What is the Difference Between Primary and Secondary Cell Culture

The main difference between primary and secondary cell culture is that the primary cell culture contains the cells directly obtained from host tissue, whereas the secondary cell culture contains sub-cultured cells from primary cell culture. Furthermore, cells are dissociated from the host tissue either through mechanical or enzymatical digestion. In addition to these, the cells in the primary cell culture have not undergone any genetic transformation, while the cells in the secondary cell culture have altered genetic makeup. 

In brief, the primary and secondary cell culture are two types of cell cultures, which allow the growth of cells in vitro in a medium under controlled conditions. 

Key Areas Covered 

1. What is Primary Cell Culture
     – Definition, Characteristics, Uses
2. What is Secondary Cell Culture
     – Definition, Characteristics, Uses
3. What are the Similarities Between Primary and Secondary Cell Culture
     – Outline of Common Features
4. What is the Difference Between Primary and Secondary Cell Culture
     – Comparison of Key Differences

Key Terms 

Cell Density, Cell Line, Homogeneity, Lifespan, Primary Cell Culture, Secondary Cell Culture

What is Primary Cell Culture 

Primary cell culture is a type of cell culture containing cells directly obtained from the host tissue. Generally, blood cells are a type of cells that is easy to isolate. However, cells in solid tissues can be obtained either through mechanical excision or enzymatic degradation of extracellular matrix with the use of enzymes such as trypsin, collagenase, and pronase. After isolation, these cells can grow in a plastic or glass container in a suitable medium. Significantly, cells in primary cell culture have the exact karyotype and biological response of the cells in the host.

Figure 1: Epithelial Cells in a Primary Cell Culture

Furthermore, there can be two types of primary cell cultures according to the type of cell growth. They are adherent cultures and suspension cultures. Generally, adherent cell cultures are anchorage-dependent and require an attachment for the growth while suspension cultures are anchorage-independent and grow in the medium. However, primary cell cultures have a limited lifespan. Usually, cells undergo programmed cell death due to contact inhibition, the requirement of survival factors. Typically, they build up toxins with the population growth while cells require growth factors for their survival, respectively. Therefore, primary cell cultures can only be maintained only for a few generations or passages in culture. 

What is Secondary Cell Culture 

Secondary cell culture or a cell line is the type of cell culture with an indefinite lifespan. The indefinite lifespan is due to the acquisition of immortality through mutations or viral transformation. In addition to these, due to the providing of survival factors continuously, cells can acquire an indefinite lifespan. Therefore, further proliferation of cells is stimulated in secondary cell cultures. Secondary cell cultures contain cells obtained through the sub-culturing of the primary cell cultures. Typically, sub-culturing is the transferring of cells in a primary cell culture into a new vessel with a fresh medium. However, cells may spontaneously acquire mutations when it goes through several sub-culturing steps.

Figure 2: HeLa Cells – Secondary Cell Culture

In addition to indefinite lifespan, secondary cell cultures have optimal cell density or a higher number of cells in comparison to primary cell culture. Also, sub-culturing increases the homogeneity of the cell culture due to the use of a more specific medium. Thus, these cells show genotypic and phenotypic uniformity in the population.  

Similarities Between Primary and Secondary Cell Culture 

• Primary and secondary cell culture are two types of cell cultures which contain living cells grown in a medium in vitro under controlled conditions. 
• Both allow the growth of cells and the maintenance of regular cell functions to a greater extent. 

Difference Between Primary and Secondary Cell Culture 

Definition 

Primary cell culture refers to the growing and maintaining of the selected cell type excised from a normal parental tissue while secondary cell culture refers to a cell line or sub-clone sub-cultured from primary cell culture. 

Origin of Cells 

Moreover, primary cell culture contains the cells directly obtained from a host tissue either through mechanical or enzymatical digestion, while secondary cell culture contains sub-cultured cells from primary cell culture. 

Homogeneity 

While primary cell cultures may be heterogeneous, secondary cell cultures are homogeneous. 

The resemblance to the Host Tissue 

Cells in primary cell cultures have the same biological response as the cells in the host tissue while cells in secondary cell culture are adapted to the culture conditions by altering their biology. 

Genetic Make up 

Cells in the primary cell culture have the similar genetic makeup to the cells of the host tissue while cells in the secondary cell culture have altered genetic makeup. 

Cell Proliferation 

Moreover, cells in the primary cell culture do not undergo proliferation while cells in the secondary cell culture undergo proliferation. 

Optimal Cell Density 

Primary cell culture does not contain a sufficient amount of cells while secondary cell culture can have an optimal cell density. 

Lifespan 

Cells in the primary cell culture have a finite lifespan while cells in the secondary cell culture have an indefinite lifespan. 

Passaging 

Whereas cells in primary cell culture are unable to maintain by passaging, cells in secondary cell culture can maintain by passaging. 

Maintenance 

Primary cell culture requires a rich mixture of amino acids, micronutrients, certain hormones, and growth factors while secondary cell cultures are easy to maintain. 

Risk of Contamination 

The risk of contamination is high in primary cell cultures, while the risk of contamination is low in secondary cell culture. 

Importance 

In addition, primary cell culture serves as an in vivo model while secondary cell culture serves as an in vitro model. 

Applications 

Primary cell cultures are important in manufacturing vaccines and therapeutic development, while secondary cell cultures are important for the production of hormones, antibodies, anticancer agents, etc. 

Conclusion 

Basically, primary cell culture is a type of initial cell culture containing cells directly come from the host tissue. These cells have a similar genetic makeup as well as a biological response of the host tissue. Therefore, these cells have a definite lifespan and are important for the production of vaccines and cells for transplantation. On the other hand, secondary cell culture contains cells sub-cultured from the primary cell culture. During sub-culturing, these cells undergo mutations, which allow obtaining an indefinite lifespan while adapting them to the culture conditions. Therefore, they are more stable and important in recombinant DNA technology. Hence, the main difference between primary and secondary cell culture is the characteristics of cells. 

References:

1. Khanal, Srijana. “Animal Cell Culture: Introduction, Types, Methods and Applications.” Learn Microbiology Online, 10 Sept. 2017, Available Here.

Image Courtesy:

1. “Epithelial-cells” By John Schmidt (CC BY-SA 3.0) via Commons Wikimedia     
2. “HeLa cells stained with Hoechst 33258” By TenOfAllTrades at English Wikipedia – Own work (Public Domain) via Commons Wikimedia