Characterisation of the host immune response to biofilm-related infections

Breast implant-associated anaplastic large-cell lymphoma (BIA-ALCL) is a recently diagnosed, rare non-Hodgkin T-cell lymphoma in tissue around a breast implant. Since 2000, its detection and incidence has risen worldwide due to the increase use of breast implants in breast surgery. Although the aetiopathogenesis is unclear, it is postulated that the cancer results from chronic bacterial antigen stimulation and sustained T-cell proliferation that potentially leads to malignant transformation. This is in conjunction with implant properties, implant exposure time and host predisposition or genetic factors. The experiments described in this thesis explore the influence of implant surface texture, bacterial load and host response in patient specimens, and initiating and potentiating factors to malignancy. The majority of BIA-ALCL cases have occurred in patients with textured implants, which have been shown to support a higher bacterial load. The work described in Chapter III of this thesis describes the development of an in vitro bacterial attachment assay to further characterise the surface texture of implants and their capacity to support bacterial growth in vitro. We describe a significant relationship between the measurement of available surface area, surface roughness and potentiation of bacterial growth for both Gram-positive and Gram-negative bacteria. In Chapter IV, we examine the influence of implant texture in vivo using a well-established porcine model. We describe the association between textured implant surfaces with bacterial attachment, biofilm formation, development of capsular contracture and host response following artificial bacterial contamination of breast implants in pigs. The role of bacteria in BIA-ALCL has recently been supported by the discovery of high levels of bacterial contamination within BIA-ALCL specimens. In Chapter V, we compare the bacterial load and host response in fresh implants and capsules from new cases of BIA-ALCL to non-tumour specimens. In Chapter VI, we utilise previous findings of a significantly higher proportion of Gram-negative pathogens present in the microbiome of BIA-ALCL specimens when compared to the microbiome surrounding non-tumour implant capsules. We interrogate BIA-ALCL cell lines derived from fresh tumour with antigens including lipopolysaccharide from Gram-negative bacterial cell wall. We demonstrate a unique response to lipopolysaccharide in BIA-ALCL cells compared to other tumour and non-tumour cell lines. In Chapter VII, we also interrogate these cell lines with staphylococcal superantigens since their potential to restrict T-cell receptor expression has recently been reported. We describe a differential response to Gram-positive bacterially derived antigens, providing support to the hypothesis of a Gram-negative antigenic trigger to malignancy. We further investigated the potentiation of BIA-ALCL tumour cell growth this time to bacterial biofilm infection composed of different pathogen species. In Chapter VIII, we develop a co-culture system of biofilm and mammalian cells and describe the differential responses of BIA-ALCL cells when challenged with biofilm consisting of Gram-negative or Gram-positive bacteria. The work described in Chapter IX, examines whether the stimulation by lipopolysaccharide is through Toll-like receptor 4 (TLR4), which positively impacts T-cell priming. We demonstrate a dampening of responses to lipopolysaccharide in BIA-ALCL cells following inhibition of TLR4 signalling. The data from this thesis provides important new insights into the aetiopathogensis of this newly characterised neoplasm.