Factor VIII bypasses CD91/LRP for endocytosis by dendritic cells leading to T-cell activation.
BACKGROUND
The development of factor VIII (FVIII) inhibitors remains the major hurdle in the clinical management of patients with hemophilia A. FVIII uptake by professional antigen-presenting cells (APC) is the first step involved in initiation of immune responses to FVIII. Studies on FVIII catabolism have highlighted the role played by CD91/LRP as a potential target for increasing FVIII half-life in patients and prolonging treatment efficiency. We investigated the involvement of CD91 in FVIII endocytosis by human dendritic cells (DC), a model of professional APC.


METHODS
Immature DC were generated from circulating monocytes from healthy donors. Surface expression of CD91 was assessed by flow cytometry. Uptake of fluorescein isothiocyanate-conjugated ligands by immature DC was studied in the presence of various blocking agents.


RESULTS
CD91 was expressed on approximately 20% of DC and mediated the internalization of its model ligand, alpha2-macroglobulin. DC internalized FVIII and activated a human FVIII-specific T-cell clone in a dose-dependent manner. FVIII uptake by DC and subsequent T-cell activation were not inhibited by receptor-associated protein.


CONCLUSIONS
Our results indicate that CD91 and other members of the LDL receptor family are not strongly implicated in FVIII internalization by monocyte-derived DC, and suggest the involvement of alternative divalent ion-dependent endocytic receptors.
Dasgupta
Suryasarathi
S
Unité 872, Institut National de la Santé et de la Recherche Médicale, Paris, France.
Navarrete
Ana Maria
AM
André
Sebastien
S
Wootla
Bharath
B
Delignat
Sandrine
S
Repessé
Yohann
Y
Bayry
Jagadeesh
J
Nicoletti
Antonino
A
Saenko
Evgueni L
EL
d'Oiron
Roseline
R
Jacquemin
Marc
M
Saint-Remy
Jean-Marie
JM
Kaveri
Srini V
SV
Lacroix-Desmazes
Sebastien
S
D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis*; D002469:Cell Separation; D003713:Dendritic Cells / Q000166:cytology*; D004705:Endocytosis; D005169:Factor VIII / Q000096:biosynthesis* / Q000378:metabolism; D006467:Hemophilia A / Q000235:genetics; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000166:cytology; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008213:Lymphocyte Activation; D051379:Mice; D009000:Monocytes / Q000166:cytology / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology*
D015703:Antigens, CD; C475476:LRP1 protein, human; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1; C078147:F8 protein, human; D005169:Factor VIII