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Distinctive effects of G-CSF, GM-CSF and TNFa on neutrophil apoptosis in systemic lupus erythematosus

D.J. Armstrong¹, E.M. Whitehead¹, A.D. Crockard², A.L. Bell³

¹United Hospitals Trust, Antrim, Co Antrim; ²Regional Immunology Laboratory, Royal Victoria Hospital, Belfast; ³Queen’s University of Belfast, Belfast, UK.

ABSTRACT
Objective
To investigate the influence of culture with G-CSF, GM-CSF and TNFa on neutrophil apoptosis, comparing neutrophils from SLE patients with rheumatoid arthritis (RA) patients and healthy control subjects.

Methods
Neutrophils were isolated from SLE (n=10), RA (n=10) and healthy control subjects (n=10), and cultured with two different concentrations of G-CSF, GM-CSF and TNFa. Proportion of apoptotic neutrophils at T=0, T=2hrs and T=24hrs was measured using FITC-labelled annexinV and flow cytometry.

Results
Significantly more neutrophils were apoptotic at T=0 in the SLE subjects than in the other groups (median, range - Control 3.5% (0.3-7.9) SLE 9.5% (2.9-29.1) RA 3.0% (0.4-23.0) p<0.05). Following culture for 24 hours with 1ng/ml G-CSF, the proportion of apoptotic neutrophils from SLE subjects was significantly increased (median, range = 51.6% (27.0-84.0) without G-CSF v 66.8% (31.8-89.2) with G-CSF, p<0.05). This was not observed with RA or control subjects, in whom the trend was towards inhibition of apoptosis. Similar trends were seen with GM-CSF. There was significant induction of apoptosis in SLE neutrophils after 2 hr culture with 1ng/ml TNFa (median, range = 2.3% (0.1-8.0) without TNFa v 5.2% (1.0-22.4) with TNFa). No significant change was seen in the other groups.
There was an inverse correlation between total neutrophil count and the degree of induction of apoptosis by G-CSF and GM-CSF, determined at a range of time-points and cytokine concentrations

Conclusions
Neutrophils from SLE patients display resistance to the apoptosis-inhibiting effects of G-CSF and possibly GM-CSF, and appear more susceptible to the apoptosis-inducing action of TNFa, the greatest resistance being observed in the more neutropenic patients.

Key words
SLE, neutrophils, apoptosis, G-CSF, GM-CSF, TNFa, rheumatoid arthritis.

Dr. Armstrong was supported by a research grant from United Hospitals Trust, Antrim, Co Antrim, UK.
Please address correspondence and reprint requests to: Dr. David J. Armstrong, Specialist Registrar, Department of Rheumatology, Musgrave Park Hospital, Stockman’s Lane, Belfast BT9 7JB, UK.
E-mail oswald17727@hotmail.com