Synergistic Deposition of C4d by Complement‐Activating and Non‐activating Antibodies in Cardiac Transplants

https://doi.org/10.1111/j.1600-6143.2007.01971.xGet rights and content
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The role of non‐complement‐activating alloantibodies in humoral graft rejection is unclear. We hypothesized that the non‐complement‐activating alloantibodies synergistically activate complement in combination with complement‐activating antibodies. B10.A hearts were transplanted into immunoglobulin knock out (Ig‐KO) mice reconstituted with monoclonal antibodies to MHC class I antigens. In allografts of unreconstituted Ig‐KO recipients, no C4d was detected. Similarly, reconstitution with IgG1 or low dose IgG2b alloantibodies did not induce C4d deposition. However, mice administered with a low dose of IgG2b combined with IgG1 had heavy linear deposits of C4d on vascular endothelium. C4d deposits correlated with decreased graft survival. To replicate this synergy in vitro, mononuclear cells from B10.A mice were incubated with antibodies to MHC class I antigens followed by incubation in normal mouse serum. Flow cytometry revealed that both IgG2a and IgG2b synergized with IgG1 to deposit C4d. This synergy was significantly decreased in mouse serum deficient in mannose binding lectin (MBL) and in serum deficient in C1q. Reconstitution of MBL‐A/C knock out (MBL‐KO) serum with C1q‐knock out (C1q‐KO) serum reestablished the synergistic activity. This suggests a novel role for non‐complement‐activating alloantibodies and MBL in humoral rejection.

Key words:

Alloantibodies
allograft
antibody‐mediated rejection
C4d
MBL

Abbreviations

Ig‐KO
immunoglobulin knock out
MHC
major histocompatibility complex
MBL
mannose binding lectin
C1q‐KO
C1q knock out
MBL‐KO
MBL‐A/C knock out
C1q/MBL‐KO
C1q/MBL‐A/C triple knock out
MASP‐1
MBL‐associated serine protease

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