Trypsinization

Trypsinization exploits trypsin's ability to cleave peptide bonds at the carboxyl side of lysine and arginine residues, thereby degrading the extracellular matrix proteins and cell–substrate adhesion molecules that anchor cells to the culture surface. In practice, the culture medium is removed, the cell monolayer is rinsed with a balanced salt solution (often phosphate-buffered saline) to remove serum proteins that inhibit trypsin, and a dilute trypsin solution (typically 0.05–0.25% in EDTA) is added. The culture is incubated at 37°C for a few minutes until cells round up and detach; the reaction is then stopped by adding serum-containing medium, as serum contains trypsin inhibitors such as alpha-1 antitrypsin.¹

Beyond routine passaging, trypsinization is essential for generating single-cell suspensions for flow cytometry, for harvesting cells for cryopreservation, and for preparing primary cultures from tissue fragments. In histopathology, enzymatic antigen retrieval with trypsin is used to unmask epitopes in formalin-fixed, paraffin-embedded tissue sections, improving immunohistochemical detection. Trypsinization also plays a role in the production of cell-based vaccines and in the isolation of cells for regenerative medicine, where controlled detachment preserves cell viability and surface markers.²

Excessive trypsinization can damage cell surface receptors and reduce viability, so exposure time and enzyme concentration are carefully optimized for each cell type. For sensitive cells, alternatives such as accutase, collagenase, or non-enzymatic dissociation buffers are used. The addition of EDTA chelates calcium and magnesium ions, which are required for cell adhesion, thereby enhancing detachment. Temperature and pH are also critical: trypsin is most active at 37°C and pH 7.4–8.0, and deviations reduce efficiency or increase cytotoxicity.³

Trypsinization has a history dating to the early 20th century, when Alexis Carrel used trypsin to dissociate tissues for explant culture. A lesser-known application is in the preparation of chromosome spreads for karyotyping, where trypsin digestion of mitotic cells is used to produce G-banding patterns. In some protocols, trypsinization is performed at 4°C to slow metabolism and reduce clumping, a technique known as cold trypsinization. Additionally, trypsin inhibitors from soybean are often used to neutralize the enzyme in serum-free systems, and the process can be monitored by observing cell morphology under an inverted microscope.⁴

Trypsin

A serine protease that cleaves peptide bonds at lysine and arginine residues.

EDTA

Ethylenediaminetetraacetic acid, a chelator of divalent cations used to enhance cell detachment.

Passaging

The transfer of cells from one culture vessel to another to maintain growth.

Antigen retrieval

A technique to expose epitopes in fixed tissue sections for antibody binding.