Determining the molecular mechanisms to activate cathelicidin for increased resistance against Streptococcus pneumoniae Público

Abstract

Understanding the interactions between pathogenic organisms and the host immune system is imperative to developing innovative treatment methods. In the case of Streptococcus pneumoniae (SPN), identification of naturally-occurring host antibiotics that can be upregulated is of the utmost importance. This is due to its increasing resistance to antibiotics and the continued rank as the leading cause of childhood morbidity and mortality worldwide. Previous research suggests that cathelicidin, which is a host-produced cationic antimicrobial peptide (CAMP), may be a factor that can be induced to prevent and combat infection, as SPN remains susceptible to attack by such factors. The production of cathelicidin is transcriptionally regulated by the Vitamin D (VD) receptor, so it can be induced by VD or 4-phenylbutyrate (PBA), which acts in conjunction with this receptor. I hypothesized that macrophages treated with PBA and VD would be able to increase killing of SPN. To investigate these interactions, differentiated human THP-1 macrophages were treated with varying concentrations of PBA, VD, or both. These were then incubated with either TIGR4 or D39 strains of SPN and bacterial killing was indicated by detecting a decrease in colony-forming units (CFU) in the treatment group compared to the negative control. There was a decrease in CFU of TIGR4 when the macrophages were treated with PBA and VD. However, this reduction was not significant. There was no significant decrease in CFU of D39 when the macrophages were treated with PBA and VD. This provides limited support of the PBA and VD induction hypothesis. Future experiments will test increased doses of PBA and VD, as well as increased incubation times with treatment before infection, in order to investigate the synergistic hypothesis further. The effects of treatment on cathelicidin mRNA and protein concentrations will also be measured in order to elucidate these mechanisms.

Table of Contents

Introduction ...................................................................................................................................................................................................................................................................................1

                      Figure 1: Process of killing SPN by CAMPs

                      Figure 2: Cathelicidin transcription induced with PBA and VD

                      Figure 3: Proposed Mechanism of activation of cathelicidin to increase resistance against SPN

Methods...........................................................................................................................................................................................................................................................................................5                                                                                                                                                        

           Stocks of SPN and Concentration Calculation

                      Table 1: Description of SPN strains used in this study

           Killing of SPN with induced THP-1 cells

Results.............................................................................................................................................................................................................................................................................................7

           Killing of SPN with induced THP-1 cells

                      Figure 4: Effect of PBA and VD on macrophage killing of SPN TIGR4

                      Figure 5: Effect of PBA and VD on macrophage killing of SPN D39

Discussion.......................................................................................................................................................................................................................................................................................9

References.....................................................................................................................................................................................................................................................................................14

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Microbiology Health Sciences, Immunology
Palabra Clave	Sodium 4-phenylbutyrate Cathelicidin Vitamin D Streptococcus Pneumoniae Antimicrobial peptide
Committee Chair / Thesis Advisor	Christopher N. LaRock, Emory University
Committee Members	Arri Eisen, Emory University William M. Shafer, Emory University

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