H1/N1-specific AFC in lymph nodes of A/X-31-primed mice resembled that of naive mice. Evidently, in this functional context, memory TH cells retained the ability to help Ab responses different in quality from that generated during their primary reaction.     

Activation of P2X(7) receptor by ATP plays an important role in regulating inflammatory responses during acute viral infection

Acute viral infection causes damages to the host due to uncontrolled viral replication but even replication deficient viral vectors can induce systemic inflammatory responses. Indeed, overactive host innate immune responses to viral vectors have led to devastating consequences. Macrophages are important innate immune cells that recognize viruses and induce inflammatory responses at the early stage of infection. However, tissue resident macrophages are not easily activated by the mere presence of virus suggesting that their activation requires additional signals from other cells in the tissue in order to trigger inflammatory responses. Previously, we have shown that the cross-talk between epithelial cells and macrophages generates synergistic inflammatory responses during adenoviral vector infection. Here, we investigated whether ATP is involved in the activation of macrophages to induce inflammatory responses during an acute adenoviral infection. Using a macrophage-epithelial cell co-culture system we demonstrated that ATP signaling through P2X(7) receptor (P2X(7)R) is required for induction of inflammatory mediators. We also showed that ATP-P2X(7)R signaling regulates inflammasome activation as inhibition or deficiency of P2X(7)R as well as caspase-1 significantly reduced IL-1β secretion. Furthermore, we found that intranasal administration of replication deficient adenoviral vectors in mice caused a high mortality in wild-type mice with symptoms of acute respiratory distress syndrome but the mice deficient in P2X(7)R or caspase-1 showed increased survival. In addition, wild-type mice treated with apyrase or inhibitors of P2X(7)R or caspase-1 showed higher rates of survival. The improved survival in the P2X(7)R deficient mice correlated with diminished levels of IL-1β and IL-6 and reduced neutrophil infiltration in the early phase of infection. These results indicate that ATP, released during viral infection, is an important inflammatory regulator that activates the inflammasome pathway and regulates inflammatory responses.