Clonal dominance of low-affinity antibodies in rabbit hyperimmune anti-streptococcal group A-variant polysaccharide antisera.

Intraveneous hyperimmunization of selectively bred rabbits with streptococcal group A-variant vaccines elicits antibody responses of restricted heterogeneity at high antibody levels. In these antisera, IgG with dissociation constants Kd = 10(-6) M constitutes 90% and IgG with Kp = 10(-9) M accounts for only 10% of the group A-variant polysaccharide-specific antibodies. The low affinity antibody fraction represents the dominant clonotypes. Preparative isoelectric focusing in granulated (Ultrodex G-75) gels was used to successfully purify single-band material belonging to dominant spectrotypes. Affinity studies with these antibody fractions with the highest reported degree of purity yielded Kd = 10(-6) M values, thus confirming that clonal dominance is exclusively associated with low-affinity antibodies. Since it is known from previous work (M. Cramer and D. G. Braun, Scand. J. Immunol. 1975. 4:63) and from the rabbit antisera used here that clonal dominance of this sort is long-lived, this work fails to support the argument of immune maturation. The data more logically relate to antibodies that emerge with different subspecificities -- recognized in the antigen as a function of time in immunization procedures -- rather than to an inherent property of the immune system.