Nucleolar changes in human phytohaemagglutinin-stimulated lymphocytes

Area of Science:

• Cell Biology
• Immunology
• Genetics

Background:

• Lymphocytes play a crucial role in the immune response.
• Nucleoli are essential for ribosome biogenesis and cellular processes.
• Understanding nucleolar dynamics is key to deciphering lymphocyte activation.

Purpose of the Study:

• To investigate the morphological and structural changes in lymphocyte nucleoli upon phytohemagglutinin (PHA) stimulation.
• To correlate nucleolar alterations with the activation status of lymphocytes.
• To elucidate the role of nucleolar organizer regions (NORs) in lymphocyte proliferation.

Main Methods:

• Studied lymphocyte nucleoli from peripheral blood and PHA-stimulated cultures.
• Utilized silver staining, RNA-specific fluorescent staining, and electron microscopy.
• Analyzed nucleolar morphology over a time course (2-96 hours) post-stimulation.

Main Results:

• Peripheral blood lymphocytes typically exhibit one ring-shaped nucleolus.
• PHA stimulation initially increases the number of cells with multiple nucleoli.
• Nucleoli transition from ring-shaped to large, then to compact forms, with fibrillar centers reappearing.
• Fibrillar centers, identified by silver staining, contain non-chromosomal proteins and may store nucleolar proteins.

Conclusions:

• Lymphocyte activation by PHA triggers dynamic changes in nucleolar structure.
• The formation of multiple nucleoli suggests activation and fusion of NORs.
• Nucleolar morphology changes reflect the progression of lymphocyte activation and cell cycle events.
• Fibrillar centers are key components of nucleoli, potentially serving as protein reservoirs.