Expression of specific granule markers on the cell surface of neutrophil cytoplasts

Area of Science:

• Immunology
• Cell Biology
• Hematology

Background:

• Human polymorphonuclear leukocytes (PMNs) are crucial immune cells.
• Cytoplasts, derived from PMNs, were widely assumed to be simple cytoplasmic vesicles.
• The presence of granule activity within PMN cytoplasts was not well-established.

Purpose of the Study:

• To investigate the presence and activity of granule membrane markers in human PMN cytoplasts.
• To challenge the assumption that PMN cytoplasts lack granule activity.
• To determine if granule-plasma membrane fusion occurs during PMN cytoplast preparation.

Main Methods:

• PMN cytoplasts were generated using Ficoll density gradient centrifugation and cytochalasin B treatment.
• Expression of granule membrane markers (Mol, cytochrome b) and other membrane antigens (LFA-1, beta 2m) was quantified.
• Release of granule enzymes (vitamin B12-binding protein, lysozyme) was measured and correlated with Mol expression.

Main Results:

• Mol expression on the plasma membrane of PMNs increased significantly after Ficoll/cytochalasin B treatment and cytoplast preparation.
• Release of granule enzymes correlated strongly with the amount of Mol antigen on the cell surface.
• Cytochrome b levels were elevated on plasma membranes isolated from cytoplasts compared to intact cells.

Conclusions:

• Human PMN cytoplasts exhibit evidence of granule membrane activity.
• The findings indicate that fusion between granule membranes and the plasma membrane occurs during PMN cytoplast preparation.
• This study refutes the notion that PMN cytoplasts are devoid of granule-associated functions.