Immunoglobulin structure: amino terminal sequences of mouse myeloma proteins that bind phosphorylcholine

Atherosclerosis Susceptibility in Mice Is Independent of the V1 Immunoglobulin Heavy Chain Gene

Supplemental Digital Content is available in the text.

The V1 (V_HS107.1.42) immunoglobulin heavy chain gene is thought to be critical in producing IgM natural antibodies of the T15-idiotype that protect against both atherosclerosis and infection from Streptococcus pneumoniae. Our aim was to determine whether genetic loss of the V1 gene increased atherosclerotic plaque burden in vivo because of a reduction in the T15-idiotype or other atheroprotective antibodies.

Diversity in the CDR3 region of V(H) is sufficient for most antibody specificities

All rearranging antigen receptor genes have one or two highly diverse complementarity determining regions (CDRs) among the six that typically form the ligand binding surface. We report here that, in the case of antibodies, diversity at one of these regions, CDR3 of the V(H) domain, is sufficient to permit otherwise identical IgM molecules to distinguish between a variety of hapten and protein antigens. Furthermore, we find that somatic mutation can allow such antibodies to achieve surprisingly high affinities. These results are consistent with a model in which the highly diverse CDR3 loops are the key determinant of specificity in antigen recognition in both T cell receptors (TCR) and antibodies, whereas the germline-encoded CDR1 and CDR2 sequences are much more cross-reactive.

Antigen binding and idiotype analysis of antibodies obtained after electroporation of heavy and light chain genes encoding phosphocholine-specific antibodies: a model for T15-idiotype dominance

Antibodies bearing the T15 idiotype dominate the murine primary immune response to phosphocholine (PC). Analysis of antigen binding of antibodies derived from V1:DFL16.1:JH1 (VH1) germline and N region-derived variant heavy (H) chains and kappa 22, kappa 24, and kappa 8 light (L) chains demonstrates that the T15H:kappa 22L (T15) antibody binds PC at least 20-40 times better than other antibodies derived from alternate germline forms of the VH1 H chain and kappa 22, kappa 24, or kappa 8 L chains. To achieve affinities in the same range as the T15 antibody, kappa 24 and kappa 8 L chain-containing antibodies must have H chains derived from variant N region or somatically mutated VH1 genes. Single amino acid differences at the VD junction of the various germline and N region variant VH1 H chains dictate the L chain that can associate with the H chain to produce a PC-specific antibody. Several H:L combinations give rise to T15 or M167 idiotype-positive antibodies that lack specificity for PC, and single amino acid substitutions or insertions at the VH1:D junction result in the loss of T15 or M167 idiotopes. Based on these observations, our data support a molecular model involving both preferential gene rearrangement and antigen-driven B cell selection to explain T15 idiotype dominance in the immune response to PC. In the absence of N region diversification, large numbers of neonatal B cells bearing the T15H:kappa 22L surface immunoglobulin M (sIgM) receptors would be selected and expanded by autologous or environmental PC antigen into the long-lived peripheral B cell pool.

Paucity of phosphorylcholine-specific clones in B cells expressing the VHT15 gene product

The aim of this work was to study the cellular basis of the phenomenon of clonal dominance. To this end we analyzed two collections of BALB/c and C.B20 hybridomas that we selected on the basis of the expression of the VHT15 gene product independently from their antigen specificity. Our study demonstrates that none of the 28 BALB/c and only 2 of the 29 C.B20 hybridomas obtained have variable regions that bind PC. We conclude therefore that the domination of the immune response to PC by particular variable regions cannot be due to the establishment of clonal dominance prior to immunization.

Methylation patterns of immunoglobulin genes in lymphoid cells: correlation of expression and differentiation with undermethylation

Different states of eukaryotic gene expression are often correlated with different levels of methylation of DNA sequences containing structural genes and their flanking regions. To assess the potential role of DNA methylation in the expression of immunoglobulin genes, which require complex rearrangements prior to expression, methylation patterns were examined in cell lines representing different stages of lymphocyte maturation. Methylation of the second cytosine in the sequence 5' C-C-G-G 3' was determined by using Hpa II/Msp I endonuclease digestion. Four CH genes (C mu, C delta, C gamma 2b, and C alpha), C kappa, V kappa, C lambda, and V lambda genes were analyzed. The results lead to the following conclusions: (i) transcribed immunoglobulin genes are undermethylated; (ii) the C gene allelic to an expressed C gene is always also undermethylated; and (iii) all immunoglobulin loci tend to become increasingly undermethylated as B cells mature.

Polymorphism in anti-phosphocholine antibodies reflecting evolution of immunoglobulin families

Complete variable (V) region amino acid sequences were determined for four heavy (H) and one light (L) chain from C57BL phosphocholine (PC)-binding monoclonal antibodies. Additional NH2-terminal sequences were obtained from H and L chains of C57BL and CBA/J origin. When these V regions were compared with previously reported anti-PC sequences, a number of observations could be made regarding the function and evolution of L and H chain segments used in these antibodies. (a) L and H chain V segments are remarkably conserved in these inbred strains, although there has been an accumulation of point mutations identifying apparently allelic forms of VK and VH. (b) Mice of each genotype use the same three VK segments in combination with a single VH segment to produce most anti-PC antibodies. An exception has been noted that indicates the occasional use of a second VH gene segment. (c) Multiple, different DH regions are used by mice of each strain, which suggests that the DH segment sequence plays no critical role in either antigen binding or VH-VL pairing. Furthermore, the DH segments and their corresponding gene families appear to be highly conserved in the inbred strains studied. (d) Most PC-binding antibodies use the JH1 joining segment. All JH1 sequences from C57BL mice differ from the BALB/c JH1 at position 105, which identifies allelic forms of the JH1 region. These studies are a first assessment of the nature of mutational events associated with the evolution of specific multigene immunoglobulin families and indicate that homologous VH, DH, JH, VK, and JK genes are similarly assembled and expressed in PC antibodies from three diverse genotypes.

A combined proton and phosphorus-31 nuclear magnetic resonance investigation of the combining site of M603, a phosphocholine-binding myeloma protein

Phosphorus-31 nuclear magnetic resonance (NMR) studies on the two phosphorus nuclei of the phosphonium analogue (Me3P+CH2CH2OPO3(2-)) of phosphocholine are used to monitor the charged subsites in the phosphocholine-binding immunoglobulin A mouse myeloma M603. Comparison of the 270-MHz 1H NMR difference spectrum on addition of either this analogue or phosphocholine to M603 and the almost identical changes in the pKa values of the phosphate groups on binding to M603 confirm that the analogue is a good model for phosphocholine. The pKa of the phosphate groups is decreased by 0.5 unit on binding to M603, which is consistent with the phosphate group being hydrogen bonding to Tyr-33H and Arg-95L, as suggested from the X-ray structure, and also implies that the binding energies for the mono- and dianion are similar. The P+Me3 moiety is used to probe the electrostatic interactions in the choline subsite. Titration of the chemical shift of the phosphonium phosphorus reflects a group on the protein that has a pKa value of less than or equal to 5, which from the refined X-ray structure (D.R. Davies, personal communication) of the site is assigned to Asp-97L. The choline subsite is monitored by using 1H NMR difference spectra, which indicates that the subsite is highly aromatic as expected from the crystal structure that places Trp-107H and Tyr-100L in this subsite. The ring current interactions from these rings can account for the 1H NMR chemical shift data on choline.

Single amino acid substitution altering antigen-binding specificity

S107, a phosphocholine-binding myeloma protein, has been cloned in soft agar, and an antigen-binding variant has been isolated and characterized. The variant does not bind phosphocholine attached to carrier or as free hapten in solution but does retain antigenic determinants (idiotypes) of the parent. Chain recombination experiments suggest that the defect in binding is entirely in the heavy chain. Amino acid sequence analysis showed a single substitution--glutamic acid to alanine at position 35--in the first hypervariable or complementarity-determining region. In terms of the three-dimensional model of the phosphocholine-binding site, glutamic acid-35 provides a hydrogen bond to tyrosine-94 of the light chain that appears to be critical for stability of this portion of the binding site. The removal of this bond and the presence of the smaller alanine side chain is thus consistent with the loss in binding activity. These results suggest that small numbers of substitutions in antibodies, such as those presumably introduced by somatic mutation, may in some situations be effective in altering antigen-binding specificity.

IgG antibodies to phosphorylcholine exhibit more diversity than their IgM counterparts

An amino acid sequence analysis of the N-terminal immunoglobulin heavy and light chain variable regions (VH and VL) from 16 hybridoma proteins which bind phosphorylcholine as well as the complete sequence analysis of 9 of these VH regions is presented. There seem to be more VH regions participating in the phosphorylcholine response than can be encoded directly by germ-line VH gene segments. Moreover, the V regions from IgG antibodies are considerably more variable than those from their IgM counterparts. These observations raise the possibility that a somatic mechanism for V region diversification produces greater diversity in IgG than in IgM antibodies.

Nucleic acid and protein sequences of phosphocholine-binding light chains

An 18-kilobase DNA fragment containing the sequence coding for both the variable and constant regions of the S107 mouse immunoglobulin light chain was cloned from total cellular DNA. The complete nucleotide sequence of the kappa-chain variable-region gene is reported. Determination of the amino acid sequence encoded by the DNA is found to be identical to the protein sequence of the T15 light chain through residue 88. Direct sequence analysis confirmed that the J1 joining segment is used in the recombination event producing the active kappa light chain gene.

Affinity labeling of residues within Hv2 of guinea pig anti-azobenzenearsonate antibodies of different isotypes and from different strains

Anti-p-azobenzenearsonate (ARS) antibodies of IgG1 and IgG2 isotypes produced in inbred strain 13 and strain 2 guinea pigs were affinity labeled with N-(bromoacetyl)-3-[(p-arsonophenyl)azo]-L-tyrosine (BAAT) or N-(bromoacetyl)-p-arsanilic acid (BAA). BAAT was shown to modify approximately 50% of the binding sites specifically and BAA approximately 30%. Both reagents preferentially modified residues in the heavy (H) chain to the extent that it contained over 80% of the affinity label associated with the native molecule. At least 80% of label borne by the variable domain of the H chain (VH) was found in the second hypervariable region (Hv2). BAAT labeled all anti-ARS antibodies exclusively at position N-59, which contains a lysyl residue. BAA labeled predominantly tyrosine at N-57 and, to a lesser extent, lysine-59 and tyrosine-50. Comparison of Hv2 sequences in anti-ARS and in antibodies reactive with other haptens has shown that tyrosine at N-50 and N-57 as well as lysine at N-59 is distinctive of antibodies with anti-ARS specificity, thus implying their involvement in antigen binding. The predominant sequence of Hv2 was identical in anti-ARS IgG1 and IgG2 molecules induced in either inbred guinea pig strain following either carrier priming or conventional immunization. Although limited variability does occur among the various populations of anti-ARS antibodies in certain residue positions in Hv2, no significant differences in the binding affinities or in the indexes of heterogeneity were seen among the various kinds of anti-ARS antibodies.

Idiotypic cross-reactivity of human and murine phosphorylcholine-binding immunoglobulins

The idiotypic cross-reactivity of mouse and human monoclonal immunoglobulins with binding activity for phosphorylcholine (PC) was investigated, using an idiotypic antibody elicited against the PC-binding human IgMFR. The isolated FR heavy chain proved to be a better inhibitor for the reaction of IgMFR with anti-FR than the FR light chain, but the intact protein was necessary for full idiotypic expression. PC was an inhibitor only at concentrations greater than 10(-3) M indicating that the idiotypic antibody was not combining site-directed. Among the murine PC-binding IgA myeloma proteins, MOPC 167 was found to be the best inhibitor, but its inhibitory capacity was about 4 orders of magnitude lower than that of the homologous IgMFR. McPC 603 was an even weaker inhibitor, while TEPC 15 effected no better inhibition than human monoclonal immunoglobulins without PC-binding activity. MOPC 167 has a most similar binding specificity to IgMFR as indicated by the high affinity for choline of these two proteins. TEPC 15 and McPC 603, on the other hand, exhibit a much lower affinity for choline. In addition to their similarity in specificity, proteins FR and MOPC 167 show important structural similarities within parts of their heavy and light chain variable domains. The data provide some evidence for the existence of idiotypic cross-reactivity between the two species man and mouse.

Genetic determination of antibody specificity. Gene translocation and fusion, the molecular basis for the differentiation of the antibody-producing cell

The best system for the study of cell differentiation is a cell which in its differentiated state differs only by one product. This is the case in the immune system. The undifferentiated, but omnipotent stem cell differentiates into a committed B cell which produces only one type of specific antibody out of a million different, genetically fixed possibilities. Gene translocation and fusion is the basis of this differentiation process.

Structural basis for the specificity of antibody-antigen reactions and structural mechanisms for the diversification of antigen-binding specificities

The ability of an organism to cope with foreign substances (antigens) depends in part on its capacity to synthesize antibodies (immunoglobulins) of the proper binding specificity to recognize and combine with these antigens. In view of the great variety of possible antigens, antibodies, or more specifically their combining sites, display considerable variation and possess structural properties such as to enable them to bind the antigenic determinants. A vast amount of immunoglobulin sequence data has become available and the three-dimensional structures of a number of immunoglobulin fragments have been elucidated. With these results we can now begin to understand the structural aspects of antibody–antigen reactions. The crystallographic results and the sequence data have been reviewed elsewhere (Capra & Kehoe, 1975; Davies, Padlan & Segal 1975a, b; Gally, 1973; Kabat, 1976; Nisonoff, Hopper & Spring, 1975; Poljak, 1975a, b). Here, an attempt is made to interpret these structural data in terms of the structural evolution of the antibody combining site and the structural basis for the specificity of the binding of antibody to antigen. First, the pertinent crystallographic and sequence data will be presented. Next, the structural studies which reveal the complementarity between antibody and ligand will be described. Then, structural mechanisms by which different combining site structures could be generated will be reviewed.

Active heterologous chain recombinants of monoclonal antibodies raised in related rabbits

Heterologous chain recombinants of homogeneous anti-streptococcal group A-variant polysaccharide antibodies produced by pedigreed rabbits regain in certain pairs the same antigen-binding capacity as the homologous pairs. In contrast, chain recombinants with antibodies from nonrelated rabbits are much less active. This data suggests random pairing of immunoglobulin heavy and light chains coded for in the germ line and subsequent selection.

Genetic marker in the variable region of kappa chains of mouse anti-phosphorylcholine antibodies

A newly discovered genetic marker in the kappa light chains of mouse immunoglobulins is described. This marker, designated kappa-PC8, is located in the L chains of those anti-phosphorylcholine (PC) antibodies which show the same functional and idiotypic characteristics as a PC-binding myeloma protein, HOPC 8 (H8). Analytical isoelectric focusing of these L chains revealed two phenotypes whose strain distribution pattern suggested a genetic association with genes that determine the T lymphocyte surface antigen(s) Ly-2/Ly-3. In four strains , AKR/J, C58/J, RF/J and PL/J (AKR-type, A) the H8-like L chains have a slightly lower isoelectric point than those of C57L/J and 12 other strains (C57L-type, B). Breeding experiments showed that the kappa-PC8-A phenotype is preferentially expressed. The most probable location of the marker is the variable region since other idiotypically related kappa-chains in C57L/J and AKR/J do not show differences in their electrophoretic mobility.

Variable region sequence of the light chain from a Waldenströms IgM with specificity for phosphorylcholine

The variable region sequence of the light chain from the human IgM FR with binding activity for phosphorylcholine has been determined. Automated Edman degradation was used for the whole chain and for a large cyanogen bromide fragment comprising the third hypervariable region and the entire constant part. The rest of the sequence was established by means of the "Dansyl-Edman" technique with tryptic peptides. The sequence of light chain FR can be assigned to the subgroup II of human light chains with which it shares 92% homology within the nonhypervariable (frame-work) residues. There is no apparent sequence homology betweeen the variable region of the human light chain FR and the aminoterminal 41 residues of the light chains published so far from the mouse myeloma proteins TEPC 15, HOPC 8, S 107, and McPC 603 with phosphorylcholine binding activity. Recent data on the light chain of the phosphorylcholin binding mouse myeloma protein MOPC 167 (see Conclusion), however, indicate a considerable structural homology between the first hypervariable region of this murine protein and that of the human IgM FR, suggesting that both IgM FR and IgA MOPC 167 might have been selected by similar antigens.

Rabbit antibody light chains: selective breeding narrows variability in framework and complementarity-determining residues

The amino acid sequence of 5 light (L) chain (b4) variable (Vl) regions and the partial sequence of VL (kappa) regions from 12 anti-streptococcal group A-varant polysaccharide (Av-CHO) and 2 anti-streptococcal group C polysaccharide (C-CHO) antibodies was determined. These sequences contain 70 invariant positions as opposed to 50 invariant positions in other rabbit VL regions. Variability within the framework residues lacks randomness, and parent offspring relationship or otherwise close familial relationship is apparent in several instances. Variability in the complementarity-determining regions is reduced by 2.3-5.5-fold in comparison with other rabbit L-chains with several identical first and third hypervariable regions. Residue positions 50-56, known to mark the second hypervariable region in human kappa-chains, are not hypervariable in L-chains from Av-CHO rabbit antibodies. Considering the 67 rabbit L-chain sequences, completely or partially known today, for counting the number of V region germ line genes, it is concluded that the species rabbit has at least 27 VL germ line genes available.

Binding of phosphorylcholine to an IgM Waldenström as studied by fluorescence spectroscopy and circular dichroism

The binding characteristics of an IgM Waldenström(FR) for the ligand phosphorylcholine has been studied by fluorescence spectroscopy. Upon phosphorylcholine addition, IgM FR exhibited 83% enhancement of the tryptophanyl fluorescence, which was associated with a red shift of the emission maximun (5nm). The same properties were observed with the 7S IgM subunits. The association constant KA for phosphorylcholine was 6X10(4) M-1 FOR IgM FR and the 7S subunit, as determined by fluorescence titration, a value in agreement with the obtained by equilibrium dialysis. No significant decrease in the KA value was found in the presence of 3 M urea; in 6 M urea, the increase in fluorescence intensity was 36% of the value obtained in the absence of denaturing agent. In contrast, only 4% of fluorescence enhancement was noted upon binding in 3 M GuHC1 and no enhancement could be seen when the concentration of GuHC1 was increased to 5 M, thus suggesting complete unfolding of the protein and subsequent loss of binding activity. The pH dependence study of the phosphorylcholine binding to IgM FR indicated no significant differences in the fluorescence enhancement between pH 5 and 8, whereas at more acidic or alkaline pH values, the enhancement became smaller. At pH 3.0 and 10.0, no enhancement was seen suggesting no binding of the ligand, a fact confirmed independently by equilibrium dialysis. When the spectroscopic properties of the IgM FR were compared with those of murine myeloma proteins that bind the same ligand large differences were recorded in the amplitude of the phosphorylcholine induced enhancement of the fluorescnece and in the shift of the emission maximum wavelength. This suggests that the human and murine proteins interact differently with the small ligand phosphorylcholine thus implying that the variable domains of these molecules are not identical

Immune response to phosphorylcholine. I. Characterization of the epitope-specific antibody

The antibodies to phosphorylcholine induced in BALB/c mice were isolated and studied with a variety of biochemical and immunochemical methods. Analysis of the idiotype and the hapten-binding specificities showed no differences to the phosphorylcholine-binding myeloma protein TEPC 15, indicating a high degree of homogeneity. However, disc electrophoresis, isoelectric focusing and amino acid composition data indicated large differences in the structure of anti-phosphorylcholine antibody and TEPC 15. By these criteria the anti-phosphorylcholine antibodies from BALB/c mice are of oligoclonal origin.

Human and murine phosphorycholine-binding immunoglobulins: conserved subgroup and first hypervariable region of heavy chains

The NH2-terminal 36 residues of the heavy chain and the NH2-terminal 40 residues of the light chain from a human Waldenström's IgM with binding activity for phosphorylcholine (phosphocholine) are compared with the published sequences of five mouse IgA myeloma proteins with the same activity. An extensive structural similarity; i.e., 3 amino acid interchanges within framework residues, and one in the hypervariable region, is noted between the heavy chains of both species. The light chains, however, show a considerable diversity and, in contrast to the heavy chain, no correlation between the primary structure of the first hypervariable region and the binding specificity is apparent. The finding of a very similar heavy chain variable region in two different species that are separated by about 75 million years in evolution favors the concept of stable transmission of variable region genes throughout evolution.

A mathematical approach to the analysis of diversity in antibody gene families

In this article, we develop a mathematical approach for the analysis of diversity in antibody gene families. This approach is arrived at by examing two general questions about protein populations: (1) What is a relative measure of the diversity exhibited by one protein family when compared with a second? (2) What is the probability that two protein populations were derived from a single common population? These quantitative approaches permit a variety of precise evolutionary, genetic, and developmental questions to be asked of antibody gene families. Using this methodology, we demonstrate that the diversity in mouse K-immunoglobulin chains is considerably greater than in their human K counterparts. We also show that the variable (Vl) regions of light chains associated with IgG and IgA immunoglobulins in the mouse appear to have been derived from a common population of Vl genes. This approach also can be used to analyse sequence data from other informational multigene families.

Size differences among immunoglobulin heavy chains from phosphorylcholine-binding proteins

The entire sequences of the heavy chain variable regions of M167 and TEPC 15 (phosphorylcholine-binding myeloma proteins of BALB/c origin) have been determined. These sequences are compared with the phosphorylcholine-binding protein M603. T15 differs from M603 at four positions, all of which are located in antigen-binding complementarity regions. M167, in addition to having differences in the complementarity regions, also has five substitutions in the conserved framework portion of the variable region when compared to T15 and M603. Each of the three proteins has a different length in the third complementarity region. It is unlikely that complementarity regions of different lengths associated with similar framework regions could be generated by proposed mechanisms of somatic mutation which are generally limited to point mutations. It appears more likely that these products are directly encoded by different structural germ line genes.

Attempts to locate residues in complementarity-determining regions of antibody combining sites that make contact with antigen

From collected data on variable region sequences of heavy chains of immunoglobulins, the probability of random associations of any two amino-acid residues in the complementarity-determining segments was computed, and pairs of residues occurring significantly more frequently than expected were selected by computer. Significant associations between Phe 32 and Tyr 33, Phe 32 and Glu 35, and Tyr 33 and Glu 35 were found in six proteins, all of which were mouse myeloma proteins which bound phosphorylcholine (= phosphocholine). From the x-ray structure of McPC603, Tyr 33 and Glu 35 are contacting residues; a seventh phosphorylcholine-binding mouse myeloma protein also contained Phe 32 and Tyr 33 but position 35 had only been determined as Glx and thus this position had not been selected. Met 34 occurred in all seven phosphorylcholine-binding myeoma proteins but was also present at this position in 29 other proteins and thus was not selected; it is seen in the x-ray structure not to be a contacting residue. The role of Phe 32 is not obvious but it could have some conformational influence. A human phosphorylcholine-binding myeloma protien also had Phe, Tyr, and Met at positions 32, 33, and 34, but had Asp instead of Glu at position 35 and showed a lower binding constant. The ability to use sequence data to locate residues in complementarity-determing segments making contact with antigenic determinants and those playing essentially a structural role would contribute substantially to the understanding of antibody specificity.

Inheritance of antibody specificity. III. A new VH gene controls fine specificity of anti-p-azobenzenearsonate coupled to the carbon atom 5 of hydroxyphenylacetic acid in the mouse

Mice of 10 inbred strains were immunized with a protein conjugate of a hapten of p-azobenzenearsonate coupled to the carbon atom 5 of hydroxphenylacetic acid (ABA-HOP), and anti-ABA-HOP titers were determined by the haptenated phage inactivation. Mean titers of C57BL/6 and BALB/c mice were significantly lower than those of A/J and CBA strains. The titers were under a polygenic control and did not correlate with allotypes in backcross mice. Fine specificity of the anti-ABA-HOP was characterized by inhibiting the haptenated phage inactivation reaction with five chemically related compounds including ABA-HOP (Fig. 1). This antibody was genetically more polymorphic than any other antibody studied. Three distinct idiotypes could be demonstrated and the number is probably greater. The idiotypes of the A/J and C57BL/6 were inherited as allotype-linked dominant Mendelian traits, the former in two and the latter in three different backcrosses. Condominance of the two alleles was shown since approximately equal amounts of the two idiotypes were produced by the population of heterozygous mice. There were many individual heterozygotes, however, in which only one parental idiotype could be detected. In other individuals of the same genotype the other parental idiotype was predominant. In many mice a mixture of the two idiotypes was indicated by doubly sigmoid inhibition curves. The causes for the variation in the expression of the two alleles in genotypically identical mice is discussed.

Similarities among hypervariable segments of immunoglobulin chains

A human lambdaV (Mcg) and a human lambdaII (Vil) myeloma protein have identical sequences in their first hypervariable segments although they differ at 21 positions throughout the variable region. If a different structural gene is responsible for each subgroup, the findings favor insertion of information for the hypervariable or complementarity-determining segments.

Constancy of amino-terminal amino-acid sequences of antibodies of defined specificity and shared idiotype from individual inbred mice

Amino-terminal amino-acid sequences were determined for the heavy (H) chains of anti-p-azophenylarsonate antibodies with shared idiotype, isolated from nine individual A/J mice. Mice chosen for investigation were those producing high titers of antibody with the cross-reactive idiotype. The antibodies were further enriched for the idiotype by isoelectric focusing. The H chains are largely or entirely unblocked at the N-terminus and appear by sequence analysis to be greatly restricted in heterogeneity. All N-terminal sequences were found to be identical. The results suggest that the framework (nonhypervariable) sequence is determined by a germ line gene and is not influenced by somatic processes.

Antibodies to idiotypes of isologous immunoglobulins

To determine if the immunoglobulins (Igs) capable of eliciting the formation of isologous anti-idiotypic antibodies are rare exceptions, BABL/c mice were immunized with five myeloma proteins of BALB/c origin. Anti-idiotypes were produced against all but one. The idiotype of the exception (T15) is remarkably abundant in BALB/c mice, whose unresponsiveness is probably due to tolerance. Nevertheless, prolonged immunization with T15 finally induced the formation of isologous antibodies that seemed largely to be specific for IgA proteins, especially those with k-light-chains; the reactions of a few of these isologous antisera with T15 were slightly inhibited by phosphorylcholine, suggesting that some anti-idiotypes were probably formed even to this unusually prevalent idiotype. It is likelythat under appropriate conditions almost any myeloma protein can elicit isologous anti-idiotypes.

Diversity of light chain variable region sequences among rabbit antibodies elicited by the same antigens

We report the complete variable region sequences of three homogeneous rabbit antibody light chains and the partial sequences of five others. Wehn these are compared to other published rabbit light chain sequences, two regions of markedly increased variability are revealed, which are homologous in position to the first and third hypervariable regions of murine and human myeloma light chains. In addition, there is increased variability among the first three residues at the aminoterminal end. A hypervariable region homologous to that identified at positions 50 to 56 in myeloma light chains is not present in these rabbit antibody light chains. The available three-dimensional models of Fab fragments based on x-ray crystallography indicate that neither the amino-terminal portion of the light chain nor the region homologous to positions 50 to 56 forms a part of the combining site. Comparison of the hypervariable regions among six light chains from antibodies to Type III pneumococcal polysaccharide and among four from antibodies to Type VIII pneumococcal polysaccharide suggests that a large number of different sequences may be found in antibodies specific for these relatively simple antigens. Certain residues outside of the hypervariable regions are invariant in the rabbit light chains and correspond to residues that are required for proper chain folding in human and murine myeloma light chains, indicating that the general conformation of myeloma light chains is the same as that of light chains of elicited antibodies.

An IgM Waldenström with specificity against phosphorylcholine

Anti-phosphorylcholine specificity has recently been shown to occur with relatively high incidence among IgA myeloma proteins secreted by oil-induced plasma cell tumors in the BALB/c strain of mice. A similar screening of human myeloma sera indicates that in man activity for phosphorylcholine is very rare. Among 904 human sera containing IgG, IgA, and IgM M-components only one reacted with phosphorylcholine-containing antigens. This serum was obtained from a patient with macroglobulinemia Waldenström. The active homogeneous protein could be isolated by affinity chromatography using a Sepharose-phosphorylcholine immunoadsorbent. It was an IgM immunoglobulin; the light chains were of the kappa type. The association constant for the reaction with phosphorylcholine was homogeneous and equalled 6.4 times 10-4 l. mol-1 at 25 degrees and 8.1 times 10-4 l. mol-1 at 2 degrees, indicating that the binding reaction is exothermic. The valences of the pentamer IgM, the 7S IgM subunit produced by reduction with cysteine, and the Fab fragment obtained by cleavage with papain were 10, 2, and 1, respectively. By all criteria available for antibody-like binding such as high specificity, restriction of the binding sites to the Fab part of the molecule and correct stoichiometry this IgM exhibits the fundamental characteristics associated with conventionally induced antibodies.