Human Flt-3-ligand-mobilized dendritic cells require additional activation to drive effective immune responses.
OBJECTIVE
Dendritic cells (DCs) play a pivotal role in the induction of immunity in response to pathogenic challenge or vaccination. As such, the fms-like tyrosine kinase 3-ligand (Flt-3L) has been used to increase DC populations in vivo, with contrasting outcomes, which include an increase in immunity, tolerance induction, or expansion of regulatory cells. This study examines the adjuvant role that human Flt-3L (hFL) administration has in generating immune responses upon immunization with a poorly immunogenic and soluble protein antigen.


METHODS
Mice were immunized with the nominal antigen, ovalbumin, alone or with antigen emulsified in complete Freund's adjuvant (CFA), with or without prior hFL-mediated expansion of DC subsets. The maturation of DC subsets and activation status of antigen-specific T cells were analyzed by flow cytometry, with effector function assessed in cytolytic T-lymphocyte assays.


RESULTS
hFL treatment expanded both conventional DC and plasmacytoid DC in vivo, resulting in increased antigen presentation by both direct and cross-presentation pathways. However, it was only in the context of CFA that antigen immunization could mature DCs and subsequently fully activate antigen-specific T cells with enhanced cytolytic activity.


CONCLUSIONS
Our studies reveal that hFL essentially acts as a coadjuvant, as hFL augments the size of an immune response but requires further adjuvant activation to alter the quality of the response.
Diener
Kerrilyn R
KR
Hanson Institute, South Australia, Australia.
Moldenhauer
Lachlan M
LM
Lyons
A Bruce
AB
Brown
Michael P
MP
Hayball
John D
JD
D000276:Adjuvants, Immunologic; D019264:Adoptive Transfer; D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects* / Q000502:physiology; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D003713:Dendritic Cells / Q000145:classification / Q000187:drug effects* / Q000276:immunology; D004527:Egg Proteins / Q000276:immunology; D005620:Freund's Adjuvant / Q000494:pharmacology; D006801:Humans; D007114:Immunization; D008198:Lymph Nodes / Q000166:cytology / Q000276:immunology; D008213:Lymphocyte Activation; D008565:Membrane Proteins / Q000276:immunology / Q000494:pharmacology* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D010047:Ovalbumin / Q000276:immunology; D010446:Peptide Fragments / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D013154:Spleen / Q000166:cytology / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology
D000276:Adjuvants, Immunologic; D004527:Egg Proteins; D008565:Membrane Proteins; C111390:OVA 323-339; C110366:OVA-8; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; C084881:flt3 ligand protein; D010047:Ovalbumin; D005620:Freund's Adjuvant