Quantitative In vitro Assay to Measure Neutrophil Adhesion to Activated Primary Human Microvascular Endothelial Cells under Static Conditions

Summary

Neutrophil adherence to the activated endothelium at sites of infection is an integral component of the host's inflammatory response. Described in this report is a neutrophil binding assay that allows for the in vitro quantitation of primary human neutrophil binding to endothelial cells activated by inflammatory mediators under static conditions.

Abstract

The vascular endothelium plays an integral part in the inflammatory response. During the acute phase of inflammation, endothelial cells (ECs) are activated by host mediators or directly by conserved microbial components or host-derived danger molecules. Activated ECs express cytokines, chemokines and adhesion molecules that mobilize, activate and retain leukocytes at the site of infection or injury. Neutrophils are the first leukocytes to arrive, and adhere to the endothelium through a variety of adhesion molecules present on the surfaces of both cells. The main functions of neutrophils are to directly eliminate microbial threats, promote the recruitment of other leukocytes through the release of additional factors, and initiate wound repair. Therefore, their recruitment and attachment to the endothelium is a critical step in the initiation of the inflammatory response. In this report, we describe an in vitro neutrophil adhesion assay using calcein AM-labeled primary human neutrophils to quantitate the extent of microvascular endothelial cell activation under static conditions. This method has the additional advantage that the same samples quantitated by fluorescence spectrophotometry can also be visualized directly using fluorescence microscopy for a more qualitative assessment of neutrophil binding.

Introduction

Since the vascular endothelium is in direct contact with the circulating blood, it is uniquely situated to initiate a rapid inflammatory response during infection or injury. Endothelial cells (ECs) express pattern recognition receptors that recognize a variety of conserved bacterial components and danger molecules, and receptors for host inflammatory mediators such as TNFα. Activation of these receptors induces ECs to secrete cytokines (e.g. IL-6, IL-8, CXCL1 and CCL2), and to upregulate adhesion molecules (e.g. E/P-selectin, VCAM-1 and ICAM-1) at their cell surface ^1,2. These molecules all facilitate the localization of leuk....

Protocol

1. Plating and Maintenance of Microvascular Endothelial Cells

1. Thaw and grow your microvascular endothelial cells according to the manufacturers supplied instructions. In this protocol, cells were grown in EGM-2 MV media (Lonza), and it is recommended that all experiments are performed within two weeks of thawing to minimize any variation due to passage number. Our experiments with HMVEC-Lung are performed between passages 4 to 9.
2. Day 1: When cells reach 80-90% confluency, trypsinize and resuspend at 120,000 cells per ml. Plate 36,000 cells (0.3 ml) per well into 48-well, polystyrene tissue culture plate(s). Include wells of HMVEC that will no....

Results

In order to obtain reliable, reproducible results using a neutrophil binding assay, it is essential that the health and the confluency of the microvascular endothelial cells are optimal on the day of the assay, as illustrated with HMVEC-Lung in Figure 1. In addition, it is imperative that low passage number microvascular ECs are used (i.e. less than 9 passages), and accordingly, we recommend performing all experiments within two weeks of thawing. The health of the neutrophils is also of utmost i.......

Discussion

The most critical steps for a successful neutrophil / microvascular endothelial cell adhesion assay are: 1) Use of low passage number (<9), healthy endothelial cells; 2) Maintaining the isolated neutrophils at a low density (i.e. <5 x 10⁶ cells / ml) and using them within two hours of isolation; and 3) Fastidious washing of the calcein AM-labeled neutrophils and use of the calcein AM-labeled neutrophils in a timely fashion to minimize EC contamination and loss of calcein from the neutroph.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
HMVEC-Lung	Lonza	CC-2527
EGM-2 MV	Lonza	CC-3202
HBSS	Life Technologies	14175-095	Can be substituted with any vendor
48-well Tissue Culture Plates	BD Falcon	353078
PBS (without phenol red)	UCSF Cell Culture Facility	CCFAL001	Can be substituted with any vendor
D-PBS (without Ca2+ and Mg2+ and phenol red)	UCSF Cell Culture Facility	CCFAL003	Can be substituted with any vendor
RPMI-1640 (without phenol red)	Life Technologies	11835-030
Polymorphprep	Axis-Shield	1114683
calcein AM	Life Technologies	C3099	(0.995 mM) stock soln
Trypan Blue Solution	Sigma-Aldrich	T8154
40 μM filters	VWR	21008-949	Can be substituted with any vendor
FLUOstar OPTIMA Spectrophotometer	BMG LABTECH	-