Inflammatory Monocyte Recruitment Is Regulated by Interleukin-23 during Systemic Bacterial Infection

Listeria monocytogenes is a Gram-positive intracellular pathogen that causes meningitis and septicemia in immunocompromised individuals and spontaneous abortion in pregnant women. The innate immune response against L. monocytogenes is primarily mediated by neutrophils and monocytes. Interleukin-23 (IL-23) is an important proinflammatory cytokine well known for its role in neutrophil recruitment in various infectious and autoimmune diseases. We have previously shown that IL-23 is required for host resistance against L. monocytogenes and for neutrophil recruitment to the liver, but not the spleen, during infection. Despite efficient neutrophil recruitment to the spleen, IL-23p19 knockout (KO) mice have an increased bacterial burden in this organ, suggesting that IL-23 may regulate the recruitment/function of another cell type to the spleen. In this study, we show that specific depletion of neutrophils abrogated the differences in bacterial burdens in the livers but not the spleens of C57BL/6 (B6) and IL-23p19 KO mice. Interestingly, L. monocytogenes-infected IL-23p19 KO mice had fewer monocytes in the spleen than B6 mice, as well as a reduction in the monocyte-recruiting chemokines CCL2 and CCL7. Additionally, the overall concentrations of tumor necrosis factor alpha (TNF-α) and nitric oxide (NO^•), as well as the percentages and total numbers of monocytes producing TNF-α and NO^•, were reduced in IL-23p19 KO mice compared to levels in B6 mice, leading to increased bacterial burdens in the spleens of L. monocytogenes-infected IL-23p19 KO mice. Collectively, our data establish that IL-23 is required for the optimal recruitment of TNF-α- and NO^•-producing inflammatory monocytes, thus revealing a novel mechanism by which this proinflammatory cytokine provides protection against bacterial infection.     

Enhancement of Innate Immunity against Mycobacterium avium Infection by Immunostimulatory DNA Is Mediated by Indoleamine 2,3-Dioxygenase

Bacterial DNA and its synthetic immunostimulatory oligodeoxynucleotide analogs (ISS-ODN) activate innate immunity and promote Th1 and cytotoxic T-lymphocyte immune responses. Based on these activities, we investigated whether ISS-ODN could modify the course of Mycobacterium avium infection. M. avium growth in vitro was significantly inhibited by ISS-ODN treatment of human and mouse macrophages, and M. avium growth in vivo was similarly inhibited in C57BL/6 mice treated with ISS-ODN. This protective effect of ISS-ODN was largely independent of tumor necrosis factor alpha (TNF-alpha), interleukin 12 (IL-12), nitric oxide, NADPH oxidase, alpha/beta interferon (IFN-alpha/beta), and IFN-gamma. In contrast, we found that the induction of indoleamine 2,3-dioxygenase (IDO) was required for the antimycobacterial effect of ISS-ODN. To evaluate the potential for synergism between ISS-ODN and other antimycobacterial agents, treatment with a combination of ISS-ODN and clarithromycin (CLA) was tested in vitro and in vivo. ISS-ODN significantly enhanced the therapeutic effect of CLA in both human and mouse macrophages and in C57BL/6 mice. This study newly identifies IDO as being involved in the antimicrobial activity of ISS-ODN and suggests the usefulness of ISS-ODN when used in combination with conventional chemotherapy for microbial infections.     

Innate Immune Training with Bacterial Extracts Enhances Lung Macrophage Recruitment to Protect from Betacoronavirus Infection

Training of the innate immune system with orally ingested bacterial extracts was demonstrated to have beneficial effects on infection clearance and disease outcome. The aim of our study was to identify cellular and molecular processes responsible for these immunological benefits. We used a murine coronavirus (MCoV) A59 mouse model treated with the immune activating bacterial extract Broncho-Vaxom (BV) OM-85. Tissue samples were analysed with qPCR, RNA sequencing, histology, and flow cytometry. After BV OM-85 treatment, interstitial macrophages accumulated in lung tissue leading to a faster response of type I interferon (IFN) signalling after MCoV infection resulting in overall lung tissue protection. Moreover, RNA sequencing showed that lung tissue from mice receiving BV OM-85 resembled an intermediate stage between healthy and viral infected lung tissue at day 4, indicating a faster return to normal tissue homoeostasis. The pharmacologic effect was mimicked by adoptively transferring naive lung macrophages into lungs from recipient mice before virus infection. The beneficial effect of BV OM-85 was abolished when inhibiting initial type I IFN signalling. Overall, our data suggest that BV OM-85 enhances lung macrophages allowing for a faster IFN response towards a viral challenge as part of the oral-induced innate immune system training.     

Galectin-3 Plays an Important Role in Innate Immunity to Gastric Infection by Helicobacter pylori

We studied the role of galectin-3 (Gal3) in gastric infection by Helicobacter pylori. We first demonstrated that Gal3 was selectively expressed by gastric surface epithelial cells and abundantly secreted into the surface mucus layer. We next inoculated H. pylori Sydney strain 1 into wild-type (WT) and Gal3-deficient mice using a stomach tube. At 2 weeks postinoculation, the bacterial cells were mostly trapped within the surface mucus layer in WT mice. In sharp contrast, they infiltrated deep into the gastric glands in Gal3-deficient mice. Bacterial loads in the gastric tissues were also much higher in Gal3-deficient mice than in WT mice. At 6 months postinoculation, H. pylori had successfully colonized within the gastric glands of both WT and Gal3-deficient mice, although the bacterial loads were still higher in the latter. Furthermore, large lymphoid clusters mostly consisting of B cells were frequently observed in the gastric submucosa of Gal3-deficient mice. In vitro, peritoneal macrophages from Gal3-deficient mice were inefficient in killing engulfed H. pylori. Furthermore, recombinant Gal3 not only induced rapid aggregation of H. pylori but also exerted a potent bactericidal effect on H. pylori as revealed by propidium iodide uptake and a morphological shift from spiral to coccoid form. However, a minor fraction of bacterial cells, probably transient phase variants of Gal3-binding sugar moieties, escaped killing by Gal3. Collectively, our data demonstrate that Gal3 plays an important role in innate immunity to infection and colonization of H. pylori.     

Innate Resistance to Babesia Infection Is Influenced by Genetic Background and Gender

Infection of severe combined immunodeficient mice with Babesia sp. strain WA1 was studied to assess the contributions of innate and adaptive immunity in resistance to acute babesiosis. The scid mutation showed little effect in genetically susceptible C3H mice and did not decrease the inherent resistance of C57BL/6 mice to the infection, suggesting that innate immunity plays a central role in determining the course of Babesia infection in these strains. In contrast, the scid mutation dramatically impaired resistance in moderately susceptible BALB/c mice, suggesting that acquired immunity may play an important secondary role. In comparison to their female counterparts, male mice of different genetic backgrounds showed increased resistance to the infection, indicating that the gender of the host may influence protection against babesiosis.     

Interleukin-1 Receptor but Not Toll-Like Receptor 2 Is Essential for MyD88-Dependent Th17 Immunity to Coccidioides Infection

Interleukin-17A (IL-17A)-producing CD4⁺ T helper (Th17) cells have been shown to be essential for defense against pulmonary infection with Coccidioides species. However, we have just begun to identify the required pattern recognition receptors and understand the signal pathways that lead to Th17 cell activation after fungal infection. We previously reported that Card9^−/− mice vaccinated with formalin-killed spherules failed to acquire resistance to Coccidioides infection. Here, we report that both MyD88^−/− and Card9^−/− mice immunized with a live, attenuated vaccine also fail to acquire protective immunity to this respiratory disease. Like Card9^−/− mice, vaccinated MyD88^−/− mice revealed a significant reduction in numbers of both Th17 and Th1 cells in their lungs after Coccidioides infection. Both Toll-like receptor 2 (TLR2) and IL-1 receptor type 1 (IL-1r1) upstream of MyD88 have been implicated in Th17 cell differentiation. Surprisingly, vaccinated TLR2^−/− and wild-type (WT) mice showed similar outcomes after pulmonary infection with Coccidioides, while vaccinated IL-1r1^−/− mice revealed a significant reduction in the number of Th17 cells in their infected lungs compared to WT mice. Thus, activation of both IL-1r1/MyD88- and Card9-mediated Th17 immunity is essential for protection against Coccidioides infection. Our data also reveal that the numbers of Th17 cells were reduced in IL-1r1^−/− mice to a lesser extent than in MyD88^−/− mice, raising the possibility that other TLRs are involved in MyD88-dependent Th17 immunity to coccidioidomycosis. An antimicrobial action of Th17 cells is to promote early recruitment of neutrophils to infection sites. Our data revealed that neutrophils are required for vaccine immunity to this respiratory disease.     

Role of Immunity in Viral-Induced Bacterial Superinfections of the Lung

Although viral illnesses are predisposing causes for pulmonary bacterial infections, the interrelationships of viral virulence and host immunity to alterations in susceptibility to bacterial infection are incompletely understood. We used two mutant strains of encephalomyocarditis virus (minimally virulent Mengo-37A and a highly virulent Columbia SK [Col-SK]) to investigate these interrelationships. Mice that had been immunized to Mengo-37A, and nonimmunized controls, were challenged with aerosols containing 10(4) plaque-forming units of Mengo-37A or Col-SK per liter. The effect of each viral infection on pulmonary antibacterial activity was assessed 3 days later by measuring the capacity of the lungs to kill inhaled radiophosphorus ((32)P)-labeled Staphylococcus aureus. The degree of antibacterial dysfunction found was proportional to the virulence of the infecting virus. If the host was immune to the infecting virus, bactericidal function was not impaired by viral challenge. Neither mutant caused significant pulmonary damage; therefore: (i) viral-induced impairment in bactericidal activity reflects, quantitatively, the virulence of the virus and (ii) viral immunity protects pulmonary bacterial defenses by preventing damage to the phagocyte from the virus or its attendant metabolic abnormalities.     

B Cells Modulate Systemic Responses to Pneumocystis murina Lung Infection and Protect On-Demand Hematopoiesis via T Cell-Independent Innate Mechanisms when Type I Interferon Signaling Is Absent

HIV infection results in a complex immunodeficiency due to loss of CD4⁺ T cells, impaired type I interferon (IFN) responses, and B cell dysfunctions causing susceptibility to opportunistic infections such as Pneumocystis murina pneumonia and unexplained comorbidities, including bone marrow dysfunctions. Type I IFNs and B cells critically contribute to immunity to Pneumocystis lung infection. We recently also identified B cells as supporters of on-demand hematopoiesis following Pneumocystis infection that would otherwise be hampered due to systemic immune effects initiated in the context of a defective type I IFN system. While studying the role of type I IFNs in immunity to Pneumocystis infection, we discovered that mice lacking both lymphocytes and type I IFN receptor (IFrag^−/−) developed progressive bone marrow failure following infection, while lymphocyte-competent type I IFN receptor-deficient mice (IFNAR^−/−) showed transient bone marrow depression and extramedullary hematopoiesis. Lymphocyte reconstitution of lymphocyte-deficient IFrag^−/− mice pointed to B cells as a key player in bone marrow protection. Here we define how B cells protect on-demand hematopoiesis following Pneumocystis lung infection in our model. We demonstrate that adoptive transfer of B cells into IFrag^−/− mice protects early hematopoietic progenitor activity during systemic responses to Pneumocystis infection, thus promoting replenishment of depleted bone marrow cells. This activity is independent of CD4⁺ T cell help and B cell receptor specificity and does not require B cell migration to bone marrow. Furthermore, we show that B cells protect on-demand hematopoiesis in part by induction of interleukin-10 (IL-10)- and IL-27-mediated mechanisms. Thus, our data demonstrate an important immune modulatory role of B cells during Pneumocystis lung infection that complement the modulatory role of type I IFNs to prevent systemic complications.     

Type 2 Innate Immunity in Helminth Infection Is Induced Redundantly and Acts Autonomously following CD11c+ Cell Depletion

Infection with gastrointestinal helminths generates a dominant type 2 response among both adaptive (Th2) and innate (macrophage, eosinophil, and innate lymphoid) immune cell types. Two additional innate cell types, CD11c(high) dendritic cells (DCs) and basophils, have been implicated in the genesis of type 2 immunity. Investigating the type 2 response to intestinal nematode parasites, including Heligmosomoides polygyrus and Nippostrongylus brasiliensis, we first confirmed the requirement for DCs in stimulating Th2 adaptive immunity against these helminths through depletion of CD11c(high) cells by administration of diphtheria toxin to CD11c.DOG mice. In contrast, responsiveness was intact in mice depleted of basophils by antibody treatment. Th2 responses can be induced by adoptive transfer of DCs, but not basophils, exposed to soluble excretory-secretory products from these helminths. However, innate type 2 responses arose equally strongly in the presence or absence of CD11c(high) cells or basophils; thus, in CD11c.DOG mice, the alternative activation of macrophages, as measured by expression of arginase-1, RELM-α, and Ym-1 (Chi3L3) in the intestine following H. polygyrus infection or in the lung following N. brasiliensis infection, was unaltered by depletion of CD11c-expressing DCs and alveolar macrophages or by antibody-mediated basophil depletion. Similarly, goblet cell-associated RELM-β in lung and intestinal tissues, lung eosinophilia, and expansion of innate lymphoid ("nuocyte") populations all proceeded irrespective of depletion of CD11c(high) cells or basophils. Thus, while CD11c(high) DCs initiate helminth-specific adaptive immunity, innate type 2 cells are able to mount an autonomous response to the challenge of parasite infection.     

Defects in Innate Immunity Predispose C57BL/6J-Leprdb/Leprdb Mice to Infection by Staphylococcus aureus

Foot and ankle infections are the most common cause of hospitalization among diabetic patients, and Staphylococcus aureus is a major pathogen implicated in these infections. Patients with insulin-resistant (type 2) diabetes are more susceptible to bacterial infections than nondiabetic subjects, but the pathogenesis of these infections is poorly understood. C57BL/6J-Lepr^db/Lepr^db (hereafter, db/db) mice develop type 2 diabetes due to a recessive, autosomal mutation in the leptin receptor. We established a S. aureus hind paw infection in diabetic db/db and nondiabetic Lepr^+/+ (+/+) mice to investigate host factors that predispose diabetic mice to infection. Nondiabetic +/+ mice resolved the S. aureus hind paw infection within 10 days, whereas db/db mice with persistent hyperglycemia developed a chronic infection associated with a high bacterial burden. Diabetic db/db mice showed a more robust neutrophil infiltration to the infection site and higher levels of chemokines in the infected tissue than +/+ mice. Blood from +/+ mice killed S. aureus in vitro, whereas db/db blood was defective in bacterial killing. Compared with peripheral blood neutrophils from +/+ mice, db/db neutrophils demonstrated a diminished respiratory burst when stimulated with S. aureus. However, bone marrow-derived neutrophils from +/+ and db/db mice showed comparable phagocytosis and bactericidal activity. Our results indicate that diabetic db/db mice are more susceptible to staphylococcal infection than their nondiabetic littermates and that persistent hyperglycemia modulates innate immunity in the diabetic host.Approximately 2 million of the estimated 16 million individuals with diabetes in the United States will develop chronic foot ulcers or infections during the course of their disease (38). An infection is initiated when the skin barrier is breached and bacteria, mostly skin commensals, gain access to the underlying tissues. Although limb-threatening infections are usually polymicrobial, Staphylococcus aureus is a major determinant of these infections (21). S. aureus is the predominant pathogen in non-limb-threatening infections, particularly in patients who have not received antimicrobial therapy (5, 26, 27). The emergence of S. aureus strains resistant to multiple antibiotics has made treatment of staphylococcal infections especially problematic. Methicillin-resistant S. aureus strains have become increasingly prevalent among both nosocomial and community-acquired infections within the United States (22, 36, 43). The prevalence of methicillin-resistant S. aureus is higher among diabetic patients than in the general population (11, 44, 45). Seven S. aureus strains resistant to vancomycin have been isolated in the United States, and four of these strains were isolated from patients with diabetes (42, 50). Complications of type 2 diabetes such as peripheral neuropathy and vasculopathy contribute to delayed wound healing. Although the increased susceptibility of the diabetic host to bacterial infections is well established, the chronicity of these infections is poorly understood. A consistent defect in the humoral or cell-mediated host immune system of diabetic patients has not been demonstrated. However, deficiencies in the host innate immune response are apparent since clinical investigations have indicated that phagocytes from type 2 diabetic patients are in a heightened state of oxidative stress and have impaired bactericidal activity and chemotaxis (6, 15, 41, 48). Clearly, numerous pathophysiologic perturbations contribute to the recurrence of soft tissue and bone infections in the lower extremity of patients with diabetes.C57BL/6J-Lepr^db/Lepr^db (hereafter, db/db) mice are a valuable model of type 2 diabetes since they are hyperglycemic and resistant to insulin, and they experience peripheral neuropathy, delayed wound healing, and myocardial disease. In this study we inoculated the hind paws of wild-type Lepr^+/+ (+/+) and diabetic db/db mice with S. aureus and evaluated the course of the ensuing infection in each host type, as well as the resultant host innate immune response to infection. Diabetic mice that were ≥4 months of age were more susceptible to staphylococcal infection than age-matched nondiabetic control animals. The db/db mice showed a heightened inflammatory response that was characterized by defects in phagocyte function.     

The Expression of Wnt4 Is Regulated by Estrogen via an Estrogen Receptor Alpha-dependent Pathway in Rat Pituitary Growth Hormone-producing Cells

Wnt signaling is important in many aspects of cell biology and development. In the mouse female reproductive tract, Wnt4, Wnt5a, and Wnt7a show differential expression during the estrus cycle, suggesting that they participate in female reproductive physiology. Although the pituitary is a major gland regulating reproduction, the molecular mechanism of Wnt signaling here is unclear. We elucidated the subcellular distribution of Wnt4 in the pituitary of estrogen-treated ovariectomized female rats. Expression of Wnt4 mRNA increased dramatically, particularly in proestrus compared with estrus and metestrus. Wnt4 protein was observed in the cytoplasm of almost all growth hormone (GH)-producing cells and in only a few thyroid-stimulating hormone β (TSHβ)-producing cells. In rat GH-producing pituitary tumor (MtT/S) cells, estrogen-induced expression of Wnt4 mRNA was completely inhibited by estrogen receptor antagonist ICI 182,780 in vitro. Thus, rat pituitary GH cells synthesize Wnt4 and this is induced by estrogen mediated via an estrogen receptor alpha-dependent pathway.     

Lactobacillus rhamnosus Affects Rat Peritoneal Cavity Cell Response to Stimulation with Gut Microbiota: Focus on the Host Innate Immunity

Inflammation - Gut microbiota contribute to shaping the immune repertoire of the host, whereas probiotics may exert beneficial effects by modulating immune responses. Having in mind the differences...     

Proteoglycans: Key Regulators of Pulmonary Inflammation and the Innate Immune Response to Lung Infection

Exposure to viruses and bacteria results in lung infections and places a significant burden on public health. The innate immune system is an early warning system that recognizes viruses and bacteria, which results in the rapid production of inflammatory mediators such as cytokines and chemokines and the pulmonary recruitment of leukocytes. When leukocytes emigrate from the systemic circulation through the extracellular matrix (ECM) in response to lung infection they encounter proteoglycans, which consist of a core protein and their associated glycosaminoglycans. In this review, we discuss how proteoglycans serve to modify the pulmonary inflammatory response and leukocyte migration through a number of different mechanisms including: (1) The ability of soluble proteoglycans or fragments of glycosaminoglycans to activate Toll‐like receptor (TLRs) signaling pathways; (2) The binding and sequestration of cytokines, chemokines, and growth factors by proteoglycans; (3) the ability of proteoglycans and hyaluronan to facilitate leukocyte adhesion and sequestration; and (4) The interactions between proteoglycans and matrix metalloproteinases (MMP) that alter the function of these proteases. In conclusion, proteoglycans fine‐tune tissue inflammation through a number of different mechanisms. Clarification of the mechanisms whereby proteoglycans modulate the pulmonary inflammatory response will most likely lead to new therapeutic approaches to inflammatory lung disease and lung infection. Anat Rec, 293:968–981, 2010. © 2010 Wiley‐Liss, Inc.     

Toll-Like Receptor 2 (TLR2) and TLR9 Play Opposing Roles in Host Innate Immunity against Salmonella enterica Serovar Typhimurium Infection

Toll-like receptors (TLRs) are evolutionarily conserved host proteins that are essential for effective host defense against pathogens. However, recent studies suggest that some TLRs can negatively regulate immune responses. We observed here that TLR2 and TLR9 played opposite roles in regulating innate immunity against oral infection of Salmonella enterica serovar Typhimurium in mice. While TLR9^−/− mice exhibited shortened survival, an increased cytokine storm, and more severe Salmonella hepatitis than wild-type (WT) mice, TLR2^−/− mice exhibited the opposite phenomenon. Further studies demonstrated that TLR2 deficiency and TLR9 deficiency in macrophages both disrupted NK cell cytotoxicity against S. Typhimurium-infected macrophages by downregulating NK cell degranulation and gamma interferon (IFN-γ) production through decreased macrophage expression of the RAE-1 NKG2D ligand. But more importantly, we found that S. Typhimurium-infected TLR2^−/− macrophages upregulated inducible nitric oxide synthase (iNOS) expression, resulting in a lower bacterial load than that in WT macrophages in vitro and livers in vivo as well as low proinflammatory cytokine levels. In contrast, TLR9^−/− macrophages showed decreased reactive oxygen species (ROS) expression concomitant with a high bacterial load in the macrophages and in livers of TLR9^−/− mice. TLR9^−/− macrophages were also more susceptible than WT macrophages to S. Typhimurium-induced necroptosis in vitro, likely contributing to bacterial spread and transmission in vivo. Collectively, these findings indicate that TLR2 negatively regulates anti-S. Typhimurium immunity, whereas TLR9 is vital to host defense and survival against S. Typhimurium invasion. TLR2 antagonists or TLR9 agonists may thus serve as potential anti-S. Typhimurium therapeutic agents.     

Susceptibility to Progressive Cryptococcus neoformans Pulmonary Infection Is Regulated by Loci on Mouse Chromosomes 1 and 9

Genetic factors that regulate the pathogenesis of pneumonia caused by the fungus Cryptococcus neoformans are poorly understood. Through a phenotypic strain survey we observed that inbred C3H/HeN mice develop a significantly greater lung fungal burden than mice of the resistant CBA/J strain 4 weeks following intratracheal infection with C. neoformans ATCC 24067. The aim of the present study was to characterize the inflammatory response of C3H/HeN mice following C. neoformans pulmonary infection and to identify genetic loci that regulate host defense. Following cryptococcal infection, C3H/HeN mice demonstrated a Th2 immune response with heightened airway and tissue eosinophilia, goblet cell metaplasia, and significantly higher lung interleukin-5 (IL-5) and IL-13 protein expression relative to CBA/J mice. Conversely, CBA/J mice exhibited greater airway and tissue neutrophilia that was associated with significantly higher pulmonary expression of gamma interferon, CXCL10, and IL-17 proteins than C3H/HeN mice. Using the fungal burden at 4 weeks postinfection as a phenotype, genome-wide quantitative trait locus (QTL) analysis among 435 segregating (C3H/HeN × CBA/J)F2 (C3HCBAF2) hybrids identified two significant QTLs on chromosomes 1 (Cnes4) and 9 (Cnes5) that control susceptibility to cryptococcal pneumonia in an additive manner. Susceptible C3H/HeN mice carry a resistance allele at Cnes4 and a susceptibility allele at Cnes5. These studies reveal additional genetic complexity of the host response to C. neoformans that is associated with divergent patterns of pulmonary inflammation.     

Neither Primary nor Memory Immunity to Mycobacterium tuberculosis Infection Is Compromised in Mice with Chronic Enteric Helminth Infection

Previously we had reported that Nippostrongylus brasiliensis, a helminth with a lung migratory phase, affected host resistance against Mycobacterium tuberculosis infection through the induction of alternatively activated (M2) macrophages. Several helminth species do not have an obligatory lung migratory phase but establish chronic infections in the host that include potent immune downregulatory effects, in part mediated through induction of a FoxP3⁺ T regulatory cell (Treg) response. Treg cells exhibit duality in their functions in host defense against M. tuberculosis infection since their depletion leads to enhanced priming of T cells in the lymph nodes and attendant improved control of M. tuberculosis infection, while their presence in the lung granuloma protects against excessive inflammation. Heligmosomoides polygyrus is a strictly murine enteric nematode that induces a strong FoxP3 Treg response in the host. Therefore, in this study we investigated whether host immunity to M. tuberculosis infection would be modulated in mice with chronic H. polygyrus infection. We report that neither primary nor memory immunity conferred by Mycobacterium bovis BCG vaccination was affected in mice with chronic enteric helminth infection, despite a systemic increase in FoxP3⁺ T regulatory cells. The findings indicate that anti-M. tuberculosis immunity is not similarly affected by all helminth species and highlight the need to consider this inequality in human coinfection studies.     

Cell-Mediated Immunity to Bacterial Infection in the Mouse. Thymus-Derived Cells as Effectors of Acquired Resistance to Listeria monocytogenes

Four lines of evidence indicated that thymus-derived (T) cells play an essential role in the expression of cell-mediated immunity (CMI) to Listeria . a) T cell depleted (ATx-BM) CBA mice were unable to generate antibacterial immunity. b) Responsiveness was restored to ATx-BM CBA mice by injection of CBA X C57BL F₁ thymocytes and essential CMI effector cells were derived from the F₁ thymocytes (identified by anti-H-2 sera). c) The activity of immune cells from intact CBA mice was abolished by anti-theta treatment but d) enriched by treatment with anti-B cell, anti-macrophage serum. Evidence from adult thymectomized mice and that described in b) above, indicated that T cells which had left the thymus more than 6 weeks or less than 3 weeks prior to immunization could act as progenitors of effector T cells, and that no cooperaiion between these 2 cell classes was necessary for an optimal response.     

Interleukin-7 Produced by Intestinal Epithelial Cells in Response to Citrobacter rodentium Infection Plays a Major Role in Innate Immunity against This Pathogen

Interleukin-7 (IL-7) engages multiple mechanisms to overcome chronic viral infections, but the role of IL-7 in bacterial infections, especially enteric bacterial infections, remains unclear. Here we characterized the previously unexplored role of IL-7 in the innate immune response to the attaching and effacing bacterium Citrobacter rodentium. C. rodentium infection induced IL-7 production from intestinal epithelial cells (IECs). IL-7 production from IECs in response to C. rodentium was dependent on gamma interferon (IFN-γ)-producing NK1.1⁺ cells and IL-12. Treatment with anti-IL-7Rα antibody during C. rodentium infection resulted in a higher bacterial burden, enhanced intestinal damage, and greater weight loss and mortality than observed with the control IgG treatment. IEC-produced IL-7 was only essential for protective immunity against C. rodentium during the first 6 days after infection. An impaired bacterial clearance upon IL-7Rα blockade was associated with a significant decrease in macrophage accumulation and activation in the colon. Moreover, C. rodentium-induced expansion and activation of intestinal CD4⁺ lymphoid tissue inducer (LTi) cells was completely abrogated by IL-7Rα blockade. Collectively, these data demonstrate that IL-7 is produced by IECs in response to C. rodentium infection and plays a critical role in the protective immunity against this intestinal attaching and effacing bacterium.     

Microbiota-Driven Immune Cellular Maturation Is Essential for Antibody-Mediated Adaptive Immunity to Staphylococcus aureus Infection in the Eye

As an immune-privileged site, the eye, and particularly the outer corneal surface, lacks resident mature immune effector cells. Physical barriers and innate mediators are the best-described effectors of immunity in the cornea. When the barriers are breached, infection can result in rapid tissue destruction, leading to loss of visual acuity and frank blindness. To determine the cellular and molecular components needed for effective adaptive immunity on the corneal surface, we investigated which immune system effectors were required for protection against Staphylococcus aureus corneal infections in mice, which are a serious cause of human eye infections. Both systemically injected and topically applied antibodies to the conserved cell surface polysaccharide poly-N-acetylglucosamine (PNAG) were effective at mediating reductions in corneal pathology and bacterial levels. Additional host factors impacting protection included intercellular adhesion molecule 1 (ICAM-1)-dependent polymorphonuclear leukocyte (PMN) recruitment, functional CD4⁺ T cells, signaling via the interleukin-17 (IL-17) receptor, and IL-22 production. In germfree mice, there was no protective efficacy of antibody to PNAG due to the lack of LY6G⁺ inflammatory cell coeffector recruitment to the cornea. Protection was manifest after 3 weeks of exposure to conventional mice and acquisition of a resident microbiota. We conclude that in the anterior eye, ICAM-1-mediated PMN recruitment to the infected cornea along with endogenous microbiota-matured CD4⁺ T cells producing both IL-17 and IL-22 is required for antibody to PNAG to protect against S. aureus infection.