Measuring Influenza Virus Infection Using Bioluminescent Reporter Viruses for In Vivo Imaging and In Vitro Replication Assays

To streamline standard virological assays, we developed bioluminescent replication-competent influenza reporter viruses that mimic their parental counterparts. These reporter viruses provide a rapid and quantitative readout of viral infection and replication. Moreover, they permit real-time in vivo measures of viral load, tissue distribution, and transmission in the same cohort of animals over the entire course of infection-measurements that were not previously possible. Here we provide detailed protocols using bioluminescent reporter viruses for in vivo imaging in mice and ferrets. We also describe cell culture-based techniques using reporter viruses for quantification of viral titers and performing microneutralization assays. The ease, speed, and adaptability of these approaches have the potential to accelerate multiple areas of influenza virus research.

LuBiA (Luciferase-Based Binding Assay): Glowing Peptides as Sensitive Probes to Study Ligand-Receptor Interactions

The quantitative and qualitative biochemical description of molecular interactions is fundamental to the study of ligand/receptor pairs and their structure/function relationships. Bioactive peptides often are active at (sub-)nanomolar concentrations, indicating they have a high affinity for their sites of action, notably binding sites on receptors. Since such receptor proteins are commonly of low abundance, highly sensitive detection methods are required to study these ligand/receptor interactions. We present a protocol for an inexpensive luminescence-based detection setup in which the peptide ligand of interest is extended with the 11-amino acid HiBiT tag. This tag can be quantified easily down to fmol amounts by its ability to reconstitute the enzymatic activity of LgBiT, a truncated version of the Oplophorus gracilirostris luciferase.

Analysis of SPI-1 Dependent Type III Secretion and Injection Using a NanoLuc Luciferase-Based Assay

Studies of bacterial protein secretion have relied on a variety of reporters that allow the tracking of secreted proteins. However, the lack of truly quantitative and highly sensitive reporters has hindered, in particular, the investigation of the kinetics of protein secretion. In this chapter, we describe a luminescence-based assay using NanoLuc luciferase to analyse secretion and injection into host cells of type III secretion (T3S) substrates encoded on Salmonella pathogenicity island-1 (SPI-1). This method has a very high sensitivity and high signal-to-noise ratio. Moreover, the simplicity of the protocol and the rapid determination and quantification of the luminescence makes it ideal for the monitoring of the kinetics of secretion but also convenient for high-throughput screenings. The protocols presented here include (1) Salmonella SPI-1 secretion assay, where the T3S substrates-NanoLuc fusions are detected by luminometry in the bacterial supernatant, and (2) Salmonella injection assays, using the split-Nanoluc (HiBiT/LgBiT) to monitor the injection of T3S substrates-HiBiT fusions into the host cells stably expressing LgBiT.