Two major idiotypes in mouse anti-(4-hydroxy-3-nitro-phenyl)acetyl (NP) antibodies are controlled by "allelic" genes.

Anti-NP [(4-hydroxy-3-nitro-phenyl)acetyl)] antibodies from the primary response of BALB/c mice contain a major idiotype NP-a that is controlled by an allotype-linked gene VHNPa. A new strain distribution pattern for a VH marker was discovered: strains BALB/c, RF, DBA, RIII and SM were positive, and strains C57BL/6, SJL, CBA, A/J, CE, AKR and NZB were negative for the idiotype NP-a. NP-a idiotype chared many characteristics with previously described idiotype NP-b and, therefore, allelism was suggested between them. Both idiotypes have lambda light chains, both seem to be conservative in evolution, both are predominant early in the antibody response. Later during the response, antibodies become increasingly idiotype-negative while at the same time, homogeneous isoelectric focusing patterns become very heterogeneous. The study of VH recombinant strains supported the concept of allelism because in every case studied, the idiotype were mutually exclusive. (C57BL/6 X BALB/c)F1 mice expressed idiotypes NP-a and NP-b regularly and in approximately equal amounts.