What are Passages in Histology?
In
Histology, the term "passages" typically refers to the process of transferring cells from one culture vessel to another. This is done to maintain cell lines and ensure their continued growth and viability. Each transfer, or "passage," involves detaching cells from their current vessel, often using enzymatic or mechanical methods, and then seeding them into a new vessel with fresh growth medium.
Cell Viability: Over time, cells can deplete the nutrients in their growth medium and produce waste products. Regular passages help replenish the nutrients and remove waste.
Cell Density: Maintaining an optimal cell density is essential for healthy cell growth. High density can lead to contact inhibition, where cells stop growing due to lack of space.
Genetic Stability: Frequent passages can help minimize the risk of genetic drift, which can alter the characteristics of the cell line over time.
Cells are first detached from the culture vessel using an enzyme like
trypsin or a mechanical method such as scraping.
The detached cells are then collected and counted to determine their concentration.
The cells are diluted to the desired density and seeded into a new culture vessel with fresh growth medium.
How Many Passages are Too Many?
The number of passages a cell line can undergo before it loses its original characteristics varies. For
primary cells, which are directly isolated from tissues, the number of passages is often limited to a few dozen. For
immortalized cell lines, the number of passages can be much higher. However, even immortalized cells can undergo
genetic drift after many passages, which can lead to changes in their behavior and characteristics.
How to Track the Number of Passages?
Keeping track of the number of passages is essential for maintaining the integrity of your cell line. Most laboratories use a
passage number system, where each passage is recorded in a log. This helps in maintaining consistency and allows researchers to know exactly how many passages a particular cell line has undergone.
Genetic Drift: Over time, cells can accumulate genetic mutations, leading to changes in their behavior and characteristics.
Senescence: Some cell lines may undergo senescence, a state where they stop dividing, after a certain number of passages.
Contamination: The risk of contamination with microorganisms, such as bacteria or fungi, increases with the number of passages.
Conclusion
The number of passages is a critical factor in maintaining healthy and genetically stable cell cultures in histology. By understanding the importance of passages and implementing best practices, researchers can ensure the integrity and reliability of their cell lines.
