Antigen-specific anti-phosphocholine antibodies: binding site studies

The present investigation extends our initial evaluation of the evolution of antigen selection mechanisms for antibodies of a "single" specificity. The binding sites of 11 mouse anti-PC antibodies produced in response to the bacterium P. morganii or the nematode A. suum were characterized for both hapten and hapten plus carrier specificity. All of the anti-P. morganii HP belonged to the M603 anti-PC antibody family, whereas all the A. suum HP belonged to the M511 family. Of the eight anti-P. morganii HP, six exhibited a fine specificity profile for PC and choline analogues only slightly different from M603 Id+ HP induced by S. pneumoniae and PC-protein. These six and a seventh HP, whose hapten binding profile was unique, were also unusual in showing strong reactivity for a soluble PC containing extract from P. morganii. All three anti-A. suum-specific HP studied in detail had hapten-binding profiles remarkably similar to each other, a finding that is in contrast to M511 Id+ HP to S. pneumoniae and PC-protein. All three HP also showed evidence for preferential binding activity for A. suum, although this was not as dramatic as that seen with the anti-P. morganii HP. These data support our hypothesis that antigen selection of anti-PC antibodies occurs not so much for PC itself as it does for the carrier (microbial) determinants to which PC is attached.

Antigen-specific anti-phosphocholine antibodies: binding site studies

The present investigation extends our initial evaluation of the evolution of antigen selection mechanisms for antibodies of a "single" specificity. The binding sites of 11 mouse anti-PC antibodies produced in response to the bacterium P. morganii or the nematode A. suum were characterized for both hapten and hapten plus carrier specificity. All of the anti-P. morganii HP belonged to the M603 anti-PC antibody family, whereas all the A. suum HP belonged to the M511 family. Of the eight anti-P. morganii HP, six exhibited a fine specificity profile for PC and choline analogues only slightly different from M603 Id+ HP induced by S. pneumoniae and PC-protein. These six and a seventh HP, whose hapten binding profile was unique, were also unusual in showing strong reactivity for a soluble PC containing extract from P. morganii. All three anti-A. suum-specific HP studied in detail had hapten-binding profiles remarkably similar to each other, a finding that is in contrast to M511 Id+ HP to S. pneumoniae and PC-protein. All three HP also showed evidence for preferential binding activity for A. suum, although this was not as dramatic as that seen with the anti-P. morganii HP. These data support our hypothesis that antigen selection of anti-PC antibodies occurs not so much for PC itself as it does for the carrier (microbial) determinants to which PC is attached.

IgA isotype-restricted idiotypes associated with T15 Id+ PC antibodies

Idiotypes are believed to be due to the structural conformation of the variable region of immunoglobulins (Ig). We have found an idiotype (C3-24) that requires both variable and constant regions of the heavy chain to be expressed. C3-24 Id is associated with both the T15 variable region from anti-phosphorylcholine (PC) antibodies and the constant region for the alpha-heavy chain. High titer anti-PC serum from a variety of inbred strains of different Ig haplotypes failed to express C3-24 Id. However, when IgA but not IgG or IgM fractions were isolated from a pool of anti-PC serum from BALB/c mice, more than 70% of the molecules expressed C3-24 Id. The high frequency of the expression of C3-24 Id in IgA anti-PC hybridoma proteins from mice of different Ig haplotypes and in the IgA fraction of normal anti-PC antibodies from BALB/c and presumably other strains of mice suggests that idiotypic determinants produced by the three-dimensional product of VH and CH regions may not be unusual.

The circular dichroism of phosphocholine-specific mouse hybridoma and myeloma proteins: unusual properties of the hybridoma protein 101.6G6

The circular dichroism (CD) spectra of five myeloma and six hybridoma proteins specific for phosphocholine were measured in the 250-310-nm range. The effect on the CD spectra of adding phosphocholine was also examined. The five myeloma proteins all had distinctive native spectra and, except for M603 and W3207, unique changes occurred on ligand binding. The hybridomas were chosen as pairs from each of the three known families of phosphocholine-specific immunoglobulins. Those from the T15 or M603 families resembled the appropriate prototype. However, the proteins from the M167 family were all distinctively different in their CD properties. In particular, the hybridoma protein 101.6G6 showed large CD changes on hapten binding and values for the association constant for phosphocholine of 1.1 X 10(5) M-1 and of 5.8 X 10(2) M-1 for acetylcholine were obtained by CD spectrophotometric titration. The CD properties of the proteins are interpreted in the light of the sequence data so far available, including the possible role of the D-segment.

T15 D region germ line amino acid sequences distinguished by monoclonal anti-idiotope antibody

Monoclonal antibody NL16, prepared with phosphorylcholine (PC)-binding myeloma protein C.BBPC3 (C3), identified an idiotope (C3-16 Id) that was present on T15 IdX+ myeloma proteins (MP) C3, T15, and H8, but not the T15 IdX- MP M167 and M603. The binding of C3 to NL16 is PC inhibitable, indicating that C3-16 Id is site associated. Inhibition studies with PC-specific hybridoma proteins (HP) demonstrated that the T15-type L chain VK22 and elements of the H chain were required for C3-16 Id expression. Studies of amino acid sequences of these PC-binding HP and MP showed that VK22+, T15 IdX+ HP, and MP that use the T15 D region (YYGSS) sequences were always C3-16 Id+. However, the reverse was not true, because all but one VK22+, T15 IdX+ HP with D region sequence changes were C3-16 Id-. This suggested that NL16 defined a specificity mainly determined by the D region of the H chain. A direct test of this hypothesis with heterologous heavy/light chain recombinant molecules obtained from C3-16 Id+ and C3-16 Id- HP of known sequence, showed that the D region was critical to idiotope expression. Additionally, an examination of the amino acid sequences of VK22+, T15 IdX- HP, HPCG14, and HPCM6 suggest that profound changes in the D region may also alter the expression of T15 IdX (an Id defined by a multispecific antiserum from A/He mice). The C3-16 Id+ was found in anti-PC serum of most Ig haplotype-inbred strains except for CBA/J, C3H, and PL, which are all of the Igh-Cj haplotype. Amino acid sequences of PC-binding CBA and PL HP showed marked changes in the D region from the T15 type, and this may account for the C3-16 Id- character of Igh-Cj strains.

T15 D region germ line amino acid sequences distinguished by monoclonal anti-idiotope antibody

Monoclonal antibody NL16, prepared with phosphorylcholine (PC)-binding myeloma protein C.BBPC3 (C3), identified an idiotope (C3-16 Id) that was present on T15 IdX+ myeloma proteins (MP) C3, T15, and H8, but not the T15 IdX- MP M167 and M603. The binding of C3 to NL16 is PC inhibitable, indicating that C3-16 Id is site associated. Inhibition studies with PC-specific hybridoma proteins (HP) demonstrated that the T15-type L chain VK22 and elements of the H chain were required for C3-16 Id expression. Studies of amino acid sequences of these PC-binding HP and MP showed that VK22+, T15 IdX+ HP, and MP that use the T15 D region (YYGSS) sequences were always C3-16 Id+. However, the reverse was not true, because all but one VK22+, T15 IdX+ HP with D region sequence changes were C3-16 Id-. This suggested that NL16 defined a specificity mainly determined by the D region of the H chain. A direct test of this hypothesis with heterologous heavy/light chain recombinant molecules obtained from C3-16 Id+ and C3-16 Id- HP of known sequence, showed that the D region was critical to idiotope expression. Additionally, an examination of the amino acid sequences of VK22+, T15 IdX- HP, HPCG14, and HPCM6 suggest that profound changes in the D region may also alter the expression of T15 IdX (an Id defined by a multispecific antiserum from A/He mice). The C3-16 Id+ was found in anti-PC serum of most Ig haplotype-inbred strains except for CBA/J, C3H, and PL, which are all of the Igh-Cj haplotype. Amino acid sequences of PC-binding CBA and PL HP showed marked changes in the D region from the T15 type, and this may account for the C3-16 Id- character of Igh-Cj strains.

The effects of idiotype on the ability of IgG1 anti-phosphorylcholine antibodies to protect mice from fatal infection with Streptococcus pneumoniae

Anti-phosphorylcholine (PC) antibodies of the mouse are found in three different idiotype families: T15, M603 and M511. These subgroups exhibit different specificities for PC analogs and utilize light chains of different VL subgroups. In this study we have found that IgG1 antibodies of the T15 idiotype are much more protective against pneumococcal infection than IgG1 antibodies of the M511 or M603 idiotypes. This finding provides additional evidence that the T15 VH and VL genes may have evolved to protect mice from infection with PC-bearing pathogens.

Anti-idiotypic regulation of an insulin-reactive T cell clone

A series of MHC-restricted, bovine-insulin-(BI) reactive T cell clones were generated. The specificity of one group was shown to be for an insulin A-chain loop determinant; the other group apparently demonstrated specificity of a B-chain determinant and/or amino acid residue A4. Guinea pig anti-idiotypic antisera were prepared against two idiotypically related BI monoclonal antibodies of similar A-chain loop specificity. These reagents were able to modulate the antigen-specific proliferation of an insulin-reactive, A-chain loop-specific T cell clone. Because the monoclonal antibodies and the T cell clone recognize a similar molecular domain of the insulin molecule, these data suggest that the anti-idiotypic sera mimic an insulin-like determinant, perhaps by bearing an "internal image" of the antigen and thereby interfering with T cell antigen recognition. Further, these results suggest that such reagents may be useful in characterization of T cell antigen receptor specificity and lend further credence to the concept of idiotypic-anti-idiotypic regulation of the immune response.

Anti-idiotypic regulation of an insulin-reactive T cell clone

A series of MHC-restricted, bovine-insulin-(BI) reactive T cell clones were generated. The specificity of one group was shown to be for an insulin A-chain loop determinant; the other group apparently demonstrated specificity of a B-chain determinant and/or amino acid residue A4. Guinea pig anti-idiotypic antisera were prepared against two idiotypically related BI monoclonal antibodies of similar A-chain loop specificity. These reagents were able to modulate the antigen-specific proliferation of an insulin-reactive, A-chain loop-specific T cell clone. Because the monoclonal antibodies and the T cell clone recognize a similar molecular domain of the insulin molecule, these data suggest that the anti-idiotypic sera mimic an insulin-like determinant, perhaps by bearing an "internal image" of the antigen and thereby interfering with T cell antigen recognition. Further, these results suggest that such reagents may be useful in characterization of T cell antigen receptor specificity and lend further credence to the concept of idiotypic-anti-idiotypic regulation of the immune response.

The role of a novel VH sequence (V11) in the formation of anti-phosphocholine antibodies

The immune response to phosphocholine (PC) in mice is highly restricted. Most anti-PC antibodies use heavy-chain variable-region (VH) sequences derived from single VH gene segment, V1. In order to investigate whether a highly homologous VH gene segment, V11, could contribute to the formation of PC-binding antibodies, we carried out chain recombination experiments with M47A, a non-PC binding myeloma protein whose H-chain is encoded by the V11 gene segment, and two PC-binding antibodies, HP101.6G6 (HP6G6) and M511. The H-chains from the non-PC-binding myeloma protein, M47A, formed a functional PC-binding site when paired with L-chains from both PC-binding antibodies. These results suggest that a second VH gene segment, V11, could theoretically be used to form PC-binding antibodies. In addition, these results provide direct evidence that a single H-chain can be used in combinatorial association with different L-chains to form antibodies of differing specificities.

Idiotypes of anti-phosphocholine antibodies: structural correlates

Phosphocholine-specific antibodies in mice are composed of three families of antibodies, the T15, the M603 and the M511, which are constructed by combinatorial association of a VH4 H chain and one of three different L chains, VK22, VK8 and VK24, respectively. Antiidiotypic antisera can be generated which (1) recognize all members of a family, i. e. anti-T15 IdX, anti-M603 IdX and anti-M511 IdX, (2) distinguish between members of a family, e. g. A/J anti-T15, or (3) recognize determinants on only a single anti-PC antibody. Consideration of protein sequences and L-chain polymorphisms and analysis of chain recombination experiments among Id-positive and -negative antibodies revealed that IdX are determined by the L chain. A similar approach demonstrated that the Id determinant defined by the A/J anti-T15 is dependent upon the L chain and the D region of the H chain.

Immunoglobulin A-mediated hepatobiliary transport constitutes a natural pathway for disposing of bacterial antigens

The possibility that hepatobiliary transport of immunoglobulin A (IgA) immune complexes might eliminate bacterial antigens was investigated in mice with pneumococcal type III capsular polysaccharide and C carbohydrate and corresponding monoclonal antibodies. Although all isotypes of antibody caused uptake by the liver, only IgA, but not IgG or IgM, antibodies transported these substances into bile where they were detected in the form of immune complexes and as free antigens. Small doses (10 micrograms or less) of passively administered IgA antibody were sufficient to induce measurable transport of capsular polysaccharide into bile. Transport of C carbohydrate was significantly correlated with the level of naturally occurring IgA antibodies specific for the phosphocholine determinant, but not with IgM or IgG antibodies. These results suggest that the continual process of hepatic uptake of circulating polymeric IgA may function to eliminate bacterial macromolecular products that are not readily susceptible to other mechanisms of disposal.

Idiotypes on monoclonal antibodies to bovine insulin. I. Two public idiotypes on anti-bovine insulin hybridomas define idiotypically distinct families of hybridomas

We used isoelectric focusing (IEF) to show that individual mice responding to bovine insulin (BI) present complex spectrotypes that are not conserved between individuals. Competition of 125I-BI-reactive bands with cold BI or cold pork insulin (PI), showed that the majority of the antibody response is sensitive to the two amino acid difference between BI and PI. This difference resides in the three amino acid intrachain disulfide-bonded A-loop. To begin dissection of the antibody response to BI, we prepared a panel of 30 monoclonal antibodies against insulin. Anti-idiotypic sera were produced in guinea pigs against seven of these hybridoma proteins (HP), and two, anti-5. 10C6 and anti-5.2B8, were found to define public idiotypes. The level of the 5.10C6 idiotype is controlled by genes linked to the Igh locus. Both the G.P. anti-5.10C6 and G.P. anti-5.2B8 were found to define distinct groups of idiotypically related HP. The 5.10C6 idiotype group contains three closely related members, 5.10C6, 5.5F10, and 5.4C5, which are shown to bear the same L chain by IEF. The 5.2B8 idiotype group has six members that are less closely related, defined by inhibition solid phase RIA. The two most closely related members of this family, 5.2B8 and 5.3C6, possess co-focusing L chains. Within each idiotype group, however, members were found that bind to distinct determinants on insulin. Four of the members of the 5.2B8 idiotype group appear to bind overlapping determinants on insulin that define a topographic region that includes the three amino acid A-loop. Two other HP that have been shown to bind the A-loop do not bear determinants that cross-react with the G.P. anti-5.2B8 antiserum.

Idiotypes on monoclonal antibodies to bovine insulin. I. Two public idiotypes on anti-bovine insulin hybridomas define idiotypically distinct families of hybridomas

We used isoelectric focusing (IEF) to show that individual mice responding to bovine insulin (BI) present complex spectrotypes that are not conserved between individuals. Competition of 125I-BI-reactive bands with cold BI or cold pork insulin (PI), showed that the majority of the antibody response is sensitive to the two amino acid difference between BI and PI. This difference resides in the three amino acid intrachain disulfide-bonded A-loop. To begin dissection of the antibody response to BI, we prepared a panel of 30 monoclonal antibodies against insulin. Anti-idiotypic sera were produced in guinea pigs against seven of these hybridoma proteins (HP), and two, anti-5. 10C6 and anti-5.2B8, were found to define public idiotypes. The level of the 5.10C6 idiotype is controlled by genes linked to the Igh locus. Both the G.P. anti-5.10C6 and G.P. anti-5.2B8 were found to define distinct groups of idiotypically related HP. The 5.10C6 idiotype group contains three closely related members, 5.10C6, 5.5F10, and 5.4C5, which are shown to bear the same L chain by IEF. The 5.2B8 idiotype group has six members that are less closely related, defined by inhibition solid phase RIA. The two most closely related members of this family, 5.2B8 and 5.3C6, possess co-focusing L chains. Within each idiotype group, however, members were found that bind to distinct determinants on insulin. Four of the members of the 5.2B8 idiotype group appear to bind overlapping determinants on insulin that define a topographic region that includes the three amino acid A-loop. Two other HP that have been shown to bind the A-loop do not bear determinants that cross-react with the G.P. anti-5.2B8 antiserum.

Resistance to Streptococcus pneumoniae is induced by a phosphocholine-protein conjugate

Previous studies demonstrated that naturally occurring antibodies to the pneumococcal cell wall hapten phosphocholine (PC) are important for the survival of mice against infection with Streptococcus pneumoniae, and that passively administered hybridoma antibody to PC results in added resistance. To determine if a PC-protein conjugate could elicit protective levels of anti-PC antibody, mice were immunized with PC-keyhole limpet hemocyanin (KLH) and tested for their ability to resist challenge with virulent S. pneumoniae. PC-KLH-immunized mice were observed to be resistant to 10- to 1000-fold more organisms than unimmunized control animals. The levels of protection were comparable to those induced with capsular polysaccharide antigens, but had the advantage of not being type-specific; immunization with PC-KLH protected mice against both type 1 and type 3 organisms. The induced immunity appeared to be antibody-mediated; it could be passively transferred with immune serum, and absorption of the immune serum with PC-Sepharose removed its protective capacity. Anti-PC antibodies in the serum of immunized mice were primarily IgM and IgG3 and possessed predominantly the T15 idiotype. Antibodies with these particular isotypes and this idiotype also arise after immunization with heat-killed rough pneumococci and recently were shown to be important in the resistance of mice to pneumococcal infection.

Resistance to Streptococcus pneumoniae is induced by a phosphocholine-protein conjugate

Previous studies demonstrated that naturally occurring antibodies to the pneumococcal cell wall hapten phosphocholine (PC) are important for the survival of mice against infection with Streptococcus pneumoniae, and that passively administered hybridoma antibody to PC results in added resistance. To determine if a PC-protein conjugate could elicit protective levels of anti-PC antibody, mice were immunized with PC-keyhole limpet hemocyanin (KLH) and tested for their ability to resist challenge with virulent S. pneumoniae. PC-KLH-immunized mice were observed to be resistant to 10- to 1000-fold more organisms than unimmunized control animals. The levels of protection were comparable to those induced with capsular polysaccharide antigens, but had the advantage of not being type-specific; immunization with PC-KLH protected mice against both type 1 and type 3 organisms. The induced immunity appeared to be antibody-mediated; it could be passively transferred with immune serum, and absorption of the immune serum with PC-Sepharose removed its protective capacity. Anti-PC antibodies in the serum of immunized mice were primarily IgM and IgG3 and possessed predominantly the T15 idiotype. Antibodies with these particular isotypes and this idiotype also arise after immunization with heat-killed rough pneumococci and recently were shown to be important in the resistance of mice to pneumococcal infection.

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.

Anti-phosphorylcholine antibodies of the T15 idiotype are optimally protective against Streptococcus pneumoniae

In the mouse, most anti-PC antibody is found in one of the three murine anti-PC idiotype families: T15, M603, or M511. The antibodies within each of these idiotypic families have characteristic fine specificities for phosphorylcholine (PC)-analogues. In this paper we compare the ability of hybridoma IgM anti-PC antibodies of the three idiotype families to protect mice from fatal infection with S. pneumoniae. Antibody bearing the T15 idiotype was approximately 8 times as effective as antibody with the M603 idiotype and approximately 30 times as protective as antibody with the M511 idiotype. Reports by others have shown that the heavy chains of virtually all mouse anti-PC antibodies are produced by translocation of a single variable region gene and that the direct translation of this gene (in the absence of somatic mutations) results in heavy chains characteristic of the T15 idiotype. Thus, our findings suggest that the T15 germ line heavy chain variable region gene may have been selected through evolution to code for antibody binding PC-containing pathogens such as S. pneumoniae. Our observations may also explain the existence of regulatory mechanisms that result in maintenance of T15 idiotype expression in murine anti-PC immune responses.

Cross-reactions among carbonic anhydrases I, II, and III studied by binding tests and with monoclonal antibodies

Cross-reactions among carbonic anhydrases (CAs) I, II, and III were studied using a variety of antisera: (1) a rabbit antiserum to bovine CA III, (2) mouse antisera to human CA I, CA II, and CA III; and (3) five monoclonal antibodies prepared by the hybridoma technique using splenocytes from a mouse immunized with human CAs I and II and bovine CA III. Cross-reactions between CAs were readily found by binding assays using these antisera. Human CA I, but not human CA II, inhibited the reaction of the rabbit anti-CA III with its homologous antigen. Mouse antisera to CA I or CA III bound the homologous I or II with nearly as great efficiency as the autologous isozyme and sometimes weakly bound CA III. Mouse antisera to CA III frequently bound CA I or II. These cross-reactions were confirmed by the first use of hybridoma-prepared, monoclonal antibodies to CAs. The mouse monoclonal antibodies to CA isozymes varied in the amount of cross-reactivity among I, III, and III: at one extreme, one monoclonal was highly specific for the autologous CA III; at the other extreme, one monoclonal weakly reacted with some examples of CSs I, II, and III.

Polymorphism in immunoglobulin heavy chains suggesting gene conversion

Complete heavy (H) chain variable region (V region; amino acids 1-118) sequences have been determined for three phosphocholine (PCho)-binding monoclonal antibodies of CBA mouse strain origin. Two of these were found to differ from the sequence of the BALB/c T15 germline VH segment (segment of the V region that includes amino acids 1-95) at four positions but were identical to the allelic form of T15 (C3) found in C57BL. The third VH segment, HP101.6G6 (6G6), was clearly the product of a second, related VH gene, probably the allele of the BALB/c V11 gene, a second member of the P-Cho VH gene family. Thus, more than one VH gene is capable of encoding heavy chains of PCho-binding antibodies. The 6G6 VH segment differs from VII at seven positions; four of these distinguishing amino acids are encoded in other membranes of the PCho VH gene family. We postulate that the origin of the 6G6 VH sequence can most easily be explained by a process of gene conversion occurring between the least three members of the PCho VH family.

Clonotypes of anti-phosphocholine antibodies induced with Proteus morganii (Potter). II. Heterogeneity, class, and idiotypic analyses of the repertoires in BALB/c and A/HeJ mice

The heterogeneity of the PC-specific IgG response of Proteus morganii (Potter) was systematically analyzed. Serum samples from individual mice were focused in paired adjacent tracks, PC-specific antibodies were detected with 125I-PC-RNase, and the resulting autoradiographs were examined for co-focusing bands. Both the number of different antibody band groups and their frequency of expression were determined. Varying qualitatively from simple to complex, the spectrotypes of 38 BALB/c and 19 A/HeJ each appeared unique. However, after thorough analysis for co-focusing bands. It was evident that each spectrotype reflected a unique combination of shared band groups rather than numerous uniquely focusing band groups. The responses of A/HeJ and BALB/c showed striking similarities qualitatively in the appearance of individual spectrotypes. The heterogeneity of the two strains was also similar quantitatively. The basis for this finite though complex heterogeneity was examined by in situ subclass analysis after IEF and idiotype analysis of IEF bands by using antibodies purified from individual BALB/c and A/HeJ. Each mouse primarily expressed IgG3, and antibody bands of this subclass ranged from pI of 6.75 to 8.2. IgG1-positive bands ranged from pI of 6 to 7. Minimal amounts of IgG2 and IgM were detected. In comparisons of individual mice, there was more heterogeneity apparent in the IgG3 subclass than in the IgG1. The idiotype, IdX-M603, was found in both subclasses and also in multiple band groups focusing at different positions within each subgroup. Possible explanations for this heterogeneity among these idiotypically related antibodies are discussed.

Clonotypes of anti-phosphocholine antibodies induced with Proteus morganii (Potter). II. Heterogeneity, class, and idiotypic analyses of the repertoires in BALB/c and A/HeJ mice

The heterogeneity of the PC-specific IgG response of Proteus morganii (Potter) was systematically analyzed. Serum samples from individual mice were focused in paired adjacent tracks, PC-specific antibodies were detected with 125I-PC-RNase, and the resulting autoradiographs were examined for co-focusing bands. Both the number of different antibody band groups and their frequency of expression were determined. Varying qualitatively from simple to complex, the spectrotypes of 38 BALB/c and 19 A/HeJ each appeared unique. However, after thorough analysis for co-focusing bands. It was evident that each spectrotype reflected a unique combination of shared band groups rather than numerous uniquely focusing band groups. The responses of A/HeJ and BALB/c showed striking similarities qualitatively in the appearance of individual spectrotypes. The heterogeneity of the two strains was also similar quantitatively. The basis for this finite though complex heterogeneity was examined by in situ subclass analysis after IEF and idiotype analysis of IEF bands by using antibodies purified from individual BALB/c and A/HeJ. Each mouse primarily expressed IgG3, and antibody bands of this subclass ranged from pI of 6.75 to 8.2. IgG1-positive bands ranged from pI of 6 to 7. Minimal amounts of IgG2 and IgM were detected. In comparisons of individual mice, there was more heterogeneity apparent in the IgG3 subclass than in the IgG1. The idiotype, IdX-M603, was found in both subclasses and also in multiple band groups focusing at different positions within each subgroup. Possible explanations for this heterogeneity among these idiotypically related antibodies are discussed.

Anti-phosphocholine hybridoma antibodies. II. Functional analysis of binding sites within three antibody families

The present investigation extends our immunochemical characterization of binding site heterogeneity among a large series of monoclonal anti-phosphocholine (PC) antibodies. Hybridoma proteins (HP) from eight genetically distinct strains are included in this study, yet no strain specific characteristics are observed. These HP, as previously shown (5), are divided into three well-defined families based on public or family-specific Id and L chain isotypes characteristic of three PC-binding myeloma proteins: T15, M603, and M511. All antibodies exhibited some degree of inter- or intra-family heterogeneity, or both. Some of this intra-family diversity was reflected by differential reactivity for PC when attached to three different carriers. In spite of this, the specificity profiles for hapten analogues of PC, as measured by hapten inhibition of binding, were the same for all members of the T15 family. Altering the carrier had no effect, thus suggesting that the binding site pocket for PC is essentially preserved, whereas that for carrier is variable. Similar conclusions were reached for most of the M603 HP, although the binding site is different from the T15 HP. The M511 HP stand in sharp contrast to the HP in the other two families because their binding sites exhibit extensive variability. The independence in reactivity for PC and PC plus carrier offers a rational explanation for idiotypic and/or structural heterogeneity within a family. More importantly it suggests interesting strategies for diversification within one group of antibodies.

Altered idiotype response to phosphocholine in mice bearing an x-linked immune defect

The x-linked CBA/N defect results in an altered idiotype expression among the anti-phosphocholine (PC) antibodies produced after antigenic challenge with the thymic dependent antigen PC-KLH but does not preclude the response to this hapten as previously suggested. The majority of immune-defective F1 male mice can be divided into 2 groups based on their T15 idiotype profile. Group 1 mice fail to produce anti-PC antibodies bearing the T15 idiotype in either a primary or secondary response, whereas group 2 mice produce low levels of T15 idiotype; however, this idiotype often appears only after secondary immunization. These responses are distinct from the anti-PC response of normal F1 females, which is predominantly of the T15 idiotype. In addition to the altered idiotype expression, F1 male mice exhibited a greatly reduced primary anti-PC response compared to normal mice, and secondary responses were approximately one-third that of normal mice. The delayed expression of anti-PC antibodies in immune defective mice appears to be due to their inability to produce IgM anti-PC antibodies in either a primary or secondary response to PC-KLH.