Studying Neutrophil Function in vitro: Cell Models and Environmental Factors

Abstract

Neutrophils are the most abundant immune cell type in the blood and constitute the first line of defense against invading pathogens. Despite their important role in many diseases, they are challenging to study due to their short life span and the inability to cryopreserve or expand them in vitro. Thus, research into neutrophils has to rely on cells freshly isolated from peripheral blood of human donors, introducing donor-dependent variation in the experimental data. To counteract these problems, researchers tried to develop adequate cell models, such as cell lines. For those functional studies that cannot rely on cell models, a standardization of protocols regarding neutrophil purification and culturing could be a solution. In this review, we provide an overview of the most commonly used models for neutrophil function (HL-60, PLB-985, NB4, Kasumi-1 and induced pluripotent stem cells). In addition, we describe the effects of glucose concentration, pH, oxygen tension and temperature on neutrophil function.

Keywords: HL-60; Kasumi-1; NB4; PLB-985; induced pluripotent stem cells; neutrophils.

Figure 1

Granulopoiesis. In the process of granulopoiesis, neutrophils develop stepwise from granulocyte-monocyte progenitor cells (GMPs). Each stage has a unique phenotype that is comprised of both morphologic features and cell surface markers. In the first step, the cell transitions into the myeloblast stage. The promyelocyte stage is characterized by the appearance of azurophilic granules. Specific granules start to develop at the myelocyte stage, and are fully present at the metamyelocyte stage; this is also the point at which the cell loses its proliferative capacity. After the metamyelocyte stage, the cell can be called a neutrophil; it acquires the distinctive banded nucleus and develops gelatinase granules and secretory vesicles. The arrows indicate the stage of the cell lines that are discussed in this paper.

Figure 2

Neutrophil functions. To combat infection, neutrophils can execute various functions. Phagocytosis is the uptake of pathogens inside the cell. NETosis is a form of cell death in which neutrophils expulse their DNA together with histones and granular proteins (neutrophil extracellular traps). During degranulation, neutrophils release enzymes and antibacterial peptides which are normally stored inside granules. During the release of reactive oxygen species, neutrophils convert oxygen to highly reactive forms that are capable of damaging pathogens. Finally, neutrophils release cytokines, activating other immune cells and attracting them to the site of infection.