Characterization of Inflammatory Responses During Intranasal Colonization with Streptococcus pneumoniae

Summary

Colonization of the murine nasopharynx with Streptococcus pneumoniae and the subsequent extraction of adherent or recruited cells is described. This technique involves flushing the nasopharynx and collection of the fluid through the nares and is adaptable for various readouts, including differential cell quantification and analysis of mRNA expression in situ.

Abstract

Nasopharyngeal colonization by Streptococcus pneumoniae is a prerequisite to invasion to the lungs or bloodstream¹. This organism is capable of colonizing the mucosal surface of the nasopharynx, where it can reside, multiply and eventually overcome host defences to invade to other tissues of the host. Establishment of an infection in the normally lower respiratory tract results in pneumonia. Alternatively, the bacteria can disseminate into the bloodstream causing bacteraemia, which is associated with high mortality rates², or else lead directly to the development of pneumococcal meningitis. Understanding the kinetics of, and immune responses to, nasopharyngeal colonization is an important aspect of S. pneumoniae infection models.

Our mouse model of intranasal colonization is adapted from human models³ and has been used by multiple research groups in the study of host-pathogen responses in the nasopharynx^4-7. In the first part of the model, we use a clinical isolate of S. pneumoniae to establish a self-limiting bacterial colonization that is similar to carriage events in human adults. The procedure detailed herein involves preparation of a bacterial inoculum, followed by the establishment of a colonization event through delivery of the inoculum via an intranasal route of administration. Resident macrophages are the predominant cell type in the nasopharynx during the steady state. Typically, there are few lymphocytes present in uninfected mice⁸, however mucosal colonization will lead to low- to high-grade inflammation (depending on the virulence of the bacterial species and strain) that will result in an immune response and the subsequent recruitment of host immune cells. These cells can be isolated by a lavage of the tracheal contents through the nares, and correlated to the density of colonization bacteria to better understand the kinetics of the infection.

Protocol

Before you begin: all steps are done in a Biohazard Level 2 (BSL2) Biological Safety Cabinet (BSC) unless otherwise stated. Please ensure that you have obtained the appropriate Biohazard Approval for use of infectious bacterial pathogens as per institutional guidelines prior to initiation of the experiments. Additionally, please ensure that you have all the materials and reagents necessary to conduct the procedure prepared beforehand. Mice used in these experiments have included female C57BL/6 mice from …

Representative Results

Figure 1 represents an overview schematic summarizing the main steps of the protocol. Figures 2-3 provide visualization of the microbiological methodology inherent to the protocols described herein. Figure 4 represents proper positioning of a mouse to perform an intranasal colonization, while Figure 5 depicts typically changes in weight of mice colonized with S. pneumoniae strain P1547. Figures 6-7 represent specific stages of t…

Discussion

In this study we presented detailed methods for the intranasal colonization of mice using a clinical isolate strain of Streptococcus pneumoniae and the subsequent isolation and characterization of the immune cells recruited to nasopharynx in response to the bacteria. We demonstrated how a bacterial inoculum can be cultured in nutrient-rich media and used to establish a colonization event in mice, which is initially restricted to the nasopharynx. We then showed how responding immune cell types that are recruited …

Materials

Name of Reagent/Material	Company	Catalog Number
Anti-Mouse Ly6C FITC	BD Pharmingen	553104
Anti-Mouse Ly6G PE	BD Pharmingen
Anti-Mouse CD45.1 eFluor 450	eBioscience	48-0453-82
Anti-Mouse F4/80 Antigen APC	eBioscience	17-4801-82
Anti-Mouse CD11c PerCP-Cy5.5	eBioscience	45-0114-82
Anti-Mouse CD11b PE-Cy7	eBioscience	25-0112-82
Anti-Mouse CD3 Alexa Fluor 700	eBioscience	56-0032-82
Anti-Mouse CD4 eFluor 605NC	eBioscience	93-0041-42
Intramedic Polyethylene Tubing – PE20	Becton Dickinson	427406
BD 1ml Syringe	Becton Dickinson	309659
BD 26G3/8 Intradermal Bevel	Becton Dickinson	305110
Buffer RLT Lysis Buffer	Qiagen	79216
Difco Tryptic Soy Agar	Becton Dickinson	236950
Defibrinated Sheep Blood	PML Microbiologicals	A0404
RNAqueous-Micro Kit	Ambion	AM1931
M-MuLV Reverse Transcriptase	New England Biolabs	M0253L
GoTaq qPCR Master Mix	Promega	A6001