C3d adjuvant effects are mediated through the activation of C3d-specific autoreactive T cells.
Complement fragment C3d covalently attached to antigens enhances immune responses, particularly for antigens lacking T-cell epitopes. Enhancement has been attributed to receptor cross-linking between complement receptor CR2 (CD21) and polysaccharide antigen to surface IgM on naïve B cells. Paradoxically, C3d has still been shown to increase immune responses in CD21 knockout mice, suggesting that an auxiliary activation pathway exists. In prior studies, we demonstrated the CD21-independent C3d adjuvant effect might be due to T-cell recognition of C3d T-helper epitopes processed and presented by major histocompatibility complex class II on the B-cell surface. C3d peptide sequences containing concentrated clusters of putative human C3 T-cell epitopes were identified using the epitope-mapping algorithm, EpiMatrix. These peptide sequences were synthesized and shown in vitro to bind multiple human leukocyte antigen (HLA)-DR alleles with high affinity, and induce interferon-γ responses in healthy donor peripheral blood mononuclear cells. In the present studies, we establish further correlations between HLA binding and HLA-specific lymphocyte reactions with select epitope clusters. In addition, we show that the T-cell phenotype of C3d-specific reactive T cells is CD4(+)CD45RO(+) memory T cells. Finally, mutation of a single T-cell epitope residing within the P28 peptide segment of C3d resulted in significantly diminished adjuvant activity in BALB/c mice. Collectively, these studies support the hypothesis that the paradoxical enhancement of immune responses by C3d in the absence of CD21 is due to internalization and processing of C3d into peptides that activate autoreactive CD4(+) T-helper cells in the context of HLA class II.
1] EpiVax Inc., Providence, RI, USA [2] Institute for Immunology and Informatics, Department of Cell and Molecular Biology, University of Rhode Island, Providence, RI, USA.
Anne S
0000000159111459
AS
De Groot
Vaccine and Gene Therapy Institute of Florida, Port Saint Lucie, FL, USA.
Ted M
TM
Ross
EpiVax Inc., Providence, RI, USA.
Lauren
L
Levitz
EpiVax Inc., Providence, RI, USA.
Timothy J
TJ
Messitt
EpiVax Inc., Providence, RI, USA.
Ryan
R
Tassone
EpiVax Inc., Providence, RI, USA.
Christine M
CM
Boyle
EpiVax Inc., Providence, RI, USA.
Amber J
AJ
Vincelli
1] EpiVax Inc., Providence, RI, USA [2] Institute for Immunology and Informatics, Department of Cell and Molecular Biology, University of Rhode Island, Providence, RI, USA.
Leonard
L
Moise
EpiVax Inc., Providence, RI, USA.
William
W
Martin
EpiVax Inc., Providence, RI, USA.
Paul M
PM
Knopf
D000276:Adjuvants, Immunologic / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D015933:Complement C3d / Q000276:immunology*; D003198:Computer Simulation; D018984:Epitopes, T-Lymphocyte / Q000737:chemistry / Q000276:immunology; D005260:Female; D018390:Gene Targeting; D006649:Histocompatibility Antigens / Q000276:immunology; D006801:Humans; D007156:Immunologic Memory / Q000276:immunology; D007371:Interferon-gamma / Q000378:metabolism; D008213:Lymphocyte Activation / Q000276:immunology; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009154:Mutation; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding; D013601:T-Lymphocytes / Q000276:immunology*; D014019:Tissue Donors
D000276:Adjuvants, Immunologic; D018984:Epitopes, T-Lymphocyte; D006649:Histocompatibility Antigens; D010455:Peptides; D015933:Complement C3d; D007371:Interferon-gamma