IgG SUBCLASS ANTIBODIES IN TRANSPLANT RECIPIENT SERA: AN IgG SUBCLASS SPECIFIC ASSAY TO DETERMINE THE 'GOOD AND BAD' IgG IMMUNOGLOBULINS

摘要

There are four human IgG subclasses dictated by a cluster of genes on chromosome 14. The serum concentration varies but generally IgG1>IgG2>IgG3=IgG4. Complement fixation (CF) is ordered with IgG3>IgG1>IgG2>IgG4. IgG2 has a poor CF and IgG4 has none. The maturation of the subclasses occurs with T helper cell dependence and IgG2 is seems to require more help and evolves as stimulation persists. In the milieu of humoral transplant immunity, pre-transplant and post-transplant HLA antibodies have been shown to have profound effects on rejection and graft outcome. Humoral immunity functions through CF and phagocytosis of target tissue and cells. Therefore subclasses of IgG that are poor at CF could be thought of as blocking antibodies. A few examples of this are: IgG4 does not have CF ability. IgG4 increases 10-100 folds after 1-2 years of allergy desensitization in successfully desensitized patients. IgG3 is a potent CF and is found as the primary antibody in erythroblastosis fetalis. Regarding phagocytosis (ADCC, opsinization), IgG4 has no FcR binding and IgG2 antibodies are efficiently recognized by the Fc-gammaRIIa (Fc-gammaRIIa-H131 allele). In contrast, G1 and G3 bind to all the Fc-gamma receptor family.