MDCK (Madin-Darby Canine Kidney) is a line of immortalized cells used extensively in biological and medical research. Grown in laboratories, these cells can divide indefinitely, providing a consistent biological system for many studies. They are recognized for their utility in virology and cell biology, serving as reproducible models to investigate complex biological processes.
The Origin and Nature of MDCK Cells
The MDCK cell line was established in 1958 by scientists Stewart H. Madin and Norman B. Darby, who isolated the original cells from the kidney tubules of a healthy adult female Cocker Spaniel. This origin is important because the cells retain many functional characteristics of kidney tissue. Specifically, MDCK cells are a type of epithelial cell, the class responsible for lining the surfaces and cavities throughout a body.
As epithelial cells, their primary function is to form a barrier that controls what passes through an organ’s lining. In the kidney, these cells transport water and salts, a function the MDCK cell line maintains in laboratory cultures.
Key Biological Characteristics
A defining feature of MDCK cells is their ability to form a polarized monolayer. When grown on a permeable support, the cells arrange themselves into a single sheet, much like paving stones. In this formation, each cell develops a distinct top and bottom surface, a property known as polarity. The top, or apical, surface faces the external environment, while the bottom, or basolateral, surface is attached to the substrate, mimicking how epithelial tissues are structured.
This polarized structure is maintained by tight junctions, which are specialized protein complexes that seal the space between adjacent cells. These junctions act like mortar between bricks, ensuring the layer is impermeable so that molecules cannot leak between the cells. This feature allows scientists to study the transport of substances across an epithelial barrier in a controlled setting.
When MDCK cells are grown within a three-dimensional gel matrix, they exhibit another behavior. Instead of forming a flat sheet, they organize themselves into hollow spheres, known as cysts, or branching tubes. These three-dimensional structures more closely resemble the microscopic architecture of a real kidney. This capability allows for the study of how cells interact to form complex tissues and organs.
Applications in Scientific Research
The biological properties of MDCK cells make them a versatile tool in scientific inquiry. Their ability to form a polarized monolayer with functional tight junctions is useful for studying cell polarity, the process by which cells establish distinct functional domains on their surface. By manipulating genes and proteins in MDCK cells, researchers can investigate how polarity is established and maintained.
These cells are also a primary model for investigating cell-cell adhesion. The tight junctions that seal the gaps between MDCK cells are dynamic structures that can be assembled and disassembled. This allows scientists to explore the molecules responsible for holding cells together and how these connections contribute to tissue integrity.
In pharmacology, a primary application is using the cells to model drug transport. Researchers can grow a layer of MDCK cells on a filter as a stand-in for the intestinal lining or other barriers. By applying a potential drug to one side of the cell layer, they can measure its rate of transport to the other, which helps predict how a drug might be absorbed and distributed.
MDCK Cells in Vaccine Development
A primary use of MDCK cells is in manufacturing vaccines, especially for the influenza virus. Traditionally, influenza vaccines were produced by growing the virus in fertilized chicken eggs. This method has limitations, including potential allergic reactions in some individuals and a lengthy production timeline. Cell-based vaccine production using MDCK cells offers a modern alternative that addresses these challenges.
In this process, MDCK cells act as a factory for the virus. The cells are grown in large quantities in controlled containers called bioreactors. Once a sufficient cell density is reached, they are infected with the specific strain of influenza virus targeted for the vaccine. The MDCK cells, being highly susceptible to the virus, replicate it to very high concentrations.
After the virus has replicated, it is harvested from the cell culture, purified, and then inactivated. The resulting product contains the viral proteins that trigger an immune response but without the ability to cause illness. This cell-based approach is faster and more scalable than egg-based production, an advantage when responding to a pandemic. It also eliminates the risk of egg-related allergies and avoids mutations that can sometimes occur when viruses adapt to growing in eggs.