The paratypic and idiotypic diversity of the BALB/c antibody response to the hemagglutinin (HA) of the influenza A/PR/8/34 virus (PR8) was investigated using a panel of 125 anti-HA hybridoma antibodies derived from 14 BALB/c mice. The paratypic diversity, as assessed by a fine specificity analysis using 51 related influenza viruses, was extensive: 104 distinct paratopes were observed. In three instances, antibodies with indistinguishable paratopes were isolated from two individual mice. A minimum estimate of the size of the adult BALB/c anti-HA paratypic repertoire, calculated from these data, is 1,500.

The generation of this diverse repertoire was studied by screening the anti-HA hybridoma panel for the presence of idiotypes (Id) that are markers for variable (V) region sequences derived from related germ line V genes. Three cross-reactive Id (IdX) that are markers for the V(k)21C, V(k)21B, and V(k)21A, D, E, or F L chain subgroups were found, respectively on 16, 1, and 10 anti-HA hybridoma antibodies derived from seven individual BALB/c mice. Thus, the V(k)21 IdX(+) hybridomas constitute 22 percent of the anti-HA hybridoma panel. The V(k)21 IdX are also present on 8.6 percent of K-bearing immunoglobulin in normal BALB/c serum. This suggests that the V(k)21 group is used preferentially in the BALB/c anti-HA immune response.

The generation of the anti-HA repertoire was further studied using large panels of anti-HA hybridomas derived from two individual adult BALB/c mice. Anti-idiotypic antisera were raised in rabbits against individual hybridomas from each mouse. One anti-Id serum defined a family of four idiotypically and paratypically related, but not identical, antibodies from mouse 36, which represented 31 percent of the hybridoma antibodies isolated from this mouse. None of the 112 anti-HA hybridoma antibodies derived from 13 other individual mice showed idiotypic cross-reactivity. Furthermore, this Id could not be detected in anti-PR8 antisera from 75 individual BALB/c mice. Another anti-Id serum defined a family of 27 idiotypically related antibodies from mouse 37, which represented 50 percent of the hybridoma antibodies isolated from this mouse. Only 1 of the 71 hybridoma antibodies isolated from 13 other individuals was idiotypically cross-reactive.

These results demonstrate that individual adult BALB/c mice express paratypically and idiotypically distinct antibody repertoires to the HA of influenza virus PR8. Based on these observations, we suggest that somatic mutation plays an important role in the generation of the adult anti-HA repertoire. Mechanisms that could account for differences in repertoire expression among individual mice are discussed.