The Role of RANTES (CCL5) In The Immune Response to Bacterial Infections

Tang, Shiying (2019) The Role of RANTES (CCL5) In The Immune Response to Bacterial Infections. Masters by Research thesis (MSc), Manchester Metropolitan University.

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Abstract

Background: Sepsis is a lethal condition that causes organ dysfunction due to a dysregulated host response to an infection. It is one of the leading causes of morbidity and mortality globally with approximately 6 million deaths occurring every year. Transfusion-associated sepsis (T-AS) can occur through the transfusion of contaminated blood components, commonly platelet concentrates (PCs). The “cytokine storm” is thought to be the main pathophysiology behind sepsis and the cytokines secreted within bacterial contaminated PCs could play a key role in the development of T-AS in recipients. This study investigated the effect of bacterially-primed platelet releasates on the activation status of neutrophils and monocytes, with the aim of understanding the link between platelet product contamination, the cytokine storm, and the severity of clinical symptoms in transfusion recipients. Findings: The cytometric bead array assay demonstrated that RANTES was significantly elevated in comparison with IL-1β, IL-6, and TNF-α when platelet rich plasma samples were incubated with planktonic and biofilm forms of Staphylococcus epidermidis and Serratia marcescens. Flow cytometric analysis of the surface markers CD54, CD11b and CD66b on U937 and HL-60 cell lines demonstrated no changes in expression when treated platelet releasates that had been primed with S. epidermidis and wild type (WT) Escherichia coli. Yet treating these cells with platelet releasates primed with multi-resistant E. coli (planktonic or biofilm form) caused a highly significant upregulation in CD54 expression. Platelet-free plasma alone was found to cause a degree of upregulation of all three surface markers in some cases suggesting minor immunomodulatory activity of plasma proteins. Despite its significant release from bacterially-primed platelets, recombinant RANTES (rhRANTES) at different concentrations did not induce significant changes in surface expression of the activation markers on U937 and HL-60 cells however, variable effects on CD54 and CD11b expression were seen on primary human neutrophils. Curiously, CD66b appeared to be downregulated with increasing exogenous rhRANTES concentration. Conclusions: The results may indicate that RANTES requires synergy with additional cytokines/chemokines in order to induce activation of neutrophils and monocytes and cannot act in isolation. Bacterial virulence appears to play a role in the resultant cytokine profiles of platelets evidenced by the stark difference in cell activation caused by multi-resistant E. coli-primed platelets in comparison with WT E. coli and S. epidermidis.