Exposure of phosphatidylserine on the outer leaflet of the cytoplasmic memb
rane is an early event during apoptotic cell death and serves as a recognit
ion signal for phagocytes. Usually the clearance of apoptotic cells does no
t initiate inflammation or immune response. We investigated the immune resp
onse in Balb/c mice towards apoptotic human T-cells, Animals injected with
apoptotic cells showed significantly reduced humoral immune responses, espe
cially Th1-dependent IgG2a titres, compared to controls immunised with viab
le cells, However, treatment of apoptotic cells with annexin V (AxV) signif
icantly increased the humoral immune response, AxV binds with high affinity
to anionic phospholipids and as a result interferes with the phosphatidyls
erine recognition by phagocytes, Our results indicate that AxV treatment ma
y be used to increase the efficiency of apoptotic cell-based vaccines, e.g.
some tumour vaccines.