Lymphocyte cell-cycle analysis by flow cytometry. Evidence for a specific postmitotic phase before return to G0

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Human lymphocytes are crucial for immune responses.
• Understanding lymphocyte cell cycle progression is vital for immunology and cancer research.
• Previous studies established basic cell cycle phases (G0, G1, S, G2/M) in stimulated lymphocytes.

Purpose of the Study:

• To investigate the cell cycle dynamics of lectin-stimulated human lymphocytes.
• To identify and characterize a potential novel late cell-cycle phase.
• To elucidate the requirements for entry into this late phase.

Main Methods:

• Flow cytometry was used to analyze cell populations.
• Acridine orange staining determined RNA and DNA content in individual cells.
• Cell cycle manipulation involved vinblastine and 5-bromo-2-deoxyuridine (BUdR) treatment.

Main Results:

• Confirmed G0 to G2/mitosis progression in the initial 3 days of culture.
• Identified a novel stationary late phase with G0 DNA and elevated RNA content.
• Demonstrated that entry into this late phase requires prior S phase and mitosis.
• Observed a strong correlation between cells in the late phase and [3H]thymidine uptake.

Conclusions:

• Stimulated lymphocytes enter a distinct late cell-cycle phase before returning to quiescence (G0).
• This phase is characterized by high RNA content and requires prior cell division.
• The findings provide new insights into lymphocyte cell cycle regulation and activation.