CD40 engagement enhances eosinophil survival through induction of cellular inhibitor of apoptosis protein 2 expression: Possible involvement in allergic inflammation.
BACKGROUND
CD40 engagement enhances eosinophil survival, suggesting a role for this receptor in the development of eosinophilia.


OBJECTIVE
We examined whether CD40 enhances eosinophil survival by inducing the expression of antiapoptotic proteins. Three members of the inhibitor of apoptosis protein (IAP) family, namely cellular (c)-IAP1, c-IAP2, and XIAP, and 2 antiapoptotic proteins of the Bcl-2 family, namely Bcl-x(L) and Bfl-1/A1, were investigated.


METHODS
Blood and sputum were obtained from healthy subjects and atopic asthmatic patients. Blood eosinophils were isolated by means of magnetic selection. Expression of CD40, IAPs, and Bcl-2 proteins was investigated by using flow cytometry, immunoblotting, or both. CD40 stimulation was achieved with agonistic antibodies or soluble ligands. Apoptosis was assessed by staining with propidium iodide and FITC-conjugated annexin-V. c-IAP2 expression was inhibited with antisense oligonucleotides.


RESULTS
Freshly isolated eosinophils from healthy and asthmatic patients did not express CD40. Conversely, eosinophils expressed CD40 spontaneously when cultured for 48 hours. At this time point, CD40 stimulation significantly delayed eosinophil apoptosis. Inhibition of eosinophil apoptosis was accompanied by induction of c-IAP2 but not c-IAP1, XIAP, Bcl-x(L), or Bfl-1/A1 expression. Antisense knockdown of c-iap2 abolished CD40-induced enhancement of eosinophil survival. Sputum cells from asthmatic patients, unlike those from healthy subjects, substantially expressed CD40 and c-IAP2. Moreover, a strong correlation was found between the percentage of eosinophils in the sputum from asthmatic patients and the sputum level of CD40 and c-IAP2 expression.


CONCLUSIONS
The results demonstrate that CD40 engagement enhances eosinophil survival through induction of c-IAP2 expression and suggest a role for this mechanism in allergic inflammation.
Department of Physiology, Faculty of Veterinary Medicine, University of Liège, Belgium.
Fabrice
F
Bureau
Grégory
G
Seumois
Fabrice
F
Jaspar
Alain
A
Vanderplasschen
Bruno
B
Detry
Paul-Pierre
PP
Pastoret
Renaud
R
Louis
Pierre
P
Lekeux
D000328:Adult; D017209:Apoptosis; D001249:Asthma / Q000276:immunology; D019013:CD40 Antigens / Q000378:metabolism / Q000502:physiology*; D002470:Cell Survival; D002478:Cells, Cultured; D004802:Eosinophilia / Q000276:immunology; D004804:Eosinophils / Q000166:cytology / Q000276:immunology*; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000276:immunology* / Q000473:pathology; D007249:Inflammation / Q000276:immunology; D051034:Inhibitor of Apoptosis Proteins; D014176:Protein Biosynthesis; D011506:Proteins; D013183:Sputum / Q000166:cytology; D044767:Ubiquitin-Protein Ligases
D019013:CD40 Antigens; D051034:Inhibitor of Apoptosis Proteins; D011506:Proteins; C494833:BIRC2 protein, human; D044767:Ubiquitin-Protein Ligases