Posttranslational association of immunoglobulin heavy chain binding protein with nascent heavy chains in nonsecreting and secreting hybridomas

A rat monoclonal antibody specific for immunoglobulin (Ig) heavy chain binding protein (BiP) has allowed the examination of the association of BiP with assembling Ig precursors in mouse B lymphocyte-derived cell lines. The anti-BiP monoclonal antibody immunoprecipitates BiP along with noncovalently associated Ig heavy chains. BiP is a component of the endoplasmic reticulum and binds free intracellular heavy chains in nonsecreting pre-B (mu+, L-) cell lines or incompletely assembled Ig precursors in (H+, L+) secreting hybridomas and myelomas. In the absence of light chain synthesis, heavy chains remain associated with BiP and are not secreted. The association of BiP with assembling Ig molecules in secreting hybridomas is transient and is restricted to the incompletely assembled molecules which are found in the endoplasmic reticulum. BiP loses affinity and disassociates with Ig molecules when polymerization with light chain is complete. We propose that the association of BiP with Ig heavy chain precursors is a novel posttranslational processing event occurring in the endoplasmic reticulum. The Ig heavy chains associated with BiP are not efficiently transported from the endoplasmic reticulum to the Golgi apparatus. Therefore, BiP may prevent the premature escape and eventual secretion of incompletely assembled Ig molecules.

Analysis of the hepatobiliary transport of IgA with monoclonal anti-idiotype and anti-allotype antibodies

The processing and fate of mixed immune complexes is influenced by the antibody isotypes present. The hepatobiliary transport of mixed immune complexes containing the mouse IgA myeloma protein J558 and corresponding monoclonal IgG or IgM anti-J558 idiotype or monoclonal IgG anti-mouse IgA allotype antibodies has been studied. The anti-idiotype or anti-allotype antibodies were radiolabeled and injected into mice with or without mouse polymeric IgA (J558). IgG anti-idiotype antibodies to J558 IgA were selectively transported into bile by J558 IgA. This process occurred with a radiolabeled Fab preparation of the IgG anti-idiotype and was inhibitable with IgA of an irrelevant antigenic specificity. Thus, polymeric IgA influenced the fate of IgA-IgG idiotype-anti-idiotype serum immune complexes. A monoclonal anti-idiotype antibody of the IgM isotype (D8-3) was not selectively transported into bile by itself or as an IgA-IgM complex. A monoclonal IgG antibody (CB5-6) to a mouse allotype determinant in the Fc portion of IgA was not selectively transported into bile. This anti-allotype monoclonal antibody inhibited the hepatobiliary transport of 125I-polymeric J558 IgA and therefore appeared to directly or indirectly block the site in the Fc region of IgA recognized by the hepatic receptor.

In vitro effect of monoclonal anti-idiotype antibodies (anti-M104E) on MOPC 104E myeloma cells

We investigated the effect of three monoclonal anti-idiotype antibodies (anti-M104E) on various functions of MOPC 104E myeloma cells in vitro. The antibodies used were N-20-2 [immunoglobulin M (IgM), BALB/c], SJL18-1 [IgM, BALB/c X SJL F1], and CD3-2 [immunoglobulin G1 (IgG1), BALB/c X A/J F1]. The two IgM antibodies were very efficient in blocking surface M104E IgM as shown by rosette inhibition, whereas the IgG1 isotype was not very effective. The reexpression of surface M104E IgM was different from antibody to antibody. The secretion of M104E IgM by MOPC 104E cells was partially blocked by the two IgM antibodies, but the IgG1 antibody had no effect. All three anti-idiotype antibodies inhibited the stem cell renewal activity of MOPC 104E cells assayed by colony formation assay. On the other hand, in suspension culture, the two IgM antibodies inhibited the growth of MOPC 104E cells in the absence of complement or effector cells of antibody-dependent cellular cytotoxicity, but IgG1 antibody had no effect. The starting tumor inoculum size was critical in the observations of the effects seen on both the growth and the colony-forming activity of MOPC 104E cells. The results of this study show the functional differences between various monoclonal anti-idiotype antibodies and also indicate that some anti-idiotype antibodies can inhibit the growth of MOPC 104E myeloma cells directly without any help of complement or effector cells of antibody-dependent cellular cytotoxicity.

Induction of germ-line anti-alpha 1-3 dextran antibody responses in mice by members of the Enterobacteriaceae family

A large panel of enteric organisms was screened for agglutination with a panel of lambda monoclonal antibodies of different heavy chain isotypes specific for alpha 1-3 dextran (DEX). Two strains were initially isolated that were bound by most of the anti-DEX antibodies. One organism, Enterobacter cloacae strain MK7, which was characterized in detail, induced a typical lambda anti-DEX response in Igh-Ca mice that had a fine idiotope profile comparable with that induced by purified B1355S dextran containing alpha 1-3 glucosidic linkages (alpha 1-3-DEX). The determinant on the bacterial surface was shown by binding inhibition with nigerotriose to contain alpha 1-3 linkages. Hyperimmunization with these organisms of normal, athymic (nu/nu), or germ-free mice induced large amounts of IgM antibodies but very little IgG. This is the first description of an organism isolated from the normal gut flora of mice that can be shown directly to be bound by alpha 1-3-DEX antibodies and to induce the typical germ-line response of the DEX family of antibodies.

Induction of germ-line anti-alpha 1-3 dextran antibody responses in mice by members of the Enterobacteriaceae family

A large panel of enteric organisms was screened for agglutination with a panel of lambda monoclonal antibodies of different heavy chain isotypes specific for alpha 1-3 dextran (DEX). Two strains were initially isolated that were bound by most of the anti-DEX antibodies. One organism, Enterobacter cloacae strain MK7, which was characterized in detail, induced a typical lambda anti-DEX response in Igh-Ca mice that had a fine idiotope profile comparable with that induced by purified B1355S dextran containing alpha 1-3 glucosidic linkages (alpha 1-3-DEX). The determinant on the bacterial surface was shown by binding inhibition with nigerotriose to contain alpha 1-3 linkages. Hyperimmunization with these organisms of normal, athymic (nu/nu), or germ-free mice induced large amounts of IgM antibodies but very little IgG. This is the first description of an organism isolated from the normal gut flora of mice that can be shown directly to be bound by alpha 1-3-DEX antibodies and to induce the typical germ-line response of the DEX family of antibodies.

Developmentally controlled expression of immunoglobulin VH genes

Although antibody diversity arises mainly from apparently random combinatorial and somatic mutational mechanisms acting upon a limited number of germline antibody genes, the antibody repertoire develops in an ordered fashion during mammalian ontogeny. A series of early pre-B and B-lymphocyte cell lines were examined to determine whether an ordered rearrangement of gene families of the variable region of immunoglobulin heavy chains (VH) may be the basis for the programmed development of the antibody response. The results indicated that the VH repertoire of fetal B-lineage cells is largely restricted to the VH 7183 gene family and that subsequent recruitment of additional VH gene families occurs during neonatal development. These results have important implications in understanding the ontogeny of immune function.

Preferential utilization of the most JH-proximal VH gene segments in pre-B-cell lines

The most JH-proximal VH gene segments are used highly preferentially to form VHDJH rearrangements in pre-B-cell lines. This result demonstrates that the rate at which immunoglobulin VH gene segments recombine is influenced by their chromosomal organization, and that the initial repertoire of VH genes expressed in pre-B cells is strikingly different from that seen in mature populations.

Analysis of the reactivity of four anti-mouse IgM allotype antibodies with mu+ B lineage cells at various stages of differentiation

We have used two rat monoclonal antibodies (Mab) (Bet-1 and 331.12), a mouse Mab (AF6-78.25), and an alloantiserum (SJA anti-BAB/14) in two-color immunofluorescence analysis and enzyme-linked immunosorbent assays to examine the expression of IgM allotypes at various stages of mouse B cell development, especially at the pre-B cell stage. In agreement with findings previously reported by others, these antibodies displayed the patterns of allotypic reactivity with IgM+ B cells and plasma cells from the appropriate strains of mice: Bet-1 antibody is specific for a allotype, AF6-78.25 and SJA anti-BAB/14 for b allotype, and 331.12 for both a and b allotypes but not e allotype. These antibodies, however, did not react with isolated mu-heavy chains prepared from secreted molecules or synthesized in situ by normal pre-B cells or pre-B cell-derived hybridomas. The requirement of light chain participation in the expression of IgM allotypic determinant(s) was additionally suggested by analysis of a fetal liver-derived hybridoma (F1-26-11) that has been shown to secrete IgM heteromolecules composed of C57BL/6-derived mu-chain and BALB/c-derived kappa-chains. In contrast to the nonreactivity with C57BL/6 mu-only pre-B cell-derived hybridomas, all three antibodies with specificity for the b allotype (AF6-78.25, SJA anti-BAB/14, and 331.12) reacted with this particular hybridoma. After treating surface IgM molecules on B lymphocytes with papain to cleave Fab fragments, the b allotype reactivity of AF6-78.25 mouse Mab, but not 331.12 rat Mab, disappeared, whereas the a allotype reactivities of two rat Mab (Bet-1, 331.12) were not altered. These results suggest that the IgM allotypic epitopes defined by these antibodies appear to be sterically dependent on the assembly of the whole IgM molecules, and rat Mab 331.12 and mouse Mab AF6-78.25 define two separate b allotype specificities, one on the Fc portion and the other on the Fab portion of the IgM molecules, respectively.

Analysis of the reactivity of four anti-mouse IgM allotype antibodies with mu+ B lineage cells at various stages of differentiation

We have used two rat monoclonal antibodies (Mab) (Bet-1 and 331.12), a mouse Mab (AF6-78.25), and an alloantiserum (SJA anti-BAB/14) in two-color immunofluorescence analysis and enzyme-linked immunosorbent assays to examine the expression of IgM allotypes at various stages of mouse B cell development, especially at the pre-B cell stage. In agreement with findings previously reported by others, these antibodies displayed the patterns of allotypic reactivity with IgM+ B cells and plasma cells from the appropriate strains of mice: Bet-1 antibody is specific for a allotype, AF6-78.25 and SJA anti-BAB/14 for b allotype, and 331.12 for both a and b allotypes but not e allotype. These antibodies, however, did not react with isolated mu-heavy chains prepared from secreted molecules or synthesized in situ by normal pre-B cells or pre-B cell-derived hybridomas. The requirement of light chain participation in the expression of IgM allotypic determinant(s) was additionally suggested by analysis of a fetal liver-derived hybridoma (F1-26-11) that has been shown to secrete IgM heteromolecules composed of C57BL/6-derived mu-chain and BALB/c-derived kappa-chains. In contrast to the nonreactivity with C57BL/6 mu-only pre-B cell-derived hybridomas, all three antibodies with specificity for the b allotype (AF6-78.25, SJA anti-BAB/14, and 331.12) reacted with this particular hybridoma. After treating surface IgM molecules on B lymphocytes with papain to cleave Fab fragments, the b allotype reactivity of AF6-78.25 mouse Mab, but not 331.12 rat Mab, disappeared, whereas the a allotype reactivities of two rat Mab (Bet-1, 331.12) were not altered. These results suggest that the IgM allotypic epitopes defined by these antibodies appear to be sterically dependent on the assembly of the whole IgM molecules, and rat Mab 331.12 and mouse Mab AF6-78.25 define two separate b allotype specificities, one on the Fc portion and the other on the Fab portion of the IgM molecules, respectively.

A biological consequence of variation in the site of D-JH gene rearrangement

One mechanism which generates diversity in immunoglobulin variable (V) regions is flexibility in the site of recombination among the constituent genetic elements. Within a specific antibody family (that is, a particular VH-VL combination), variability in V-D-J rearrangement not only leads to sequence diversity at the boundary of the juxtaposed genes, but also enables the total length of the third complementarity-determining region (CDR-3) of the heavy chain to be conserved. We demonstrate here that the junctional diversity inherent in rearranged immunoglobulin genes can have consequences for the biology of the immune system. Sequence analysis of the expressed immunoglobulin genes of idiotypically variant as opposed to conventional B lymphocytes of a dominant antibody family showed that the variant B cells undergo a novel D-JH joining event such that an extra amino acid is inserted into the heavy chain CDR-3. The unique D-region conformation possessed by the variant B cells accounts for previous observations which showed that variant and conventional B cells could be differentially regulated in vivo by an autologous set of idiotope-specific B lymphocytes. Our findings indicate that D-region structure can determine the expression of regulatory idiotopes and suggest that the conservation of heavy-chain CDR-3 length within an antibody family may reflect regulatory as well as functional constraints.

Monoclonal antibodies against protease-sensitive pneumococcal antigens can protect mice from fatal infection with Streptococcus pneumoniae

Monoclonal antibodies were raised against surface determinants of Streptococcus pneumoniae by hyperimmunizing X-linked immunodeficient (xid) CBA/N mice with the heat-killed rough strain R36A. 17 hybridomas produced antibody that bound intact R36A and did not cross-react with phosphocholine, an antigen common in the cell wall of all S. pneumoniae. The antibody produced by at least two of these hybridomas, Xi64 (IgM) and Xi126 (IgG2b), could protect mice from a lethal intravenous challenge of type 3 S. pneumoniae strains WU2 and A66 and of the type 2 strain D39. The minimum amount of antibody required to protect xid mice from 100 WU2 was 4.5 micrograms/mouse for Xi64 and 2.6 micrograms/mouse for Xi126,. Free phosphocholine, C-polysaccharide, and type 3 capsular polysaccharide all failed to inhibit the binding of Xi64 or Xi126 to R36A. These antibodies appeared to bind surface polypeptides, since treatment of R36A with either pepsin or trypsin, or of R36A lysate with trypsin, effectively eliminated the ability of Xi64 and Xi126 to bind antigens in these preparations. Binding studies indicated that these two antibodies recognized different epitopes that were expressed on several but not all serotypes of pneumococci.

Cellular expression of idiotopes defined by monoclonal antibodies

Monoclonal anti-idiotype (Id) antibodies with specificities for determinants related to the antigen-binding sites of 3 BALB/c myeloma proteins, MOPC-460, HOPC-8 and J558, were used to study Id expression on murine lymphocytes. The monoclonal antibodies were shown to react only with Id structures associated with immunoglobulin on B cells. None of these 3 Id nor a VH Id, detected by a monoclonal antibody made against HOPC-8 heavy chain, were found on T cells. These Id were detected on splenic B cells in neonatal mice; the frequencies in normal, nude and germ-free mice were similar: MOPC-460 Id+: 1.05 +/- 1.7/10(4) spleen cells, HOPC-8 Id+: 1.45 +/- 1.2/10(4) and J558: 0.35 +/- 0.6/10(4). Almost all Id+ cells bore surface IgM, a few expressed surface IgG. MOPC-460 Id+ IgG+ cells were mainly gamma 2a+ or gamma 2b+, whereas J558 and HOPC-8 Id+ IgG+ cells were gamma 3+.

Quantitation of complement factor D in human serum by a solid-phase radioimmunoassay

A sensitive solid-phase radioimmunoassay is described which quantitates human D to 1-2 ng/ml. The assay was used to measure the concentration of D in normal and acute-phase sera and sera from individuals with systemic lupus erythematosus. All 3 groups of sera had comparable levels of D with mean values of 1.8, 2.3 and 2.5 micrograms/ml, respectively. Also tested were sera decomplemented in vitro by activators of the classical and alternative pathways. The results indicated that D is not depleted by alternative or classical pathway activation. However, heat inactivation (56 degrees C, 30 min) of serum resulted in almost complete loss of antigenic D.

Isotype specificity of helper T cell clones. Peyer's patch Th cells preferentially collaborate with mature IgA B cells for IgA responses

The nature of the IgA B cell precursors that receive preferential help from selected clones of T helper cells from mouse Peyer's patches (PP Th A) were studied. Activation of the PP Th A clones required the presence of antigen, sheep erythrocytes (SRBC), in a culture system supporting development of antibody-secreting plasma cells. Two types of PP Th A cells were used. Both gave vigorous IgA responses; the first also supported low IgM, and the second low IgM and IgG subclass antibody responses. Removal of sIgA+ B cells from either splenic or PP B cell cultures selectively depleted precursors of IgA antibody producers. Cultures of purified sIgA+ B cells, cloned PP Th A cells and SRBC, selectively yielded IgA antibody producers. Finally, PP Th A cells did not support IgA responses in B cell cultures derived from spleens of young mice (days 1-25), and full IgA responses were not seen until the donor mice were 6-7 wk of age. These results suggest that cloned T helper cells can recognize and collaborate with mature, IgA committed B cells.

The use of monoclonal antibodies as probes of the three-dimensional structure of human complement factor D

The monoclonal antibodies (MAb) were studied for their binding specificities and their effects on the hemolytic and proteolytic activities of human D. One Mab, FD10-1, was obtained from mice immunized with native D; the other, JA4-2, was similarly obtained from mice immunized with BSA coupled to a synthetic nonapeptide (Arg-Ile-Leu-Gly-Gly-Arg-Glu-Ala-Tyr) containing the seven NH2-terminal amino acids of D. By using a PEG-precipitation assay system, lactoperoxidase-iodinated D was precipitated by FD10-1 cell culture supernatant as well as by the purified MAb. Conversely, with the use of the same assay system, neither the JA4-2 cell culture supernatant nor the purified MAb precipitated any significant amount of 125I-D. In contrast, by using a solid-phase binding assay, radiolabeled JA4-2 as well as FD10-1 bound to D-coated wells. In addition, the binding of purified JA4-2 to D-coated wells could be completely inhibited by the nonapeptide, whereas the binding of purified FD10-1 at equivalent concentrations was unaffected. These binding studies correlated with the results of functional assays. FD10-1 was found to inhibit the hemolytic activity of the alternative complement pathway in human serum as well as the cleavage of radiolabeled B by D in the presence of cobra venom factor, whereas JA4-2 had no significant inhibitory effect in either of these assays. These data suggest that the NH2-terminus of native D, like that of other active serine proteases, is buried inside the molecule where it is inaccessible to the bulky JA4-2 MAb.

The use of monoclonal antibodies as probes of the three-dimensional structure of human complement factor D

The monoclonal antibodies (MAb) were studied for their binding specificities and their effects on the hemolytic and proteolytic activities of human D. One Mab, FD10-1, was obtained from mice immunized with native D; the other, JA4-2, was similarly obtained from mice immunized with BSA coupled to a synthetic nonapeptide (Arg-Ile-Leu-Gly-Gly-Arg-Glu-Ala-Tyr) containing the seven NH2-terminal amino acids of D. By using a PEG-precipitation assay system, lactoperoxidase-iodinated D was precipitated by FD10-1 cell culture supernatant as well as by the purified MAb. Conversely, with the use of the same assay system, neither the JA4-2 cell culture supernatant nor the purified MAb precipitated any significant amount of 125I-D. In contrast, by using a solid-phase binding assay, radiolabeled JA4-2 as well as FD10-1 bound to D-coated wells. In addition, the binding of purified JA4-2 to D-coated wells could be completely inhibited by the nonapeptide, whereas the binding of purified FD10-1 at equivalent concentrations was unaffected. These binding studies correlated with the results of functional assays. FD10-1 was found to inhibit the hemolytic activity of the alternative complement pathway in human serum as well as the cleavage of radiolabeled B by D in the presence of cobra venom factor, whereas JA4-2 had no significant inhibitory effect in either of these assays. These data suggest that the NH2-terminus of native D, like that of other active serine proteases, is buried inside the molecule where it is inaccessible to the bulky JA4-2 MAb.

Identification and characterization of an apparent germline set of auto-anti-idiotypic regulatory B lymphocytes

By fusing BALB/c splenic lymphocytes from mice immunized with phosphorylcholine (PC) to an immunoglobulin nonproducing plasmacytoma cell line, a B cell hybridoma was isolated (MM-60) that has been shown by multiple criteria to produce a bona fide auto-anti-(anti-T15 idiotype) antibody. In vivo administration of MM-60 antibody suppressed T15+ anti-PC antibody production in an idiotope-specific manner by activation of an intervening set of anti-T15 B cells. These T15-specific B cells i) appeared to express germline-encoded variable region gene products, ii) developed in parallel to, but independent of, T15+ B cells, and iii) suppressed the anti-PC response in a T cell-independent fashion. Variants of T15+ anti-PC B cells possessing aberrant immunoglobulin heavy chain D region structure escaped from the suppression imposed by this anti-T15 B cell set, suggesting that a function of the heavy chain D region may be to contribute to the formation of molecular target sites for idiotype-directed regulatory cells and/or antibodies. The indigenous nature of these particular populations of anti-idiotypic and anti-(anti-idiotypic) B cells and the ability of their immunoglobulin products to regulate antigen-specific B cells in vivo provides strong supportive evidence for the significant role idiotype-directed network interactions play in regulating specific antibody production during a normal immune response.

Identification and characterization of an apparent germline set of auto-anti-idiotypic regulatory B lymphocytes

By fusing BALB/c splenic lymphocytes from mice immunized with phosphorylcholine (PC) to an immunoglobulin nonproducing plasmacytoma cell line, a B cell hybridoma was isolated (MM-60) that has been shown by multiple criteria to produce a bona fide auto-anti-(anti-T15 idiotype) antibody. In vivo administration of MM-60 antibody suppressed T15+ anti-PC antibody production in an idiotope-specific manner by activation of an intervening set of anti-T15 B cells. These T15-specific B cells i) appeared to express germline-encoded variable region gene products, ii) developed in parallel to, but independent of, T15+ B cells, and iii) suppressed the anti-PC response in a T cell-independent fashion. Variants of T15+ anti-PC B cells possessing aberrant immunoglobulin heavy chain D region structure escaped from the suppression imposed by this anti-T15 B cell set, suggesting that a function of the heavy chain D region may be to contribute to the formation of molecular target sites for idiotype-directed regulatory cells and/or antibodies. The indigenous nature of these particular populations of anti-idiotypic and anti-(anti-idiotypic) B cells and the ability of their immunoglobulin products to regulate antigen-specific B cells in vivo provides strong supportive evidence for the significant role idiotype-directed network interactions play in regulating specific antibody production during a normal immune response.

Fine idiotype analysis of B cell precursors in the T-dependent and T-independent responses to alpha 1-3 dextran in BALB/c mice

In this study BALB/c B cell precursors responsive to the T-independent (TI) type 2 (TI-2) antigen, dextran B1355S (DEX), and the T-dependent (TD) derivative, dextran-Limulus hemocyanin (DEX-Hy) were examined for isotype and idiotope expression using the splenic focus assay. The predominant isotype detected in the TI assay was IgM, while IgA was the predominant isotype expressed in the TD assay. There was also a fourfold increase in the number of foci secreting more than one isotype in the TD assay vs. the TI assay without an overall change in anti-DEX precursor frequency, suggesting that carrier-primed T cells enhance the expression of non-IgM isotypes possibly by increasing the frequency of isotype switching by individual B cell precursors. A panel of distinct monoclonal antiidiotype antibodies (MAIDs) was then used to examine idiotope expression by antibodies secreted in splenic foci responding to DEX and DEX-Hy. This analysis revealed considerable diversity in the idiotope profiles expressed by all isotypes tested. There appeared to be no differences in idiotope diversity among the various isotypes. A similar diversity of idiotope profiles was obtained from both TI and TD splenic foci, indicating that a comparable degree of diversity was associated with the antibodies generated by TI and TD precursors. Idiotype analysis of IgM-IgA-secreting foci with a panel of monoclonal antiidiotope antibodies revealed slight idiotypic differences between the two isotypes secreted in the same focus in about half the cases. These results suggest that somatic variation occurs during the antigen-driven maturation of B cell precursors, within the 15-d time frame of the splenic focus assay, and may be associated with isotype switching.

Analysis of idiotypic heterogeneity in the anti-alpha 1-3 dextran and anti-phosphorylcholine responses using monoclonal anti-idiotype antibodies

Panels of monoclonal anti-idiotype antibodies (MAIDs) specific for individual (IdI) and cross-reactive (IdX) idiotopes were prepared and used to study the expression of these idiotopes on anti-DEX and anti-PC antibodies produced in response to antigenic stimulation in vivo, clonal expression of idiotopes in an in vitro splenic focus assay, and the alterations in the idiotypic profile of these responses after in vivo administration of monoclonal anti-Id antibodies. Using these panels of MAIDs, it was possible to inactivate IdI-bearing B cells both in neonates and adult mice without affecting the responsiveness of IdI- B cells. By contrast, suppression with IdX-specific antibodies resulted in greatly reduced antibody responses. By studying the idiotypic profile of anti-DEX clones in the splenic focus assay, it was shown that IgM, IgG, and IgA antibody Id were diverse and paralleled those expressed in serum. Within some clones there was evidence that idiotope-isotype associations differed, suggesting that V region variants may have been generated within the progeny of a clone following stimulation by dextran. An anti-anti-Id antibody isolated from a BALB/c mouse undergoing a normal immune response to R36A was shown to have a T-cell independent highly idiotope-specific regulatory effect on the T15+ anti-PC response, apparently affecting induction of anti-idiotypic B cells.

Localization of the phosphocholine-binding sites on C-reactive protein by immunoelectron microscopy

C-reactive protein (CRP) was reacted with monoclonal IgG antibody or Fab antibody fragments directed against the phosphocholine- (PC) binding site or a second unrelated site. The resulting immune complexes were viewed by a negative stain immunoelectron microscopy technique. Monoclonal anti-PC-binding site antibody bound to a single epitope on each of the five CRP subunits. The orientation of the PC-binding sites was determined to be slightly medial to one of the planar faces (A-face) of the molecule. The second monoclonal antibody, which was not PC-binding site related, bound to epitopes (one per CRP subunit) that were located slightly lateral to the other planar face (B-face) of the CRP molecule, i.e., opposite of the PC-binding site. Thus, the PC-binding site and the non-PC-binding site are oriented nearly perpendicular but on opposite sides with respect to the plane of the CRP molecule. The functional significance of this configuration is discussed.

Localization of the phosphocholine-binding sites on C-reactive protein by immunoelectron microscopy

C-reactive protein (CRP) was reacted with monoclonal IgG antibody or Fab antibody fragments directed against the phosphocholine- (PC) binding site or a second unrelated site. The resulting immune complexes were viewed by a negative stain immunoelectron microscopy technique. Monoclonal anti-PC-binding site antibody bound to a single epitope on each of the five CRP subunits. The orientation of the PC-binding sites was determined to be slightly medial to one of the planar faces (A-face) of the molecule. The second monoclonal antibody, which was not PC-binding site related, bound to epitopes (one per CRP subunit) that were located slightly lateral to the other planar face (B-face) of the CRP molecule, i.e., opposite of the PC-binding site. Thus, the PC-binding site and the non-PC-binding site are oriented nearly perpendicular but on opposite sides with respect to the plane of the CRP molecule. The functional significance of this configuration is discussed.

Analysis of the anti-alpha 1 leads to 3 dextran response with monoclonal anti-idiotype antibodies

The antibody response to alpha 1 leads to 3 dextran (DEX) in BALB/c mice consists of a family of closely related yet highly heterogeneous molecules. Although these antibodies have been previously characterized both idiotypically and structurally, detailed analysis of responding clones has not been possible using conventional anti-idiotype antibodies. Monoclonal syngeneic and allogeneic anti-idiotype antibodies (MAIDs) specific for anti-DEX antibodies were used in this study to dissect the serum antibody response to DEX in BALB/c mice. The constructed MAIDs showed considerable heterogeneity by isoelectric focusing and by their binding characteristics to a series of DEX specific myeloma and hybridoma proteins. The predominant heavy chain isotype of these MAIDs was gamma 1. These antibodies were used to identify individual idiotypic structures (IdI) on J558, or M104E as well as cross-reactive determinants common to both (IdX). Although both IdX and IdI MAIDs were obtained, IdI specific antibodies were obtained more frequently. BALB/c mice immunized with DEX produced antibodies expressing both IdI but in highly variable amounts. A large percentage of, but not all DEX specific antibody, could be accounted for by IdX bearing antibodies. Suppression of adult and neonatal mice by IdI specific MAIDs was effective with precise elimination of only those clones expressing IdI determinants leaving the total lambda bearing anti-DEX response intact. Suppression of adults and neonates by an IdX specific MAID resulted in a temporary and partial suppression of the total lambda bearing anti-DEX response along with total suppression of the IdX portion of the response. Unlike other systems these monoclonal antibodies produce only suppression, and under a variety of conditions enhancement of anti-DEX responses has not been observed.