Immunological and physiological effects of venom on mammals

Abstract

The selective and potent molecules contained within venom target a broad diversity of physiological targets. In humans, the consequence of envenomation ranges from innocuous to lethal. This thesis examines venom-induced immune dysregulation and its contribution to the pathology of box jellyfish envenomation. Secondly, this thesis investigates snake venom as a potential source of T lymphocyte modulators. Immunological responses to box jellyfish venom Box jellyfish envenoming represents a public health threat in tropical waters throughout the world. Yet despite more than 50 years of research, the biochemistry and underlying mechanisms of Chironex fleckeri and Carukia barnesi envenomation remain poorly elucidated. This study examined venom-induced cytokine responses from human and murine leukocytes to determine whether systemic inflammation may have a role in the symptoms of envenomation. We show that C. fleckeri venom is cytotoxic to human PBMCs in culture, while nonlethal doses produced strong local edema and transient IL-6 response in vivo. In contrast, we confirmed that C. barnesi venom activates monocytes, macrophages, T cells, and B cells in culture, independent of cytotoxicity. Additionally, C. barnesi venom stimulates sustained systemic cytokine release and lung inflammation in vivo. We further developed a mouse model of Irukandji syndrome suitable for investigating sting pathology and testing efficacy of new therapies over 24 h. Finally, we demonstrated that innate detection of C. barnesi venom is mediated via pattern recognition receptor (PRR) signalling. These findings provided evidence for the first time that proinflammatory cytokines may contribute to the pathology of Irukandji syndrome. The immunosuppressive potential of venom-derived compounds Venoms act with remarkable specificity upon a broad diversity of physiological targets. Venoms are composed of proteins, peptides, and small molecules, providing the foundation for the development of novel therapeutics. This study assessed the effect of venom from the red-bellied black snake (Pseudechis porphyriacus) on human primary leukocytes using bead-based flow cytometry, mixed lymphocyte reaction, and cell viability assays. We show that venom treatment had a significant immunosuppressive effect, inhibiting the secretion of interleukin (IL)-2 and tumour necrosis factor (TNF) from purified human T cells by 90% or greater following stimulation with mitogen (phorbol 12-myristate 13-acetate and ionomycin) or via cluster of differentiation (CD) receptors, CD3/CD28. In contrast, venom treatment did not inhibit TNF or IL-6 release from antigen-presenting cells stimulated with lipopolysaccharide. The reduced cytokine release from T cells was not associated with inhibition of T cell proliferation or reduction of cell viability, consistent with an anti-inflammatory mechanism unrelated to the cell cycle. Deconvolution of the venom using reverse-phase HPLC identified four fractions responsible for the observed immunosuppressive activity. These data suggest that compounds from P. porphyriacus venom may be potential drug leads for T cell-associated conditions such as graft versus host disease, rheumatoid arthritis, and inflammatory bowel disease.