The D segment defines the T15 idiotype: the immunoresponse of A/J mice to Pneumococcus pneumoniae

Generalization of single immunological experiences by idiotypically mediated clonal connections

Clonal interactions of B cells by idiotope-specific mutual recognition of their antigen receptors with the participation of T cells were assumed to form a web of unknown density, referred to as the idiotypic network. Although these clonal connections were proposed to fulfill important internal regulatory functions, their biological significance, especially in relation to antigen-induced immune responses, remained a mystery. In view of this, we postulate that the basic function of the idiotypic internal connection between B and T cell antigen receptors is to transform antigen-induced cellular activations, by idiotypic crossreactivity, into the regulation of cell clones with different antigen specificities. This process leads not only to the suppression of major clones but also to the activation of minor ones. The latter activating property may allow the generalization of single antigenic experiences, so that the immune system in its entirety benefits in its battle against environmental microbes. Such idiotypic clonal interactions are particularly effective in early ontogeny. During a short neonatal imprinting period, maternal immunological knowledge in the form of somatically mutated, high-affinity IgG antibodies, acquired through a continuous encounter with external antigens, guides the initial ontogenetic development of the immune system and so exerts long-lasting transgenerational advantageous effects in the offspring.

Primary structure of the variable regions encoding antibody to NG2, a tumour-specific antigen on the rat chondrosarcoma HSN. Correlation of idiotypic specificities with amino acid sequences

Eight syngeneic rat monoclonal antibodies that recognize structurally overlapping epitopes on the chondroitin proteoglycan NG2, a tumour-specific antigen on the chemically induced rat chondrosarcoma HSN, have been analysed for the sequence of their immunoglobulin heavy (H) and light (L) chain variable (V) regions. This analysis defined five groups of antibodies which are very similar for both the H and L chains and revealed that a wide range of different V regions are capable of binding to the same antigenic determinant. However, three mAbs, 11/160, ALN/12/17 and ALN/9/94, which recognize a sequential epitope, were found to use almost identical heavy (V-D-J) and light (V-J) chains in regions demonstrating an exclusivity in specific protein-protein interaction for this particular epitope. Two other mAbs, ALN/11/53 and AL/3/12, used similar V and J segments but totally different D regions. With the exception of the pair ALN/11/53 and AL/3/12, this grouping of antibodies matches that derived from the idiotypic specificity study we have reported previously. The reactivity pattern of Ab1 11/160, ALN/12/17 and ALN/9/94 with six anti-idiotopic mAbs raised against 11/160 demonstrated that the idiotope recognized by Ab2 HIM/3/41 was defined by a single amino acid, Asn, at position 52 within the CDR2 loop of the VH region; whereas the D region of Ab1 ALN/11/53 was implicated as the structural correlate of idiotypy. The substitution of AsnH52 influenced the Id recognition but Ag binding was not affected suggesting that Ab2 HIM/3/41 did not mimic the NG2 Ag.

Antigenicity and immunogenicity of antigenized antibodies. Studies on B and T cells

This laboratory has been testing the possibility of using the complementarity-determining region (CDR) loops of the antibody molecule to express oligopeptide epitopes in an immunologically-accessible and conformationally-suitable way. The new process consists in grafting peptides epitopes derived from antigens other than immunoglobulins into antibody CDR loops. This process, "antibody antigenization," utilizes the immunoglobulin fold as a scaffold to immobilize and present oligopeptide epitopes to the immune system as the integral part of the immunoglobulin molecule. Here we describe some of the initial results with antigenized antibodies (AgAbs).

Fine specificity and VJ usage of light chains in antibodies to the phosphorylcholine hapten

In the memory response to the phosphorylcholine hapten (PC) two major groups of anti-PC antibodies with different fine specificities are elicited. Group I antibodies are mainly PC specific, whereas Group II antibodies are comprised of two specificities directed against the phenyl-PC and the phenyl moiety of the PC hapten. The VL gene usage of 17 monoclonal memory anti-PC antibodies were investigated by Southern blot analysis and nucleotide sequencing. Six out of eight Group I memory PC-specific antibodies used the same VK22-JK5 rearrangement as the major T15 primary response idiotype. One expressed a mutated JK1 and one employed another VK22 gene family member. A shift in specificity from PC (Group I) towards phenyl-PC (Group II) was accompanied with the usage of either VK1C-JK1 or VK1A-JK5 rearrangements. The phenyl-specific Group II antibodies expressed the V lambda 1-J lambda 1 L chain rearrangement in combination with VH M141 expressing H chains. In this specific segment of Group II antibodies most mutations were found. Thus four different VL genes were found to contribute to the fine specificity of memory response antibodies to the PC hapten in a clear structure-function relationship. The diversified fine specificity in the memory response derives mainly from the usage of different L chains with particular VJ rearrangements in combination with VH of the dominant initial response clonotype and is not primarily due to mutational events.

The same few V genes account for a majority of oxazolone antibodies in most mouse strains

The early primary anti-phenyloxazolone antibodies of 12 mouse strains were studied by determining proportions of two defined subsets id495 (the classical phOx idiotype) and id350. Id495-positive antibodies bear an H chain encoded by VHOx1 gene (family Q52) and an L chain usually coded for by VKOx1 but occasionally by other VK genes. Id350-positive antibodies are encoded by a VK gene VK45.1, and usually by a VH gene of the S107 family. All 12 strains (representing nine H-chain and four kappa-chain haplotypes) produced id350-positive anti-phOx antibodies. While id495 is the predominant major subset in the BALB/c response (originally studied), id350 seems to be the predominant subset of early anti-phOx antibodies in the mouse species. The combined proportion of the two subsets varied from ca. 50 to almost 100% of the total in all strains except C57BL.

V genes of oxazolone antibodies in 10 strains of mice

One pair of V genes (V kappa 45.1 and V11) code for a great portion of phenyloxazolone (anti-phOx) antibodies in 10 strains of mice. This combination replaces the first-known major combination VHOx1-V kappa Ox1 in some strains, and is important in most strains. C57BL/10 and SJL mice have an additional subset of antibodies encoded by genes V kappa 45.1 and V13 (a relative of V11). All three genes involved (V kappa 45.1, V11 and V13) have "allelic" variation. Four alleles of V11 were found, one in Igh haplotypes a, c and g, the second in haplotypes d, j and n, the third in b, and the fourth in f. The most distant alleles d, j, n and f had 10 nucleotide differences out of 429 determined (97.7% homology). Only one allele of the V13 gene was found from anti-phOx hybridomas but two others have been published. Three alleles of the V kappa 45.1 gene were found; one in NZB mice (Ig kappa haplotype b) another in CE (haplotype f), and the third in eight strains including representatives of three Ig kappa haplotypes (a, c and e). The three alleles had greater than 99.0% homology. The V11 and V13 genes that code for anti-phOx antibodies in C57BL/10 and SJL mice were different from the related genes found from the C57BL/10 germ line. C57BL/10 mice must have a chromosome bearing two V11 and two V13 genes. RF mice were found to have two V11 genes, and both code for anti-phOx antibodies. Our data show that the majority of antibodies in the anti-phOx response are encoded by the same restricted collection of V genes in most mouse strains. Antibody responses appear to be no less heritable than other functions of the body.

Specific immunosuppression by Trichinella: fine specificity and effect on lymphocyte function in vivo

Muscle-phase Trichinella larvae depress the immune response of mice to the phosphorylcholine (PC)-bearing Trichinella antigen FCp without affecting responses to other PC-bearing or non-PC antigens. The depressive activity is independent of antigen dose and Trichinella species and, in adoptive cell transfer experiments with lethally irradiated recipient mice, depended on the state of the recipient (infected recipients had a depressed response even a month after their encysted larvae had been killed and regardless of whether the donor had been exposed to FCp) but not on the state of the transferred cells. We conclude that lymphocytes are not permanently altered by the depressive action, that the agent responsible persists in the host at least a month after the death of the encysted Trichinella larvae, and that the alteration does not eliminate lymphocyte immunological memory.

A private idiotype can become recurrent through genetic recombination and gene(s) unlinked to the Igh locus governs its expression

Any immune response is characterized by its idiotypic profile. Two different kinds of idiotype (Id) have been described. Private Id are restricted to a few individuals from a species while recurrent Id appear in a large majority of individuals from the same species immunized with the same antigen. We describe, in this report, an experimental model whereby a private Id can become recurrent through genetic recombination. The immune response of A mice against the hapten arsonate is characterized by a recurrent Id called cross-reactive idiotype A (CRIA). A strongly CRI, called CRIA-like, can be occasionally detected in some BALB/c mice (5% to 10%) immunized with arsonate. Molecular studies show that CRIA and CRIA-like antibodies have highly homologous D segments and identical light chains. By contrast, their VH segments are vastly dissimilar. We have examined the anti-arsonate response of inbred strains of mice whose Igh loci are recombinant between those of A/He and BALB/c. Interestingly, we have observed that the CRIA-like Id which is private in BALB/c becomes recurrent in the AXC-1 strain which harbors the VH genes from BALB/c, the DH and CH genes from A/He. Structural studies demonstrate that highly homologous, VH, VL and D segments are used in BALB/c and AXC-1 mice. The basis for this differential expression of highly similar genes could be linked to the DH locus. However, F1 mice stemming from the cross between AXC-1 and BALB/c do not express the Id. The backcross analysis shows that the non-expression of the Id in F1 mice depends on genes unlinked to the Igh locus.

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.

Genetic control of early antibody responses

By using a pair of strains that have similar VK haplotypes but different VH haplotypes (e.g. BALB/c and C57BL) it is possible to demonstrate VH-controlled genetic differences in antibodies. By using a pair that have similar VH haplotypes but different VK haplotypes (RF and BALB/c) it is possible to demonstrate VK-controlled genetic differences in antibodies. A plausible explanation for the high frequency of certain V-gene combinations in the primary response is a high affinity of the product without somatic mutations. The products of two such major primary response combinations (VHOx1/VKOX1(H3) and VH186.2/V lambda 1) have an affinity for the immunogen well above 10(6). One combination of V genes, VHOx1/VKOx1(H3) has a major role in the primary anti-phOx response of several mouse strains - the product is idiotype 260. C57BL/10 mice lack the VHOx1 and RF mice the VKOx1(H3) gene. They use the remaining partner of the pair for the response in combination with other genes, but the affinity of the product is lower than the affinity of id. 260. Concordantly, the frequency of these "half-idiotypes" is lower in the primary response than the frequency of the full combination (23% and 16% instead of 50%). When the product of a V-gene combination is very frequent in the primary response, the affinity for the immunogen must be high, but the reverse is not always true. The product of a combination can have an unusually high affinity but the frequency is low. The simplest explanation then is that the frequency of available virgin B cells is low. It can be low because of a low rearrangement frequency of one of the V genes, VH or VK. Another possibility is that only a small proportion of B cells that have the particular combination rearranged can be recruited to the response. We have discussed an example where strict heavy chain CDR3 requirements must strongly limit available B cells.

The use of defined peptides in characterizing idiotypes

The structural correlates of idiotypes have been sought in several antibody systems. The cumulative results suggest that the hypervariable regions (or complementarity-determining regions) of the heavy and light chains are the structural basis of idiotypes. However, in most cases, it is exceedingly difficult to associate a particular idiotypic determinant with a specific amino acid sequence. Recently, synthetic peptides were used to induce antibodies specific for predefined determinants in intact proteins. These findings led us and others to use synthetic peptides corresponding to the hypervariable regions/complementarity-determining regions to induce anti-idiotypes. These novel anti-idiotypic antibodies are easy to prepare, and are ideal reagents for structural and genetic studies of antibody responses.

Serologic and molecular characterization of the T15 idiotype--II. Structural basis of independent idiotope expression on phosphorylcholine-specific monoclonal antibodies

We examined the expression of T15 idiotopes (Id) on phosphorylcholine (PC)-binding monoclonal immunoglobulins and defined the structural correlates of these Id. The seven monoclonal anti-Id antibodies used as probes recognize distinct determinants that range from the antigen binding site to the CH1 domain on TEPC15. Competition between a series of PC-specific immunoglobulins and radiolabelled TEPC15 for binding to anti-Id in solid phase revealed a broad spectrum of idiotopic crossreactivity. A strong crossreactivity with TEPC15 was observed only in proteins possessing the VK22 light chain. Each of the seven discrete, overlapping T15 Id may be expressed independently of each other on PC-binding immunoglobulins, indicating a significant idiotopic heterogeneity among T15 B-cell clones. No correlation was found between the public (shared) expression of an Id and its position relative to the antigen-binding site. Variations in the primary sequences of PC-binding immunoglobulins were correlated with their effect on individual Id expression. Regions influencing the expression of three Id were localized on a computer display of the three-dimensional structure of the closely related PC-binding myeloma protein McPC603. These data show that some, but not all individual Id determinants may be influenced by amino acid substitutions in the first and third hypervariable loops.

Immune response to Trichinella epitopes: the antiphosphorylcholine plaque-forming cell response during the biological cycle

Phosphorylcholine (PC), an immunodominant component of the cell wall of certain bacteria, fungi and nematodes, is known to induce low anti-PC antibody levels during natural infection by Trichinella spiralis. This article reports a study in which spleen cells from BCF1 mice infected with Trichinella sp. larvae were found to produce large numbers of direct haemolytic plaques in response to PC conjugated to sheep red blood cells (SRBC) after muscle-encysted larvae had been killed by treatment with mebendazole. Inhibition of the response by PC-chloride, immunodiffusion and immunoelectrophoretic studies with the anti-PC IgA (TEPC-15) and anti-idiotype T15 serum assays showed the plaque-forming cell (PFC) response to be specific for PC. The absence of haemolytic plaques when unconjugated SRBC or TNP-SRBC were used as indicator cells ruled out involvement of a polyclonal response. Greatest anti-PC PFC response was found to be associated with a microsomal fraction designated FCp1, a particulate fraction behaving as a thymus-dependent antigen. The FCp1 fractions from all four strains of Trichinella employed induced anti-PC PFC responses when injected into mice. These results suggest that FCp1 is a suitable antigen for use in detailed studies of immune responses to Trichinella and related parasites.

Immunologic memory to phosphorylcholine (PC). VIII. Expression of the VH-12 gene product in the response to PC-keyhole limpet hemocyanin

Three murine anti-phosphorylcholine (PC) hybridomas with group II-like fine specificity patterns isolated during a memory response to PC-keyhole limpet hemocyanin (KLH) are examined at the molecular level to determine the origins of the VH and VL used by these antibodies. Southern blots of Hind III cut DNA were hybridized with a probe specific for the V1 gene of the T15 VH family. The V1 germ-line configuration is retained in these hybridomas indicating that this gene which encodes the VH gene product expressed by most group I anti-PC hybridomas is not used for antibody production. Southern blots of Eco RI cut DNA hybridized to a probe specific for JH1-JH4 indicated that all three hybridomas PCG1-2, PCG1-3 and PCM-23 share a 5.2-kb rearranged JH band, suggesting utilization of a common VH gene segment. N-terminal amino acid sequence analysis of the heavy chains of two of the hybridoma proteins PCG1-2 and PCG1-3 indicates that they belong to mouse heavy chain subgroup II and are closest in sequence to a VH-12 isotype anti-PC hybridoma protein, HPC-104, derived from BALB/c mice suppressed for the T15 idiotype; PCG1-2 and PCG1-3 each differed from HPC-104 at only 1/20 residues. In addition, these proteins have in common a lysine at position 1 which has not been found previously in 203 other heavy chain sequences reported. N-terminal sequences of the light chains of PCG1-2 and PCG1-3 are each shown to differ at only 1/22 residues from V kappa 24, and PCM-23 had previously been shown to use V kappa 8; both of these have been associated previously with heavy chains derived from the V1 gene in anti-PC antibodies. These results indicate that the VH-12 isotype can be used during a normal antibody response to PC and thus that heavy chains derived from both subgroup II and subgroup III (the T15 heavy chain) contribute to the molecular heterogeneity observed in memory responses to PC-KLH.

Several V genes participate in the early phenyloxazolone response in various combinations

Seventeen monoclonal anti-2-phenyloxazolone antibodies from the early (day 7) primary response were partially sequenced with an mRNA method. Ten antibodies expressed the VH-Ox1 gene. The remaining seven express at least four but probably six different germ-line VH genes belonging to Dildrop's groups 1, 5, 6 and 7 (Immunol. Today 1984. 5: 85). Two of them have been met before in other antibodies, one (group 6) in J606 and the other (group 7) in antibodies to the influenza virus hemagglutinin. Eleven kappa chains were partially sequenced and five of them (all VH-Ox1 antibodies) express the V kappa-Ox1 gene. One expresses another germ-line gene of the V kappa-Ox1 family, one the V kappa 89.4 gene, three the V kappa 45.1 gene and one a new V kappa gene. The V kappa 45.1 gene was found to form anti-phOx antibodies with two new VH genes. The frequency of somatic mutations in day 7 antibodies was estimated by comparing germ-line sequences and antibody sequences. It is low (one mutation per 2500 nucleotides sequenced), twenty times lower than in antibodies obtained a week later. Two anti-idiotype antisera (495 and 260) are useful in the typing of monoclonal antibodies. 260 bound only to antibodies coded by both VH-Ox1 and V kappa-Ox1 genes. 495 bound strongly to antibodies coded by the VH-Ox1 gene and weakly to antibodies coded by the (related) VH101 gene regardless of the light chain partner.

Molecular events during maturation of the immune response to oxazolone

Sequence analysis of the heavy- and light-chain messenger RNA of hybridomas immunized with a specific hapten yields important clues about the interplay between genetic and selective events during the onset and maturation of the immune response. The maturation of the primary response to the hapten 2-phenyl-5-oxazolone is characterized by a drift to higher-affinity somatic variants of a germline-encoded basic sequence, whereas hybridomas from the secondary response demonstrate a further maturation dominated by a shift to alternative germline combinations.

Synthetic peptides corresponding to third hypervariable region of human monoclonal IgM rheumatoid factor heavy chains define an immunodominant idiotype

Synthetic peptides corresponding to eight individual heavy chain complementarity-determining regions (CDR) of three human monoclonal IgM anti-IgG (rheumatoid factor [RF]) paraproteins elicited rabbit antibodies with markedly different properties. All antisera recognized the immunizing peptide, and several reacted with the isolated IgM heavy chain on immunoblots. However, only the antisera against peptides representing the third CDR bound consistently and specifically to the intact IgM-RF molecule. These data indicate that the third CDR of human mu chains comprises an immunodominant idiotype, and suggest that the D gene segment may be especially important in creating idiotypic diversity. Synthetic peptides corresponding to the third heavy chain CDR of human paraproteins may be clinically useful for the specific induction of antiidiotypic antibodies.

Drastic change in idiotypic but not antigen-binding specificity of an antibody by a single amino-acid substitution

In proliferating B lymphocytes, somatic mutation of rearranged antibody variable (V)-region genes occurs at high frequency and may have a key role in the selection of these cells. It is of interest in this context to learn in which way single mutations can affect antigen binding and/or idiotypic specificity of an antibody. Previous investigations have analysed spontaneous mutants of myeloma and hybridoma cells in which the mutation affected the antigen-binding specificity of the antibody. Here we describe an antibody mutant that has fully retained antigen-binding specificity but has lost or drastically changed all V-region antigenic determinants (idiotopes) of the wild type as defined by monoclonal anti-idiotope antibodies. The mutant phenotype is generated by a glycine to arginine exchange in the middle of the diversity (D) element, at position 103 of the heavy chain.

Structure of primary anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) antibodies in normal and idiotypically suppressed C57BL/6 mice

Eight monoclonal antibodies from the primary response of C57BL/6 mice against the hapten (4-hydroxy-3-nitrophenyl)acetyl (NP) were isolated. The antibodies carry lambda 1 light chains and have similar affinities for the immunizing hapten. Sequence analysis at the level of mRNA reveals that all antibodies express the VH gene 186.2 and all but one the DFl 16.1 gene segment. The J segment of the heavy chain is JH2 in six cases and JH4 in two. Somatic point mutations are scarcely detectable in the antibodies, but there is extensive sequence variability at the boundaries of the D gene segment, mainly at its 5' end. However, seven of eight antibodies express tyrosine in position 99 of the heavy chain, encoded either by the 5' codon of DFl 16.1 or by presumed N sequences. In the former case, the tyrosine is the first of a stretch of three (positions 99-101). In the latter, a similar stretch (positions 99, 101, 102) is interrupted by aspartic acid, asparagine or cysteine in position 100. These variations profoundly affect idiotypic specificity. Six of the eight monoclonal antibodies came from mice neonatally suppressed by an anti-idiotope antibody whose target idiotope is regularly expressed in primary anti-NP responses and depends upon a non-germ-line-encoded aspartic acid in position 100 of the heavy chain. The sequence data show that the mice circumvent suppression by expressing antibodies which lack this aspartic acid but are otherwise structurally very similar to anti-NP antibodies from normal animals. Since suppression in the animals is partly controlled by regulatory T cells, we conclude that these T cells are highly restricted in their specificity in that they preferentially see a determinant which also depends upon the aspartic acid in position 100. The data suggest that the VH to D boundary serves as a target of idiotypic selection.