Application of high-intensity focused ultrasound to the study of mild traumatic brain injury.

Though intrinsically of much higher frequency than open-field blast overpressures, high-intensity focused ultrasound (HIFU) pulse trains can be frequency modulated to produce a radiation pressure having a similar form. In this study, 1.5-MHz HIFU pulse trains of 1-ms duration were applied to intact skulls of mice in vivo and resulted in blood-brain barrier disruption and immune responses (astrocyte reactivity and microglial activation). Analyses of variance indicated that 24 h after HIFU exposure, staining density for glial fibrillary acidic protein was elevated in the parietal and temporal regions of the cerebral cortex, corpus callosum and hippocampus, and staining density for the microglial marker, ionized calcium binding adaptor molecule, was elevated 2 and 24 h after exposure in the corpus callosum and hippocampus (all statistical test results, p < 0.05). HIFU shows promise for the study of some bio-effect aspects of blast-related, non-impact mild traumatic brain injuries in animals.

Sequential Plasmodium chabaudi and Plasmodium berghei infections provide a novel model of severe malarial anemia.

Lack of an adequate animal model of Plasmodium falciparum severe malarial anemia (SMA) has hampered the understanding of this highly lethal condition. We developed a model of SMA by infecting C57BL/6 mice with P. chabaudi followed after recovery by P. berghei infection. P. chabaudi/P. berghei-infected mice had an initial 9- to 10-day phase of relatively low parasitemia and severe anemia, followed by a second phase of hyperparasitemia, more profound anemia, reticulocytosis, and death 14 to 21 days after infection. P. chabaudi/P. berghei-infected animals had more intense splenic hematopoiesis, higher interleukin-10 (IL-10)/tumor necrosis factor alpha and IL-12/gamma interferon (IFN-γ) ratios, and higher antibody levels against P. berghei and P. chabaudi antigens than P. berghei-infected or P. chabaudi-recovered animals. Early treatment with chloroquine or artesunate did not prevent the anemia, suggesting that the bulk of red cell destruction was not due to the parasite. Red cells from P. chabaudi/P. berghei-infected animals had increased surface IgG and C3 by flow cytometry. However, C3(-/-) mice still developed anemia. Tracking of red cells labeled ex vivo and in vivo and analysis of frozen tissue sections by immunofluorescence microscopy showed that red cells from P. chabaudi/P. berghei-infected animals were removed at an accelerated rate in the liver by erythrophagocytosis. This model is practical and reproducible, and its similarities with P. falciparum SMA in humans makes it an appealing system with which to study the pathogenesis of this condition and explore potential immunomodulatory interventions.

Decay-accelerating factor mitigates controlled hemorrhage-instigated intestinal and lung tissue damage and hyperkalemia in swine.

BACKGROUND: Activation of complement system has been associated with tissue injury after hemorrhage and resuscitation in rats and swine. This study investigated whether administration of human recombinant decay-accelerating factor (DAF; a complement regulatory protein that inhibits classical and alternative pathways) reduces tissue damage in a porcine model of hemorrhagic shock. METHODS: Male Yorkshire swine assigned to four groups were subjected to controlled, isobaric hemorrhage over 15 minutes to a target mean arterial pressure of 35 mm Hg. Hypotension was maintained for 20 minutes followed by a bolus intravenous injection of DAF or vehicle and then animals were observed for 200 minutes. Blood chemistry and physiologic parameters were recorded. Tissue samples from lung and small intestine were subjected to histopathological evaluation and detection of tissue deposition of complement proteins by immunohistochemistry and Western blot analyses. RESULTS: Administration of DAF significantly reduced intestinal and lung tissue damage in a dose-dependent manner (5, 25, and 50 µg/kg). In addition, DAF treatment improved hemorrhage-induced hyperkalemia. The protective effects of DAF appear to be related to its ability to reduce tissue complement activation and deposition on affected tissues. CONCLUSIONS: DAF treatment decreased tissue complement activation and deposition in hemorrhaged animals and attenuated tissue damage at 200 minutes after treatment. The observed beneficial effects of DAF treatment on tissue injury after 20 minutes of severe hypotension presents an attractive model of small volume resuscitation, particularly in situations with a restrictive medical logistical footprint such as far-forward access to first responders in the battlefield or in remote rural or mountainous environments.

Pathogenic natural antibodies recognizing annexin IV are required to develop intestinal ischemia-reperfusion injury.

Intestinal ischemia-reperfusion (IR) injury is initiated when natural IgM Abs recognize neo-epitopes that are revealed on ischemic cells. The target molecules and mechanisms whereby these neo-epitopes become accessible to recognition are not well understood. Proposing that isolated intestinal epithelial cells (IEC) may carry IR-related neo-epitopes, we used in vitro IEC binding assays to screen hybridomas created from B cells of unmanipulated wild-type C57BL/6 mice. We identified a novel IgM mAb (mAb B4) that reacted with the surface of IEC by flow cytometric analysis and was alone capable of causing complement activation, neutrophil recruitment and intestinal injury in otherwise IR-resistant Rag1(-/-) mice. mAb B4 was found to specifically recognize mouse annexin IV. Preinjection of recombinant annexin IV blocked IR injury in wild-type C57BL/6 mice, demonstrating the requirement for recognition of this protein to develop IR injury in the context of a complex natural Ab repertoire. Humans were also found to exhibit IgM natural Abs that recognize annexin IV. These data in toto identify annexin IV as a key ischemia-related target Ag that is recognized by natural Abs in a pathologic process required in vivo to develop intestinal IR injury.

IL-17 producing CD4+ T cells mediate accelerated ischemia/reperfusion-induced injury in autoimmunity-prone mice.

Elements of the innate and adaptive immune response have been implicated in the development of tissue damage after ischemic reperfusion (I/R). Here we demonstrate that T cells infiltrate the intestine of C57BL/6 mice subjected to intestinal I/R during the first hour of reperfusion. The intensity of the T cell infiltration was higher in B6.MRL/lpr mice subjected to intestinal I/R and reflected more severe tissue damage than that observed in control mice. Depletion of T cells limited I/R damage in B6.MRL/lpr mice, whereas repletion of B6.MRL/lpr lymph node-derived T cells into the I/R-resistant Rag-1(-/-) mouse reconstituted tissue injury. The tissue-infiltrating T cells were found to produce IL-17. Finally, IL-23 deficient mice, which are known not to produce IL-17, displayed significantly less intestinal damage when subjected to I/R. Our data assign T cells a major role in intestinal I/R damage by virtue of producing the pro-inflammatory cytokine IL-17.

Decay-accelerating factor attenuates remote ischemia-reperfusion-initiated organ damage.

Complement activation contributes to the expression of local and remote organ injury in animal models of ischemia-reperfusion (IR). We demonstrate here that a soluble form of decay-accelerating factor (DAF) protects normal C57Bl/6 and autoimmunity-prone B6.MRL/lpr mice subjected to hindlimb IR from remote intestinal and lung injury without affecting the degree of local skeletal muscle injury. In addition, DAF treatment attenuates remote organ injury in mice subjected to mesenteric IR. Soluble DAF allowed the deposition of complement 3 in local and remote injury sites while it limited the presence of terminal membrane attack complex and did not increase animal susceptibility to sepsis. These data provide evidence that soluble DAF might offer clinical benefit to patients suffering remote intestinal or lung damage in response to muscle or other organ injury.

Anti-ribonucleoprotein antibodies mediate enhanced lung injury following mesenteric ischemia/reperfusion in Rag-1(-/-) mice.

Natural Abs and autoantibodies bind antigens displayed by ischemia-conditioned tissues, followed by complement activation and enhanced tissue injury during reperfusion. Anti-ribonucleoprotein (RNP) Ab is associated with lung disease in patients with autoimmune disease but it is not known whether these abs contribute to lung injury. Mesenteric I/R in mice leads to local and remote lung injury. Accordingly, we used this model to investigate whether anti-RNP Abs would reconstitute I/R damage with prominent lung damage in injury-resistant Rag1(-/-) animals. Rag1(-/-) mice injected with anti-RNP Ab containing serum and subjected to mesenteric I/R suffered greater intestinal injury than control-treated and sham-operated animals. The magnitude of the reconstituted damage was anti-RNP Ab titer-dependent. Anti-RNP Ab-treated animals demonstrated a dose-dependent increase in lung histologic injury scores compared to control and sham animals. Anti-RNP mediated injury was shown to be complement dependent. These experiments reveal a novel mechanism whereby anti-RNP Abs contributes to the development of pulmonary pathology in patients with autoimmune diseases following exposure of remote organs to I/R injury.

Anti-RNP immunity: implications for tissue injury and the pathogenesis of connective tissue disease.

Certain autoantibodies are characteristic of autoimmune disease manifestations and contribute to organ pathology. The presence of high-titer antibodies to U1-RNP are associated with mixed connective tissue disease, although these antibodies may also be present in systemic lupus erythematosus and systemic sclerosis. However, the role of antibodies to U1-RNP in the pathogenesis of connective tissue disease remains unclear. Data from recent experimental studies promote the hypothesis that U1-RNP antibodies participate in both innate and adaptive immune responses, implicating them in the pathogenesis of connective tissue disease.

Rgs1 and Gnai2 regulate the entrance of B lymphocytes into lymph nodes and B cell motility within lymph node follicles.

Signaling by G protein-coupled receptors coupled to Galpha(i) assists in triggering lymphocyte movement into and out of lymph nodes. Here, we show that modulating the signaling output from these receptors dramatically alters B cell trafficking. Intravital microscopy of adoptively transferred B cells from wild-type and Rgs1-/- mice revealed that Rgs1-/- B cells stick better to lymph node high endothelial venules, home better to lymph nodes, and move more rapidly within lymph node follicles than do wild-type B cells. In contrast, B cells from Gnai2-/- mice enter lymph nodes poorly and move more slowly than do wild-type B cells. The Gnai2-/- mice often lack multiple peripheral lymph nodes, and their B cells respond poorly to chemokines, indicating that Galpha(i1) and Galpha(i3) poorly compensate for the loss of Galpha(i2). These results demonstrate opposing roles for Rgs1 and Gnai2 in B cell trafficking into and within lymph nodes.

Regulation of chemokine-induced lymphocyte migration by RGS proteins.

G-protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by inducing the G-protein alpha (Galpha) subunit to exchange guanosine diphosphate for guanosine triphosphate. Regulators of G-protein signaling (RGS) proteins enhance the deactivation of Galpha subunits, thereby reducing the activation of downstream effectors. Several members of the RGS family are expressed in lymphocytes. Among RGS proteins with the highest levels of expression are RGS1, RGS2, RGS10, RGS13, RGS14, RGS16, and RGS19. Perhaps the most important G-protein-coupled receptors in lymphocytes potentially subject to regulation by RGS proteins are the chemokine receptors. By signaling through these receptors, chemokines help orchestrate immune cell trafficking both during the development of the immune system and during responses to exogenous or infectious agents. Thus, the level and regulation of RGS proteins in lymphocytes likely significantly impact lymphocyte migration and function. This article provides some tools for the analysis of RGS protein expression in lymphocytes and outlines a number of methods for the analysis of the effects of RGS proteins on lymphocyte migration and chemokine receptor signaling.

Abnormal B-cell responses to chemokines, disturbed plasma cell localization, and distorted immune tissue architecture in Rgs1-/- mice.

Normal lymphoid tissue development and function depend upon chemokine-directed cell migration. Since chemokines signal through heterotrimeric G-protein-coupled receptors, RGS proteins, which act as GTPase-activating proteins for Galpha subunits, likely fine tune the cellular responses to chemokines. Here we show that Rgs1(-/-) mice possess B cells that respond excessively and desensitize improperly to the chemokines CXCL12 and CXCL13. Many of the B-cell follicles in the spleens of Rgs1(-/-) mice have germinal centers even in the absence of immune stimulation. Furthermore, immunization of these mice leads to exaggerated germinal center formation; partial disruption of the normal architecture of the spleen and Peyer's patches; and abnormal trafficking of immunoglobulin-secreting cells. These results reveal the importance of a regulatory mechanism that limits and desensitizes chemokine receptor signaling.

In vitro and in vivo assays of B-lymphocyte migration.

The development and functional activities of B lymphocytes critically depend on their migratory capacity. Both in vitro and in vivo assays can be used to assess the migratory ability of B cells. Filter-based transwell assays measure both spontaneous and chemoattractant-induced cell migration in vitro. Flow cytometric analysis of labeled cell subsets present in the input and migratory cells from transwell assays allows the assessment of the migratory capacity of specific cell types in a complex mixture of cells. A similar approach can be used to assess the migratory capacity of B cells transfected with a green fluorescent fusion protein. Despite the success of the transwell assay, attempts to image directionally migrating B cells have been limited. The assessment of the in vivo migratory capacity of genetically modified or pharmacologically treated B cells usually involves their adoptive transfer into recipient mice. The localization of transferred cells in lymphoid organs can be determined by immunohistochemistry and/or flow cytometric analysis of harvested tissues or cells. Because the proper localization of B cells in lymphoid organs is a multistep process, abnormal positioning can occur even in the absence of an intrinsic defect in cell migration.

Role of RGS proteins in regulating the migration of B lymphocytes.

The migration of B lymphocytes into distinct microenvironments in secondary lymphoid tissues and maintenance of cells in these micro-domains is strictly structured and likely supports the proper regulation of immune responses to both foreign and self-antigens. Chemokines' and other chemoattactants' signals serve as signposts to direct cell migration. They signal cells through heptahelical receptors, which couple to heterotrimeric G proteins (G protein-coupled receptors or GPCRs). The regulation of the signals transduced through these receptors ultimately determines the positioning of cells in lymphoid tissues. A variety of mechanisms regulate GPCR signaling including a family of approximately 25 proteins termed regulators of G protein signaling (RGS). These proteins act as GTPase activating proteins for G alpha subunits and can also function as effector antagonists of specific G alpha subunits, thereby attenuating signaling through GPCRs such as chemokine receptors. RGS proteins possess some degree of receptor and G alpha subunit specificity. Thus, the particular spectrum of RGS proteins and their expression levels within a cell will determine the duration and magnitude of G protein signaling initiated by chemokines. In this review we illustrate the role RGS proteins have in regulating B cell signaling responses to chemoattractant stimuli during homeostasis as well as during an immune response.

Toll-like receptor signaling alters the expression of regulator of G protein signaling proteins in dendritic cells: implications for G protein-coupled receptor signaling.

Conserved structural motifs on pathogens trigger pattern recognition receptors present on APCs such as dendritic cells (DCs). An important class of such receptors is the Toll-like receptors (TLRs). TLR signaling triggers a cascade of events in DCs that includes modified chemokine and cytokine production, altered chemokine receptor expression, and changes in signaling through G protein-coupled receptors (GPCRs). One mechanism by which TLR signaling could modify GPCR signaling is by altering the expression of regulator of G protein signaling (RGS) proteins. In this study, we show that human monocyte-derived DCs constitutively express significant amounts of RGS2, RGS10, RGS14, RGS18, and RGS19, and much lower levels of RGS3 and RGS13. Engagement of TLR3 or TLR4 on monocyte-derived DCs induces RGS16 and RGS20, markedly increases RGS1 expression, and potently down-regulates RGS18 and RGS14 without modifying other RGS proteins. A similar pattern of Rgs protein expression occurred in immature bone marrow-derived mouse DCs stimulated to mature via TLR4 signaling. The changes in RGS18 and RGS1 expression are likely important for DC function, because both proteins inhibit G alpha(i)- and G alpha(q)-mediated signaling and can reduce CXC chemokine ligand (CXCL)12-, CC chemokine ligand (CCL)19-, or CCL21-induced cell migration. Providing additional evidence, bone marrow-derived DCs from Rgs1(-/-) mice have a heightened migratory response to both CXCL12 and CCL19 when compared with similar DCs prepared from wild-type mice. These results indicate that the level and functional status of RGS proteins in DCs significantly impact their response to GPCR ligands such as chemokines.

CXCR3 is induced early on the pathway of CD4+ T cell differentiation and bridges central and peripheral functions.

Chemokine receptors on T cells are frequently categorized as functioning either in immune system homeostasis within lymphoid organs, or in peripheral inflammation. CXCR3 is in the latter category and is reported to be expressed selectively on Th1 cells. We found that CXCR3 was expressed in vivo on newly activated tonsillar CD4(+) T cells. Using CD4(+) T cells from cord blood, we found that CXCR3 was induced by cellular activation in vitro independently of the cytokine milieu, although on resting cells, expression was maintained preferentially on those that had been activated in type 1 conditions. In inflamed tonsils, CXCR3(+)CD4(+) T cells were localized around and within germinal centers. The inference that CXCR3 has a role in germinal center reactions was supported by the finding that the CXCR3 ligand CXC chemokine ligand 9 was expressed in a pattern demarcating a subset of germinal centers both in tonsil and in lymph nodes from an HIV-infected individual. We next investigated the role of CXCR3 on peripheral effector/memory CD4(+) T cells by comparing its pattern of expression with that of CCR5, another Th1-cell associated chemokine receptor. Analysis of cells directly from peripheral blood and after activation in vitro suggested that CXCR3 expression preceded that of CCR5, supporting a model of sequential induction of chemokine receptors during CD4(+) T cell differentiation. Taken together, our data show that CXCR3 can be expressed at all stages of CD4(+) T cell activation and differentiation, bridging central function in lymphoid organs and effector function in peripheral tissues.

RGS13 regulates germinal center B lymphocytes responsiveness to CXC chemokine ligand (CXCL)12 and CXCL13.

Normal lymphoid tissue development and function depend upon directed cell migration. Providing guideposts for cell movement and positioning within lymphoid tissues, chemokines signal through cell surface receptors that couple to heterotrimeric G proteins, which are in turn subject to regulation by regulator of G protein signaling (RGS) proteins. In this study, we report that germinal center B lymphocytes and thymic epithelial cells strongly express one of the RGS family members, RGS13. Located between Rgs1 and Rgs2, Rgs13 spans 42 kb on mouse chromosome 1. Rgs13 encodes a 157-aa protein that shares 82% amino acid identity with its 159-aa human counterpart. In situ hybridization with sense and antisense probes localized Rgs13 expression to the germinal center regions of mouse spleens and Peyer's patches and to the thymus medulla. Affinity-purified RGS13 Abs detected RGS13-expressing cells in the light zone of the germinal center. RGS13 interacted with both Gialpha and Gqalpha and strongly impaired signaling through G(i)-linked signaling pathways, including signaling through the chemokine receptors CXCR4 and CXCR5. Prolonged CD40 signaling up-regulated RGS13 expression in human tonsil B lymphocytes. These results plus previous studies of RGS1 indicate the germinal center B cells use two RGS proteins, RGS1 and RGS13, to regulate their responsiveness to chemokines.