Reduction of alloantibody response to class I major histocompatibility complex by targeting synthetic allopeptides for presentation by B cells
MacDonald, C.M.; Bolton, E.M.; Jaques, B.C.; Walker, K.G.; Bradley, J.A.
Transplantation 63(7): 926-932
1997
ISSN/ISBN: 0041-1337 PMID: 9112341 Document Number: 482789
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 et-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-adisparate 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-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.