Inhibition of respiratory pathogens Mycobacterium tuberculosis and SARS-CoV-2 by human serum and monoclonal antibodies

Antibodies are a key host immune response against pathogens. Yet the effects of antibodies on Mycobacterium tuberculosis (Mtb) at the cellular level are incompletely understood, as is the effect of HIV co-infection on antibody-mediated immunity to SARS-CoV-2. By investigating these questions at the epicenter of the HIV/TB co-epidemic in KwaZulu-Natal, South Africa, I have: 1) Cloned immunoglobulins from B cells of Mtb-exposed donors and investigated the effect of Mtb-specific polyclonal and monoclonal antibodies on infection of macrophages; 2) Characterised antibody responses in viraemic, virologically suppressed, and HIV-negative Covid-19 patients to determine whether HIV status and viraemia influence neutralization of SARS-CoV-2. Sera from TB-exposed individuals on average increased host cell survival and inhibited intracellular bacterial growth compared to non-specific control serum, although there was a wide range of individual variation. I cloned several Mtb-specific antibodies from South African donors including one which significantly inhibited intracellular bacterial growth in THP-1 monocytes and primary macrophages. I developed a live virus neutralisation assay for SARS-CoV-2 to circumvent the problem of a lentiviral pseudovirus neutralization assay being incompatible with samples containing antiretrovirals for HIV. Among Covid-19 patients, the kinetics of RBD-binding and neutralising antibodies differed little between HIV-uninfected and virologically suppressed people living with HIV (PLWH), whereas viraemic PLWH had a much lower and delayed response. In addition, I observed that plasma from individuals either previously infected with earlier variants of SARS-CoV-2 or vaccinated with AstraZeneca’s AZD1222 recombinant adenovirus vaccine showed decreases in neutralisation against newer variants of concern. Taken together, these results demonstrate that antibody-mediated immunity is relevant to the control of TB but is highly heterogeneous. Similarly, there is individual heterogeneity in the neutralisation response to SARS-CoV-2, with the latter partially determined by HIV status and suppression state

Investigation into the changing colonisation of skin bacteria during isotretinoin treatment for acne vulgaris

Poster presentatio

Thesis submitted in fulfillment of the requirements for the Degree MSc

Masters of ScienceThe Coronaviridae family consists of RNA viruses within the order Nidovirales. The family is classified into two genera, namely the corona- and toroviruses. Coronaviruses are enveloped, single stranded, positive sense RNA viruses with genomes ranging between 27-32kb in size. The 5’ two-thirds of the genome encodes for the 1a/b polyprotein, while the 3’ one-third of the genome encodes for the structural proteins that mediate viral entry into the host cell. These structural proteins include the spike (S), envelope (E), membrane (M) and nucleocapsid (N) proteins. The nucleocapsid protein is expressed at high levels within an infected cell. Studies have shown that this protein plays a key regulatory role in different cellular pathways, including the inhibition of interferon production and the up-regulation of the AP1 signal transduction pathway, amongst others. Also, the N protein is vital in the formation of the ribonucleocapsid core by binding to the viral RNA during virion assembly. The focus of this study is the immune response in whole blood cultures to the presence of human coronavirus (HCoV) NL63 N protein. To characterise the stimulation of the immune activity against HCoV-NL63 N in blood cultures, the HCoV-NL63 N gene was expressed in a bacterial system. In this pilot study, GSTtagged N constructs were then purified and used to treat whole blood cultures from three volunteers. ELISAs were used to measure the cytokine response in these treated whole blood cultures. Results showed that the nucleocapsid protein has an inflammatory response on whole blood cultures. These results have generated vital information in the potential function of the HCoV-NL63 N protein on the immune system. It is suffice to say that the HCoV-NL63 N protein is able to elicit an effective inflammatory response within the host cell. Future studies into the cellular pathways affected by the HCoV-NL63 N protein will clarify its exact role in stimulating the host immune system

Inactivation of pathogens on food and contact surfaces using ozone as a biocidal agent

This study focuses on the inactivation of a range of food borne pathogens using ozone as a biocidal agent. Experiments were carried out using Campylobacter jejuni, E. coli and Salmonella enteritidis in which population size effects and different treatment temperatures were investigate

Vector-borne diseases: studies in human West Nile Virus and canine Lyme nephritis

Vector-borne diseases are a resurgent focus in public health. As concern about climate change mounts, the close relationship between these diseases and the environment has garnered growing attention. This dissertation examines the relationship between environment and vector-borne disease in both human and veterinary medical contexts and on both a local and national scale. The first study investigated using a novel Internet-based surveillance system for risk mapping of West Nile Virus (WNV) in the contiguous United States from 2007-2014, with meteorological, demographic, and land use variables as predictors. The study found that annual average temperature, minimum temperature, precipitation, and human population density were predictive of WNV reports, but that the novel surveillance data appeared to have systematic gaps that impair the utility of the model. However, the results may help to guide improvements in novel surveillance systems. The second study used the logistic regression model developed in the first study to predict the risk of WNV in the contiguous United States in 2050 and 2070 under four projected climate scenarios. The study found that Southern California is likely to remain the area of greatest risk under all scenarios and that risk would be expected to increase across much of the West under the scenario of uncontrolled carbon dioxide emissions. The results of this study may inform development of more sophisticated models and may help to direct public health resources to areas of greatest impact. The third study investigated the relationship between cases of canine Lyme nephritis and precipitation in the months prior to diagnosis. Precipitation three months prior to diagnosis was found to be associated with the development of Lyme nephritis (hazard ratio for 1 inch/month 1.125, 95% confidence interval 1.009 – 1.254). This finding may improve diagnostic accuracy for dogs with protein-losing nephropathies and may guide studies of additional risk factors