Cellular basis of host defence in pyelonephritis. III. Deletion of individual components.

Hosts were depleted of individual cellular components to determine the effects of these manipulations on cellular defence mechanisms in acute and chronic pyelonephritis. T-lymphocytes were found to have little or no involvement in host protection but cyclosporin A administration had a dramatic effect on the gross pathology and bacteriological status of experimentally induced pyelonephritis. This change represented a major depression of host defence status. Cyclosporin A also activated resolved lesions in chronic pyelonephritis, associated with an increase in bacterial numbers. Administration of antineutrophil serum also led to a 1000-fold increase in bacterial numbers in the acute phase but had little effect on the host-parasite balance in chronic pyelonephritis. Macrophage blockade, on the other hand, did not affect the course of either acute or chronic infection. These studies have provided additional information on the immunobiology of experimental pyelonephritis and have focussed attention on the role of neutrophils, and an unidentified mechanism, affected by cyclosporin A, in host defence to renal infection.     

Cellular basis of host defence in pyelonephritis. II. Acute infection

We have investigated the cellular basis of host defence mechanisms in experimental pyelonephritis. Cellular components of the host defence system were depleted using cyclophosphamide, methylprednisolone or radiation. Depletion of cellular competence did not affect the course of infection during the first 16 h after challenge with Escherichia coli, but after 96 h up to a 1000-fold increase in bacterial numbers in the kidneys of cytodepleted animals was demonstrable. When quantitative aspects of the relationship between cellular competence and host defence were studied, it was found that severe depletion of cellular components was necessary before host defence mechanisms were adversely affected. Thus while cellular mechanisms are quantitatively adequate and contribute to host defence in pyelonephritis they have little impact on the immediate post-infection phase. Non-cellular factors however, do limit bacterial proliferation in the acute phase and may be important determinants in the biology of pyelonephritis.     

Cellular basis of host defence in pyelonephritis. I. Chronic infection

Infection persists for long periods in chronic pyelonephritis, but the cellular basis of the host-parasite relationship is poorly understood. We have obtained quantitative data on the relationship between the pathogen (E. coli) and cellular defence mechanisms. Depletion of cellular components was carried out using whole body irradiation, methylprednisolone, cyclophosphamide or carrageenan and silica particles. A system of administering cyclophosphamide and methylprednisolone through the use of a slow release carrier, as well as graded doses of irradiation, was then developed to allow the controlled reduction of cellular competence. Quantitative studies in a host with chronic pyelonephritis and normal cellular defence reserves showed that severe depletion of granulocytic cells is necessary before host defence mechanisms are adversely affected. This finding conflicts with the observation that microorganisms survive and persist in the kidney for extended periods. Additionally, noncellular factors may also limit bacterial growth.     

Cellular basis of host defence in pyelonephritis. II. Acute infection.

We have investigated the cellular basis of host defence mechanisms in experimental pyelonephritis. Cellular components of the host defence system were depleted using cyclophosphamide, methylprednisolone or radiation. Depletion of cellular competence did not affect the course of infection during the first 16 h after challenge with Escherichia coli, but after 96 h up to a 1000-fold increase in bacterial numbers in the kidneys of cytodepleted animals was demonstrable. When quantitative aspects of the relationship between cellular competence and host defence were studied, it was found that severe depletion of cellular components was necessary before host defence mechanisms were adversely affected. Thus while cellular mechanisms are quantitatively adequate and contribute to host defence in pyelonephritis they have little impact on the immediate post-infection phase. Non-cellular factors however, do limit bacterial proliferation in the acute phase and may be important determinants in the biology of pyelonephritis.     

Cellular basis of host defence in pyelonephritis. I. Chronic infection.

Infection persists for long periods in chronic pyelonephritis, but the cellular basis of the host-parasite relationship is poorly understood. We have obtained quantitative data on the relationship between the pathogen (E. coli) and cellular defence mechanisms. Depletion of cellular components was carried out using whole body irradiation, methylprednisolone, cyclophosphamide or carrageenan and silica particles. A system of administering cyclophosphamide and methylprednisolone through the use of a slow release carrier, as well as graded doses of irradiation, was then developed to allow the controlled reduction of cellular competence. Quantitative studies in a host with chronic pyelonephritis and normal cellular defence reserves showed that severe depletion of granulocytic cells is necessary before host defence mechanisms are adversely affected. This finding conflicts with the observation that microorganisms survive and persist in the kidney for extended periods. Additionally, noncellular factors may also limit bacterial growth.     

Cellular and molecular basis of age-related sarcopenia.

Sarcopenia, the decline in muscle bulk and performance associated with normal aging, is an important component of frailty in the elderly. The gradual loss of both motor nerves and muscle fibers during senescence appears to be the major problem. Atrophy (especially in fast-twitch fibers) and impaired function of the surviving cells also contribute to sarcopenia. Although skeletal muscle has the capacity to regenerate itself, this process is not activated by the gradual age-related loss of muscle fibers. The endocrine, autocrine, and paracrine environment in old muscle is less supportive of protein synthesis, reinnervation of muscle fibers, and satellite cell activation, proliferation, and differentiation. Lifelong exposure of DNA to free radical damage results in accumulation of somatic mutations in nerves and muscle fibers. Reduced protein synthesis leads to atrophy, and slower fractional protein turnover contributes to longer retention of proteins that may have been damaged by free radicals. Many genes are differentially expressed in young and old muscle, but additional research is needed to determine which of these genes have a significant role in the pathogenesis or adaptation to sarcopenia.     

Antimicrobial peptides in mammalian and insect host defence

During the past year, additional insights into systems that regulate antimicrobial peptide production in Drosophila were reported. Granulysin, a peptide stored in the cytoplasmic granules of human natural killer cells and cytolytic T cells, was shown to kill Mycobacterium tuberculosis. More data implicating antimicrobial peptides in the pathogenesis of bronchopulmonary infections in cystic fibrosis appeared. Studies that examined the potential contributions of antimicrobial peptides to regional innate immunity gained in prominence. Efforts to design peptide analogues to prevent or treat infections continued.     

Mechanisms involved in the evasion of the host defence by Pseudomonas aeruginosa.

Pseudomonas aeruginosa, an extracellular opportunistic pathogen, utilizes two major mechanisms to evade the host defence system. One of these mechanisms is the production of a large number of extracellular products, such as proteases, toxins, and lipases. The two proteases, alkaline protease and elastase, inhibit the function of the cells of the immune system (phagocytes, NK cells, T cells), inactivate several cytokines (IL-1, IL-2, IFN-r, TNF), cleave immunoglobulins and inactivate complement. Inhibition of the local immune response by bacterial proteases provides an environment for the colonization and establishment of chronic infection. The other mechanism by which P. aeruginosa evades the host defence system is the biofilm mode of growth of the bacteria in chronic infections. The biofilm-grown bacteria induce a low phagocyte response, and provide a barrier for the bacteria against antibodies, complement, and the cells of the immune system. Protection from the host defence system combined with increased antibiotic resistance of the bacteria in the biofilm are the major reasons for the persistence of P. aeruginosa in chronic infections.     

Cellular basis of graft-versus-host reactions

The biologic basis of Graft-Versus-Host Disease (GVHD) is presented as an extremely complex immunopathologic syndrome that involves interaction between many different donor and host cell types. A model of acute lethal GVHD was employed where adult unirradiated (DA X LEW)F₁ rats were injected with LEW spleen and lymph node cells. Controls received the same dose of syngeneic cells. At intervals from 2 to 21 days after cell injection, GVHD and control animals were killed and nonadherent cell suspensions prepared from their lymph nodes, spleen and peripheral blood. Cell suspensions were treated with LEW-anti-DA-alloantiserum or normal LEW serum and then analyzed for sIgM⁺ (B cells), W 3/13⁺ (T cells), and IgG-Fc receptors (FcR). Evidence is discussed for the selective removal of host cells with the alloantiserum. In addition, the level of naturally cytolytic (NK/NC) cells was assessed by adding GVHD and control nonadherent lymphoid cells to heterologous lymphoma and sarcoma target cells. Evidence is presented that during acute GVHD, in this parental →F₁ combination, there is an early increase within most compartments of donor as well as host W 3/13⁺ and W 3/13⁺FcR⁺ cells. NK/NC cells are increased as well at day 7. During middle stages of acute GVHD, host sIgM⁺ cells predominate. Late-stage acute GVHD rats contain few donor and host W 3/13⁺FcR⁺, and NK/NC cells but many null cells most of which are FcR^?. The importance of unraveling the nature of donor- and host-cell interactions occurring during acute GVHD, which result in rats whose lymphoid tissues are severely depleted of all nonadherent lymphoid cells but FcR^? null cells, is discussed.     

Cellular basis of anti-SB response

Cloning of cells allosensitized in vitro against SB1, SB2, and SB3 antigens was performed by micromanipulation. One hundred and twenty-six clones were tested for both proliferative and cytolytic responses; 14 proliferative, noncytotoxic clones and one clone which demonstrated both proliferative and cytotoxic reactivity specific for SB antigens were obtained. The proliferative noncytotoxic clones tested and the clone with both cytotoxic and proliferative activity were all able to produce IL-2-like activity upon specific antigen stimulation in vitro and were positive for OKT3, OKT4 but negative for OKT8. The proliferative clones fit the characteristics of helper T cell (Th) clones while the clone with both cytotoxic and proliferative reactivities is analogous to the class of antigen-driven, helper cell-independent cytotoxic (HITc) clones. No cytolytic nonproliferative SB specific clones were detected. The prevalent induction of Th clones strongly suggests that the biological function of SB antigens is similar to other class II antigens of HLA. The existence of an SB specific HITc clone demonstrates that a determinant on an SB molecule can induce both proliferative and cytolytic responses.     

Modifications of host defence mechanisms by an acute non-immunological inflammatory reaction.

Mice developing an acute non-immunological inflammatory reaction were examined for modification of specific and non-specific defence mechanisms on the basis of previous observations that these animals displayed an increased resistance to bacterial and parasitic infections but an impaired resistance to neoplasia. Local acute inflammation was induced by injection into the pleural cavity of a non-antigenic, endotoxin-free irritant--calcium pyrophosphate microcrystals or low-molecular-weight dextran. Effector functions of macrophages at remote sites from the inflammatory focus were markedly stimulated. This was shown by: (a) an accelerated elimination of Listeria monocytogenes in the liver and spleen of mice with inflammation; (b) the acquisition of cytostatic activity for tumour cells by peritoneal macrophages; and (c) an enhancement of chemiluminescence emission and superoxide production in response to phagocytosis. Natural killer activity of spleen and peritoneal cells was stimulated in a biphasic manner. In contrast, cytolytic T cell differentiation upon in vitro immunization of spleen cells against allogeneic tumour cells was impaired. All these effects were observed very early (2 h) after the onset of inflammation and were still detectable at least 3 days after the inflammatory process had disappeared.     

Cellular and humoral aspects of host resistance in murine salmonellosis.

Mice were challenged with a highly virulent strain of Salmonella typhimurium by intraperitoneal injections. At relatively low infecting doses, immunizations with either viable attenuated or heat killed Salm. typhimurium were found to be equally protective against otherwise fatal infections. Pre-opsonization of virulent salmonellae significantly increased the survival rate of mice infected with small numbers of the pathogen. By a cell culture method, peritoneal macrophages of mice were shown to be innately capable of destroying the ingested virulent Salm. typhimurium. Macrophages from previously infected mice did not appear to have any significant increase in their bactericidal activity against salmonellae, but they possessed cytophilic antibodies specific against the H and the O antigens of Salm. typhimurium. It is believed that humoral elements play an important role in acquired immunity in murine salmonellosis by opsonization of the pathogen.     

Cell adhesion molecules in the pathogenesis of and host defence against microbial infection.

Eukaryotic cell adhesion molecules (CAMs) are used by various cells and extracellular molecules in host defence against infection. They are involved in many processes including recognition by circulating phagocytes of a site of inflammation, transmigration through the endothelial barrier, diapedesis through basement membrane and extracellular matrix, and release of effector mechanisms at the infected site. CAMs involved in leucocyte-endothelial cell interaction include the selectins, integrins, and members of the immunoglobulin superfamily. However, CAMs are also used by various microorganisms (protozoa, fungi, bacteria, and viruses) during their pathogenesis. For example, bacteria that utilise CAMs include Mycobacterium tuberculosis, Listeria monocytogenes, Yersinia spp, enteropathogenic Escherichia coli, Shigella spp, Neisseria spp, Bordetella spp, and Borrelia burgdorferi. In addition, CAMs are involved in the pathogenetic effects of the RTX toxins of Pasteurella haemolytica, Actinobacillus actinomycetemcomitans, and the superantigen exotoxins of Staphylococcus aureus and Streptococcus pyogenes. A recurrent and topical theme of potential importance within the bacterial group is the intimate relation between CAMs, bacterial protein receptors, and type III secretion systems. For example, the IpaBCD protein complex is secreted by the type III system of Shigella flexneri and interacts with alpha 5 beta 1 integrin on the eukaryotic cell surface, followed by Rho mediated internalisation; this illustrates the relevance of cellular microbiology. CAMs might prove to be novel therapeutic targets. Comparative genomics has provided the knowledge of shared virulence determinants among diverse bacterial genera, and will continue to deepen our understanding of microbial pathogenesis, particularly in the context of the interaction of prokaryotic and eukaryotic molecules.     

Neutrophil-macrophage cooperation in the host defence against mycobacterial infections

CD-1 mice inoculated intraperitoneally with Mycobacterium avium, M. bovis, M. microti or M. kansasii showed a persistent peritoneal granulocytosis (above 10(6) cells, i.e. more than 15% of total cells) throughout the 3 month period of infection studied. By contrast, in mice inoculated with the non-pathogenic M. aurum or with heat-killed M. avium the number of granulocytes decreased progressively after the first 15 days. No mycobacteria were found in granulocytes except in the first 2 days of infection. The mycobacteria-induced chronic granulocytosis was accompanied by phagocytosis of granulocytes by macrophages. Throughout the 3 months of infection, macrophages were found to contain intracellular lactoferrin. Macrophages with lactoferrin were also found in subcutaneous infection caused by M. marinum and in systemic infection caused by M. avium or M. kansasii. The in vitro activity of mouse peritoneal macrophages against M. avium and M. microti was increased after ingestion of granulocyte material by macrophages. These results lead us to propose that granulocytes participate in the host response to mycobacterial infections, not as phagocytes but rather through an indirect mechanism, as a source for the macrophages of molecules involved in antimicrobial mechanisms (e.g., lactoferrin and myeloperoxidase) lacking in the mature macrophage.