Suppression of host humoral immunity by Borrelia burgdorferi varies over the course of infection

Borrelia burgdorferi, the spirochetal agent of Lyme disease, utilizes a variety of strategies to evade and suppress the host immune response, which enables it to chronically persist in the host. The resulting immune response is characterized by unusually strong IgM production and a lack of long-term protective immunity. Previous studies in mice have shown that infection with B. burgdorferi also broadly suppresses host antibody responses against unrelated antigens. Here, we show that mice infected with B. burgdorferi and concomitantly immunized with recombinant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein had an abrogated antibody response to the immunization. To further define how long this humoral immune suppression lasts, mice were immunized at 2, 4, and 6 weeks post-infection. Suppression of host antibody production against the SARS-CoV-2 spike protein peaked at 2 weeks post-infection but continued for all timepoints measured. Antibody responses against the SARS-CoV-2 spike protein were also assessed following antibiotic treatment to determine whether this immune suppression persists or resolves following clearance of B. burgdorferi. Host antibody production against the SARS-CoV-2 spike protein returned to baseline following antibiotic treatment; however, anti-SARS-CoV-2 IgM remained high, comparable to levels found in B. burgdorferi-infected but untreated mice. Thus, our data demonstrate restored IgG responses following antibiotic treatment but persistently elevated IgM levels, indicating lingering effects of B. burgdorferi infection on the immune system following treatment.

Mannose-Coated Reconstituted Lipoprotein Nanoparticles for the Targeting of Tumor-Associated Macrophages: Optimization, Characterization, and In Vitro Evaluation of Effectiveness

Reconstituted high-density lipoprotein nanoparticles (rHDL NPs) have been utilized as delivery vehicles to a variety of targets, including cancer cells. However, the modification of rHDL NPs for the targeting of the pro-tumoral tumor-associated macrophages (TAMs) remains largely unexplored. The presence of mannose on nanoparticles can facilitate the targeting of TAMs which highly express the mannose receptor at their surface. Here, we optimized and characterized mannose-coated rHDL NPs loaded with 5,6-dimethylxanthenone-4-acetic acid (DMXAA), an immunomodulatory drug. Lipids, recombinant apolipoprotein A-I, DMXAA, and different amounts of DSPE-PEG-mannose (DPM) were combined to assemble rHDL-DPM-DMXAA NPs. The introduction of DPM in the nanoparticle assembly altered the particle size, zeta potential, elution pattern, and DMXAA entrapment efficiency of the rHDL NPs. Collectively, the changes in physicochemical characteristics of rHDL NPs upon the addition of the mannose moiety DPM indicated that the rHDL-DPM-DMXAA NPs were successfully assembled. The rHDL-DPM-DMXAA NPs induced an immunostimulatory phenotype in macrophages pre-exposed to cancer cell-conditioned media. Furthermore, rHDL-DPM NPs delivered their payload more readily to macrophages than cancer cells. Considering the effects of the rHDL-DPM-DMXAA NPs on macrophages, the rHDL-DPM NPs have the potential to serve as a drug delivery platform for the selective targeting of TAMs.

The mitochondrial UPR regulator ATF5 promotes intestinal barrier function via control of the satiety response

Organisms use several strategies to mitigate mitochondrial stress, including the activation of the mitochondrial unfolded protein response (UPR^mt). The UPR^mt in Caenorhabditis elegans, regulated by the transcription factor ATFS-1, expands on this recovery program by inducing an antimicrobial response against pathogens that target mitochondrial function. Here, we show that the mammalian ortholog of ATFS-1, ATF5, protects the host during infection with enteric pathogens but, unexpectedly, by maintaining the integrity of the intestinal barrier. Intriguingly, ATF5 supports intestinal barrier function by promoting a satiety response that prevents obesity and associated hyperglycemia. This consequently averts dysregulated glucose metabolism that is detrimental to barrier function. Mechanistically, we show that intestinal ATF5 stimulates the satiety response by transcriptionally regulating the gastrointestinal peptide hormone cholecystokinin, which promotes the secretion of the hormone leptin. We propose that ATF5 protects the host from enteric pathogens by promoting intestinal barrier function through a satiety-response-mediated metabolic control mechanism.

Neutrophils Are More Effective than Monocytes at Phagosomal Containment and Killing of Listeria monocytogenes

Neutrophils and inflammatory monocytes are innate immune cells essential for protection during Listeria monocytogenes infection. Although certain functions have been generally assigned to each of the cells, similarities and differences in functions necessary for bacterial clearance have not previously been investigated. In the current study, phagocytosis, phagosomal containment, bacterial killing, and cytokine production by neutrophils and monocytes during L. monocytogenes infection were studied. Data obtained via in vitro studies show that neutrophils are more effective at L. monocytogenes uptake, phagosomal containment, and killing than monocytes. However, monocytes were found to be more effective at cytokine production during L. monocytogenes infection, in vivo. Additionally, the data demonstrated that neutrophils and monocytes are also capable of producing IL-1α, a cytokine that does not yet have a clearly defined role during infection with L. monocytogenes Furthermore, we were able to demonstrate a population of monocytes producing both TNF-α and IL-α, concurrently. This study highlights the multifunctional capabilities of neutrophils and monocytes, further adding to our knowledge of these innate immune cells during L. monocytogenes infection.

Neutrophils are more effective than monocytes at containment and killing of Listeria monocytogenes

Neutrophils and monocytes have previously been shown to be important for host protection during infection with Listeria monocytogenes (Lm). Previous studies have shown that simultaneous depletion of neutrophils and monocytes with the Gr-1 antibody leads to susceptibility to Lm infection. The purpose of these studies is to delineate differences in function between neutrophils and monocytes during Lm infection. Neutrophils obtained from the bone marrow, liver and spleen of C57BL/6 mice were more effective at phagocytosis of Lm in comparison to monocytes as they had a higher total bacteria MFI than the monocytes. To determine differences in the ability of the cells to keep bacteria contained in the phagosome, the cells were infected with a strain of Lm that only expresses GFP when the bacteria escapes out of the phagosome into the cytosol. Comparison of the MFI of total bacteria present vs escaped bacteria showed that monocytes allowed for more bacteria to escape in comparison to neutrophils. Therefore, monocytes are less effective at bacterial containment in comparison to neutrophils. To ascertain differences in killing ability, bone marrow neutrophils and monocytes were sorted for a killing assay and neutrophils were also more effective than monocytes at bacterial killing. In conclusion, although both cell types are important for protection during Lm infection, neutrophils appear to be essential for protection as they are more effective at phagocytosis, phagosomal containment and bacteria killing. Future studies, such as measurement of ROS/RNS as well as cytokine production, will aid in further defining specific functional differences between neutrophils and monocytes during intracellular bacterial infection.

The effects of ROS on neutrophil containment of the intracellular bacteria, Listeria monocytogenes

Extracellular superoxide dismutase (ecSOD) is commonly regarded as having a protective function during ROS induced inflammation. However, using ecSOD congenic mice expressing differing levels of ecSOD activity (HI, WT & KO), we found that high ecSOD activity is not conducive to host survival during Listeria monocytogenes (Lm) infection. Interestingly, although the infected ecSOD HI mice had a higher percentage of neutrophils present in the target organs in comparison to the ecSOD KO mice, they also had a higher bacterial burden. To better understand the function of neutrophils during infection with Lm, we studied phagosomal containment in the context of varying levels of ecSOD activity. A higher percentage of KO neutrophils took up and allowed for phagosomal escape of Lm. However, although there was no difference in the relative amount of Lm that escaped per neutrophil in the context of ecSOD activity, the KO neutrophils took up more Lm than the HI neutrophils. Therefore, neutrophils from the KO mice were more effective at keeping Lm contained in comparison to the HI neutrophils. The effect of ecSOD on the ability of monocytes to contain Lm was also analyzed. It was observed that ecSOD had no effect on monocyte association and phagosomal containment of Lm. However, independent of ecSOD, a lower percentage of monocytes associate with and allow for phagosomal escape of Lm, in comparison to neutrophils. In conclusion neutrophils are more effective than monocytes at phagocytosis of Lm and ecSOD activity hinders neutrophil phagosomal containment of Lm. Future studies focused on how ecSOD activity modulates downstream neutrophil functions, such as Lm killing, will lead to a better understanding of the overall effects of ROS on neutrophil functions.

The Essential Role of Neutrophils during Infection with the Intracellular Bacterial Pathogen Listeria monocytogenes

Neutrophils have historically been characterized as first responder cells vital to host survival because of their ability to contain and eliminate bacterial and fungal pathogens. However, recent studies have shown that neutrophils participate in both protective and detrimental responses to a diverse array of inflammatory and infectious diseases. Although the contribution of neutrophils to extracellular infections has been investigated for decades, their specific role during intracellular bacterial infections has only recently been appreciated. During infection with the Gram-positive intracellular pathogen Listeria monocytogenes, neutrophils are recruited from the bone marrow to sites of infection where they use novel bacterial-sensing pathways leading to phagocytosis and production of bactericidal factors. This review summarizes the requirement of neutrophils during L. monocytogenes infection by examining both neutrophil trafficking and function during primary and secondary infection.

The role of ecSOD in phagosomal containment of Listeria monocytogenes by neutrophils

Extracellular superoxide dismutase (ecSOD) is an enzyme associated with the extracellular matrix that plays a protective role during reactive oxygen species mediated inflammatory responses. Previously, we reported that neutrophils are essential for protection during infection with Listeria monocytogenes (LM), and that high ecSOD activity is detrimental to host resistance during infection, while lack of ecSOD activity is beneficial. Furthermore, using depletion studies, it was determined that neutrophils from ecSOD KO mice are more protective than neutrophils from ecSOD expressing mice during LM infection. To understand how ecSOD modulates neutrophil function during LM infection, bacterial uptake and phagosomal escape were measured. A higher percentage of neutrophils from the spleen and liver of ecSOD KO mice associated with and allowed for phagosomal escape of LM. However, using MFI as an indicator of the relative number of bacteria per neutrophil, we observed that the ratio of cell associated to cytosolic bacteria was higher in ecSOD KO neutrophils in comparison to neutrophils with ecSOD activity. These data suggest that the absence of ecSOD activity enhances neutrophil association with LM and simultaneously limits LM escape from the phagosome. Future studies utilizing neutrophils obtained from other organs as well as from infected mice should help conclusively determine how the lack of ecSOD activity enhances the protective capabilities of neutrophils.

Foley balloon catheter to prevent or manage bleeding during treatment for cervical and Cesarean scar pregnancy

OBJECTIVE

To demonstrate the efficacy of placement and inflation of Foley balloon catheters prophylactically to prevent, or as an adjuvant therapy to control, bleeding in women undergoing treatment for Cesarean scar pregnancy (CSP) or cervical pregnancy (CxP).

METHODS

This was a retrospective study of 18 women with either CSP (n = 16) or CxP (n = 2), who underwent Foley balloon catheter placement under continuous transvaginal or transabdominal ultrasound guidance to prevent or manage bleeding following treatment, which in most cases comprised local (intragestational sac) and intramuscular (IM) methotrexate (MTX) injections. In eight cases, the balloon catheter was placed immediately following local and/or IM MTX treatment, either because of bleeding or prophylactically; in eight cases, the catheter was placed as part of a two-step protocol, with patients first treated with local and IM MTX injection, then suction aspiration on Day 4 or 5, followed by planned insertion of a balloon catheter; in one patient the balloon was placed on Day 21 after local and IM MTX treatment, due to sudden bleeding; and in one case of a heterotopic pregnancy, one intrauterine and one cervical, the balloon was placed due to severe bleeding. Human chorionic gonadotropin (hCG) levels were evaluated weekly following MTX injection.

RESULTS

Gestational ages at balloon placement ranged between 5 and 12 + 2 weeks. All embryos/fetuses, with the exception of the cervical heterotopic one, had heart activity and catheter placement was well-tolerated by all women. The balloon tamponade effectively reduced or prevented maternal vaginal bleeding in all except one patient; this woman had a heterotopic CxP and required abdominal robotic cerclage to control the bleeding. Catheters were kept in place for a mean of 3.6 (range, 1-6) days. hCG levels returned to low or zero levels within 19-82 days following MTX injection. Fifteen women required antibiotic treatment following the procedure. One woman with CSP developed an arteriovenous malformation requiring uterine artery embolization.

CONCLUSION

Ultrasound-guided placement and inflation of Foley balloon catheters was easy to perform and well-tolerated by patients undergoing treatment for CSP or CxP, and successfully prevented or helped in the management of bleeding complications. Based on our experience and previous publications we suggest having the option of balloon catheter insertion available when local treatment of CSP or CxP is undertaken.

Chronic psychological stress suppresses contact hypersensitivity: potential roles of dysregulated cell trafficking and decreased IFN-γ production

Increasing evidence shows that psychological stress can have dramatic impacts on the immune system, particularly the cutaneous immune response in dermatological disorders. While there have been many studies examining the impact of acute psychological stress on contact hypersensitivity there are relatively few studies concerning the impact of chronic psychological stress. Furthermore, the local immunological mechanisms by which chronic psychological stress impacts contact hypersensitivity still remain to be explored. Here we show that restraint-induced chronic psychological stress stimulates activation of the hypothalamus-pituitary-adrenal axis and delays weight gain in female BALB/c mice. We observed that chronic psychological stress reduces the cutaneous immune response as evidence by reduced ear swelling. This correlated with a significant decrease in the inflammatory cell infiltrate. On the other hand, chronic psychological stress does not influence T cell proliferation, activation, or sensitivity to corticosterone but does increase CD4(+) and CD8(+) T cell percentages in draining lymph nodes during a contact hypersensitivity reaction. Chronic psychological stress induces a decrease in overall circulating white blood cells, lymphocytes, and monocytes during a contact hypersensitivity reaction suggesting extravasation from the circulation. Finally, we found markedly reduced local IFN-γ production in chronically stressed animals. Based on these findings we propose that chronic psychological stress reduces contact hypersensitivity due to dysregulated cell trafficking and reduced production of IFN-γ.

Extracellular superoxide dismutase inhibits innate immune responses and clearance of an intracellular bacterial infection

Reactive oxygen species and reactive nitrogen species play important roles during immune responses to bacterial pathogens. Extracellular superoxide dismutase (ecSOD) regulates extracellular concentrations of reactive oxygen species and reactive nitrogen species and contributes to tissue protection during inflammatory insults. The participation of ecSOD in immune responses seems therefore intuitive, yet is poorly understood. In the current study, we used mice with varying levels of ecSOD activity to investigate the involvement of this enzyme in immune responses against Listeria monocytogenes. Surprisingly, our data demonstrate that despite enhanced neutrophil recruitment to the liver, ecSOD activity negatively affected host survival and bacterial clearance. Increased ecSOD activity was accompanied by decreased colocalization of neutrophils with bacteria, as well as increased neutrophil apoptosis, which reduced overall and neutrophil-specific TNF-α production. Liver leukocytes from mice lacking ecSOD produced equivalent NO· compared with liver leukocytes from mice expressing ecSOD. However, during infection, there were higher levels of peroxynitrite (NO(3)·(-)) in livers from mice lacking ecSOD compared with livers from mice expressing ecSOD. Neutrophil depletion studies revealed that high levels of ecSOD activity resulted in neutrophils with limited protective capacity, whereas neutrophils from mice lacking ecSOD provided superior protection compared with neutrophils from wild-type mice. Taken together, our data demonstrate that ecSOD activity reduces innate immune responses during bacterial infection and provides a potential target for therapeutic intervention.

Specific depletion reveals a novel role for neutrophil-mediated protection in the liver during Listeria monocytogenes infection

Previous studies have suggested that neutrophils are required for resistance during infection with multiple pathogenic microorganisms. However, the depleting antibody used in those studies binds to both Ly6G and Ly6C (anti-Gr-1; clone RB6-8C5). This antibody has been shown to deplete not only neutrophils but also monocytes and a subset of CD8(+) T cells. Recently, an antibody against Ly6G, which specifically depletes neutrophils, was characterized. In the present study, neutrophils are depleted using the antibody against Ly6G during infection with the intracellular bacterium Listeria monocytogenes (LM). Our data show that neutrophil-depleted mice are much less susceptible to infection than mice depleted with anti-Gr-1. Although neutrophils are required for clearance of LM, their importance is more pronounced in the liver and during a high-dose bacterial challenge. Furthermore, we demonstrate that the protection mediated by neutrophils is due to the production of TNF-α, but not IFN-γ. Additionally, neutrophils are not required for the recruitment of monocytes or the generation of adaptive T-cell responses during LM infection. This study highlights the importance of neutrophils during LM infection, and indicate that depletion of neutrophils is less detrimental to the host than depletion of all Gr-1-expressing cell populations.

IL-22 production is regulated by IL-23 during Listeria monocytogenes infection but is not required for bacterial clearance or tissue protection

Listeria monocytogenes (LM) is a gram-positive bacterium that is a common contaminant of processed meats and dairy products. In humans, ingestion of LM can result in intracellular infection of the spleen and liver, which can ultimately lead to septicemia, meningitis, and spontaneous abortion. Interleukin (IL)-23 is a cytokine that regulates innate and adaptive immune responses by inducing the production of IL-17A, IL-17F, and IL-22. We have recently demonstrated that the IL-23/IL-17 axis is required for optimal recruitment of neutrophils to the liver, but not the spleen, during LM infection. Furthermore, these cytokines are required for the clearance of LM during systemic infection. In other infectious models, IL-22 induces the secretion of anti-microbial peptides and protects tissues from damage by preventing apoptosis. However, the role of IL-22 has not been thoroughly investigated during LM infection. In the present study, we show that LM induces the production of IL-22 in vivo. Interestingly, IL-23 is required for the production of IL-22 during primary, but not secondary, LM infection. Our findings suggest that IL-22 is not required for clearance of LM during primary or secondary infection, using both systemic and mucosal models of infection. IL-22 is also not required for the protection of LM infected spleens and livers from organ damage. Collectively, these data indicate that IL-22 produced during LM infection must play a role other than clearance of LM or protection of tissues from pathogen- or immune-mediated damage.

A novel immunoregulatory function for IL-23: Inhibition of IL-12-dependent IFN-γ production

Most studies investigating the function of IL-23 have concluded that it promotes IL-17-secreting T cells. Although some reports have also characterized IL-23 as having redundant pro-inflammatory effects with IL-12, we have instead found that IL-23 antagonizes IL-12-induced secretion of IFN-γ. When splenocytes or purified populations of T cells were cultured with IL-23, IFN-γ secretion in response to IL-12 was dramatically reduced. The impact of IL-23 was most prominent in CD8(+) T cells, but was also observed in NK and CD4(+) T cells. Mechanistically, the IL-23 receptor was not required for this phenomenon, and IL-23 inhibited signaling through the IL-12 receptor by reducing IL-12-induced signal transducer and activator of transcription 4 (STAT4) phosphorylation. IL-23 was also able to reduce IFN-γ secretion by antagonizing endogenously produced IL-12 from Listeria monocytogenes (LM)-infected macrophages. In vivo, LM infection induced higher serum IFN-γ levels and a greater percentage of IFN-γ(+)CD8(+) T cells in IL-23p19-deficient mice as compared with WT mice. This increase in IFN-γ production coincided with increased LM clearance at days 2 and 3 post-infection. Our data suggest that IL-23 may be a key factor in determining the responsiveness of lymphocytes to IL-12 and their subsequent secretion of IFN-γ.

IL-23 is required for protection against systemic infection with Listeria monocytogenes

Listeria monocytogenes (LM) is a Gram-positive, intracellular bacterium that can induce spontaneous abortion, septicemia, and meningitis. Although it is known that neutrophils are required for elimination of the bacteria and for survival of the host, the mechanisms governing the recruitment of neutrophils to LM-infected tissues are not fully understood. We demonstrate here that IL-23 and the IL-17 receptor A (IL-17RA), which mediates both IL-17A and IL-17F signaling, are necessary for resistance against systemic LM infection. LM-infected IL-23p19 knockout (KO) mice have decreased production of IL-17A and IL-17F, while IFN-gamma production is not altered by the lack of IL-23. LM induces the production of IL-17A from gammadelta T cells, but not CD4, CD8, or NK cells. Furthermore, a lack of efficient neutrophil recruitment to the liver is evident in both IL-23p19 KO and IL-17RA KO mice during LM infection. Immunocytochemical analysis of infected livers revealed that neutrophils were able to localize with LM in IL-23p19 KO and IL-17RA KO mice, indicating that IL-23 and IL-17RA do not regulate the precise localization of neutrophils with LM. The importance of IL-23-induced IL-17A was demonstrated by injecting IL-23p19 KO mice with recombinant IL-17A. These mice had reduced LM bacterial burdens compared with IL-23p19 KO mice that did not receive IL-17A. These results indicate that during LM infection, IL-23 regulates the production of IL-17A and IL-17F from gammadelta T cells, resulting in optimal liver neutrophil recruitment and enhanced bacterial clearance.

Interleukin-23 is required for protection against Listeria monocytogenes (133.24)

Listeria monocytogenes (LM) is a gram-positive, intracellular bacterium that can induce spontaneous abortion, septicemia, and meningitis. Recently, it has been demonstrated that interleukin (IL)-17A is necessary for an optimal immune response against LM in the liver. As IL-23-dependent cytokines, IL-17A and IL-17F induce the mobilization of neutrophils to sites of infection. The importance of IL-23 during infection with LM has not been studied. We demonstrate here that IL-23 and the IL-17 receptor A (IL-17RA), which mediates both IL-17A and IL-17F signaling, are necessary for resistance against LM infection. During infection with LM, mice deficient in either IL-23 (IL-23p19 KO) or the IL-17RA (IL-17RA KO) have increased susceptibility to infection and increased bacterial burden in the spleen and liver. Interestingly, IL-17A, IL-17F, and IL-22 are decreased in supernatants from cells of LM infected IL-23p19 KO mice. Furthermore, neutrophils are decreased in IL-23p19 KO and IL-17RA KO mice at early time points. When IL-23p19 KO mice are rescued with the administration of exogenous IL-17A, a protective phenotype similar to that seen during infection of wild-type mice is achieved. Therefore, it is likely that IL-23 regulates the optimal production of IL-17A/F during LM infection which results in early neutrophil recruitment and bacterial clearance.

A novel IL-17-dependent mechanism of cross protection: respiratory infection with mycoplasma protects against a secondary listeria infection

Immune responses to pathogens occur within the context of current and previous infections. Cross protection refers to the phenomena where infection with a particular pathogen provides enhanced resistance to a subsequent unrelated pathogen in an antigen-independent manner. Proposed mechanisms of antigen-independent cross protection have involved the secretion of IFN-gamma, which activates macrophages, thus providing enhanced innate immunity against the secondary viral or bacterial pathogen. Here we provide evidence that a primary infection with the chronic respiratory pathogen, Mycoplasma pulmonis, provides a novel form of cross protection against a secondary infection with Listeria monocytogenes that is not mediated by IFN-gamma, but instead relies upon IL-17 and mobilization of neutrophils. Mice infected with M. pulmonis have enhanced clearance of L. monocytogenes from the spleen and liver, which is associated with increased numbers of Gr-1(+)CD11b(+) cells and higher levels of IL-17. This enhanced clearance of L. monocytogenes was absent in mice depleted of Gr-1(+) cells or in mice deficient in the IL-17 receptor. Additionally, both the IL-17 receptor and neutrophils were essential for optimal clearance of M. pulmonis. Thus, a natural component of the immune response directed against M. pulmonis was able to enhance clearance of L. monocytogenes.

IL-23 acts in a novel fashion by antagonizing IL-12 induced IFN-γ secretion (95.16)

Most studies have concluded that interleukin-23 (IL-23) plays a unique role in promoting IL-17 secreting T cells. While some reports have also characterized IL-23 as having redundant pro-inflammatory effects with IL-12, we have instead found that IL-23 can regulate the innate immune response in a novel manner, by antagonizing IL-12 induced secretion of interferon-γ (IFN-γ). Our recent data documents the rapid, innate production of IFN-γ from memory CD8 T cells, as well as NK cells, stimulated with IL-12 and IL-18. When splenocytes are cultured with IL-23, IFN-γ secretion in response to IL-12 is dramatically reduced, as measured by ELISA and intracellular cytokine staining. The impact of IL-23 is most prominent in CD8 T cells, but can also be seen in NK, NK-T, and CD4 T cells. We also show that IL-23 can regulate the induction of IFN-γ by endogenously produced IL-12 from Listeria monocytogenes infected macrophages. Furthermore, IL-23 appears to act directly on purified CD8 T cells to negatively regulate IFN-γ induced by IL-12. We are currently investigating the mechanism by which IL-23 inhibits IFN-γ secretion. In addition, experiments to determine if IL-23 can inhibit other effector functions are ongoing. Our data suggest that IL-23 may be a key player in determining the responsiveness of lymphocytes to IL-12 and their subsequent secretion of IFN-γ.

This research is supported by NIH AI064592.

Differential secretion of IL-12 and IL-18 based on intracellular localization of Listeria monocytogenes (44.2)

Listeria monocytogenes (LM) is a gram-positive, intracellular bacterium that is commonly used to investigate the immune response to infection. Pro-inflammatory cytokines, such as IL-12 and IL-18, are secreted during LM infection to promote clearance of the bacteria through the induction of IFN-γ. LM secretes listeriolysin O (LLO) which allows the bacterium to invade the cytoplasm. Neither heat-killed LM (HKLM) nor LLO deficient LM (LLO−LM) actively produce LLO. When bone marrow derived macrophages (macs) and dendritic cells (DCs) are infected with LM, HKLM, or LLO−LM and co-cultured with naïve splenocytes, only macs or DCs infected with LM are able to induce IFN-γ secretion. ELISA data demonstrates that IL-12 is secreted from LM, HKLM, or LLO−LM infected macs and DCs, but IL-18 is only secreted from macs and DCs infected with LM. Therefore, IL-12 can be secreted by macs and DCs regardless of cytoplasmic invasion of LM whereas the secretion of IL-18 requires LM to gain access to the cytoplasm. When mice are infected with HKLM, there is no detectable IFN-γ secretion and this can be attributed to a lack of both IL-12 and IL-18. This implies that IL-12 is induced differently in response to HKLM in vivo versus in vitro. Further studies are ongoing to determine which pattern recognition receptors and cell types are responsible for recognizing and secreting IL-12 and IL-18 during in vivo LM infection.

Supported by NIH AI064592.

Imatinib Mesylate Inhibits Antigen-Specific Memory CD8 T Cell Responses In Vivo

Imatinib mesylate (IM) is effective at inducing complete cytogenetic remission in patients with chronic myelogenous leukemia. Because its influence on CD8 T cell responsiveness in vivo is unknown, we investigated the effects of IM by analyzing the response of OT-1 CD8 T cells to Listeria monocytogenes (LM) that express the cognate epitope OVA(257-264) (LM-OVA). In vitro, IM had no effect on Ag-specific expansion, cell division, cell cycle progression, or IFN-gamma expression in naive or memory OT-1 T cells. However, IM induced apoptosis of naive and memory OT-1 T cells at doses of >5 microM. At 15 microM IM, OT-1 T cells did not survive in in vitro cultures. The primary response of OT-1 T cells in vivo to LM-OVA infection was unaltered. In contrast, continuous IM treatment resulted in a diminished memory OT-1 response. The expression of IL-7Ralpha, a receptor required for memory cell survival, was lower (on OT-1 cells) in animals receiving IM. These results indicate that IM treatment affects the ability of the CD8 memory pool to respond to Ag and has the potential to increase susceptibility to infection.

The role of CD8 T cells in innate immunity and in antigen non-specific protection

The role of CD8 T cells in adaptive immune responses is well understood. These lymphocytes respond through their T cell receptors to diverse antigens presented by MHC class I molecules by proliferating, secreting cytokines and chemokines, and directly lysing infected cells. Recently, a role for CD8 T cells in the innate immune response has become apparent. Independent of T cell receptor ligation, CD8 T cells can mount a response against pathogens by secreting cytokines and can defend against tumors by directly killing transformed cells. This innate response has been shown to be beneficial in controlling several types of bacterial infections. However, a subset of CD8 T cells that have innate non-antigen-specific capabilities has been implicated in self-reactivity, which could lead to autoimmunity.

Thymus-dependent memory phenotype CD8 T cells in naive B6.H-2Kb-/-Db-/- animals mediate an antigen-specific response against Listeria monocytogenes

B6.H-2Kb-/-Db-/- (DKO) mice have greatly reduced numbers of mature CD8alphabeta T cells in their periphery. However, these non-class Ia-selected CD8alphabeta T cells are able to mediate immune responses to a number of pathogens. Approximately 60% of the CD8alphabeta T cells in the spleen and peripheral lymph nodes of naive DKO mice display a memory (CD44high) phenotype. To investigate the origins of these non-class Ia-selected CD8alphabetaCD44high cells, we traced the phenotype of recent thymic emigrants and found that most were CD44low. We also determined whether their appearance was thymus dependent and found that only a small percentage of non-class Ia-selected CD8alphabetaCD44high cells develop in a thymus-independent pathway. Functionally, CD8alphabetaCD44high cells from DKO mice are able to secrete IFN-gamma in response to IL-12 and IL-18 in the absence of cognate Ag. When challenged with anti-CD3 in vivo, nearly half of these cells produce IFN-gamma within 3 h. When purified CD8alphabetaCD44high cells from Thy1.2.DKO mice were transferred into Thy1.1 DKO recipients and then challenged with Listeria monocytogenes, an Ag-specific anti-L. monocytogenes response was observed 6 days later. Our data suggest that non-class Ia-selected CD8alphabetaCD44high cells in naive animals can respond rapidly to Ag and play a role in the innate as well as the early phase of the acquired immune response.

Relative contributions of NK and CD8 T cells to IFN-gamma mediated innate immune protection against Listeria monocytogenes

During the innate immune response to Listeria monocytogenes (LM), the secretion of IFN-gamma is crucial in controlling bacterial numbers. We have shown recently that CD8 T cells have the ability to rapidly secrete IFN-gamma independent of Ag, in response to IL-12 and IL-18, during a LM infection. In the current study, we compared the relative abilities of NK and CD8 T cells to provide innate immune protection. Upon transfer of either NK or memory OT-I T cells (specific for the OVA protein) into IFN-gamma-deficient hosts that were infected subsequently with wild-type LM, both cell types were found in the spleen and had the ability to secrete IFN-gamma. However, the OT-I T cells were more effective at providing innate immune protection as determined by spleen and liver LM burdens. We used immunocytochemistry to demonstrate that upon infection with LM, marginal zone macrophages were localized to the T cell area of the splenic follicle. Transferred memory OT-I T cells were also found in the T cell area of the spleen, co-localizing with the LM and macrophages. In sharp contrast, NK cells were found predominantly in the red pulp region of the spleen. In addition, memory OT-I T cells were also found to be associated with LM lesions in the liver. These results highlight the importance of CD8 T cells in innate immune responses to LM and suggest that their increased protective ability compared with NK cells is the result of their colocalization with LM and macrophages.

Maturational stage-dependent thymocyte responses to TCR engagement

Thymocyte positive and negative selection are dependent on avidity-driven TCR-mediated recognition events in the thymus. High-avidity recognition events result in negative selection, while low-avidity recognition events result in positive selection. However, it has not been established how thymocytes maturation stages affect their responses to TCR signals of different avidities. We gained insight into this question when we reduced thymocyte selection to an in vitro system, in which full maturation of developmentally synchronized immature double-positive thymocytes was induced on a cloned line of thymic epithelial cells. Our analysis of the kinetics of thymocyte development supports a multi-phasic model of thymic selection. In it, thymocyte maturation stages as well as interaction avidity control the outcome TCR stimulation. Positive selection is initiated during a primary recognition event that proceeds independently of the TCR avidity. During a secondary recognition event the final fate of thymocyte, full maturation versus negative selection, is determined by TCR avidity.

The role of TCR stimulation and TGF-beta in controlling the expression of CD94/NKG2A receptors on CD8 T cells

Following antigen recognition, murine CD8 T cells express CD94/NKG2A receptors. Our results show that this up-regulation occurs rapidly in vitro and is accompanied by an approximately 8-fold increase in CD94 and approximately 125-fold increase in NKG2A mRNA. In contrast, only a twofold increase in NKG2C mRNA is noted. The addition of TGF-beta, but not IL-10, IL-12 or IL-15, leads to a further increase in cell membrane expression of these receptors, as well as a approximately 6-fold increase in mRNA for both chains. TGF-beta also increases CD94/NKG2A expression on memory CD8 T cells that are re-exposed to antigen. The effect of TGF-beta on increasing CD94/NKG2A expression on both naive and memory CD8 T cells occurs only when there is a concurrent stimulation through the TCR. In contrast, TGF-beta does not increase expression of CD94/NKG2A on resting or activated NK cells. We also show by using purified CD8 T cells, that TGF-beta acts directly on these cells. These results implicate a role for both antigen and TGF-beta in increasing expression of inhibitory CD94/NKG2A receptors on CD8 T cells.

The role of CD94/NKG2 in innate and adaptive immunity

CD94/NKG2 is a heterodimer expressed on natural killer (NK) and a small subset of T cells. This receptor varies in function as an inhibitor or activator depending on which isoform of NKG2 is expressed. The ligand for CD94/NKG2 is HLA-E in human and its homolog, Qa1 in mouse, which are both nonclassical class I molecules that bind leader peptides from other class I molecules. Although <5% of CD8 T cells express the receptor in a naïve mouse, its expression is upregulated upon specific recognition of antigen. Similar to NK cells, most CD8 T cells that express high levels of CD94 co-express NKG2A, the inhibitory isoform. The engagement of this receptor can lead to a blocking of cytotoxicity. However, these receptors have also been implicated in the cell survival of both NK and CD8 T cells. The level of CD94 expression is inversely correlated with the level of apoptosis in culture. Thus, CD94/NKG2 receptors may regulate effector functions and cell survival of NK cells and CD8 T cells, thereby playing a crucial role in the innate and adaptive immune response to a pathogen.

Memory CD8+ T cells provide innate immune protection against Listeria monocytogenes in the absence of cognate antigen

Interferon (IFN)-γ plays an important role in the innate immune response against intracellular bacterial pathogens. It is commonly thought that natural killer cells are the primary source of this cytokine that is involved in activating antibacterial effects in infected cells and polarizing CD4⁺ T cells toward the Th1 subset. However, here we show that both effector and memory CD8⁺ T cells have the potential to secrete IFN-γ in response to interleukin (IL)-12 and IL-18 in the absence of cognate antigen. We demonstrate that memory CD8⁺ T cells specific for the ovalbumin protein secrete IFN-γ rapidly after infection with wild-type Listeria monocytogenes (LM). Furthermore, small numbers of ovalbumin-specific, memory CD8⁺ T cells can reduce spleen and liver bacterial counts in IFN-γ–deficient mice 3 d after LM infection. Up-regulation of the receptors for IL-12 and IL-18 provides a mechanism for the ability of memory CD8⁺ T cells to respond in this antigen nonspecific manner. Thus, CD8⁺ T cells play an important role in the innate immune response against intracellular pathogens by rapidly secreting IFN-γ in response to IL-12 and IL-18.

Preferential survival of CD8 T and NK cells expressing high levels of CD94

The Qa-1(b)/Qdm tetramer binds to CD94/NKG2 receptors expressed at high levels on approximately 50% of murine NK cells. Although very few CD8 T cells from naive mice express CD94/NKG2 receptors, approximately 50% of CD8 T cells taken from mice undergoing a secondary response against Listeria monocytogenes (LM) are CD94(high) and bind the tetramer. Although CD94(int) NK cells do not bind the tetramer, CD94(int) CD8 T cells do, and this binding is dependent on the CD8 coreceptor. We found that the extent of apoptosis in CD8 T and NK cells was inversely related to the expression of CD94, with lower levels of apoptosis seen in CD94(high) cells after 1-3 days of culture. The difference in CD8 T cell survival was evident as early as 6 h after culture and persisted until nearly all the CD94(neg/int) cells were apoptotic by 48 h. In contrast, expression of inhibitory Ly-49A,G2,C/I molecules was associated with higher levels of apoptosis. Cross-linking CD94/NKG2 receptors on CD8 T cells from a mouse undergoing an LM infection further reduced the percentage of apoptotic cells on the CD94-expressing populations, while cross-linking Ly-49I had no effect on CD8 T cells expressing Ly-49I. Cross-linking CD3 on CD8 T cells from a mouse undergoing a secondary LM infection increases the extent of apoptosis, but this is prevented by cross-linking CD94/NKG2 receptors at the same time. Similar results were observed with NK cells in that the CD94(high) population displayed less apoptosis than CD94(int) cells after 1-3 days in culture. Therefore, the expression of CD94/NKG2 is correlated with a lower level of apoptosis and may play an important role in the maintenance of CD8 T and NK cells.

Contribution of CD8+ T cells to innate immunity: IFN-gamma secretion induced by IL-12 and IL-18

The role of CD8+ T cells in adaptive immunity is well documented and involves numerous effector mechanisms including direct cytolysis of targets and secretion of cytokines. The role of CD8+ T cells in innate immunity has not been previously appreciated. Using J774 macrophages infected in vitro with the intracellular bacterium, Listeria monocytogenes (LM), we show that CD8+ T cells isolated from naïve C57BL/6 (B6) mice respond rapidly by secreting IFN-gamma. CD8+ T cells secreting IFN-gamma can also be found in naïve B6 mice 16 h after infection with LM. This rapid IFN-gamma response is TCR-independent and mediated through the actions of IL-12 and IL-18. Cell surface staining and cell sorting experiments indicate that these novel CD8+ T cells express memory markers. In vitro CFSE-labeling experiments show that IFN-gamma-secreting CD8+ T cells proliferate rapidly after 2 days in culture and after 4 days constitute the majority of the CD8+ T cell population. Together, these data suggest an important role for IFN-gamma-secreting CD8+ T cells in the innate response to bacterial pathogens.

A physiological ligand of positive selection is recognized as a weak agonist

Positive selection is a process that ensures that peripheral T cells express TCR that are self-MHC restricted. This process occurs in the thymus and requires both self-MHC and self-peptides. We have recently established a TCR transgenic (TCR(trans)(+)) mouse model using the C10.4 TCR restricted to the MHC class Ib molecule, H2-M3. Having defined H2-M3 as the positively selecting MHC molecule, the severely limited number of H2-M3 binding peptides allowed us to characterize a mitochondrial NADH dehydrogenase subunit 1-derived 9-mer peptide as the physiological ligand of positive selection. Here, we demonstrate that the NADH dehydrogenase subunit 1 self-peptide is seen by mature C10.4 TCR(trans)(+) T cells as a weak agonist and induces positive selection at a defined concentration range. We also found that the full-length cognate peptide, a strong agonist for mature C10.4 TCR(trans)(+) T cells, initiated positive selection, albeit at significantly lower concentrations. At increased peptide concentrations, and thus increased epitope densities, either peptide only induced the development of partially functional T cells. We conclude that successful positive selection only proceeded at a defined, yet fairly narrow window of avidity.

A physiological ligand of positive selection is seen with high specificity

Positive selection is a process that ensures that peripheral T cells express TCR that are restricted to self-MHC molecules. This process requires both self-MHC and self-peptides. We have recently established a TCR transgenic mouse model (C10.4 TCRtrans+) in which the transgenic TCR was selected on the nonclassical MHC class Ib molecule H2-M3 in conjunction with a physiologically occurring peptide derived from the mitochondrial NADH-dehydrogenase subunit 1 gene (9-mer peptide). Here, the specificity of positive selection of C10.4 TCRtrans+ T cells was examined using a fetal thymic organ culture system. We demonstrated that at low peptide concentrations, shortening the NADH-dehydrogenase subunit 1 gene 9-mer peptide or mutating its surface-exposed side chains severely impaired its ability to induce positive selection. We concluded that under physiological conditions positive selection of C10.4 TCRtrans+ T cells was highly specific and occurred at low epitope densities.

Rural Minnesota family physicians. Practice characteristics, gender, income, and job satisfaction

This study investigated rural physicians' job satisfaction, income, and working conditions through a survey of a random sample of rural family physicians in Minnesota. Of the 300 surveys sent, 210 (70%) were returned and usable. Male physicians reported more years of experience, work hours, and call hours per week than female physicians (p < 0.0005). On a scale of 1 to 5, average overall job satisfaction among the physicians was 4.04, with men averaging 4.0 and women, 4.3. Overall job satisfaction was positively correlated with the presence of a hospital in town (p < 0.05) and negatively correlated with the number of work hours, including hours on call, per week (p < 0.05). Overall job satisfaction was lowest for those in practice 20-34 years. Average reported annual income was $127,213 (men, $131,400; women, $97,800; p < 0.0001). In a comparison of physicians working the same number of hours including call, men earned more than women. Rural Minnesota family physicians reported high job satisfaction. Income was positively correlated with size of practice, years of experience, and number of hours worked. In addition, men earned more than women, and physicians whose pay was based on production earned more than physicians on straight salary.

Positive selection of an H2-M3 restricted T cell receptor

Thymocytes are positively selected for alphabeta T cell antigen receptors (TCR) that recognize antigen in conjunction with self-major histocompatibility complex (MHC) molecules. MHC bound peptides participate in positive selection; however, their role has remained controversial. A TCR transgenic mouse was established using a TCR restricted to the MHC class Ib molecule, H2-M3. Having defined H2-M3 as the positively selecting MHC molecule, the severely limited number of H2-M3 binding peptides allowed us to characterize an NADH dehydrogenase subunit 1 (ND1)-derived peptide as the physiological ligand of positive selection. This peptide bears no apparent sequence homology to the cognate peptide, is expressed ubiquitously, and yet does not interfere with peripheral T cells. Our studies also suggest that positive selection becomes promiscuous at high epitope densities.

[Health risks of vaccination of farmed fish]

In 1991, three cases of anaphylactoid reactions among vaccinators of farmed fish were registered in Norway. The reactions developed after repeated accidental self-injection of vaccine against salmon furunculosis. In 1991, some 60 million salmon were vaccinated against furunculosis at approximately 50 grams body weight. Following such self-injection of vaccine, inflammatory reactions are seen in the injected finger, also spreading occasionally to the hand. More seldom a "flu" like syndrome with fever, muscle aches, and general malaise is experienced probably caused by endotoxins in the vaccine. Devices to protect the fingers against accidental self-injection have been developed and, so far, the results are promising.

An algorithm for planning stereotactic brain implants

A computer software package was developed for the planning and execution of brain biopsy and radioactive implant procedures with the BRW Stereotaxic System. With the application of computer graphics and a zero-one integer variable programming algorithm, an implant plan with accompanying isodose distributions and stereotactic coordinates can be easily accomplished at the time of the operation when the computer imaging terminal and a printer/plotter is placed in the operating room.