Which antibody class is most often implicated in hyperacute graft rejection due to preformed donor antibodies?

Which antibody class is most often implicated in hyperacute graft rejection due to preformed donor antibodies?

• A. IgM
• B. IgA
• C. IgG
• D. IgE

Answer: (C)

Hyperacute graft rejection happens when the recipient already has antibodies against donor antigens, so these antibodies bind the graft endothelium and trigger the classical complement pathway, causing rapid clotting and loss of the transplanted organ. IgG antibodies are most often implicated because they are the predominant circulating antibody type against donor HLA or ABO antigens and are highly efficient at fixing complement and promoting inflammatory injury once bound to the graft. This leads to quick, fulminant damage of the graft vessels. IgM can also activate complement and contribute, particularly with ABO mismatches, but the clinical and mechanistic emphasis in hyperacute rejection is on IgG. IgA and IgE are not typically involved in this rapid vascular injury to transplanted tissue.

Hyperacute graft rejection happens when the recipient already has antibodies against donor antigens, so these antibodies bind the graft endothelium and trigger the classical complement pathway, causing rapid clotting and loss of the transplanted organ.

IgG antibodies are most often implicated because they are the predominant circulating antibody type against donor HLA or ABO antigens and are highly efficient at fixing complement and promoting inflammatory injury once bound to the graft. This leads to quick, fulminant damage of the graft vessels.

IgM can also activate complement and contribute, particularly with ABO mismatches, but the clinical and mechanistic emphasis in hyperacute rejection is on IgG. IgA and IgE are not typically involved in this rapid vascular injury to transplanted tissue.