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

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Abstract
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 KD = 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.