Surface Molecule Loss and Bleb Formation by Human Germinal Center B Cells Undergoing Apoptosis: Role of Apoptotic Blebs in Monocyte Chemotaxis

Human tonsil germinal center (GC) B cells rapidly undergo apoptosis in culture. Annexin-V binding shows an early event in this process. In the present study, this method has been used to label apoptotic GC B cells and to analyze additional surface molecules. The expression of all of the molecules st...

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Veröffentlicht in:Blood 1999-08, Vol.94 (3), p.1012-1020
Hauptverfasser: Segundo, Carmen, Medina, Francisco, Rodrı́guez, Carmen, Martı́nez-Palencia, Rosalı́a, Leyva-Cobián, Francisco, Brieva, José A.
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Sprache:eng
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Zusammenfassung:Human tonsil germinal center (GC) B cells rapidly undergo apoptosis in culture. Annexin-V binding shows an early event in this process. In the present study, this method has been used to label apoptotic GC B cells and to analyze additional surface molecules. The expression of all of the molecules studied was reduced in apoptotic (annexin-V+) GC B cells, and the reduction was more marked for CD11a, CD21, CD22, CD49d, and CD54, molecules that participate in survival interaction for GC B cells. The analysis of CD54, one of the molecules that was more drastically reduced, showed that GC, but not mantle zone, B cells actively secrete CD54 to the culture supernatant (SN). The secreted CD54 was partly released from the GC B cells in a particulate form as demonstrated by centrifugation. Further experiments using filtration, fluorescence microscopy, electron microscopy, and flow cytometry analysis showed that GC B cells released to the culture SN a population of spherical membranous vesicles of about 0.18 μm in size, similar to the blebs described in other apoptosis systems. Bleb formation depended on active metabolism, Ca2+, and, in part, on microfilament integrity. GC B-cell–derived blebs were clearly associated with apoptosis, as antiapoptotic stimuli prevented their formation. In addition, GC B-cell–derived blebs contained the adhesion molecules previously studied. Consequently, bleb formation might contribute to the surface molecule loss occurring in apoptotic GC B cells. Finally, a chemotaxis assay showed that GC B-cell blebs were chemotactic for human monocytes, suggesting that this mechanism might operate in vivo.
ISSN:0006-4971
1528-0020
DOI:10.1182/blood.V94.3.1012.415k05_1012_1020