Epithelial antimicrobial peptides in host defense against infection

One component of host defense at mucosal surfaces seems to be epithelium-derived antimicrobial peptides. Antimicrobial peptides are classified on the basis of their structure and amino acid motifs. Peptides of the defensin, cathelicidin, and histatin classes are found in humans. In the airways, α-defensins and the cathelicidin LL-37/hCAP-18 originate from neutrophils. β-Defensins and LL-37/hCAP-18 are produced by the respiratory epithelium and the alveolar macrophage and secreted into the airway surface fluid. Beside their direct antimicrobial function, antimicrobial peptides have multiple roles as mediators of inflammation with effects on epithelial and inflammatory cells, influencing such diverse processes as proliferation, immune induction, wound healing, cytokine release, chemotaxis, protease-antiprotease balance, and redox homeostasis. Further, antimicrobial peptides qualify as prototypes of innovative drugs that might be used as antibiotics, anti-lipopolysaccharide drugs, or modifiers of inflammation.     

Role of inflammasomes in host defense against Citrobacter rodentium infection

Citrobacter rodentium is an enteric bacterial pathogen of the mouse intestinal tract that triggers inflammatory responses resembling those of humans infected with enteropathogenic and enterohemorrhagic Escherichia coli. Inflammasome signaling is emerging as a central regulator of inflammatory and host responses to several pathogens, but the in vivo role of inflammasome signaling in host defense against C. rodentium has not been characterized. Here, we show that mice lacking the inflammasome components Nlrp3, Nlrc4, and caspase-1 were hypersusceptible to C. rodentium-induced gastrointestinal inflammation. This was due to defective interleukin (IL)-1β and IL-18 production given that il-1β(-/-) and il-18(-/-) mice also suffered from increased bacterial burdens and exacerbated histopathology. C. rodentium specifically activated the Nlrp3 inflammasome in in vitro-infected macrophages independently of a functional bacterial type III secretion system. Thus, production of IL-1β and IL-18 downstream of the Nlrp3 and Nlrc4 inflammasomes plays a critical role in host defense against enteric infections caused by C. rodentium.     

Characterization of murine grancalcin specifically expressed in leukocytes and its possible role in host defense against bacterial infection

Such phagocytic leukocytes as macrophages and neutrophils are the key cellular components of innate immunity. The actin cytoskeleton is essential for their recruitment and activation in infected tissues. We have previously identified p65/L-plastin with Ca(2+)-, calmodulin-, and beta-actin-binding domains in macrophages. In order to further investigate the p65/L-plastin-involved cellular functions, we cloned the cDNA for murine grancalcin, a possible binding partner of p65/L-plastin. According to the sequence, grancalcin is a member of the penta-EF-hand protein family. We prepared recombinant (r) grancalcin for functional studies and found that it exhibited Ca(2+)-dependent precipitation. High-titer antibodies against the protein enabled us to detect intracellular grancalcin. A flow cytometric analysis revealed grancalcin to be highly expressed in macrophages and neutrophils. The protein was particularly abundant in those cells recovered from bacteria-infected sites. Immunohistochemical studies clarified that grancalcin was translocated to the actin cytoskeleton in macrophages upon exposure to bacterial lipopolysaccharide. These findings suggest that grancalcin plays a key role in leukocyte-specific functions that are responsible for host defense.     

Vector preference and host defense against infection interact to determine disease dynamics

Vector preference based on host infection status has long been recognized for its importance in disease dynamics. Prior theoretical work has assumed that all hosts are uniformly susceptible to the pathogen. Here we investigated disease dynamics when this assumption is relaxed using a series of vector–host epidemiological compartment models with variable levels of host resistance or tolerance to infection – collectively termed defense. In our models, vectors cannot acquire the infection from resistant hosts but can acquire from tolerant hosts. Specifically, we investigated the interacting effects of vector preference and host defense in a series of single‐ and two‐patch models. Results indicate that resistant host types generally reduce disease prevalence and pathogen spillover, independent of vector preference. The epidemiological consequences of host tolerance, however, depended on vector preference. When vectors preferred diseased hosts, tolerance reduced incidence compared to susceptible hosts; when vectors avoided diseased hosts, tolerance enhanced disease prevalence. Finally, a variation of the model that included preference‐based vector patch leaving rates suggests that both resistance and tolerance can promote pathogen spillover if vectors prefer diseased hosts, because of increased vector dispersal into susceptible patches. Collectively, we found complex, context‐dependent effects of vector preference and host defense on disease dynamics. In the context of management programs for vector‐borne diseases, managers should consider both the precise form of host defense present in a population, breed, or cultivar, as well as vector feeding behavior.     

Systemic and local CC chemokines production in a murine model of Listeria monocytogenes infection

Repeated intragastric inoculation of Listeria monocytogenes into BALB/c mice resulted in prolonged bacteraemia and severe hepatic infection. Bacteria could also be isolated from the brain tissue of all experimental mice. During the inflammatory process, chemokine concentrations typically increased at the local site in comparison to the systemic level. The liver-to-serum ratio was more pronounced in the case of macrophage inflammatory protein 1 alpha (MIP-1 alpha), suggesting its role in the inflammatory response in the liver. The ratio of brain-to-serum concentration of monocyte chemoattractant protein 1 (MCP-1) remained the same as in the control animals, while it was lower in the infected mice, both in the case MIP-1alpha and in the case of regulated on activation, normal T cell expressed and secreted (RANTES). This is in correlation with slight inflammatory infiltrates found in the brain tissue early in infection.     

S100A8/A9 is not involved in host defense against murine urinary tract infection

Background

Inflammation is commonly followed by the release of endogenous proteins called danger associated molecular patterns (DAMPs) that are able to warn the host for eminent danger. S100A8/A9 subunits are DAMPs that belong to the S100 family of calcium binding proteins. S100A8/A9 complexes induce an inflammatory response and their expression correlates with disease severity in several inflammatory disorders. S100A8/A9 promote endotoxin- and Escherichia (E.) coli-induced sepsis showing its contribution in systemic infection. The role of S100A8/A9 during a local infection of the urinary tract system caused by E. coli remains unknown.

Methodology/Principal Findings

We investigated the contribution of S100A8/A9 in acute urinary tract infection (UTI) by instilling 2 different doses of uropathogenic E. coli transurethrally in wild type (WT) and S100A9 knockout (KO) mice. Subsequently, we determined bacterial outgrowth, neutrophilic infiltrate and inflammatory mediators in bladder and kidney 24 and 48 hours later. UTI resulted in a substantial increase of S100A8/A9 protein in bladder and kidney tissue of WT mice. S100A9 KO mice displayed similar bacterial load in bladder or kidney homogenate compared to WT mice using 2 different doses at 2 different time points. S100A9 deficiency had little effect on the inflammatory responses to E. Coli-induced UTI infection, as assessed by myeloperoxidase activity in bladder and kidneys, histopathologic analysis, and renal and bladder cytokine concentrations.

Conclusions

We show that despite high S100A8/A9 expression in bladder and kidney tissue upon UTI, S100A8/A9 does not contribute to an effective host response against E. Coli in the urinary tract system.     

Lung and salivary scavenger receptor glycoprotein-340 contribute to the host defense against influenza A viruses

The lung scavenger receptor-rich protein glycoprotein-340 (gp-340) is present in bronchoalveolar lavage (BAL) fluids and saliva and mediates specific adhesion to and aggregation of bacteria. It also binds to surfactant proteins A and D (SP-A and -D). Prior studies demonstrated that SP-A and SP-D contribute to innate defense against influenza A virus (IAV). We now show that lung and salivary gp-340 inhibit the hemagglutination activity and infectivity of IAV and agglutinate the virions through a mechanism distinct from that of SP-D. As in the case of SP-A, the antiviral effects of gp-340 are mediated by noncalcium-dependent interactions between the virus and sialic acid-bearing carbohydrates on gp-340. Gp-340 inhibits IAV strains that are resistant to SP-D. Concentrations of gp-340 present in saliva and BAL fluid of healthy donors are sufficient to bind to IAV and inhibit viral infectivity. On the basis of competition experiments using competing saccharide ligands, it appears that SP-D does not entirely mediate that anti-IAV activity of BAL fluid and contributes little to that of saliva. Furthermore, removal of gp-340 from BAL fluid and saliva significantly reduced anti-IAV activity. Hence, gp-340 contributes to defense against IAV and may be particularly relevant to defense against SP-D-resistant viral strains.     

Role of interferon-gamma in Valpha14+ natural killer T cell-mediated host defense against Streptococcus pneumoniae infection in murine lungs

Previously, we demonstrated that Valpha14+ NKT cells and IFN-gamma are important upstream components in neutrophil-mediated host defense against infection with Streptococcus pneumoniae. In the present study, we extended these findings by elucidating the role of IFN-gamma in this Valpha14+ NKT cell-promoted process. Administration of recombinant IFN-gamma to Jalpha18KO mice prolonged the shortened survival, promoted the attenuated clearance of bacteria and improved the reduced accumulation of neutrophils and synthesis of MIP-2 and TNF-alpha in the lungs, in comparison to wild-type (WT) mice. In addition, intravenous transfer of liver mononuclear cells (LMNC) from WT mice into Jalpha18KO mice resulted in complete recovery of the depleted responses listed above, whereas such effects were not detected when LMNC were obtained from IFN-gammaKO or Jalpha18KO mice. Activation of Valpha14+ NKT cells by alpha-galactosylceramide (alpha-GalCer) significantly enhanced the clearance of bacteria, accumulation of neutrophils and synthesis of MIP-2 and TNF-alpha in the infected lungs; this effect was significantly inhibited by a neutralizing anti-IFN-gamma antibody. Finally, in a flow cytometric analysis, TNF-alpha synthesis was detected largely by CD11b(bright+) cells in the infected lungs. Our results demonstrated that IFN-gamma plays an important role in the neutrophil-mediated host protective responses against pneumococcal infection promoted by Valpha14+ NKT cells.     

Heat stress-induced modulation of host defense against Toxoplasma gondii infection in mice

This study examined the effects of burn injury on murine immune response against Toxoplasma gondii infection. Male C57BL/6 mice were divided into 3 groups: T. gondii infection (group T), burn injury (group B), and burn injury followed by T. gondii infection (group BT). The survival of group BT was significantly lower than those of group B and group T. Parasite abundance in the tissues was determined by quantitative competitive-polymerase chain reaction. Group BT exhibited significantly higher numbers of T. gondii than group T. Antibody production against T.g.HSP30 in group BT was significantly lower than that in group T, whereas no significant difference was observed in SAG1-specific antibody production. Delayed-type hypersensitivity (DTH) specific for 2,4-dinitrofluorobenzene (DNFB) of both group B and group BT was significantly lower than that of group T. One week after infection, serum interferon-gamma (IFN-gamma) and interleukin (IL)-10 levels in group BT were significantly lower, whereas serum IL-6 levels were significantly higher than in group T Serum TNF-alpha levels in both group T and group BT were elevated at 1 wk after infection, although there was no significant difference between them. Serum IFN-gamma, IL-10, and TNF-alpha levels in group B were not elevated during the experimental term. In conclusion, the impaired antigen-specific antibody production and DTH response, together with the modulated patterns of cytokine responses, seemed to be strongly involved in the development of burn-induced immunosuppression and the consequent increased susceptibility to T. gondii infection in mice.     

应用特异性抗原刺激树突细胞增强小鼠抵抗烟曲霉感染的能力

目的 探讨曲霉抗原刺激树突细胞(DC)应用于小鼠后对小鼠抵抗曲霉感染能力的影响.方法 小鼠骨髓制备DC,尾静脉接种小鼠;腹腔内注射环磷酰胺后,鼻腔内滴入烟曲霉孢子制备侵袭性肺曲霉病小鼠模型;获取小鼠肺组织并进行匀浆,假丝酵母(念珠菌)显色培养基接种后进行菌落计数,酶联免疫吸附试验(ELISA)检测mγ干扰素(mIFN-γ)含量,部分肺组织进行HE和GMS染色;以反转录-聚合酶链反应(RT-PCR)的方法检测小鼠脾脏中细胞因子IFN-γ的mRNA表达.结果 与单纯接种DC和热灭活烟曲霉(HAF)的小鼠相比,烟曲霉抗原刺激DC回输的小鼠存活率显著增高,脾脏内IFN-γ的mRNA表达增加,肺组织烟曲霉负荷明显降低,肺组织匀浆中IFN-γ含量(3.60±1.57ng/ml)亦高于非刺激DC免疫小鼠(HAF,1.35±0.47ng/ml;单纯DC,1.1±0.42ng/ml,P＜0.01),接受单纯DC和HAF的小鼠肺组织可见烟曲霉孢子、菌丝生长,有支气管壁的破坏,支气管周围坏死,肺泡和间质内炎症细胞浸润,而接受烟曲霉抗原刺激DC的小鼠肺内浸润炎症细胞减少,未发现坏死和真菌生长.结论 应用烟曲霉抗原刺激DC,可以在小鼠体内诱导特异性Th1型反应,增强小鼠抵抗烟曲霉感染的能力.     

Lactoferrin: Role in iron homeostasis and host defense against microbial infection

The transferrin family of non-heme iron binding glycoproteins are believed to play a central role in iron metabolism and have been implicated in iron transport, cellular iron delivery and control of the level of free iron in external secretions. Lactoferrin (LF) is a member of this family that is widely localized in external fluids including milk and mucosal secretions, in addition to being a prominent component of the secondary granules of neutrophils. Although structurally related to transferrin, LF appears to have a broader functional role mediated by both iron dependent and iron independent mechanisms. In this review, we will focus on our current understanding on the role of LF in regulating iron homeostasis and its role in host protection against microbial infection at the mucosal surface. In addition, recent insights obtained from analyzing the phenotypic consequences of LF ablation in lactoferrin knockout mice (LFKO), which challenge the long held dogma that LF is required for intestinal iron absorption in the neonate, are summarized.     

CXC chemokines modulate IgE secretion and pulmonary inflammation in a model of allergic asthma

The pathophysiology of asthma is influenced by exposure to allergens and endotoxin. Although the role of allergen-induced eosinophilia has been widely studied, neutrophil-mediated responses remain elusive. A role for neutrophils in the asthmatic responses is likely since human neutrophils have been shown to express IgE receptors, as well as receptors for many cytokines and chemokines implicated in the pathogenesis of asthma. In this study we investigated neutrophil involvement in a novel, house dust extract (HDE) induced model of asthma-like pulmonary inflammation. Mice were immunized and challenged with HDE containing high levels of cockroach allergens, 377 U/ml Bla g1 and 6249 ng/ml Bla g2. The biological activity of the murine chemokines KC and MIP-2 was inhibited with specific rabbit antisera. Differential counting of cells recovered from the bronchoalveolar lavage (BAL) fluid showed that neutralization of KC and MIP-2 significantly decreased pulmonary recruitment of neutrophils (reduced 86%) and lymphocytes (reduced 76%). Neutralization of these chemokines also exerted a systemic effect with a significant decrease in plasma IgE levels, 547 ng/ml+/-65 compared to 1314 ng/ml+/-247 for control sera treated animals. This study shows that CXC chemokines play an important role in allergy and asthma both at the level of pulmonary cell recruitment and systemic immune responses.     

Excessive increase of serum interleukin 6 jeopardizes host defense against multi-bacterial infection

Serum interleukin 6 (IL-6) is elevated among patients who have undergone surgery, trauma, and thermal injury. It is well known that the greater the increase of serum IL-6, the higher the incidence of post-injury morbidity and mortality is. However, it has not been determined whether the physiological effects of IL-6 increase the rate of morbidity and mortality or if IL-6 is just a bystander that only indicates the severity of the injury. To elucidate this, we planned to investigate the effect of IL-6 on a multi-bacterial infection, one of the most frequent post-injury complications. CDF1 male mice were administered recombinant human IL-6 (hIL-6) continuously at a dose of 0, 1, or 10 microg/day. The mice then underwent cecal ligation without puncture that induced slow multi-bacterial infection. The survival rate of mice receiving 10 microg/day of hIL-6 was significantly lower (38.5%) than the rate of those receiving 0 (83.3%) or 1 (92.3%) microg/day of hIL-6. The result of this study showed that only excessive increases in serum IL-6, to levels that were observed among patients who underwent severe injury or extensive surgery with high incidence of post-injury infection, jeopardize the host's defense against bacterial infection.     

Impaired pulmonary host defense in mice lacking expression of the CXC chemokine lungkine

Lungkine (CXCL15) is a novel CXC chemokine that is highly expressed in the adult mouse lung. To determine the biologic function of Lungkine, we generated Lungkine null mice by targeted gene disruption. These mice did not differ from wild-type mice in their hematocrits or in the relative number of cells in leukocyte populations of peripheral blood or other tissues, including lung and bone marrow. However, Lungkine null mice were more susceptible to Klebsiella pneumonia infection, with a decreased survival and increased lung bacterial burden compared with infected wild-type mice. Histologic analysis of the lung and assessment of leukocytes in the bronchioalveolar lavage revealed that neutrophil numbers were normal in the lung parenchyma, but reduced in the airspace. The production of other neutrophil chemoattractants in the Lungkine null mice did not differ from that in wild-type mice, and neutrophil migration into other tissues was normal. Taken together, these findings demonstrate that Lungkine is an important mediator of neutrophil migration from the lung parenchyma into the airspace.     

Modulation of neutrophil function in host defense against disseminated Candida albicans infection in mice

Neutrophils (PMNs) constitute the main mechanism of host defense against acute invasive and disseminated candidiasis. Recent studies have demonstrated that tumor necrosis factor-alpha (TNFalpha), interleukin-6 (IL-6) and granulocyte colony-stimulating factor (G-CSF) play an important role in the recruitment of PMNs at the site of invasive Candida infection. In the absence of either TNFalpha or IL-6, the course of experimental disseminated candidiasis is more severe, due to defective PMN recruitment. Treatment of mice with recombinant G-CSF (rG-CSF) leads to a significantly reduced mortality during disseminated candidiasis. The outgrowth of Candida albicans from the organs of rG-CSF-treated mice is significantly decreased. Treatment with the combination of rG-CSF and fluconazole has an additive effect on the reduction of fungal load in the organs. In subacute or chronic disseminated Candida infection, rG-CSF is less effective, indicating that neutrophil recruitment and activation are crucial in acute, life-threatening candidiasis, whereas other host defense mechanisms control the outcome of less overwhelming invasive Candida infection.     

ST2 deficient mice display a normal host defense against pulmonary infection with Mycobacterium tuberculosis

Tuberculosis, caused by Mycobacterium (M.) tuberculosis, is a devastating infectious disease causing many deaths world-wide every year. Successful host defense mainly depends on a strong Th type 1 response. We investigated the role of T1/ST2 (recently identified as the receptor for IL-33), a typical Th2 marker in the assumption that a shift towards a beneficial Th1 response would occur in the absence of ST2. For this, ST2 KO and WT mice were intranasally infected with a virulent strain of M. tuberculosis (150 CFU). In line with our hypothesis, ST2 KO animals displayed increased numbers of lymphocytes infiltrating the lung after 2 weeks of infection, increased IFNγ production by splenocytes in ST2 KO mice early in infection and enhanced lung IFNγ levels at the chronic phase of the disease. However, we did not detect any differences between ST2 KO and WT mice in mycobacterial loads in lungs or liver after M. tuberculosis infection. The pulmonary inflammatory response, as measured by relative lung weights, cytokine and chemokine levels as well as histopathological analysis, was similar in ST2 KO and WT mice. These data suggest that apart from inducing a modest shift towards the Th1 response, the role of ST2 during murine M. tuberculosis infection is limited.