Qualitative and Quantitative Analysis of the Immune Synapse in the Human System Using Imaging Flow Cytometry

Summary

Here, we describe a complete workflow for the qualitative and quantitative analysis of immune synapses between primary human T cells and antigen-presenting cells. The method is based on imaging flow cytometry, which allows the acquisition and evaluation of several thousand cell images within a relatively short period of time.

Abstract

The immune synapse is the area of communication between T cells and antigen-presenting cells (APCs). T cells polarize surface receptors and proteins towards the immune synapse to assure a stable binding and signal exchange. Classical confocal, TIRF, or super-resolution microscopy have been used to study the immune synapse. Since these methods require manual image acquisition and time-consuming quantification, the imaging of rare events is challenging. Here, we describe a workflow that enables the morphological analysis of tens of thousands of cells. Immune synapses are induced between primary human T cells in pan-leukocyte preparations and Staphylococcus aureus enterotoxin B (SEB)-loaded Raji cells as APCs. Image acquisition is performed with imaging flow cytometry, also called In-Flow microscopy, which combines features of a flow cytometer and a fluorescence microscope. A complete gating strategy for identifying T cell/APC couples and analyzing the immune synapses is provided. As this workflow allows the analysis of immune synapses in unpurified pan-leukocyte preparations and hence requires only a small volume of blood (i.e., 1 mL), it can be applied to samples from patients. Importantly, several samples can be prepared, measured, and analyzed in parallel.

Introduction

T cells are major regulators of the adaptive immune system and are activated through antigenic peptides that are presented in the context of major histocompatibility complexes (MHC). Full T-cell activation requires two signals, the competence signal via the antigen-specific T-cell receptor (TCR)/CD3 complex and the costimulatory signal via accessory receptors. Both signals are generated through the direct interaction of T cells with antigen-presenting cells (APCs). Mature APCs provide the competence signal for T-cell activation through MHC-peptide complexes, and they express costimulatory ligands (e.g., CD80 or CD86) to assure the progression of T-cell activa....

Protocol

1. Preparation of Pan-leukocytes

1. Draw 1 mL of peripheral blood from a healthy donor (or patient) in a heparinized syringe. Make sure to have approval by the responsible ethics committee for the blood donation.
2. Mix 1 mL of human peripheral blood with 30 mL of ACK lysis buffer (150 mM NH₄Cl, 1 mM KHCO₃, and 0.1 mM EDTA, pH 7.0) in a 50 mL tube and incubate for 8 min at room temperature.
3. Fill the tubes with PBS and centrifuge at 300 x g for 6 min. Aspirate the supernatant and resuspend the pellet in 30 mL of ACK lysis buffer.
4. Repeat steps 1.2 and 1.3 until the supernatant is clear. Finally, wash the....

Results

A major goal of the method described here is the quantification of protein enrichment (e.g., F-actin) in the immune synapse between surrogate APCs (Raji cells) and T cells in unpurified pan-leukocytes taken from low-volume (1 mL) human blood samples. The screenshot in Figure 1 gives an overview of the critical gating strategy of this method. It shows the image gallery on the left and the analysis area on the right (Figure 1). The image gallery sh.......

Discussion

The workflow presented here enables the quantification of immune synapses between human T cells (ex vivo) and APCs. Notably, erythrocyte-lysed pan-leukocytes were used as T-cell sources, making T-cell purification steps dispensable. The B-cell lymphoma cell line Raji served as surrogate APCs. This bears significant advantages, since it allows comparisons between blood donors of the T-cell side of the immune synapse. Furthermore, autologous DCs are hardly available directly from peripheral human blood. The production of m.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
>Multifuge 3 SR	Heraeus
RPMI 1640	LifeTechnologies	#11875085	500 mL
FCS	Pan Biotech#3302-P101102
Polystyrene Round Bottom Tube	Falcon	#352054	5 mL
Kulturflasche	Thermo Scientific	#178883
Dulbecco's Phosphate Buffered Saline	Sigma	D8662
Bovine Serum Albumin	Roth	#8076.3
Saponin	Sigma	S7900
Paraformaldehyde	Sigma Aldrich	#16005
FACS Wash Saponin		PBS 1% BSA 0.15 Saponin
ReaktiosgefaB	Sarstedt	72.699.002	0.5 mL
Speed Bead	Amnis	#400041
Minishaker MS1	IKA Works	MS1
Mikrotiterplatte	Greiner Bio One	#650101	96U
Enterotoxin SEB	Sigma Aldrich	S4881
DAPI	Sigma Aldrich	D9542	1:3000
CD3-PeTxR	Invitrogen	MHCD0317	1:30
Phalloidin-AF647	Molecular Probes	A22287	1:150
IS100	Amnis		Imaging flow cytometer
IDEAS	Amnis		Software
INSPIRE	Amnis		Software