FLEXIBILITY OF HUMAN-IGG SUBCLASSES

A variable region (Id)-matched set of genetically engineered human IgG 1,-2, -3, and -4 subclass molecules was analyzed by electron microscop y for hinge-mediated differences in flexibility, The hinge-mediated be nding was studied, as was the ability of the subclasses to form immune complexes with two anti-Id mAbs, The data show that the Yank order (m ost to least flexible) of the Ige subclasses for hinge-folding mode of flexibility between Fab arn is is IgG3 > IgG1 > IgG4 > IgG2. The mean Fab-Fab angles for the subclasses are IgG3, 136 degrees; IgG4, 128 de grees; IgG2, 127 degrees; and IgG1, 117 degrees. Fab-Fc angles were si milarly analyzed. By sampling of equimolar mixtures of Id-bearing IgGs and each of two anti-ld mAb after incubation over time (1.5 min to 3. 5 h), different kinetic profiles of immune complex formation of define d geometry were documented, Both anti-Id mAbs displayed unique kinetic profiles when complexed with the four IgG subclass molecules but also shaved important features, Most notable was the higher propensity to form closed bivalent ring Id-anti-Id dimers with IgG3 than with IgG2 a nd IgG4, IgG1 was intermediate in its ability to form such dimers.