The role of C5a and antibody in the release of heparan sulfate from endothelial cells

The activation of endothelial cells is thought to contribute to the host response to infection and to the pathogenesis of autoimmune disease. It was recently shown that antibody and complement can activate endothelial cells leading to cleavage and release of heparan sulfate from the cells. We show here that release of heparan sulfate from endothelial cells is mediated by antibody and the complement fragment C5a and that assembly of the membrane attack complex and lysis of endothelial cells is not necessarily involved. These data suggest that the generation of C5a in conditions such as autoimmunity and infection in which anti-endothelial cell antibodies may also be present, might amplify tissue injury by a novel mechanism involving endothelial cell activation and loss of heparan sulfate mediated by antibody and C5a.     

The immunological aspects of latency in tuberculosis

A unique feature of Mycobacterium tuberculosis is its ability to exist in the granuloma of an asymptomatic host in a latent state that can subsequently reactivate to cause active disease. The latent state of infection poses a major obstacle to eradicating tuberculosis. In latent tuberculosis, the host immune response is capable of controlling the infection and yet falls short of eradicating the pathogen. That the host immune response contributes to the maintenance of latent tuberculous infection is supported by the observation that certain immunodeficient states, including those associated with the human immunodeficiency virus and tumor necrosis factor neutralization therapy, are associated with increased risks for developing reactivation disease. Latent tuberculosis is the product of a complex set of interactions between M. tuberculosis and the host immune response. The molecular basis for the persistence phenotype of M. Tuberculosis and the pertinent host immune mechanisms that contribute to the maintenance of tuberculous latency are just beginning to be understood. This review discusses the interactions between M. tuberculosis and the macrophage, the primary host cell that the tubercle bacillus parasitizes.     

The role of mannose receptor during experimental leishmaniasis

The primary host cells for Leishmania replication are macrophages (MP). Several molecules on the surface of professional phagocytic cells have been implicated in the initial process of parasite internalization and initiation of signaling pathways. These pattern recognition receptors distinguish molecular patterns on pathogen surfaces. Mannose receptor (MR), specifically, recognizes mannose residues on the surface of Leishmania parasites. We studied the role of MR in the pathogenesis of experimental cutaneous and visceral leishmaniasis using MR-deficient [MR-knockout (KO)] C57BL/6 mice. MR-deficient MP exhibited a comparable infection rate and cytokine production. In the absence of MR, the clinical course of Leishmania major and Leishmania donovani infections was similar in MR-KO and wild-type mice (MR-WT). Furthermore, immunohistochemistry of cutaneous lesions from MR-KO and MR-WT mice revealed no differences in lesion architecture or cell components. Inhibition of MP responses is a hallmark of Leishmania infection; our data demonstrate further that host MR is not essential for blocking IFN-gamma/LPS-induced IL-12 production and MAPK activation by Leishmania. Thus, we conclude that the MR is not essential for host defense against Leishmania infection or regulation of IL-12 production.     

Leishmania donovani-reactive Th1- and Th2-like T-cell clones from individuals who have recovered from visceral leishmaniasis.

Infections in humans by Leishmania donovani parasites can result in a fatal disease, visceral leishmaniasis (VL), or in a self-limiting asymptomatic infection. In murine models of the infection employing Leishmania major, the course of the disease can be directed into a VL-like syndrome by interleukin-4 (IL-4)-producing Th2 cells, or cure may result by Th1 cells secreting gamma interferon (IFN-gamma). The present study examined the potential of human T cells to generate Th1 or Th2 responses to L. donovani. The profiles of IFN-gamma, IL-4, and lymphotoxin secretion after antigen stimulation were analyzed in a panel of L. donovani-reactive CD4+ human T-cell clones generated from individuals who had recovered from VL after antimonial treatment. Two of the T-cell clones produced large amounts of IL-4 without production of IFN-gamma, seven clones produced both IFN-gamma and IL-4, and eight produced only IFN-gamma. This is the first report of a Th1- and Th2-type response in human leishmaniasis. These results suggest that in analogy with murine models, there is a dichotomy in the human T-cell response to L. donovani infections. Preferential activation of IL-4-producing Th2-like cells may be involved in the exacerbation of human VL, whereas activation of IFN-gamma-producing Th1 cells may protect the host from severe disease. Identification of leishmanial antigens activating one or the other type of T cells will be important in the development of vaccines against leishmaniasis.     

Increased frequency of regulatory T cells and T lymphocyte activation in persons with previously treated extrapulmonary tuberculosis

Extrapulmonary tuberculosis may be due to underlying immune compromise. Immunosuppressive regulatory T cells (Treg cells), and CD4(+) T lymphocytes in general, are important in the host immune response to Mycobacterium tuberculosis. We evaluated T lymphocytes from patients after recovery from extrapulmonary tuberculosis, which may reflect conditions before M. tuberculosis infection. A case-control study was conducted among HIV-uninfected adults with previously treated extrapulmonary tuberculosis and 3 sets of controls: (i) subjects with previously treated pulmonary tuberculosis, (ii) close tuberculosis contacts with M. tuberculosis infection, and (iii) close tuberculosis contacts with no infection. Monocyte-depleted peripheral blood mononuclear cells (PBMC-M) were stained for CD4(+) CD25(hi) CD127(low) FoxP3(+) cell (Treg cell) and T lymphocyte activation. Both characteristics were compared as continuous variables between groups with the Kruskal-Wallis test. There were 7 extrapulmonary tuberculosis cases, 18 pulmonary tuberculosis controls, 17 controls with M. tuberculosis infection, and 18 controls without M. tuberculosis infection. The median Treg cell proportion was highest among persons with previous extrapulmonary tuberculosis (1.23%) compared to subjects with pulmonary tuberculosis (0.56%), latent M. tuberculosis infection (0.14%), or no M. tuberculosis infection (0.20%) (P = 0.001). The median proportion of CD4(+) T lymphocytes that expressed the activation markers HLA-DR and CD38 was highest for CD4(+) T lymphocytes from persons with previous extrapulmonary tuberculosis (0.79%) compared to subjects with pulmonary tuberculosis (0.44%), latent M. tuberculosis infection (0.14%), or no M. tuberculosis infection (0.32%) (P = 0.005). Compared with controls, persons with previously treated extrapulmonary tuberculosis had the highest Treg cell frequency, but also the highest levels of CD4(+) T lymphocyte activation. Immune dysregulation may be a feature of individuals at risk for extrapulmonary tuberculosis.     

Defensins: key players or bystanders in infection, injury, and repair in the lung?

Antimicrobial peptides have been identified as key elements in the innate host defense against infection. Recent studies have indicated that the activity of antimicrobial peptides may be decreased in cystic fibrosis, suggesting a major role for these peptides in host defense against infection. One of the most intensively studied classes of antimicrobial peptides are defensins. Defensins comprise a family of cationic peptides that in human subjects can be divided into the alpha- and beta-defensin subfamilies. The alpha-defensins are produced by neutrophils and intestinal Paneth's cells, whereas beta-defensins are mainly produced by epithelial cells. Although studies on beta-defensins have so far focused on their antimicrobial activity, studies on alpha-defensins have suggested a role of these peptides in inflammation, wound repair, and specific immune responses. alpha-Defensins, which accumulate in airway secretions of patients with various chronic inflammatory lung disorders, were shown to be cytotoxic toward airway epithelial cells and to induce chemokine secretion in several cell types. Furthermore, the capacity of alpha-defensins to promote bacterial adherence to epithelial cells in vitro further supports a role for these peptides in the pathogenesis of chronic obstructive pulmonary disease and cystic fibrosis. Increased numbers of neutrophils are also present in the airways of patients with asthma, suggesting that neutrophils are involved in the pathogenesis of this disease. Because defensins are able to induce histamine release by mast cells and increase the airway hyperresponsiveness to histamine, it is tempting to speculate that defensins may also contribute to the inflammatory processes in asthma. Besides these proinflammatory effects, alpha-defensins may also display anti-inflammatory activities, including regulation of complement activation and proteinase inhibitor secretion. Finally, defensins may be involved in wound repair because defensins increase epithelial cell proliferation. Thus recent defensin research has revealed potential links between the innate and acquired immune system.     

Trypanosoma cruzi trans-sialidase potentiates T cell activation through antigen-presenting cells: role of IL-6 and Bruton's tyrosine kinase

Polyclonal lymphocyte activation and hypergammaglobulinemia characterize the acute phase of Chagas' disease, a debilitating condition caused by Trypanosoma cruzi. Such pathogenic hyper-reactivities not only compromise specific host defense against the pathogen, but may also contribute to infection-induced chronic autoimmune responses. Recent studies showed that T. cruzi trans-sialidase (TS) directly stimulates the polyclonal proliferation and Ig secretion of normal murine B cells in a T-independent, Bruton's tyrosine kinase (Btk)-dependent manner. Related to this observation, we now show that parasite-derived and recombinant TS potentiate the proliferation and cytokine secretion of normal T cells triggered by antigen-specific and non-specific stimuli. TS potentiates T cell activation through stimulating B cells and macrophages, independent of CD40/CD40L and CD43 pathways. In contrast, optimal TS potentiation requires interleukin-6 (IL-6) and Btk, as it is significantly reduced in splenocytes from IL-6-/- and Btk-defective Xid mice. The results suggest that TS, directly and indirectly, activates both antigen-presenting cell and T cell compartments, and that TS-induced IL-6 may further amplify such activation. These observations open up the possibility that TS drives the polyclonal lymphocyte activation in acute T. cruzi infection, a phenomenon contributing to the pathogenesis of Chagas' disease.     

What animal models teach humans about tuberculosis

Animal models have become standard tools for the study of a wide array of human infectious diseases. Although there are no true animal reservoirs for Mycobacterium tuberculosis, many different animal species are susceptible to infection with this organism and have served as valuable tools for the study of tuberculosis (TB). The most commonly used experimental animal models of TB are the mouse, rabbit, and guinea pig. Although substantial differences in TB susceptibility and disease manifestations exist between these species, they have contributed significantly to the understanding of TB immunopathogenesis, host genetic influence on infection, efficacy of antimicrobial therapy, and host/pathogen interactions that determine the outcome or severity of infection. Among the three species, mice are relatively resistant to TB infection, followed by rabbits and then guinea pigs, which are extremely vulnerable to infection. Mice are most often used in experiments on immune responses to TB infection and drug regimens against TB. Rabbits, unlike the other two animal models, develop cavitary TB and offer a means to study the factors leading to this form of the disease. Guinea pigs, due to their high susceptibility to infection, have been ideal for studies on airborne transmission and vaccine efficacy. In addition to these three species, TB research has occasionally involved nonhuman primates and cattle models. Current concepts in TB pathogenesis have also been derived from animal studies involving experimentally induced infections with related mycobacteria (e.g., Mycobacterium bovis) whose manifestations in select animal hosts mimic human TB.     

The importance of gd T cells in the resolution of pathogen-induced inflammatory immune responses

Summary: The aim of our research is to determine the biological function of gd T lymphocytes and in particular the role they play in microbial immunity. Although evidence of gd T‐cell activation and expansion has been obtained from numerous infectious diseases, how they contribute to pathogen-induced immune responses is still not clear. Based upon extensive studies of gd T‐cell involvement in the immune response to viral and bacterial pathogens in both mice and humans, we have uncovered evidence of their direct involvement in terminating host immune responses to infection and preventing chronic disease. We have identified an interaction between peripheral gd T cells and a population of activated, pro-inflammatory macrophages elicited by infection that occurs late in the course of infection during or after pathogen clearance. As a result of this interaction, activated gd T cells acquire cytotoxic activity and kill the stimulatory macrophages, leading us to propose a model for gd T‐cell–macrophage interactions that contributes to macrophage homeostasis, the resolution of inflammatory immune responses, and prevention of chronic inflammatory disease.     

Involvement of caspase-9 in the inhibition of necrosis of RAW 264 cells infected with Mycobacterium tuberculosis

In order to know how caspases contribute to the intracellular fate of Mycobacterium tuberculosis and host cell death in the infected macrophages, we examined the effect of benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethane (z-VAD-fmk), a broad-spectrum caspase inhibitor, on the growth of M. tuberculosis H37Rv in RAW 264 cells. In the cells treated with z-VAD-fmk, activation of caspase-8, caspase-3/7, and caspase-9 was clearly suppressed, and DNA fragmentation of the infected cells was also reduced. Under this experimental condition, it was found that the treatment markedly inhibited bacterial growth inside macrophages. The infected cells appeared to undergo cell death of the necrosis type in the presence of z-VAD-fmk. We further found that z-VAD-fmk treatment resulted in the generation of intracellular reactive oxygen species (ROS) in the infected cells. By addition of a scavenger of ROS, the host cell necrosis was inhibited and the intracellular growth of H37Rv was significantly restored. Among inhibitors specific for each caspase, only the caspase-9-specific inhibitor enhanced the generation of ROS and induced necrosis of the infected cells. Furthermore, we found that severe necrosis was induced by infection with H37Rv but not H37Ra in the presence of z-VAD-fmk. Caspase-9 activation was also detected in H37Rv-infected cells, but H37Ra never induced such caspase-9 activation. These results indicated that caspase-9, which was activated by infection with virulent M. tuberculosis, contributed to the inhibition of necrosis of the infected host cells, presumably through suppression of intracellular ROS generation.     

Lipopolysaccharide binding protein-deficient mice have a normal defense against pulmonary mycobacterial infection

Lipopolysaccharide (LPS) binding protein (LBP) facilitates the transfer of LPS of Gram-negative bacteria to the pattern recognition receptor CD14, resulting in activation of immunocompetent cells. LBP can also facilitate the binding of lipoarabinomannan, a major cell wall component of mycobacteria, to immune cells. To determine the role of LBP in the immune response to pulmonary Mycobacterium tuberculosis infection, LBP gene-deficient (-/-) and normal wild-type (WT) mice were intranasally infected with M. tuberculosis. LBP-/- mice displayed a similar survival and mycobacterial outgrowth in lungs and liver, although they demonstrated a reduced lymphocyte recruitment and activation during the early stages of infection. The clearance of pulmonary infection with the non-pathogenic M. smegmatis was also unaltered in LBP-/- mice. These data suggest that LBP does not contribute to an effective host response in M. tuberculosis infection.     

人类传染性疾病的遗传易感性

双生子、寄养子、家系和基于群体的关联研究表明机体遗传因素在决定人类传染性疾病的易感性中起着极为重要的作用。除少数基因已被揭示与疟疾和艾滋病的遗传易感性强烈相关外,还有其它大量基因显示与结核病、麻疯病和慢性乙型肝炎等传染性疾病的易感性相关。一些免疫相关基因可能在介导传染性疾病的遗传易感机制中担负重要角色。上述研究大多表明,绝大多数常见传染性疾病属于典型的多基因疾病(复杂性状),是致病微生物和宿主之间在长期的进化过程中交互作用的结果。后基因组时代人类基因组学的快速发展必然大大加速传染病遗传易感基因的鉴定,这有助于今后研发针对这些疾病的新的预防和治疗策略。但是,这一领域仍然面临着诸多需要克服的困难。     

Role of host phosphotyrosine phosphatase SHP-1 in the development of murine leishmaniasis.

Activation of host phosphotyrosine phosphatase SHP-1 by Leishmania and its subsequent impact on tyrosine phosphorylation-based signaling cascades were shown to represent an important mechanism whereby this pathogen may alter host cell functions. Herein, we report that Leishmania-induced macrophage SHP-1 activity is necessary for its survival within phagocytes through the attenuation of nitric oxide-dependent and -independent microbicidal mechanisms. In vivo, Leishmania major infection, which footpad inflammation is mostly undetectable in SHP-1-deficient viable motheaten mice, was accompanied by increased inducible nitric oxide synthase and activation of neutrophils. These enhanced cellular activities were paralleled by a marked activation of signaling events usually negatively regulated by SHP-1. Overall, this study firmly establishes that modulation of the signaling terminator SHP-1 by Leishmania is essential for its installment and propagation.