published_or_final_version / Microbiology / Master / Master of Philosophy

published_or_final_version / Medicine / Master / Master of Philosophy

Cathepsin, matrix metalloproteinase (MMP) enzyme and tissue inhibitor of MMP (TIMP) distribution in J774 mouse macrophages has not been comprehensively studied. The distribution and vesicle regulation, trafficking and release of these is important, possibly suggesting drug targets for the therapeutic regulation of inflammatory disease and phagosomal killing of pathogenic organisms in J774 and other macrophages. Percentage immunofluorescence and ultrastructural enzyme and inhibitor distribution, together with LysoTracker (acidity) and lysosome-associated membrane proteins (LAMPs) colocalisation (both indicating late endosome or “lysosomal” association), western blot estimates of percentage processed- and unprocessed intracellular and secreted enzyme and inhibitor, and vesicle size was used to assign enzyme and inhibitor to “classical” vesicle types. Antibodies against TIMP-1 and TIMP-2 were raised and all antibodies characterised for this purpose. Together these were used to assign cathepsins H, S, D, B and L to possible secretory vesicles (±20 nm, non-acidic, LAMPs-negative, containing precursor enzymes) and identify at least 6 other endosome-“lysosome-like” vesicles. Cathepsin H appears to be present in classical early endosomes (±100 nm, non-acidic, LAMPs-negative) and cathepsin S in late endosomes(±50 nm, acidic, LAMPs-positive) and possibly “lysosomal” (“hybrid” or digestive organelles) (±150-200 nm, acidic, LAMPs-positive). Both cathepsins H and S, however, seem only reliable markers if used together with additional markers. Cathepsin D appearsmainly associated with “lysosomal” (“hybrid” or digestive organelles) (±150-200 nm, acidic, LAMPs-positive), possibly consisting of further subpopulations which requires furtherinvestigation e.g. labelling for LAMP-1 and LAMP-2 and cathepsin D. Cathepsins B and Lmay occur in late endosomes and/or hybrid organelles and “secretory lysosomes” containing cathepsins B, D and L may also exist (±30-50 nm, acidic, LAMPs-positive). The distribution of MMP-9, TIMP-1 and -2 in vesicles (non-acidic, LAMP-2-negative) thatappear novel and distinct from late endosome-“lysosome” vesicles were also demonstrated. In LPS-stimulated cells, the identity of the large (±450 nm), possible recycling endosomes (Rab11-positive, LAMPs-negative), containing colocalised MMP-9 and TIMP-1, needs investigation i.e., requires further verification with triple labelling and EM. Possible cell membrane and recycling endosome localisation of TIMP-2 needs confirmation with labelling of non-permeabilised cells and labelling for MT1-MMP and proMMP-2, respectively. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Pseudomonas aeruginosa is an opportunistic human pathogen which, like many other Gram negative pathogens, employs quorum sensing - regulated virulence factors to establish an infection in its host. Quorum sensing in P. aeruginosa populations is controlled by low molecular weight (hapten) signalling molecules known as homoserine lactones (HSLs). Blocking bacterial communication using antibodies is an attractive strategy for infection control as QS takes a central role in P. aeruginosa infections, and antibodies can recognise their targets with exquisite specificity. There are two well-studied QS circuits in P. aeruginosa- the Las system and the Rhl system, controlled by two autoinducers compounds, 3-oxo-C12-HSL and C4-HSL respectively. Antibodies raised against HSL compounds can reduce the expression of virulence factors controlled by QS circuit and the immunomodulatory effects of 3- oxo-C12-HSL. In order to generate antibodies with high sensitivities against the autoinducer compounds of P. aeruginosa, a panel of HSL compounds was synthesised, conjugated to the carrier protein and used for sheep immunisation. High specificity anti-HSL antibodies were isolated from an immunised sheep antibody repertoire using phage display technology. These phage antibody hits were converted into single chain antibody (scAb) format, which possessed a HuCκ gene for detection and 6x histidine tag for purification. Soluble scAbs expressed in E. coli were purified and characterised using ELISA. Unique clones showing high sensitivity for free HSL compounds were reformatted into sheep-mouse chimeric IgGs, expressed transiently in COS 7 cells and characterised using biochemical assays. These cross-reactive monoclonal antibodies were shown to recognise HSL compounds in low nanomolar concentrations and have the potential to reduce virulence gene expression in P. aeruginosa.

Natural killer (NK) cells are important in limiting tumor dissemination. The NK activity in C57B1/6 mice bearing Lewis lung carcinoma (LLC) was monitored during tumor development. During the initial period of tumor growth, NK activity was enhanced. As tumor growth progressed, NK activity became suppressed. Depletion of macrophages from the spleen cells of tumor-bearing mice restored the NK cytotoxic response. Plasma prostaglandin E2 (PGE2) concentrations were measured by a radioimmunoassay and found to become elevated during the course of tumor growth. To determine whether the suppressed NK activity might have been a result of the elevated levels of PGE2, mice were treated with a prostaglandin synthesis inhibitor, indomethacin. Indomethacin treatment prevented the rise in plasma PGE2 concentrations and the suppression in NK activity. These results support the hypothesis that the suppression of NK activity in tumor bearers is mediated by PGE2 which might be produced by the host's suppressor macro-phages.

The spontaneous tumoricidal ability of pulmonary alveolar macrophages (PAM) isolated from C57B1/6 mice bearing either a metastatic or a nonmetastatic cloned variant of Lewis lung carcinoma (LLC) was examined in vitro. During the early weeks of tumor development the cytotoxicity mediated by macrophages was enhanced in the tumor-bearing mice, especially in the metastatic tumor bearers. Later in tumor progress (week 4) the spontaneous cytotoxicity of both groups typically declined to levels less than those of normal macrophages. Experiments were performed to determine if macrophages could be activated further in vitro by incubation in a mixture of lymphokine and lipopolysaccha ride. The macrophages from the metastatic tumor bearers were consistently activated in vitro. However, macrophages isolated from mice bearing large tumors and whose spontaneous cytotoxicity was suppressed could not be activated.The secretion of prostaglandin E2 (PGE2) by macrophages at different times during tumor development was measured to determine if PGE2 levels corresponded with the ability or inability of macrophages to kill tumor cells. Secretion of PGE2 typically corresponded with the capacity to kill rather than with an inability to kill target cells. Similarly, the production of PGE2 by macrophages was not responsible for the decline in the ability of macrophages to kill tumor cells.These results suggest that PAM are activated to be cytotoxic during the period when pulmonary metastases are developing. The successful establishment of these metastases does not appear to depend on the capacity of the tumor to suppress alveolar macrophage cytotoxicity. / Department of Biology

Factors that can influence the transmission of aquatic viruses in fish production facilities and natural environment are the immune defense of host species, the ability of viruses to infect host cells, and the environmental persistence of viruses. In this thesis, fish cell lines were used to study different aspects of these factors. Five viruses were used in this study: viral hemorrhagic septicemia virus (VHSV) from the Rhabdoviridae family; chum salmon reovirus (CSV) from the Reoviridae family; infectious pancreatic necrosis virus (IPNV) from the Birnaviridae family; and grouper iridovirus (GIV) and frog virus-3 (FV3) from the Iridoviridae family. The first factor affecting the transmission of fish viruses examined in this thesis is the immune defense of host species. In this work, infections of marine VHSV-IVa and freshwater VHSV-IVb were studied in two rainbow trout cell lines, RTgill-W1 from the gill epithelium, and RTS11 from spleen macrophages. RTgill-W1 produced infectious progeny of both VHSV-IVa and -IVb. However, VHSV-IVa was more infectious than IVb toward RTgill-W1: IVa caused cytopathic effects (CPE) at a lower viral titre, elicited CPE earlier, and yielded higher titres. By contrast, no CPE and no increase in viral titre were observed in RTS11 cultures infected with either genotype. Yet in RTS11 all six VHSV genes were expressed and antiviral genes, Mx2 and Mx3, were up regulated by VHSV-IVb and -IVa. However, replication appeared to terminate at the translational stage as viral N protein, presumably the most abundant of the VHSV proteins, was not detected in either infected RTS11 cultures. In RTgill-W1, Mx2 and Mx3 were up regulated to similar levels by both viral genotypes, while VHSV-IVa induced higher levels of IFN1, IFN2 and LGP2A than VHSV-IVb. The second part of the thesis examined the ability of two Ranaviruses, GIV and FV3, to infect non-host fish cells. This is referred to as cellular tropism and is one of many host-virus interaction events required to established successful infection in new organisms. Grouper iridovirus (GIV), belonging to the Ranavirus genus of the Iridoviridae family, was demonstrated to differentially express viral genes and induce apoptosis in three non-host fish cell lines rainbow trout monocyte/macrophage (RTS11), Chinook salmon embryon (CHSE-214) and fathead minnow Epithelioma papulosum cyprinii (EPC). These cells were challenged with GIV and virus entry into all three cell lines was confirmed by the expression of viral immediate early genes. The expression of the late major capsid protein gene was detected in CHSE-214 and EPC, but not in RTS11, suggesting an earlier termination in the viral replication cycle in RTS11. Approximately 12 h after infection with GIV, cell death was prominent in all three non-host cell lines. Death was later confirmed to be apoptosis by the presence of chromosomal DNA fragmentation and phosphatidylserine externalization. To determine whether apoptosis was protein related or gene expression related, the three cell lines were infected with heat-inactivated GIV and UV-treated GIV (GIVUV). The heat inactivation abolished apoptosis in all three cell lines, but each cell line responded differently to GIVUV. Relative to GIV, GIVUV caused no apoptosis in CHSE-214, decreased apoptosis in RTS11, and increased apoptosis in EPC. These results suggest that early GIV gene expression was needed for apoptosis in CHSE-214 but impeded apoptosis in EPC. At the cellular level, only EPC was a permissive host as EPC was the only cell line of the three capable of producing a moderate increase in virus titre. The three non-host cell lines present a good system for potentially identifying different components of GIV-induced apoptotic pathways in future studies. Rainbow trout are not highly susceptible to frog virus 3 (FV3) induced diseases, and had been suggested to be a potential carrier for the virus. To determine which rainbow trout cell types are permissive for FV3 and act as a potential source for virus replication in vivo, the ability of rainbow trout cell lines from gonads (RTG-2), skin (RTHDF), liver (RTL-W1), gills (RTgill-W1), intestine (RTgut-GC) and spleen (RTS11), and primary leukocyte cultures from peripheral blood (PBL) and head kidney (HKL) to support FV3 infection was examined. RTG-2 supported a moderate level of FV3 replication while viral replication in RTL-W1 was minimal. The rest of the cell lines did not support viral replication but all succumbed to the infection and were killed by FV3. Lymphocyte-like cells from PBL and HKL were not killed by FV3 while macrophage-like cells were. Most of the cell lines died by an apoptosis-independent mechanism, presumably necrosis, while the monocyte/macrophage cell line, RTS11, died by an apoptosis-dependent mechanism. In addition, neoplastic macrophage-like human U937 cell line, and T lymphocyte-like PEER cell line were also infected with FV3 to compare their response to that of rainbow trout immune cells. U937 cells were killed by FV3 in an apoptosis-dependent manner; however, PEER T cells did not die from FV3 infection, a result similar to the lymphocyte-like fraction of rainbow trout PBL and HKL. In summary, most rainbow trout cell lines do not support significant FV3 replication; furthermore, cells of the lymphocyte origin appeared refractory to FV3 induced cell death while those of macrophage origin underwent apoptosis as a response to FV3. The last factor affecting the transmission of aquatic viruses examined in this thesis is the persistence of viruses in the aquatic environment. Virus persistence is influenced by natural environmental factors such as temperature, pH, desiccation and salinity, but the often unexplored anthropogenic factors can play a role. Therefore, the focus of this section was on the effect of one particular anthropogenic substance, Corexit 9500, on the infectivity of aquatic viruses with different physical characteristics. The effect of Corexit 9500, a dispersant used to clean up oil spills, on invertebrates, lower vertebrates, birds and human health have been examined but there is a significant lack of study on the effect of this dispersant on aquatic viruses. In this study, the effect of Corexit 9500 on four aquatic viruses of different structural composition was examined. Corexit 9500 reduced the titre of the enveloped viral hemorrhagic septicemia virus (VHSV) at all concentrations (10% to 0.001%) examined. The titre of frog virus 3 (FV3), a virus with both enveloped and non-enveloped virions, was only reduced at the high Corexit 9500 concentrations (10% to 0.1%). Corexit 9500 was unable to reduce the titre of non-enveloped infectious pancreatic necrosis virus (IPNV), but enhanced the titre of chum salmon reovirus (CSV) by 2-4 logs. With the ability to inactivate enveloped viruses and possibly enhance some non-enveloped viruses, Corexit 9500 has the potential to alter the aquatic virosphere.

Wear particle-induced inflammation leading to periprosthetic osteolysis remains a major cause of hip implant failure. As polyethylene particles from conventional metal-on-polyethylene implants have been associated with these failures, an interest in lower wear metal-on-metal (MM) bearings has emerged. However, the biological effects of nanometer-size chromium oxide particles, predominant type of wear particles produced by MM implants, remain mostly unknown. Therefore, this study aimed to determine the cytotoxicity of nanometer-size Cr2O3 particles on macrophages in vitro, by analyzing their effects on cell mortality and cytokine release and comparing them with those of similarly-sized alumina (Al2O3) particles (known to be relatively bioinert). Results showed that at high concentrations, nanometer-size Cr2O3 particles can be cytotoxic to macrophages, inducing significant decreases in total cell numbers and increases in necrosis. Results also showed that, at high concentrations, the cytotoxicity of Cr2O3 particles was overall higher than that of Al2O3 particles, even though Cr2O3 and Al2O3 are both stable forms of ceramic materials. However, it appeared to be lower than that of previously reported conventional polyethylene and CoCrMo particles. Therefore, chromium oxide particles may not be the main culprit in initiating the inflammatory reaction in MM periprosthetic tissues.

ABCA1 is a key plasma membrane protein required for the efflux of cellular cholesterol to extracellular acceptors, particularly to apoA-I. This process is essential to maintain cholesterol homeostasis in the body. The detailed molecular mechanisms, however, are still insufficiently understood. Also, the molecular identity of ABCA1, i.e. channel, pump or flippase, remains unknown. In this study we analyzed the extracellular ATP levels in the medium of ABCA1-expressing BHK cells and RAW macrophages and compared them to the medium of relevant non-expressing cells. We found that the extracellular ATP concentrations are significantly elevated when cells express ABCA1. Importantly, a dysfunctional ABCA1 mutant (A937V), when expressed similarly as WT-ABCA1, is unable to raise extracellular ATP concentration. This suggests a causal relationship between functional ABCA1 and elevated extracellular ATP. To explore the physiological role of elevated extracellular ATP, we analyzed ABCA1-mediated cholesterol efflux under the conditions where extracellular ATP levels were modulated. We found that increasing extracellular ATP within the physiological range, i.e. < μM, promotes cholesterol efflux to apoA-I. On the other hand, removing extracellular ATP, either by adding apyrase to the medium or by expressing a plasma membrane bound ecto-nucleotidase CD39, abolishes cholesterol efflux to apoA-I. Based on these results we conclude that, through direct or indirect mechanisms, ABCA1 functions to raise ATP levels in the medium. This elevated extracellular ATP is required for ABCA1-mediated cholesterol efflux to apoA-I.

During inflammatory responses, macrophages make and secrete cytokines, including the proinflammatory cytokine TNF-alpha (TNF). TNF is a highly potent activator of immune responses with pleiomorphic effects throughout the body. TNF is a key causative agent of chronic inflammatory diseases and is of an intense clinical interest as a therapeutic target. At the outset of this thesis, little was known about how macrophages secrete TNF. Notably, the pathways, carriers and molecules that regulate TNF secretion had not been characterised. A main goal of this work was to identify compartment and molecules involved in the intracellular trafficking of TNF. Live cell imaging of GFP-TNF was established and this provided novel and important new insights into trafficking. Both endogenous and GFP-tagged TNF were followed in macrophages using fluorescence microscopy. The trafficking of other molecules in macrophages was also studied. The major findings of this work include the identification of a new two-step secretory pathway for TNF and other proteins from the trans-Golgi Network (TGN) to the cell surface. This pathway goes via the recycling endosome as an intermediate station. Pleiotrophic tubular-vesicular carriers containing TNF bud off the TGN for the post-Golgi trafficking of TNF and their characterization both in live cell imaging and in biochemical analysis of isolated vesicles constituted the main parts of this work. Functional studies, including endosome inactivation and overexpression of Rab11 mutants (proteins functioning at the level of the recycling endosome) revealed that recycling endosomes have indeed an essential role in the exocytic trafficking of TNF in macrophages. This thesis also provides further insight into recycling endosomes as a possible intermediate step in the exocytic trafficking of several other proteins including the adhesion protein E-Cadherin, that function at the cell surface. Finally, the last chapter of this thesis examines endocytic pathways in activated macrophages. Assays for fluid phase endocytosis and receptor-mediated endocytosis were established and the regulation of both pathways was compared. The results show that LPS has opposite effects on fluid phase and receptor mediated endocytosis, decreasing and increasing their activity respectively. Recycling of transferrin through the recycling endosome was also measured, providing a link with studies on TNF exocytosis. Overall, the work in this thesis has made a major contribution to our understanding of TNF trafficking in macrophages, of macrophage pathways more generally and of trafficking at a fundamental level. The findings herein set the stage for more in depth analysis at a single molecular level to explore TNF regulation in normal and disease cells.