Affinity maturation in the arsonate system: lack of dominance of high-affinity antibody subpopulations

Affinity maturation was studied by the analysis of the kinetics of the appearance of antibody subpopulations with different affinities during the immune response, using an hapten-inhibition ELISA. The immune response in KLH-Ar-immunized A/J mice was used as a model system. Five antibody subpopulations of different affinity (10(3)-10(7) M-1) could be detected, the relative concentrations of which changed during affinity maturation. The high-affinity antibody subpopulations did not represent the major fraction at any stage during affinity maturation. The appearance of the highest affinity subpopulation (10(7) M-1), despite exhibiting relative concentrations no higher than 12%, produced an important increase in average affinity. On the other hand, its disappearance at the end of the maturation process could explain the average affinity decrease observed at this stage. Our results indicate that affinity maturation cannot be explained by the dominance of high-affinity clones, as proposed by Siskind & Benacerraf (1969). The increase in affinity could rather be due to the progressive appearance of low percentages of high-affinity clones, which are not present in the primary response and never become dominant.