IgM allotypes in rabbit: I.a Locus associated allotypic determinants

Appearance of neoantigen in mouse IgG1 upon reduction of interchain disulfide bridges: assessment of local and general conformational rearrangements using monoclonal antibody and small-angle X-ray scattering

Mouse hybridoma antibody E5D2 reacting with murine mono- and polyclonal IgG1 has been produced. MonAb E5D2 recognizes the antigenic determinant (epitope) buried in intact IgG1 and expressed upon mild reduction of interchain S-S bridges. Neither H nor L chains alone maintain epitope E5D2. Reassociation of gamma 1 chains (H chains of IgG1) with L chains results in complete restoration of this antigenic determinant. The data strongly suggest that epitope E5D2 depends on the quaternary structure of IgG1. The epitope is also expressed by reduced F(ab)2 fragment of IgG1 but is not connected with its antigen binding site. The likely localization of the epitope E5D2 is the interface between CH and CL domains. The second produced monAb F6C2 reacts with CH1-CL region of reduced mouse IgG2. Small-angle X-ray scattering experiments have demonstrated pronounced decrease of the radius of gyration of reduced IgG1 as compared to the intact one. This indicates general conformational changes of IgG1 molecule following mild reduction of Fab region S-S groups. Epitope E5D2 is the first quaternary antigenic subclass specific determinant described for C the region of mouse IgG. Thus, serologic expression of epitope E5D2 reveals precise conformational perturbations of small area near reduced S-S bridges while small-angle scattering demonstrates accompanying general transformation of IgG structure.

Allotypic and isotypic specificities of rabbit IgM: localization to the Fab mu or Fc mu fragments

IgM from trypanosome-infected rabbits was digested with trypsin under different conditions to obtain Fab mu or Fc5 mu fragments suitable for analysis with anti-allotype and anti-isotype antibodies. The Fab mu but not the Fc5 mu fragment was shown to have the n-locus allotypic specificities, n80, n81, n82, n83 and n87, characteristic of the IgM class of immunoglobulins. Thus, the n82 and n83 allotypic specificities, conformationally dependent on the a VH locus for expression, and the n80, n81 and n87 allotypic specificities, independent of the a VH locus for expression, are in either the CH1 or CH2 domain of IgM heavy chains. In addition, two high-affinity mouse monoclonal antibodies (MoAbs) specific for IgM and able to bind IgM in direct-binding radioimmunoassays were produced and characterized. One MoAb (3C1) was specific for an isotypic determinant (epitope) in the Fab mu fragment, presumably in the CH1 or CH2 domain, whereas another MoAb (8C2) was specific for an isotypic epitope in the Fc5 mu fragment, presumably in the CH3 or CH4 domain. The proximity of the n-locus allotypic specificities (CH1 or CH2 domain) to the VH domain is consistent with the finding that some IgM allotypic specificities are expressed only in conjunction with certain a VH locus allotypic specificities.

The quaternary Gs3 and Gs7 allotypes of the rabbit: generation of the determinants by interspecies molecular hybridization

A number of allotypic markers of the rabbit immunoglobulins are present only on intact immunoglobulin molecules and not on the isolated heavy or light chains. Some of these markers, although determined by the kappa light chain, are limited to a single heavy chain class of Ig. They can be generated by in vitro hybridization of the kappa light chain with the appropriate heavy chain. The quaternary IgG allotypic determinants Gs3 and Gs7 which are determined respectively by the b4.1 and b4.2 allelic variants of the kappa b4 light chain can be generated not only by in vitro hybridization of these light chains with a rabbit gamma chain, but also to a certain extent by their hybridization to gamma chains derived from other species.

Production of IgG-specific auto-anti-allotypes in b4.2-suppressed rabbits

Rabbits were completely suppressed for kappa chain allotype b4.2, and autoantibodies against b4.1 or b4.2 could be raised in 2 out of 3 animals. The animal immunized with b4.1 produced anti-b4 and anti-Ms3, two activities which have never as yet been found together in one antiserum. Both autoantisera lacked the capacity to bind b4.2-IgM, whereas they precipitated 4.2-IgG very well. In one animal, anti-b4 IgM activity appeared after the sixth immunization, at the age of 14 months. Allotype suppression was maintained in both rabbits till the end of their lives whereas all control animals recovered within 6 months. The autoantisera which were specific for b4 IgG could not induce suppression in vivo. However, specific inhibition of b4 IgG secretion was observed in vitro.

Rabbit heavy chain haplotypes--allotypic determinants expressed by VH-CH recombinants

This report summarizes our current understanding of the heavy chain haplotypes found in our laboratories' rabbits. Independently derived data from several laboratories have been synthesizes into a consistent picture of the linked inheritance of allotypic markers found on the different heavy chain classes and subclasses of rabbit immunoglobulins in pedigreed rabbits, including the families of three apparent VH-CH recombinants. In one recombinant, the entire group of CH markers (C mu, C gamma, and C alpha) recombined with the set of VH. Although in the other two recombinants all CH markers may also have recombined as a group, in one of these only IgG and IgA CH genes were informative; in the other recombinant, only the IgG allotypes were informative. Some allotypic determinants found on IgM molecules ("conformational") appear only when a specific variable region allotype (VHa) is combined with a specific mu constant region allotype (C mu). New combinations of VHa and C mu allotypes were generated in two of the genetic recombinants and led to new "conformational" determinants. The gains and losses observed lend support to the hypothesis that the determinants result from conformations generated by the combination of allotype-specific VH and C mu protein sequences. Conceivably, DNA events that join VH to diversity (D)- and joining (J)-coding sequences or mRNA processing events that splice J to C mu could be involved in generating the sequences that form allotype-specific determinants.

An increase in the number of recombinant molecules and other effects of the simultaneous allotype suppression of trans-chromosomal a VH and n Cmu Ig gene products

The concomitant effects of trans-chromosomal allotype suppression of both an a VH and an n Cmu locus allotype in multiheterozygous rabbits were investigated. For example of the expression of the a2 VH and n81 Cmu allotypes were suppressed in a multiheterozygous rabbit having the a1 chi-y-n81de12,15f73g74/a2 chi 32y33n80de12.14f69g77 genotype. This trans-chromosomal allotype suppression led to the concomitant suppression of other CH allotypes in the same parental haplotype as the suppressed-n81 allotype (i.e. the e15, f73 and g74 allotype) and the partial suppression of the a1 VH allotype (from the normal level of 70% of the total Ig to 10%), and also led to compensation by other VH allotypes from the same parental haplotype as the suppressed-a2 allotype (i.e. the x32 and y33 allotypes). The x32 and y33 allotypes were expressed on Ig molecules with the CH allotypes coded by the same haplotype (i.e. the cis molecules). In a further analysis of the IgG molecules having the partially-suppressed-a1 allotype, one-half (5%) of these molecules were trans-chromosomal recombinant molecules (i.e. a1e14 IgG) and the other half (5%) were cis-chromosomal molecules (i.e. a1e15 IgG). The trans-chromosomal a1e14 IgG molecules probably were derived from the expansion of a limited number of lymphoid clones that normally produce only 1.5% trans-chromosomal recombinant molecules. The cis-chromosomal a1e15 IgG molecules were probably derived either from lymphoid clones that survived the suppression by the anti-n81 Ab, or from lymphoid clones that bore a different subclass of IgM (i.e. n-negative IgM).

Suppression of VH, C gamma and C mu gene products in rabbits by maternal immunization against IgM allotype and detection of somatic recombinant molecules in these animals

Suppression of the mu-chain allotype Ms16 was obtained in young heterozygous Ms16/Ms17 rabbits by immunizing the Ms17 mother against the paternal Ms16 allotype. Examination of the concentration of the VH and CH allotypes of paternal origin (a2,Ms16 and e14) in the offspring, revealed not only Ms16 suppression but also VH and C gamma allotypic suppression. The degree of suppression for the C gamma markers (4-25-fold decrease) was much less than that for the C mu or VH markers (50-150-fold decrease). The excess C gamma marker (e14) was found to be present for the major part on molecules possessing the VH allotype derived from the homologous allelic chromosome. The pattern of persistence of molecules with the suppressed C gamma marker in the serum is consistent with the idea that these molecules arise by somatic recombination and that the gene order is VH, C mu and C gamma.