Reduction of alloantibody response to class I major histocompatibility complex by targeting synthetic allopeptides for presentation by B cells.
BACKGROUND
PVG.RT1(u) rats develop a strong CD4 T cell-dependent alloantibody response to class I major histocompatibility complex (MHC) A(a) antigen, during which CD4 T helper cells recognize and respond to A(a)-derived peptides presented by recipient class II MHC (indirect allorecognition). On the basis of evidence that CD4 T cells that encounter antigen presented by resting B cells become tolerant, we have targeted synthetic A(a)-derived allopeptides for in vivo presentation to class I MHC-disparate CD4 T cells by resting recipient B cells.


METHODS
PVG.RT1(u) rats were treated with two peptides, P1 and P2, corresponding to the alpha-helical regions of A(a) (residues 57-80 and 143-163), which were conjugated via an N-terminal cysteine residue to monovalent Fab fragments of OX60 monoclonal antibody, which labels membrane IgD-positive B cells.


RESULTS
RT1(u) rats primed with free (nonconjugated) P1 or P2 emulsified in complete Freund's adjuvant produced strong peptide-specific antibody responses and a heightened anti-A(a) antibody response to an A(a)-disparate PVG.R8 heart graft, confirming that each peptide encompasses one or more major T cell determinant for B cell help. Pretreatment of PVG.RT1(u) rats with a mixture of OX60-Fab-P1/P2 conjugates markedly reduced their ability to mount an A(a) antibody response when challenged with either A(a)-disparate blood transfusion or an A(a)-disparate heart graft, although PVG.R8 heart graft survival was not prolonged.


CONCLUSIONS
In this report, we show that synthetic A(a)-derived allopeptides are able, when targeted for in vivo presentation to CD4 T cells by resting B cells, to impair the ability of RT1(u) rats to mount an antibody response to A(a) antigen. All subclasses of IgG anti-A(a) alloantibody were profoundly reduced, suggesting that the responsible mechanism is more likely to be CD4 T helper cell unresponsiveness rather than Th1/Th2 T cell polarization.
MacDonald
C M
CM
Division of Immunological Science, University of Glasgow, Scotland.
Bolton
E M
EM
Jaques
B C
BC
Walker
K G
KG
Bradley
J A
JA
D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D016027:Heart Transplantation / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D007108:Immune Tolerance; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007518:Isoantibodies / Q000276:immunology*; D008297:Male; D010446:Peptide Fragments / Q000276:immunology*; D051381:Rats; D011994:Recombinant Proteins / Q000276:immunology; D014181:Transplantation Immunology / Q000276:immunology*
D015395:Histocompatibility Antigens Class I; D007140:Immunoglobulin Fab Fragments; D007518:Isoantibodies; D010446:Peptide Fragments; D011994:Recombinant Proteins