Aged mice exhibit distinct peripheral B-cell phenotypes differing in apoptotic susceptibility: an ex vivo analysis.
BACKGROUND
Age-related changes in the antibody response have been classically associated with alterations in T-cell help, but increasing evidence shows that intrinsic B-cell defects exist. This article analyzes the apoptotic susceptibility of peripheral B-cells in aged and young control mice.


METHODS
Freshly isolated lymphocytes from spleen and Peyer's patches (PPs) were labeled for B-cell lineage (B220(+) cells) and germinal center B subset (GCs, B220(+)/PNA(+) cells). Alternatively, splenic B-cells purified by MACS were used. Apoptosis was monitored by the Annexin V binding, incorporation of 3,3(')-dihexyloxacarbocyanine iodide (DiOC(6)(3)), propidium iodide (PI) staining, and morphological changes. Moreover, intracellular Bcl-2 expression and Bad phosphorylation status were also analyzed in B-cells.


RESULTS
We showed in aging mice an enhanced Annexin V(+)/PI(-) cell percentage in splenic B-lymphocytes, which was correlated with a lower DeltaPsi(m). By contrast, no change in apoptosis was observed in compartments known to be enriched in activated B-cells (GCs and PPs). Analysis of Bcl-2 levels revealed no modification. When using B-cells purified by MACS, we strongly confirm data obtained on staining cells. Moreover, enhanced spontaneous apoptosis of splenic B-cells in aged mice was found to be correlated with a reduced phosphorylated Bad expression.


CONCLUSIONS
Increased apoptosis of resting B-cells in old mice may be determined by an altered Bad phosphorylation, which in turn contributes to cell death by lowering the mitochondrial threshold for apoptosis.
Verdier
Mireille
M
Laboratoire de Physiologie Moléculaire Mitochondriale et Immunitaire, EA 3842 Homéostasie Cellulaire and Pathologie, Faculté de Médecine, Limoges, France.
Malissein
Emilie
E
Munteanu
Eliza
E
Jayat-Vignoles
Chantal
C
Ratinaud
Marie-Hélène
MH
Troutaud
Danielle
D
D000375:Aging / Q000502:physiology*; D000818:Animals; D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D001402:B-Lymphocytes / Q000166:cytology / Q000502:physiology*; D015415:Biomarkers / Q000378:metabolism; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D017493:Leukocyte Common Antigens / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D010581:Peyer's Patches / Q000166:cytology; D010641:Phenotype; D010766:Phosphorylation; D013154:Spleen / Q000166:cytology; D051025:bcl-Associated Death Protein / Q000378:metabolism
D017304:Annexin A5; D015415:Biomarkers; D051025:bcl-Associated Death Protein; D017493:Leukocyte Common Antigens