Abstracts (complete list) - Wissenschaft Online

Fabia T.L. Rocha, Rüdiger Arnold, Renate Rutz, Michael Kirschfink
The role of FLIP Long in C5a-modulated spontaneous apoptosis
of neutrophils
Neutrophils (PMN) are the most abundant type of immune cell in the circulation, and
one of their key characteristics is their short life span (8-20 hours). In the absence of
survival factors they undergo spontaneous apoptosis, a process critical to resolution of
inflammation. The exact influence of the complement system in neutrophil apoptosis is
still obscure. C5a has been described to delay PMN apoptosis through the Bad-mediated
signaling pathway in mitochondria (intrinsic pathway), however, its possible impact on
the extrinsic death receptor pathway in PMN apoptosis is still unknown.
A possible involvement of C5a in the modulation of spontaneous PMN apoptosis was
investigated by analysis of the extrinsic pathway regulator cellular FLIPLong (c-FLIPL ).
Neutrophils were isolated from 20 healthy adult donors. FACS analysis of annexin V
binding was carried out to evaluate apoptosis. Activity of caspases 9, 8, and 3 was
measured by substrate cleavage using AFC fluorescence. c-FLIPL and β-actin were
quantified using LightCycler-RT-PCR. For all experiments, neutrophils were analysed
after 1 hour or 21 hours of incubation with or without C5a. After 21 hours of incubation
we observed a significant delay in spontaneous apoptosis upon C5a treatment, however
only in a subgroup of donors (10/20, p < 0.005). Delay in spontaneous PMN apoptosis
of these individuals went along with a significant up regulation of the regulator c-FLIPL (p < 0,05), but not with reduced caspase 8 activity.
These findings suggest that - in contrast to previous reports - C5a acts as a PMN
survival factor only under certain conditions, which appear to involve the regulatory
activity of c-FLIP. In our study we demonstrated for the first time the expression of
FLIPL in neutrophils and its upregulation in cases where C5a delayed neutrophil
apoptosis.
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