A minimally invasive optical trapping system to understand cellular interactions at onset of an immune response.

David G Glass,Owain R Millington,Amanda J Wright,Niall Mcalinden

doi:10.1371/journal.pone.0188581

David G Glass, Owain R Millington + Show 2 more

Open Access

https://doi.org/10.1371/journal.pone.0188581

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Journal: PloS one	Publication Date: Dec 8, 2017
Citations: 15	License type: CC BY 4.0

Affiliation: University of Strathclyde, University of Nottingham

Abstract

T-cells and antigen presenting cells are an essential part of the adaptive immune response system and how they interact is crucial in how the body effectively fights infection or responds to vaccines. Much of the experimental work studying interaction forces between cells has looked at the average properties of bulk samples of cells or applied microscopy to image the dynamic contact between these cells. In this paper we present a novel optical trapping technique for interrogating the force of this interaction and measuring relative interaction forces at the single-cell level. A triple-spot optical trap is used to directly manipulate the cells of interest without introducing foreign bodies such as beads to the system. The optical trap is used to directly control the initiation of cell-cell contact and, subsequently to terminate the interaction at a defined time point. The laser beam power required to separate immune cell pairs is determined and correlates with the force applied by the optical trap. As proof of concept, the antigen-specific increase in interaction force between a dendritic cell and a specific T-cell is demonstrated. Furthermore, it is demonstrated that this interaction force is completely abrogated when T-cell signalling is blocked. As a result the potential of using optical trapping to interrogate cellular interactions at the single cell level without the need to introduce foreign bodies such as beads is clearly demonstrated.

Highlights

Using a high numerical aperture microscope objective lens and a laser beam, optical trapping provides three dimensional control and manipulation of objects ranging in size from hundreds of nanometers to tens of microns [1]
The optical trapping system consisted of a Ventus IR, 3 W, TEM00, continuous wave laser (Laser Quantum, UK) with a wavelength of 1064 nm that was expanded to just overfill a spatial light modulator (SLM; Boulder Nonlinear Systems, USA)
For the experiments presented here it is important that the relationship between trapping force and laser beam power is correctly calibrated so that the cellular interaction force can be inferred from the laser beam power required to separate a cell pair

Summary

Introduction

Using a high numerical aperture microscope objective lens and a laser beam, optical trapping provides three dimensional control and manipulation of objects ranging in size from hundreds of nanometers to tens of microns [1]. Applications range from manipulation and positional control, to the measurement of forces within the pico-Newton range, a magnitude that is comparable to many biological functions [2, 3]. Holographic optical traps can provide re-configurable positional control of several trap positions simultaneously [5], allowing cell orientation and cell contact time to be controlled and giving precise control over multiple particles. Using an optical trap it is possible to control the length of a specific interaction and ensure that the interaction studied is the initial contact between a cell pair. Optical trapping provides an excellent route to control and to quantify relative interaction forces on the pico-Newton scale, making them ideal for initial stage cell pair interaction studies [4]

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