Use of JH4 joining segment gene by an anti-arsonate antibody that bears the major A-strain cross-reactive idiotype but displays diminished antigen binding.

One of the antibody families utilized by the A/J mouse in its response to p-azophenylarsonate (Ars) is characterized by the expression of the major anti-arsonate cross-reactive idiotype (CRI) of the A strain. This family has been termed the Ars-A family. A hybridoma antibody (HP 101F11 ) obtained after immunization of an A/J mouse with Ars was identified initially as displaying the CRI, but was subsequently found to bind antigen at a level much lower than most members of the Ars-A family. The results of binding studies suggested that HP 101F11 possesses reduced avidity for antigen. When isolated light and heavy chains were allowed to recombine with the heavy and light chains of a strongly antigen-binding, strongly CRI-positive antibody of the Ars-A family (HP 93G7 ), the low level of antigen binding by HP 101F11 was found to be due to a structurally variant heavy chain. Whereas antibodies of the Ars-A family with normal avidity for antigen had been shown to use the JH2 joining segment gene, amino acid sequence analysis of HP 101F11 revealed that this antibody has a JH segment with a sequence identical to that encoded by a portion of a different JH gene, JH4 . The implication that 101F11 uses the JH4 gene instead of JH2 was supported by the observation that the productively rearranged gene is associated with an Eco R1 restriction fragment 0.95 Kb smaller than the corresponding fragments of Ars-A hybridomas with normal avidity for antigen. The size difference of 0.95 Kb corresponds exactly to the known distance between the JH2 and JH4 genes in BALB/c germline DNA. In addition to the structural differences immediately attributable to the use of JH4 , HP 101F11 has shown an amino acid interchange in the DH segment, and a single amino acid deletion at the DH-JH boundary. These results show that variation among members of the Ars-A family in the DH and/or JH segments provides alternative structural forms of Ars-A antibodies upon which selective processes can operate during the course of an immune response.