Structural and evolutionary comparisons of four alleles of the mouse immunoglobulin kappa chain gene, Igk-VSer

Two kappa immunoglobulin light chains are secreted by an anti-DNA hybridoma: implications for isotypic exclusion

An anti-DNA hybridoma derived from an MRL/lpr mouse secretes two different kappa light chains in combination with a single heavy chain. Multiple single cell clones express and secrete immunoglobulin containing both kappa light chains. The N-terminal protein sequences of the light chains correspond to sequences predicted from functionally rearranged mRNAs subjected to reverse transcription and amplified by polymerase chain reaction (PCR). Karyotype analysis of the hybridoma indicates a clonal line derived from the fusion of two cells. By amino acid sequence comparison and PCR analysis, both functional kappa light chains are derived from the MRL/lpr spleen. The two functional light chain cDNAs were cloned and co-transfected into COS-7 cells with the heavy chain cDNA. Only one of the light chains in combination with mAb 3E10 heavy chain confers anti-DNA reactivity. The presence of two separate kappa light chains and, therefore, two separate antigen receptors on a single B cell may have ramifications for both polyclonal activation and toleration of lupus B cells.

Polymorphism in V kappa 10 genes encoding L chains of antibodies bearing the Ars-A and A48 cross-reactive idiotypes

p-azophenylarsonate-specific antibodies of A/J mice which bear the Ars-A crossreactive idiotype utilize the V kappa-Ars-A gene segment, a member of the V kappa 10 family. Southern hybridization of genomic DNA from several inbred strains using a probe from the 5' flanking region of the V kappa-Ars-A gene demonstrated three patterns of restriction fragment length polymorphisms (RFLP). Six genes corresponding to hybridizing bands were obtained from DNA libraries of C.AKR, PERU and A/J mice, and nucleotide sequence comparisons revealed two allelic groups: AKR1 (Igk-V10.1a), AJ1 (Igk-V10.1b) and PERU1 (Igk-V10.1c); AKR2 (Igk-V10.2a), AJ2 (Igk-V10.2b), and PERU2 (Igk-V10.2c). The Igk-V10.1b gene of the A/J strain is the V kappa-Ars-A gene used in Ars-A idiotype-positive antibodies. The product of the C.AKR allele (Igk-V10.1a) contained four amino acid substitutions in CDR3 as compared with Igk-V10.1b. These substitutions probably explain the failure of AKR mice and other strains with the same V kappa 10 RFLP pattern to provide in genetic crosses a L chain which, together with the A/J VH-ArsA gene product, form Ars-A idiotype-positive antibodies. Also, the nucleotide sequence identity between the Igk-V10.1c and Igk-V10.1b alleles and the Igk-V10.2c and Igk-V10.2b alleles is significantly greater than that seen in comparisons with the Igk-V10.1a and Igk-V10.2a alleles, respectively, suggesting an evolutionary pathway similar to that of the linked Igk-J locus. BALB/c antibodies bearing the A48 regulatory idiotype contain L chains encoded by the BALB/c Igk-V10.1b and Igk-V10.2b alleles. Strongly A48 idiotype-positive antibodies utilize the Igk-V10.1b chain, and weakly A48-positive antibodies use the Igk-V10.2b L chain. The possible effects of amino acid substitutions specified by the Igk-V10.1a, Igk-V10.1c, Igk-V10.2a, and Igk-V10.2c alleles on their ability to provide L chains used in A48 idiotype-positive antibodies are discussed.

Structural and evolutionary comparisons of four alleles of the mouse Igk-J locus which encodes immunoglobulin kappa light chain joining (J kappa) segments

The Igk-J locus of the mouse encodes the immunoglobulin kappa light chain joining (J) segments. Four Igk-J alleles have been described on the basis of restriction enzyme length polymorphisms. The nucleotide sequences of the Igk-Ja allele (type strain, C.C58), Igk-Jc allele (type strain, SJL/J), and Igk-Jd allele (type strain, SK/CamRk) have been determined and are compared with the previously reported Igk-Jb allele sequence (type strain, BALB/c). The mouse sequences are also compared with published sequences for rat and human J kappa sequences. Far more differences were found between the Igk-Ja allele and the other mouse alleles than between any two of the latter. These result in two amino acid substitutions which distinguish the J2 and J3' segments of the Igk-Ja allele from the other three alleles. Use of the Phylogenetic Analysis Using Parsimony program to generate a phylogenetic tree strongly indicates that after divergence from the rat ancestor, there appears to have been an early split between the Igk-Ja allele and the evolutionary precursor of the other mouse alleles. There also appears to have been far less divergence from the ancestral condition in the Igk-Ja allele than in the other alleles. Also, the presence of only one convergent mutation among the four mouse alleles provides strong evidence against any crossing over within the Igk-J locus during the history of these alleles. Finally, the differences in rates of evolution of the Igk-J alleles are in marked contrast to the relatively uniform rates of divergence of four alleles of a mouse V kappa gene, Igk-VSer.

Mouse Vk gene classification by nucleic acid sequence similarity

Analyses of immunoglobulin (Ig) variable (V) region gene usage in the immune response, estimates of V gene germline complexity, and other nucleic acid hybridization-based studies depend on the extent to which such genes are related (i.e., sequence similarity) and their organization in gene families. While mouse Igh heavy chain V region (VH) gene families are relatively well-established, a corresponding systematic classification of Igk light chain V region (Vk) genes has not been reported. The present analysis, in the course of which we reviewed the known extent of the Vk germline gene repertoire and Vk gene usage in a variety of responses to foreign and self antigens, provides a classification of mouse Vk genes in gene families composed of members with greater than 80% overall nucleic acid sequence similarity. This classification differed in several aspects from that of VH genes: only some Vk gene families were as clearly separated (by greater than 25% sequence dissimilarity) as typical VH gene families; most Vk gene families were closely related and, in several instances, members from different families were very similar (greater than 80%) over large sequence portions; frequently, classification by nucleic acid sequence similarity diverged from existing classifications based on amino-terminal protein sequence similarity. Our data have implications for Vk gene analyses by nucleic acid hybridization and describe potentially important differences in sequence organization between VH and Vk genes.