Air-Liquid Interface Culture Research | ALI Cell Culture | Corning

Air-liquid interface (ALI) research has long been the gold standard in representing in vivo biology in an in vitro culture environment. Because it exposes one side of the culture to liquid media and surrounds the other by air, the technique is ideal for studying respiratory tract epithelial cells, which interact with both, liquid and air in vivo.

Though ALI experimentation has been vital in researching multiple respiratory diseases, such as asthma and chronic obstructive pulmonary disease, it's extremely critical now as scientists explore the respiratory underpinnings of the novel coronavirus. Already, ALI has expanded scientists' understanding of the virus that causes COVID-19; studies have been published in the New England Journal of Medicine and other elite medical journals, and several more are to come.

ALI is set to become even more pivotal for preclinical research. We spoke with Shabana Islam, MS, PhD, Product Line Manager at Corning Life Sciences, to understand why, and to learn best practices that researchers should consider as they apply ALI techniques in the lab.

ALI systems consist of apical and basolateral compartments, which are separated by a porous filter support, such as a precoated permeable support. Cells are cultured atop the apical surface; when they become confluent, they move across the basal-apical threshold. Because the media remains on the basal side, the cells on the apical interface are surrounded by air, after which they differentiate and generate an apical microenvironment.

The basal surface has access to the media so that it can feed and humidify the apical side via diffusion through the microporous membrane. As the cells differentiate, based on cell source, for example, airway epithelial cells, they secrete mucus into the apical compartment. This activity aligns well with respiratory research, Islam notes, because it physiologically mimics the behavior of the epithelium in vitro.

"Cell differentiation is a characteristics feature of airway epithelial cells," Islam says. "Therefore, models should include the ability of the cells to differentiate and maintain, and that can be achieved with air-liquid interface."

When establishing ALI cultures from primary cells, the first step is to isolate the cells from the tissue. Then, dilute the cells and seed them on a permeable membrane of a cell culture insert. Surfaces coated with an extracellular matrix such as collagen I or IV are good options for culturing cells.

Grow the cells for three to six weeks, depending on the cell type and the time needed for culturing. The epithelium cells will fully differentiate, forming the ciliated cells, goblet cells, and basal cells that represent in vivo human epithelial cells.

End-to-end solutions for this workflow can include uncoated or precoated permeable supports. Multi-well companion plates, such as Corning^® Falcon^® 6-well Deep Well Plates, are long-term culture solutions that can reduce the frequency of media changes, save on labor, and minimize contamination risk.

Because it can culture in vivo-like cells in in vitro models, air-liquid interfaces are commonly used to investigate lung diseases, both for cell-to-cell signaling and for disease modeling. Corning customer Epithelix, for example, has successfully used ALI methodology for its popular MucilAir in vitro cell model of the human airway epithelium.

ALI's potential applications in researching cystic fibrosis also hold intriguing promise, too. Cystic fibrosis is a rare pulmonary disorder affecting 70,000 people worldwide, the Cystic Fibrosis Foundation says, and its patient-to-patient treatment response is highly variable, driving a need for more research into personalized treatments. Nasal cells collected from patients and cultured with ALI could help fill those knowledge gaps.

"The nice thing about using nasal cells is that they're easy to obtain from patients to create ALI cultures," Islam says. Without ALI, she adds, researchers' ability to explore personalized approaches would be inherently limited.

"Animal models are very expensive and time-consuming, and there's considerable animal-to-animal variation," she says. "With air-liquid interface culture of nasal cells, you minimize that variability and can grow cells faster."

And yet ALI's possibilities are not limited to the respiratory system. Some studies, the journal Reproduction in Domestic Animals notes, have explored its potential uses in the female reproductive tract, including studies of the embryonic microenvironment and effects on assisted reproduction. Other studies have explored applications in the digestive tract and organotypic skin equivalence for wound healing, dermal remodeling, and cancer research.

One significant benefit of ALI models is that they're less variable than animal models. To maximize that benefit, Islam advises consistency from end-to-end and recommends using cell models that are representative of the target tissue.

"Whatever the target tissue is in vivo and the endpoint aim, you should try to create cell models that are representative with relevant and comparable factors, for example, dose metrics and similar statistics comparisons to develop a standard," she says. "And when you're using the permeable supports, know that pore size, pore densities of the membrane, and choice of culture media are all variables that you can control."

There's a lot of momentum in the ALI cell culture space — and as the prevalence and profile of respiratory diseases rise as COVID-19 persists, that momentum will likely gain steam. Given ALI culturings' low cost and relatively fast uptake, opportunities abound for scientists who want to get involved — and there are more innovative supplies than ever to help accelerate your research.

Need help stocking your lab with the right equipment and supplies for your next ALI project? Contact us for customized recommendations.