Inheritance of an idiotype associated with the immune response of inbred mice to phosphorylcholine

Defining the recognition elements of Lewis Y-reactive antibodies

Antibody response to carbohydrate antigens is often independent of T cells and the process of affinity/specificity improvement is considered strictly dependent on the germinal centers. Antibodies induced during a T cell-independent type 2 (TI-2) response are less variable and less functionally versatile than those induced with T cell help. The antigen specificity consequences of accumulation of somatic mutations in antibodies during TI-2 responses of Marginal Zone (MZ) B cells is a fact that still needs explanation. Germline genes that define carbohydrate-reactive antibodies are known to sculpt antibody-combining sites containing innate, key side-chain contacts that define the antigen recognition step. However, substitutions associated with MZ B cell derived antibodies might affect the mobility and polyspecificity of the antibody. To examine this hypothesis, we analyzed antibodies reactive with the neolactoseries antigen Lewis Y (LeY) to define the residue subset required for the reactive repertoire for the LeY antigen. Our molecular simulation studies of crystallographically determined and modeled antibody-LeY complexes suggests that the heavy-chain germline gene VH7183.a13.20 and the light-chain Vκ cr1 germline gene are sufficient to account for the recognition of the trisaccharide-H determinant Types 1–4, while the specificity for LeY is driven by the CDR3 backbone conformation of the heavy chain and not the side chain interactions. These results confirm that these monoclonals use germline-encoded amino acids to recognize simple carbohydrate determinants like trisaccharide-H but relies on somatic mutations in the periphery of the combining site to modify affinity for LeY through electrostatic interactions that leads to their optimized binding. These observations bring further attention to the role of mutations in T-cell independent antibodies to distinguish self from non-self carbohydrate antigens.

The link between antibodies to OxLDL and natural protection against pneumococci depends on D(H) gene conservation

Germline D_H sequences are required for the generation of natural antibodies reactive to bacterial phosphorylcholine but not for those reactive to self-antigen.

Selection and physiological production of protective natural antibodies (NAbs) have been associated with exposure to endogenous antigens. The extent to which this association depends on germline NAb sequence is uncertain. Here we show that alterations in germline D_H sequence can sever the association between the production of self-reactive NAbs and NAbs that afford protection against a pathogen. In unmanipulated hosts, the availability of the evolutionarily conserved DFL16.1 gene segment sequence profoundly affected the serum levels of NAbs against bacterial phosphorylcholine but not oxidized low-density lipoprotein. Mice with partially altered DFL16.1 sequence could use N nucleotides to recreate the amino acid sequence associated with the classical protective T15 idiotype–positive NAbs, whereas those without DFL16.1 could not. DFL16.1 gene–deficient mice proved more susceptible to challenge with live Streptococcus pneumoniae. Our findings indicate that although production of self-reactive NAbs can be independent of germline D_H sequence, their capacity to provide protection against pathogens cannot. The potential relevance of these findings for the rational design of vaccines is discussed.

The M603 idiotype is lost in the response to phosphocholine in terminal deoxynucleotidyl transferase-deficient mice

The majority of anti-phosphocholine (PC) antibodies induced by the PC epitope in Proteus morganii (PM) express the M603 idiotype (id), which is characterized by an invariant Asp to Asn substitution at the V(H):D(H) junction. To elucidate the molecular basis by which M603-like B cells acquire the mutations resulting in this invariant substitution, we analyzed the immune response to PC-PM in terminal deoxynucleotidyl transferase (TdT) gene knockout (KO) mice. In the absence of TdT, T15-id antibodies comprised 80-100% of the primary response to PC-PM. Less than 10% of the response in wild-type mice is T15-id(+). In TdT KO mice, the secondary response to PC-KLH was higher than in wild-type mice and was dominated by the germ-line T15-id. About 10% of this response, in both TdT KO and wild-type mice, comprised M167-id(+) antibodies. Additionally, none of the functionally rearranged V1/DFL16.1/J(H)1 cDNA isolated from PC-PM-immunized TdT KO mice showed the Asp/Asn substitution characteristic of PC-binding, PC-PM-induced M603-like antibodies. These data indicate that production of M603-id antibody is TdT dependent, while generation of M167-id antibody is TdT independent, and that in the absence of competition from M603-like B cells, T15-id B cells can respond to PC-PM.

T15-idiotype-negative B cells dominate the phosphocholine binding cells in the preimmune repertoire of T15i knockin mice

T15i knockin (KI) mice express a H chain that is encoded by a rearranged T15 VDJ transgene which has been inserted into the J(H) region of chromosome 12. This T15H chain combines with a kappa22-33 L chain to produce a T15-Id+ Ab having specificity for phosphocholine (PC). Inasmuch as T15-Id+ Abs dominate the primary immune response to PC in normal mice, it was surprising to find that 80% of the PC-dextran-binding B cells in unimmunized homozygous T15i KI mice were T15-Id-. Analysis of L chains expressed in these T15-Id-, PC-specific B cells revealed that two L chains, kappa8-28 and kappa19-15, were expressed in this population. The V(kappa) region of these L chains was recombined to J(kappa)5, which is typical of L chains present in PC-specific Abs. When T15i KI mice were immunized with PC Ag, T15-Id+ B cells expanded 6-fold and differentiated into Ab-secreting cells. There was no indication that the T15-Id- B cells either proliferated or differentiated into Ab-secreting cells following immunization. Thus, T15-Id- B cells dominate the PC-binding population, but they fail to compete with T15-Id+ B cells during a functional immune response. Structural analysis of T15H:kappa8-28L and T15H:kappa19-15L Abs revealed L chain differences from the kappa22-33 L chain which could account for the lower affinity and/or avidity of these Abs for PC or PC carrier compared with the T15-Id+ T15H:kappa22-33L Ab.

Neo-self antigens and the expansion of B-1 cells: lessons from atherosclerosis-prone mice

The pathogenesis of atherosclerosis involves an inflammatory process that is modulated by the immune system, and within these complex responses we have discerned a possible role for an archetypic B-1 clone. We speculate that due to their immunogenicity and in vivo distribution the "neo"-self determinants created in oxidatively modified LDL are highly stimulatory for certain B-1 cell clones. These neo-self determinants, which can be created chemically, by somatic processes, may in fact represent the molecular analogues of somatic maturation, or even aging. These changes, including those on non-protein antigens induced by oxidative metabolism, amongst others, create neo-determinants against which the host no doubt can not develop rigorous B-cell tolerance. The onset of expression of these oxidative neo-determinants relatively late in development may well serve a useful function for the highly evolved mammalian immune system, as targeting by evolutionarily selected B-1 clones may facilitate the amplification of other useful antibody-mediated physiologic functions. As in the case of the T15 clone, these antibodies may aid in protection against common microbial pathogens. Hence we postulate that during the evolution of the adaptive immune system the neo-self antigenic milieu may have been exploited for the natural selection of primordial clonal specificities. The T15 B-1 clone may then illustrate a common paradigm in which there has been natural selection based on utility for the defense of the individual from environmental threats, as well as for possible "housekeeping" role(s) and the maintenance of cellular homeostasis.

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.

Transient dominance of the early primary immune response by a highly conserved B-cell clone that is distinguished by its lack of memory, high threshold of activation, and a high affinity

We establish here that the very early primary response to the hapten phthalate (Xmp) is distinguished by a restricted heterogeneity with over 80% of the anti-Xmp antibodies expressing a single well-defined cross-reactive idiotype (CRIXmp-1) associated with a previously described highly conserved clonotype that is expressed by most inbred strains of mice and many outbred mouse populations as well. The characteristic early dominance of this one clonotype in the primary response is transient. While the CRIXmp-1 clonotype is present later in the primary and throughout the secondary response, it represents only a very small proportion of the total anti-Xmp antibody population at these times. The early dominance of the single clonotype is rapidly replaced by a heterogeneous population of antibodies. Differential activation thresholds for the primary response clonotype (CRIXmp-1) and secondary response clonotypes, and the failure of the dominant primary response clonotype to expand in the secondary response (i.e., absence of memory) suggest the presence of two distinct B-cell lineages.

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.

Human anti-pneumococcal polysaccharide antibodies are secreted by the CD5- B cell lineage

To determine whether human antibody responses to T cell-independent pneumococcal polysaccharide antigens are derived from CD5+ or CD5- B cells, we utilized an ELISPOT assay to detect individual anti-polysaccharide antibody-secreting cells. Human anti-type IV pneumococcal polysaccharide antibody-secreting cells were found in the CD5- B cell subpopulation. An EBV transformed anti-pneumococcal antibody-secreting B cell line was also CD5-. The ontogeny of CD5 expressing B cells correlated with the age at which polysaccharide responsiveness is acquired (generally around age 2 years in humans). The CD5- B cell subset represents only 25-30% of the B cells in young children, but this fraction increases throughout childhood to a plateau of 70-80% of the B cells in adults. These results support the hypothesis that the developmental change in responsiveness to T cell-independent polysaccharide antigens in humans is associated with maturation of the CD5- B cell subset.

Comparison of junctional diversity in the neonatal and adult immunoglobulin repertoires

Junctional diversity in immunoglobulin (Ig) from an adult mouse contributes significantly to the size of the final Ig repertoire. In adult pre-B cells, N region addition and deletion of nucleotides form coding regions produces very heterogenous CDR3 sequences. In contrast, Ig from fetal and newborn mice show very restricted junctional diversity. The reasons for this are: (a) the lack of N regions; and (b) the predominance of certain junctional sequences. These common junctional sequences all appear to occur by targeted rearrangement to short stretches of sequence homology near the ends of the segments to be joined. Targeted rearrangement may play a role in the overexpression of certain Vh genes early in ontogeny. These non-random junctional sequences in the neonate will reproducibly create certain Ig, for example, the dominant T15 anti-PC antibodies. Thus the immune system first creates a small repertoire of predictable Ig sequences. To the extent that these Ig are expressed in long-lived B cells, these early Ig sequences may persist in the adult. Superimposed upon this early repertoire is an enormously diverse adult Ig repertoire.

Selection of antigen-specific, idiotype-positive B cells in transgenic mice expressing a rearranged M167-mu heavy chain gene

Flow cytometric analysis of antigen-specific, idiotype-positive (id+), B cell development in transgenic mice expressing a rearranged M167-mu gene shows that large numbers of phosphocholine (PC)-specific, M167-id+ B cells develop in the spleen and bone marrow of these mice. Random rearrangement of endogenous V kappa genes, in the absence of a subsequent receptor-driven selection, should give rise to equal numbers of T15- and M167-id+ B cells. The observed 100-500-fold amplification of M167-id+ B cells expressing an endogenous encoded V kappa 24]kappa 5 light chain in association with the M167 VH1-id transgene product appears to be an antigen driven, receptor-mediated process, since no amplification of non-PC-binding M167 VH1/V kappa 22, T15-id+ B cells occurs in these mu-only transgenic mice. The selection and amplification of antigen-specific, M167-id+ B cells requires surface expression of the mu transgene product; thus, no enhancement of M167-id+ B cells occurs in the M167 mu delta mem-transgenic mice, which cannot insert the mu transgene product into the B cell membrane. Surprisingly, no selection of PC-specific B cells occurs in M167-kappa-transgenic mice although large numbers of B cells expressing a crossreactive M167-id are present in the spleen and bone marrow of these mice. The failure to develop detectable numbers of M167-id+, PC-specific B cells in M167-kappa-transgenic mice may be due to a very low frequency of M167-VH-region formation during endogenous rearrangement of VH1 to D-JH segments. The somatic generation of the M167 version of a rearranged VH1 gene may occur in less than one of every 10(5) bone marrow B cells, and a 500-fold amplification of this M167-Id+ B cell would not be detectable by flow cytometry even though the anti-PC antibody produced by these B cells is detectable in the serum of M167-kappa-transgenic mice after immunization with PC.

Fine specificity and isotype expression of anti-PC antibodies in BALB/c, MRL/Mp-lpr/lpr, and -(+)/+ mice at different ages

The MRL/Mp congenic mouse strains develop autoimmune disease with age. We have investigated age- and autoimmune-related changes in fine specificity, isotype spectra and T15 idiotype expression of the anti-phosphorylcholine (PC) response in BALB/c, MRL/Mp- + and -lpr congenic mice and in (BALB/c x MRL/Mp-lpr) F1 hybrids. Two groups of anti-PC antibodies with distinct fine specificity are elicited in the memory response. Group I antibodies recognize the PC moiety and express the T15 idiotype. Antibodies of group II are specific for phenyl-phosphorylcholine and are found predominantly in the memory response. In the MRL/Mp-lpr and - + strains only a minor population of antibodies expresses the T15 idiotype at all ages. However, a third group of antibodies was observed which binds to PC-coated proteins and to Diplococcus pneumoniae R-36A. This binding was not inhibited by PC-chloride and appeared mainly in the memory response at old age. The isotype distribution among anti-PC antibodies was similar in all strains analysed. In the initial response primarily mu, gamma 3 and gamma 1 isotypes were produced, while in the memory response gamma 1 was dominant. Thus autoimmune defects and ageing result in altered anti-PC antibody and idiotype profile, probably related to altered states in both the T- and B-cell compartments.

Identification and surface phenotypic characterization of phosphorylcholine-specific idiotype-bearing T cells

We have employed two-color staining with monoclonal anti-T-cell markers and a broadly reactive, nonbinding site monoclonal anti-idiotype to permit direct visualization of idiotype-bearing T cells in mouse lymph nodes following immunization with phosphorylcholine. Double positive cells peak in incidence on Days 8 to 12, as 17% of total idiotype+ cells but as only 0.7% of T cells. Such cells are antigen-specific, appearing in peripheral lymph nodes only following phosphorylcholine challenge. While Lyt-2+ and L3T4+ subsets are represented and both subsets reexpress the idiotypic determinant following its enzymatic removal, the L3T4+ subset represents the majority of idiotype+Thy-1+ cells. These findings raise the possibility that antigen-specific receptors on T and B cells, encoded by entirely different genetic information, may exhibit similarities in tertiary structure in portions of the molecules not directly involved in antigen binding. This is the first determination of the phenotype and chronology of appearance of idiotype-bearing normal T cells following immunization. It is consistent with previous reports of functionally defined idiotype-bearing T cells and provides direct support for the existence of such cells.

Coexistence of antigen-specific and idiotype-specific suppressor T cells in mice injected neonatally with a mixture of antigen and anti-idiotype antibody

Specific tolerance to phosphorylcholine (PC) can be induced in BALB/c mice by neonatal injection with either pneumococcal C-polysaccharide (PnC) containing PC or anti-TEPC-15 idiotype (T15id) antibody which recognizes the predominant idiotype of anti-PC antibody of BALB/c mice. Suppressor T cells (Ts) induced after treatment with anti-T15id antibody react with the T15id and PnC-induced Ts cells appear to recognize PC. A brief incubation of anti-id-induced, T15id-specific Ts with PnC-induced, PC-reactive Ts resulted in complete cancellation of their suppressor functions. However, both types of Ts were present in mice neonatally injected with mixtures of PnC and anti-T15id antibody. Neutralization experiments using either PnC-induced or anti-id-induced suppressor T cells strongly suggest that only one of the Ts cell types is functionally dominant in those mice: most frequently, T15id-specific Ts cells. The suppressor function of the other population is detectable only when the predominant Ts cell population is removed by anti-id or monoclonal IgM anti-PC (SP45) plus complement. However, both suppressor activities are completely eliminated when one of the Ts populations is removed by adherence to either antigen or T15id. These results suggest that mice neonatally injected with a mixture of antigen and anti-id antibody possess both types of suppressor T cells, yet only one type is functionally dominant.

Functional characterization of monoclonal auto-anti-idiotype antibodies isolated from the early B cell repertoire of BALB/c mice

A large number of hybridomas were constructed by fusion of B cells from perinatal liver and spleen. Many of these showed multispecificity, high interconnectivity and anti-idiotype (Id) activity. Several of these were subjected to a detailed analysis to evaluate their influence on the developing immune system. A hybridoma BD2 (mu,kappa), derived from 2-day-old liver, was shown to have anti-T15 and anti-J558 activity by inhibition enzyme-linked immunosorbent assay and by in vivo administration. BD2 reduced primary T15 and J558 Id in adult BALB/c by 50%. In contrast, timed administration of this antibody during neonatal periods resulted in enhancement of responses to phosphorylcholine (PC) and alpha (1----3)-linked dextran (Dex) when these mice were challenged as adults. Another hybridoma DB3 (mu,kappa), derived from a lipopolysaccharide-stimulated fetal liver, reacts with GB4-10 (anti-T15) and not with PC. It also reacts with BD2. It is thus anti-anti-Id with respect to T15 and J558. Early administration of this antibody also led to an enhancement of anti-PC and anti-Dex responses, apparently via expansion of a set of intermediate anti-Id BD2-like B cells. In adult mice it suppressed responses to both antigens. A third hybridoma FC4 (mu,kappa), derived from 3-day-old spleen, reacts with GB4-10 as well as EB3-7 (anti-J558). Introduction of this antibody into neonatal mice enhanced anti-Dex responses while in adults it caused suppression of T15 Id. The results presented here suggest a possible role for neonatal anti-Id B cells in the primary activation of antigen-reactive B cells by Id selection.

In vivo suppression of perinatal multispecific B cells results in a distortion of the adult B cell repertoire

The isolation of multispecific B cell hybridomas with a variety of anti-idiotype (anti-Id) activities from the lymphoid organs of fetal and neonatal BALB/c mice suggested that the development of the immune system may depend on Id interactions among autologous B cells. In vitro analysis of antibodies secreted by these hybridomas showed extensive sharing of an idiotope defined by the monoclonal antibody FD5-1. Early and timed administration of this antibody during the perinatal period results in a distortion of the phosphorylcholine (PC) and alpha (1----3)dextran (Dex)-specific B cell precursor compartment of the developing repertoire and is reflected by a drastic reduction of antibody responses to these antigens when challenged as adults. These observations provide strong evidence for the involvement of the early appearing multispecific B cells in Id interactions that bring about the uniform development of the normal adult B cell repertoire. Interference with these interactions at critical stages of developmental results in permanent deficiencies in the adult B cell repertoire.

Lack of expression of the VHS107 gene family in the lipopolysaccharide-sensitive B cell subset of X-linked immunodeficiency-defective mice

The expression of the VH T15 gene product was analyzed in the sera and in the supernatants of polyclonally activated B cells of X-linked immunodeficient (xid) mice. We found that defective males, contrary to normal females, do not express the VH T15 gene product even on antibodies devoid of anti-PC specificity. RNA analysis of polyclonally activated cells with VH specific probes revealed that xid-defective B cells do not express the entire S107 or part of the J606 VH family. Members of the J558 family, on the other hand, are equally well expressed among defective males and normal female B cells. These results strongly suggest that VH families are asymmetrically represented among B cell subsets.

The antibody response to specific immune complexes is under genetic control and correlates with the expression of a recurrent idiotype

The primary antigen-specific antibody response of various strains of mice to TEPC-15/PnC immune complexes has been examined. We found that both BALB/c and C3H mice were good responders to the PnC antigen; however, C3H mice were low responders, whereas BALB/c mice were high responders to the TEPC-15/PnC complexes. Using congenic strains on the C3H and BALB/c background, we have shown that the response to the complexes is not restricted by gene products of the H-2 complex or by the Igh (allotype) locus. However, responsiveness may be controlled by genes linked to the Igh locus, since we have shown that strains that are Ighj, Ighd, and Ighf are low responders, whereas strains that are Igha, Ighb, and Ighe are high responders to the immune complex. Moreover, responsiveness correlates with the expression of the T15 Id as measured using the anti-T15 monoclonal antibody, AB1-2. Thus, strains such as BALB/c, BALB.B, BALB.K, and CB-20, which express high levels of T15 (AB1-2) Id in their PFC response to PnC are relatively high responders to TEPC-15/PnC complexes, whereas C3H, C3H.SW, and C3H-OH, which express low levels of the T15 (AB1-2) Id, are low responders to the complexes. Finally, we found that BALB/c mice are high responders to complexes formed with T15+ antibodies, whereas they are low responders to complexes formed using T15- antibodies. The results suggest that the antigen-specific response to these immune complexes is Id-restricted.

Effects of phosphorylcholine-lipopolysaccharide conjugates on the induction of anti-idiotype-mediated B-cell tolerance

Preincubation of BALB/c spleen cell cultures for 24 hr with phosphorylcholine (PC)-containing antigen together with antibody against the major idiotype (id) of anti-PC antibody renders them irreversibly unresponsive to subsequent stimulation with the antigen alone. In contrast, cultures preincubated for 24 hr with anti-id antibody, either alone or together with lipopolysaccharide (LPS), resulted in an anti-PC response comparable to that induced in control cultures incubated with mock anti-id antibody. After such a 24-hr preincubation with anti-id antibody and various PC-LPS conjugates possessing intact activity for polyclonal B-cell activation, the anti-PC response was inversely proportional to the epitope (PC) density on the LPS conjugates. In addition, similar preincubation of cultures with a non-mitogenic low dose of PC-LPS in the presence of anti-id antibody induced suppression of the anti-PC response as observed with a specific antigen. These results suggest that specific epitope delivers an additional tolerogenic signal during induction of B-cell suppression by anti-id antibody. This epitope effect cannot be replaced by, and is antagonistic to, the mitogenic signal of LPS in the course of B-cell inactivation.

The influence of Igh-1 genes on the class and subclass distribution of oxazolone-specific antibodies

Previous studies have demonstrated that the level of the oxazolone-specific antibody response induced by contact sensitization is under the control of H-2 and Igh-1-linked genes. The aim of the present study was to clarify the role of H-2 and Igh-1 genes in the regulation of antibody affinity and isotype composition of oxazolone-specific antibodies. Analysis of the antibody response to oxazolone has revealed different ratios of IgG2a and IgG2b antibodies in mice carrying the Igh-1b allele and in strains carrying alleles a, c, and e. The characteristic ratio of IgG2a and IgG2b isotypes persisted during the whole period of the primary and secondary antibody response of CBA and CBA-Igb Igh-C congenic mice. The Igh-1-linked genes influenced the isotype distribution and not the affinity of oxazolone-specific antibodies induced by contact sensitization.

Immune mechanisms in autoimmune chronic active hepatitis

Autoimmune chronic active hepatitis is a disease of unknown aetiology in which a dense mononuclear cell infiltrate in the portal areas of the liver is associated with ongoing necrosis of periportal hepatocytes. The finding of autoantibodies in serum, an increased frequently of HLA B8 DR3, a female predominance, an association with autoimmune diseases and the histological features all suggest a role for immunological reactions in the pathogenesis. Various immunological reactions have been demonstrated in vitro which could be of relevance to pathogenesis, including antibodies in serum directed against antigens expressed on the liver cell membrane, antibody-dependent cell-mediated cytotoxicity for autologous hepatocytes. T cell sensitisation to undefined hepatocyte antigen(s) and both antigen- and non-antigen-specific suppressor T cell defects. However, it is still unclear how these various phenomena interact in vivo and further studies are required to clarify their exact role in pathogenesis.

Studies on antibody repertoire: ontogenic development of mitogen-reactive B cells producing phosphorylcholine-specific and/or T15-associated 10/13 idiotope-positive antibodies

Very high frequencies of phosphorylcholine-specific and 10/13 idiotope-positive precursor cells were observed in spleen and liver cells polyclonally stimulated by lipopolysaccharide in BALB/c mice. These frequencies do not show any significant difference at birth, in young and adult mice, suggesting that antibody molecules analyzed arose from a single germ line heavy chain variable region gene segment. The order of magnitude of these frequencies was comparable in germ-free mice and conventionally reared BALB/c mice. Therefore, external antigenic stimulation does not seem to be involved in the establishment of antibody specificity available repertoire.

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

In the immune response of BALB/c mice (Igha) to Pneumococcus the majority of antibodies express the idiotype of the myeloma protein TEPC 15 (T15). In contrast mice of the A/J strain (Ighe) do not express this idiotype. Using (BALB/c X A/J)F1, F2 or backcross mice it could be shown that in allotype heterozygous animals (Igha/e) Pneumococcus pneumoniae preferentially stimulates B cells expressing a heavy chain (H) encoded by genes in the BALB/c H chain gene complex. Phosphorylcholine (PC)-specific hybridoma lines were established from BALB/c and A/J spleen cells and idiotypically analyzed using monoclonal antibodies (mAb) specific for the T15 idiotopes 32/65, 10/13, 16/13 or 21A5. Whereas the majority of the BALB/c PC-binding mAb express these idiotopes, only some of the A/J mAb are positive for one or the other of the idiotopes formed by the variable (V) regions of the H and the light chain of the myeloma protein T15. However, 80% of the A/J PC-binding hybridoma proteins were bound by the anti-idiotopic mAb 21A5. This mAb is specific for a determinant partially formed by the C alpha and partially by the V regions of the myeloma protein T15. The mRNA of one of these T15- A/J PC-binding hybridoma lines was sequenced. VH and V kappa were identical with sequences found for BALB/c T15-like antibodies. The sequence of the D segment was structurally very different. The importance of the D segment in the dominant expression of the T15 idiotype is discussed.

Frequencies of phosphorylcholine-specific and T15-associated 10/13 idiotope-positive B cells within lipopolysaccharide-reactive B cells of adult BALB/c mice

The frequencies of lipopolysaccharide-reactive B lymphocytes in adult BALB/c spleen cells were determined by limiting dilution experiments to be between 1 in 50 and 1 in 100. Within this reactive population, the frequencies of B lymphocytes specific for phosphorylcholine (PC) and/or binding a TEPC 15-associated idiotope-specific monoclonal antibody (10/13) were found to be between 1 in 50 and 1 in 500. Binding of these antibodies to immobilized PC or to monoclonal idiotope-specific antibodies could be inhibited by soluble PC in a solid-phase radioimmunoassay. Around half the PC-specific B cell clones were found to also bind 10/13 idiotope-specific monoclonal antibody, while the rest were either PC specific, but idiotope-negative or idiotope-positive, and unable to bind immobilized PC.

Analysis of nondominant idiotypes expressed during alloimmune responses

The antibody response of Lewis rats (RT1.A) to class I MHC antigens of the Brown Norway rat (RT1.An) was studied. Diversity of the serum alloimmune response was analyzed using syngeneic anti-idiotype raised against monoclonal antibodies of the same specificity. Cross-reactive idiotypes were detected on approximately one in one thousand Lewis anti-RT1.An serum antibodies, at concentrations ranging from 20 to 600 ng/ml. The kinetics of idiotype expression coincided with that of total anti-BN antibody production, suggesting that both were regulated by the same mechanism. To determine whether humoral anti-idiotype was involved in such regulation, sera from these animals were screened for anti-idiotype content. Using an RIA sensitive to 20 ng/ml, no humoral anti-idiotype could be detected during any phase of the alloimmune response.

1984: all idiotypes are equal, but some are more equal than others

Our analysis of idiotypic dominance suggests that 3 elements play an important role. The first is the genetic material that encodes the dominant idiotype. As dominant idiotypes appear to reflect germ-line-encoded sequences, one can not express a particular idiotype unless that sequence is present in the germ line. The germ-line-encoded sequences, in turn, would, I predict, be specific for commonly encountered or former environmental pathogens. The second element is the environmental antigens themselves. These antigens will induce the production of idiotype, and will prime idiotype-bearing B cells, such that idiotypic dominance emerges. In the absence of such influences, the pattern of idiotypic expression appears to differ. The third influence is regulatory. My own studies have shown that idiotype found in normal serum plays an important role in the maturation and/or function of one such cell, an idiotype-specific helper T cell. It is my working hypothesis that such cells play several roles in idiotypic dominance, but that this is the least of their important roles. Rather, such cells, being specific for idiotopes associated with antibodies specific for environmentally encountered pathogens, would be important in the priming and rapid reactivation of B cells bearing such idiotopes. As such, they speak to the basic role of the immune system, the protection of the organism from infection.

H-2 hierarchy in the IR-gene controlled responses to hapten-modified mouse serum albumin

Five hapten-modified autogenous mouse serum albumins (MSA), TNP11MSA, FITC8MSA, DNP64MSA, DNP5MSA, and PC2MSA, were tested for their ability to induce hapten-specific antibody responses in H-2 congenic mice of the H2d, H-2b, H-2a, and H-2f haplotypes. Four of the five modified MSAs, TNP11MSA, FITC8MSA, DNP64MSA, and PC2MSA, stimulated responses found to be under H-2-linked Ir gene control, whereas DNP5MSA failed to induce responses in any strain tested. H-2d, H-2D, and H-2a mice responded to FITC8MSA; H-2d and H-2b responded to TNP11MSA; and only H-2d mice were high responders to DNP64MSA and PC2MSA. H-2f mice failed to respond to any of the stimulating antigens. Thus, a hierarchy of H-2 haplotypes was observed in the responsiveness to modified MSA with H-2d greater than H-2b greater than H-2a greater than H-2f. Primed lymph node cells from PC2MSA immunized H-2d mice were challenged with antigen in vitro to assess the nature of the determinant recognized by T cells in the response to modified MSA. Lymph node cells proliferated only when challenged with PC2MSA. Unmodified MSA or TNP11MSA did not stimulate a proliferative response, suggesting that the immune T cells recognize a neodeterminant present on the modified PC2MSA.

Anti-phosphorylcholine antibodies with a preferred reactivity for either PC or PC-phenyl represent independent expressions

Anti-hapten antibodies to phosphorylcholine(PC)-conjugated proteins can be divided into antibodies reacting preferentially with PC (group I) or with PC-phenyl (group II). We have selected two hybridomas producing group II-type anti-PC antibodies of the IgM and IgE classes, respectively. With one exception, NH2-terminal amino acid sequence analyses of the light chains are identical in their first 21 residues and similar to that of M460, but differ from that of group I-type light chains. These results suggest that PC-phenyl-specific group II antibodies are expressed independently of PC-specific group I antibodies.

An idiotypic determinant formed by both immunoglobulin constant and variable regions

Immunoglobulin idiotypes are serologically defined determinants associated with the variable (V) region of antibody molecules (reviewed in refs 1-4). One of the best defined idiotype systems is that borne by the phosphorylcholine (PC)-binding IgA proteins TEPC15 (T15) and HOPC8 (H8). The T15 idiotype, defined by sera raised in A strain mice, or in rabbits, is considered identical to that expressed by the majority of BALB/c anti-PC antibodies. To define the idiotypic determinants (idiotopes) of which the T15 idiotype is comprised, monoclonal anti-T15 antibodies were used here to examine both serum and monoclonal anti-PC antibodies. The latter were found to differ from T15 with respect to the idiotope defined by the monoclonal anti-idiotope antibody, 21A5, in that the '21A5 idiotope' was absent from anti-PC sera; of the monoclonal anti-PC antibodies examined, only those which were both T15+ and of the IgA isotype seemed to express this idiotype fully. This result suggests that not only the V region, but also the constant (C) region, of the immunoglobulin molecule can contribute to the formation of an idiotypic determinant. Isotype-restricted idiotopes may be involved in the regulation of antibody responses of particular classes.

Thymus-independent induction and antigen-dependent recovery of idiotype-specific suppression

BALB/c nude (nu/nu) mice and euthymic (nu/+) littermates were treated as neonates with anti-T15 antibody and challenged at various ages with either a thymus-independent, PC-Brucella abortus (PC-BA), or thymus-dependent, PC-keyhole limpet hemocyanin (PC-KLH), form of phosphorylcholine (PC). Nu/nu mice challenged with PC-KLH received KLH-primed splenic T cells prior to immunization. Neither neonatally anti-idiotype-treated nu/+ nor nu/nu mice responded with the production of T15-positive anti-PC antibodies after challenge with either form of PC antigen. It is concluded that neither induction nor maintenance of a state of T15-specific suppression requires thymus-matured T cells. Recovery of anti-PC responsiveness in suppressed nu/+ or nu/nu mice was similar and was found to be related to the form of antigen used to elicit the response. Immunization with PC-KLH revealed a long-lasting unresponsiveness (up to 16 weeks). In contrast, immunization with PC-BA elicited a full anti-PC response as early as at 6.5 weeks of age.

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.

Expression of a distinct B cell clonotype profile after recovery from antigen-induced unresponsiveness

The purpose of these experiments was to determine whether the B cell clonotype profile expressed in mice which have recovered from antigen-induced unresponsiveness is similar to that of nontolerized mice. Unresponsiveness to phosphorylcholine (PC) was initiated by injection of neonatal mice with PC-coupled human gamma globulin, resulting in the inability to respond to challenge with PC-lipopolysaccharide at 1.5 months of age. By 3 months of age, pretreated mice were 50% responsive while by 5 and 7.5 months of age, full responsiveness was observed. At each time point two differences distinguished the anti-PC antibody from nonpretreated mice. First, whereas nonpretreated mice displayed T15 dominance, pretreated mice did not. Second, the average avidity of T15-negative antibody produced in pretreated mice was greater than that in nonpretreated mice and similar to that of T15-positive antibody. Possible mechanisms for this "permanent" alteration of the antibody profile are discussed.

Immunization of mice against African trypanosomiasis using anti-idiotypic antibodies

Anti-idiotypic (anti-Id) antibodies were raised against three protective monoclonal antibodies, each with specificity for the variable antigen type (VAT) of a clone of Trypanosoma rhodesiense. The IgG1 fractions of each were pooled and administered to BALB/c mice 3-4 wk before homologous challenge. The course of primary parasitemia was altered in 19 of 30 anti-Id-treated animals. The immunity was manifested as either: (a) complete protection, (b) reduced parasitemia, or (c) selection against parasites bearing the original VAT. The three idiotypes (Id) were found in variable levels in serum during the course of infection in control animals. However, in all anti-Id-treated mice that displayed immunity, one Id in particular (7H11) was detectable much earlier in infection and in higher levels than in control mice or anti-Id-treated, nonimmune mice. Six of nine mice treated with the anti-7H11 Id alone also displayed immunity, manifested in this case exclusively as selection against parasites bearing the original VAT. The effect was again associated with the more rapid appearance of the Id after infection. Specificity of the anti-Id-induced immunity was supported by the failure of anti-7H11 Id treatment to alter the course of infection with a heterologous clone of T. rhodesiense. To our knowledge, this is the first report of the antigen-independent induction of antimicrobial immunity using anti-Id antibodies.

Mice with the xid defect have helper cells for T15 idiotype-dominant anti-phosphorylcholine primary and secondary plaque-forming cells responses

We have examined the abilities of helper T cells from commercially available (CBA/N X BALB/c)F1 (NBF1) xid male and phenotypically normal female mice to help T15+ and T15- B cells to produce thymus-dependent phosphorylcholine (PC)-specific direct plaque-forming cell responses. Carrier-primed T cells from both male and female mice were found (a) to restore T15+ TD responses in congenitally athymic BALB/c mice, (b) to help PC-primed BALB/c splenic B cells produce predominantly T15+ responses, and (c) to provide help for T15+ and T15- PFC responses generated by PC-primed normal F1 splenic B cells. Furthermore, carrier-primed irradiated xid and normal recipients contributed adequate helper activity for T15 dominant responses. We therefore conclude that male and female NBF1 mice are equally capable of helping T15+ responses.

Alteration of clonal profile. III. T15 ontogenetic advantages are not sufficient for establishing idiotypic dominance in adoptive transfer

We have examined the ontogeny of BALB/c plaque-forming cell (PFC) responses to phosphorylcholine (PC) from fetal and neonatal liver by using the (CBA/N x BALB/c)F1 transplantation model. In this system, thymus-dependent (PC-keyhole limpet hemocyanin) and thymus-independent class 1 (PC-Brucella abortus, PC-lipopolysaccharide) PC antigens stimulate B cell subpopulations, which functionally emerge early after transfer. Responsiveness to a thymus-independent class 2 antigen, C-polysaccharide extract of a Streptococcus pneumoniae mutant, is acquired later. The response to PC antigens tested initially exhibited T15 dominance. Non-T15 clones, which are not expressed to a great degree in normal BALB/c mice, are inherently slow in their rate of maturation; in adoptive transfer, however, they eventually comprise much of the transplanted anti-PC PFC response. Obviously, the advantages the T15 subset has in ontogeny do not result in idiotypic dominance once the immature cells are removed from the intact BALB/c environment. We discuss possible regulatory mechanisms involved in the alteration of the T15+:T15- ratio.

Mechanisms of idiotype suppression. IV. Functional neutralization in mixtures of idiotype-specific suppressor and hapten-specific suppressor T cells

Specific tolerance to phosphorylcholine (PC) can be induced in BALB/c mice by neonatal injection with either pneumococcal C-polysaccharide (PnC) or anti-TEPC 15 idiotype (T15Id) antibody specific for the major idiotype (Id) of anti-PC antibody. Spleen cells from these tolerant mice exhibited T cell-mediated active suppression of anti-PC response when they were co-cultured with normal spleen cells. Suppressor cells from the PnC-injected mice appeared to bear either Lyt-1 or Lyt-2 antigens, whereas suppressor cells from anti-Id-treated mice expressed Lyt-2 antigens. Analyses of the specific receptors of these suppressor T cells, based on either adherence to PC and T15-coated petri dishes or cytolysis by rabbit anti-T15Id and monoclonal IgM anti-PC antibody with complement, revealed that receptors of PnC-induced suppressor T cells recognize PC, whereas receptors of anti-Id-induced suppressor T cells react with the T15Id. The possible interaction of the two different types of suppressor T cells was examined by co-culturing normal spleen cells with mixtures of the different suppressor cell types in various cell ratios in the presence of the T-independent PC-antigen, R36a. A brief incubation of anti-Id-induced, T15Id-specific suppressor T cells with PnC-induced, hapten-specific, and T15Id-bearing suppressor T cells resulted in complete cancellation of their suppressor function. These results suggest that idiotype network regulation may also occur among suppressor T cell population.

Cross-reactivity between C-reactive protein and idiotypic determinants on A phosphocholine-binding murine myeloma protein

Binding of human 125I-C-reactive protein (CRP) to sheep erythrocytes sensitized with pneumococcal C polysaccharide (E-PnC) was found to be Ca++ dependent and inhibitable by phosphocholine, CRP, and HOPC 8. Binding of 125I-HOPC 8 to EPnC was Ca++ -independent but could also be inhibited by phosphocholine, CRP, and HOPC 8. Thus, CRP and HOPC 8, despite a differential Ca++ requirement, share a common binding specificity for phosphocholine. A monoclonal anti-idiotypic antibody (MAB), GB4-10, prepared in A/J mice immunized with BALB/c HOPC 8 inhibited the binding of both 125I-CRP and 125I-HOPC 8 to E-PnC. In addition, both proteins bound to GB4-10 immobilized on polysterene tubes. Interestingly, binding of 125I-CRP to GB4-10 required Ca++. Similar results were also obtained with another MAB (AB1-2) prepared similarly to GB4-10, whereas neither protein bound to a control MAB (EB3-7) against an alpha1 leads to 3 dextran-binding myeloma protein, J558. Binding of 125I-HOPC 8 to GB4-10 could be inhibited by HOPC 8, keyhole limpet hemocyanin-phosphocholine but not phosphocholine but not phosphocholine, and in the presence of Ca++ by CRP. These data indicate that CRP bears antigenic determinants cross-reacting with certain idiotypic determinants on HOPC 8. They also suggest that Ca++ acts as an allosteric effector, perhaps stabilizing the phosphocholine-binding site of CRP.

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.

Loss of an individual idiotype on chemical modification. A strategy for assigning idiotypic determinants

Two dextran-binding myeloma proteins, J558 and Hdex 24, which possess the same individual idiotype (IdI) were diazotized to low levels (1-3.3 groups per subunit) with 1-[14C]-p-aminobenzoate. Both proteins lost the IdI idiotype under these conditions with most of the label incorporated on the heavy chains of each protein. When the diazotization ws carried out in the presence of the hapten 1-O-methyl-alpha-D-glucopyranoside the loss of idiotypic reactivity could be prevented for J558 but not for Hdex 24. Under these conditions most of the label was incorporated on the light chains of J558, but on the heavy chains of Hdex 24. For J558, these results show that a major determinant of the individual idiotype is within the hypervariable positions of the heavy chain. For Hdex 24 the determinant being modified is on the heavy chain but not involved in hapten binding. These results are consistent with previous work showing that J558 and Hdex 24 differ in amino acid sequence in the D and the J segments of the heavy chain and offer an alternative and complementary strategy for assigning idiotypic determinants.

Anti-inulin [beta-(2 leads to 1)-linked polyfructose] and anti-grass levan [beta-(2 leads to 6)-linked polyfructose] antibody response in mice

Anti-inulin [beta-(2 --> 1) polyfructosan Brucella abortus (InuBA)] and anti-grass levan [beta-(2 --> 6) polyfructosan] antibody responses in BALB/c and C57BL mice and in their F(1) and backcross progeny, as well as in immunoglobulin congenic and Bailey recombinant inbred strains derived from BALB/c and C57BL mice, were examined. The anti-inulin antibodies could accommodate both beta-(2 --> 1)- and beta-(2 --> 6)-linked polyfructosans, and 97% of the anti-inulin plaque-forming cells (PFC) from BALB/c mice expressed the cross-reactive idiotypes (InuIdX) shared by the BALB/c inulin- and levan-binding myeloma proteins. Of the C57BL mice, only 25% produced high anti-inulin response, and none exhibited the InuIdX of BALB/c anti-inulin antibodies. The percentages of InuIdX(+) anti-inulin PFC were also examined in other strains with high anti-inulin response. In C58 and AL mice, 80% of anti-inulin PFC were InuIdX(+), whereas in A/He and RIII mice, only 40% were InuIdX(+). All strains examined developed high anti-grass levan response, and the antibodies were specific for beta-(2 --> 6) structures and did not exhibit InuIdX. Comparison of the magnitude of the anti-inulin antibody titers in response to InuBA in BALB/c, C57BL, and their F(1) and backcross progeny, as well as in immunoglobulin congenic (i.e., B.C-8, BAB-14, and C.B-20) and recombinant inbred strains derived from BALB/c and C57BL mice, showed that all mice having the IgCH(a)(BALB/c) allotype gave high anti-inulin response. In addition to the InuIdX structural genes, the effects of allotype-linked or unlinked "regulatory" genes were also indicated by the lower anti-inulin response in B.C-8 and BAB-14 mice compared with BALB/c mice and the higher anti-inulin response in C.B-20 mice compared with C57BL mice. A multigene interaction in controlling the production of the anti-inulin antibodies was implicated.

Suppression of phosphorylcholine-specific IgE antibody formation in BALB/c mice by isologous anti-T 15 antiserum

In order to study the regulation of IgE antibody formation, isologous anti-idiotypic antisera against the phosphoryl choline (PC)-specific BALB/c myeloma proteins T 15 and M 167 were passively administered to BALB/c in the course of an anti-PC IgE response. Isologous anti-T 15 antiserum had a long-lasting suppressive effect on the formation of IgE antibodies with PC specificity, whereas administration of anti-M 167 antiserum had no or only little effect, similar to that of normal BALB/c serum. This indicates that anti-PC IgE antibodies consist mainly of the T 15 idiotype or of cross-reacting idiotypes, and that IgE response is accessible to regulation with anti-idiotypic antibodies. This murine model may permit the study of regulation of an IgE response largely restricted to few defined idiotypes characterized as tumor proteins.