Functional Relationship Between T15 and J558 Idiotypes in BALB/c Mice

In inbred strains of mice, antiphosphorylcholine (PC) and anti-α1,3 dextran (DEX). antibodies are structurally distinct from each other and have been shown to exhibit noncrossreactive antigen binding and idiotypic specificities. However, the prototype anti-PC and anti-DEX antibodies, TEPC15 and J558, respectively, were shown to be connected via a common autoantiidiotypic monoclonal antibody isolated from newborn BALB/c mice. The capacity of various monoclonal anti-PC and anti-DEX antibodies as well as the antigens PC and DEX to modulate T15 and J558 idiotypes in BALB/c mice was tested by their administration to newborn mice. Anti-PC antibodies of the .T15 idiotype injected into 2-4-day-old mice, at a time when T15 anti-PC precursors develop in BALB/c mice, suppressed the anti- PC response of these mice at 6 weeks of age. Similarly, J558 antibodies injected into 8-12-day-old mice, at a time when J558 precursors normally develop, suppressed the response to DEX. As a further demonstration of this connectivity, the injection of J558 into 4-day-old mice led to a down modulation of T15 idiotype, whereas both T15 and a minor idiotypeexpressing antibody M167 when injected into 8-12-day-old mice caused a reduction in expression of the J558 idiotype. As predicted from in vitro analysis, injection of anti-PC antibodies of the M167 idiotype 2 to 4 days after birth enhanced the subsequent response to PC. However, anti-PC antibodies expressing another minor M603 idiotype did not affect the PC. response. The results parallel the in vitro enhancement of M167 antibodies but not M603 on T15 binding to antiidiotype in vitro. Similarly, anti-DEX antibodies expressing the M104E idiotype had no detectable effects on the capacity to respond to PC or DEX or on the expression of T15 and J558 idiotypes as adults. Exposure of newborn mice to PC led to a dramatic reduction in the response to DEX as adults, whereas exposure to DEX at this stage of development had no effect on response to PC as adults. Collectively, these observations provide evidence for a complex functional connectivity between T15 and J558 idiotype-bearing B cells during ontogeny and extend our previous observations that development of these idiotypes is regulated by idiotype-directed interactions between B cells or their immunoglobulin products.     

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.     

Regulatory effects of isologous anti-idiotypic antibodies on the formation of different immunoglobulin classes in the immune response to phosphorylcholine in BALB/c mice

BALB/c mice were immunized with purified phosphorylcholine (PC)-specific myeloma protein of the TEPC-15 tumor, which bears the major idiotype of the anti-PC response (T15 Id) in this mouse strain. Four months after establishing the anti-idiotypic response, animals were immunized with PC-keyhole limpet hemocyanin under conditions which normally lead to IgE antibody formation. The expression of anti-PC antibodies of each immunoglobulin class was compared to a group of matched control mice not immunized with T15. In BALB/c mice producing anti-idiotypic antibodies the formation of anti-PC IgM, IgG1, IgG2, IgG3 and IgE was suppressed to various extents and for different lengths of time. An exception to this observation was the formation of anti-PC IgA antibodies, in that no significant difference was measured between the two groups of mice. BALB/c mice immunized in the same way with the PC-specific myeloma proteins of the MOPC-167, MOPC-511 and MOPC-603 tumors produced normal levels of anti-PC IgE and IgG antibodies. These results suggest that T15 idiotype-positive antibodies are probably formed within all classes of specific antibodies expressed during an immune response to PC. The possibility of extending the phenomena of anti-idiotype-induced suppression to the level of various classes of specific antibodies, including IgE, might be of interest in the treatment of some allergic diseases.     

Induction and characterization of "autologous" anti-isiotypic antibodies.

Upon immunization with phosphorylcholine (PC), conventional BALB/c mice produce anti-PC antibodies bearing predominantly the idiotype characteristic of the BALB/c PC-binding myeloma protein TEPC 15 (T15). To investigate whether BALB/c mice are able to produce antibodies to the autologous T15 idiotype, conventional (T15-positive) and neonatally suppressed (T15-negative) BALB/c mice were immunized with purcific for the T15 idiotype. However, anti-T15 antibodies were more readily induced in neonatally suppressed mice which in turn produced higher anti-T15 titers than conventional mice. Such "autologous" anti-T15 antibodies are able to (a) change the idiotypic pattern of the anti-PC response of conventional BALB/c mice in situ and, (b) inhibit the induction of an anti-PC response in vitro by spleen cells from T15-positive but not T15-negative BALB/mice. Thus, BALB/c mice are capable of producing anti-T15 antibodies upon immunization with an isologous myeloma protein which bears the autologous T15 isiotype. We suggest that isiotypes should not be strictly considered as "self-antigens" since the dramatic increase in their concentration, subsequent to antigen stimulation, might confer upon them immunogenic properties not shared by self-antigens.     

Monoclonal vs. heterogeneous anti-H-8 antibodies in the analysis of the anti-phosphorylcholine response in BALB/c mice

Biological activities of monoclonal A/J antibodies to the T15 idiotype in BALB/c mice were compared to heterogeneous antibodies raised by conventional immunization procedures. Two monoclonal antibodies, AB1-2 and GB4-10, which are of the γ₁,? class, appeared to have identical specificities by binding criteria and reacted similarly to conventional antibodies in their abilities to induce neonatal suppression, inhibit plaque-forming cell induction by phosphorylcholine (PC) antigens and to inhibit specifically, anti-PC plaque-forming cells. However, in functional analyses of anti-PC responses in various strains of mice, discrepancies were noted in the T15 responses as defined by monoclonal antibodies and conventional antisera. This heterogeneity was also observed in adult mice suppressed with the GB4-10 monoclonal antibody. These animals eventually produced an anti-PC response of AB1-2 idiotype but lacking the GB4-10 marker. These results show that the T15 IgM anti-PC response in BALB/c and other strains of mice is heterogeneous and probably consists of a family of clones. Particular clones can be precisely eliminated by the use of appropriate monoclonal antibodies, and the anti-PC response that eventually recovers is still T15⁺ but lacking the suppressed clones.     

Phosphorylcholine-binding hybridoma proteins of normal and idiotypically suppressed BALB/c mice. I. Characterization and idiotypic analysis

The immune response of BALB/c mice to phosphorylcholine (PC) is dominated by an antibody bearing the idiotype of the myeloma protein TEPC 15 (MP T15). Anti-PC antibody of a different idiotype can be elicited in BALB/c mice by neonatal suppression with an anti-T15 idiotypic antiserum (anti-Id-T15). In an attempt to further characterize the immune response to PC, spleen cells of normal and idiotypically suppressed mice have been fused with the myeloma line X63-Ag8, and hybrid lines secreting anti-PC antibodies have been isolated. The antibodies were characterized by two-dimensional gel electrophoresis and their affinity for Pneumococcus pneumoniae was measured. Using both an A/J and a rabbit anti-Id-T15 serum, we could show that 4 out of 5 hybridomas obtained from normal BALB/c spleen cells secreted antibodies which, within the limits of the analysis, were idiotypically and structurally indistinguishable from MP T15 (T15⁺). Hybridomas obtained from suppressed BALB/c mice, on the other hand, secreted anti-PC antibodies which differed idiotypically from MP T 15: of the six lines, two were negative for T15 idiotopes (T15^?), while four showed some cross-reactivity with the T15 idiotype (T15^cr). All six, however, showed structural differences in one or more immunoglobulin chains. Inhibition of anti-PC plaque-forming cells induced in neonatally suppressed mice revealed that the idiotypic spectrum of the hybridoma proteins was representative of clones arising under such conditions in BALB/c mice. The majority of the anti-PC antibodies in idiotypically suppressed mice still bear idiotopes resembling MP T15. Only a minority, less than 20%, are truly T15^?.     

Expression of new idiotypes following neonatal idiotypic suppression of a dominant clone.

The anti-PC antibodies of BALB/c origin bear predominantly the idiotype characteristic of the phosphorylcholine (PC)-binding T15 idiotype than sera from adult mice, and, unlike the latter, they also contain detectable amounts of anti-T15 antibodies. By 2 weeks of age the anti-T15 antibodies are no longer detectable while the T15 idiotype has reached adult levels. Injection of neonatal mice with anti-idiotypic antibodies renders them unresponsive to PC until the 15th week of life. Furthermore, this treatment induces a chronic suppression of the T15 idiotype, since on recovery from unresponsiveness, the neonatally suppressed mice produce anti-PC antibodies which are predominantly T15-negative. In contrast, treatment of adult mice with anti-idiotypic antibodies induces only a transient state of unresponsiveness to PC, and the antibodies produced upon recovery bear the T15 idiotype. These findings are discussed in the context of idiotype anti-idiotype interactions and their possible role in immuno-regulation.     

Compensation for idiotype suppression. I. Acquirement of ability to compensate for TEPC-15 idiotype suppression in mice during the early neonatal period

Neonatal injection of BALB/c mice with antibodies specific for the idiotype of TEPC-15 myeloma protein (T15id), which is serologically identical to the major idiotype of anti-phosphorylcholine (PC) antibody, renders the recipients completely unresponsive to PC. C57BL/6, (BALB/c X C57BL/6)F1 and C.B20 mice, similarly treated with anti-T15id antibody, also displayed tolerance to PC although they were relatively more resistant (8-13%) than BALB/c mice (less than 2% control response). When anti-T15id antibody was injected into 15-day-old neonates, the resistance to the tolerance in C57BL/6 and C.B20 mice was much more apparent (up to 80% of the control response) in contrast to that in BALB/c mice, which was not significant. Adoptive transfer of spleen cells from idiotypically suppressed BALB/c mice into 20-day-old, normal C. B20 mice resulted in suppression of T15id but not in tolerance to PC, due to increased production of non-T15id-bearing anti-PC antibody. These results suggest that the ability of clonal compensation for T15id suppression is acquired during early life (2-10 days), under the influence of gene(s) associated or linked with the Igh.     

Fine Specificity and Isotype Expression of Anti-PC Antibodies in BALB/c, MRL/Mp-1pr/1pr, 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.     

Sequence changes at the V-D junction of the VH1 heavy chain of anti- phosphocholine antibodies alter binding to and protection against Streptococcus pneumoniae

X-linked immune deficient (Xid) mice fail to produce anti- phosphocholine (PC) antibodies even after immunization with Streptococcus pneumoniae. Consequently, Xid mice are extremely susceptible to infection with S. pneumoniae, PC-specific B cells appear to undergo clonal deletion in Xid mice; however, a new thymus-dependent form of PC, 6-(O-phosphocholine)hydroxyhexanoate (EPC), can rescue PC- specific B cells from the bone marrow presumably by providing T cell help before clonal deletion. Analysis of PC-specific IgG hybridomas from Xid mice revealed utilization of several V-D junctional variants of the VH1 gene segment rearranged to different D and JH gene segments. The majority of Xid anti-PC antibodies exhibit an Asp-->Gly95H replacement at the V-D junction. These Gly95H VH1 variants associate with kappa 1C L chains to produce anti-PC antibodies that: (1) have low relative affinity for PC, (ii) are heteroclitic for nitrophenylphosphocholine and (iii) fall to bind to or provide protection against S. pneumoniae. Single prototypic V-D variants of the T15 idiotype (Asp95H), M603 idiotype (Asn95H) and M167 idiotype (Asp95H- Ala96H) were also induced in Xid mice. The M603-like and M167-like antibodies bound to and protected against S. pneumoniae even though they exhibited Kas for PC which were lower than T15 idiotype+ antibodies. These data demonstrate that small changes in the V-D junctional sequence of the T15 (VH1) heavy chain alter L chain usage and the structure of the PC binding site so that the PC expressed on S. pneumoniae is no longer recognized.      

Biological and serological comparison of syngeneic and allogeneic anti-idiotypic antibodies

The majority of BALB/c antibodies with specificity for the (1→3)-glucosidic linkage of dextran B1355, fraction S (-dextran), share an idiotype crossreactive with the -dextran-binding BALB/c myeloma proteins J558 and MOPC104E. This crossreactive idiotype (IdX558) is denned by an allogeneic antiidiotypic antiserum raised in mice of strain A/HeJ against J558 myeloma protein (Carson & Weigert, 1973). Allogeneic anti-IdX558 antisera induce a long lasting complete suppression of the total anti--dextran immune response when given neonatally to BALB/c mice. Mice which recover from suppression fail to express the IdX558. In contrast, when BALB/c mice are immunized by use of J558 myeloma protein, no measurable effect on the subsequent total anti--dextran immune response or on the expression of IdX558 is found in mice making anti-J558 themselves nor in those mice which received the syngeneic anti-J558 idiotype antibody neonatally. In addition, no significant alteration of the anti--dextran response can be detected in BALB/c mice which were immunized against MOPC104E protein prior to -dextran immunization. This different suppressive capacity may be explained by different specificities of the allogeneic and syngeneic antiidiotype antisera. Hemagglutination and isoelectric focusing studies of the antisera show that BALB/c mice fail to produce antibodies against the crossreactive idiotype whereas in the allogeneic situation the anti-IdX558 is the overwhelming one. Syngeneic anti-idiotypic antibodies react only with the corresponding myeloma protein used for immunization, thus defining individual idiotypes (IdI558 and IdI104). IdI558 and IdI104 are expressed by every BALB/c mouse in response to -dextran but as a minor component of their idiotypic spectrum.     

Evidence for the endogenous production of T cell receptors bearing idiotypic determinants.

Unprimed thymus-derived (T) cells from spleens of either conventional TEPC 15+ (T15+) BALB/c mice or neonatally suppressed T15- BALB/c mice were used to reconstitute neonatally suppressed T15- BALB/c nude mice and conventional T15+ BALB/c nude mice, respectively. In so doing, the idiotypes produced by phosphorycholine (PC)-specific bone marrow-derived (B) cells were dissociated from idiotypes putatively produced by PC-specific T cells. Subsequent to priming of the reconstituted BALB/c nude mice with either anti-T15 antisera or PC-MOPC 315, their splenic T cells were assessed for PC-specific helper activity and expression of the T15 idiotype. Our results indicate that expression of the T15 idiotype by T cells as determined by (a) the ability to prime PC-specific helper cells with anti-T15 antibodies, and (b) the ability to inhibit PC-specific helper function with anti-T15 antibodies, depended on the idiotype of the unprimed donor T cell source and not that of the B cells in the reconstituted recipients. We conclude that the idiotype-bearing T cell receptor specific for PC is not a passively adsorbed B cell product.     

Fine specificity and idiotype expression of anti-phosphorylcholine IgE and IgG antibodies

The immune response to the phosphorylcholine (PC) hapten elicited in BALB/c mice by PC-keyhole limpet hemocyanin (KLH) is composed of 2 groups of antibodies with specificity to PC and phenyl-PC, respectively. They were designated as group I and group II anti-PC antibodies. In this report we demonstrate that anti-PC IgE antibodies elicited by PC-KLH or PC-ovalbumin belong to the group II and do not express the T15 idiotype. Anti-PC IgG1, IgG2a and IgG2b antibodies express group I characteristics in the primary response and bear the T15 idiotype. Later, after 5 weeks and 3 injections of PC-KLH or PC-ovalbumin, a change in these isotypes to group II antibodies is observed. In contrast, anti-PC IgE is a group II antibody throughout progression of the immune response. The regulation of group I and group II antibody expression in serum is independent of the genetic background of the animals.     

Autologous anti-idiotypic antibody response is regulated by the level of circulating complementary idiotype.

BALB/c mice injected with lyophilized vaccine from Streptococcus pneumoniae R36a (Pn) predominantly responded with antibody molecules the vast majority of which expressed the public idiotype T15 and were directed to the immunodominant epitope phosphorylcholine (PC). However, after a single immunization with Pn vaccine young (3-month-old) BALB/c mice did not produce any specific anti-T15 antibody response. In contrast, young D1.LP mice were able to mount a specific anti-T15 response upon primary immunization with pneumococcal vaccine. The anti-PC response in the two mouse strains differed in that the proportion of antibody molecules that expressed the T15 idiotype for Pn-primed D1.LP mice showed a smaller proportion of PC-specific antibody expressing the T15 idiotype. Neonatal injection of anti-T15 monoclonal antibodies led to a long-term suppression of the PC-specific T15+ B-cell clones but at young/adult age these mice maintained the ability to produce a normal amount of PC-specific antibody. Interestingly, the idiotypically-suppressed BALB/c mice mounted a significant anti-T15 response during the primary response to Pn. We interpreted these data as showing that the level of circulating idiotype may regulate the production of the complementary anti-idiotypic antibody. In addition, in vitro experiments demonstrated that the lack of the anti-T15 response during primary antibody response in BALB/c mice is probably because of a state of tolerance that is regulated by T cells.     

Divergency in the specificity of the induction and maintenance of neonatal suppression

Neonatal treatment of BALB/c mice with anti-VHT15 antibodies suppresses serum expression of VHT15 immunoglobulins in adult animals (2 months) which remains for over 8 months in half of the cases. Suppressed mice, however, contain control numbers of B cells expressing genes of the S107VH family and producing VHT15 after mitogenic stimulation. Furthermore, immunization with phosphorylcholine (PC) breaks suppression and stimulates the production of VHT15 anti-PC antibodies. These animals, however, contain no detectable B lymphocytes expressing the T15 idiotype and produce no T15 idiotype-positive antibodies in response to PC. These results are discussed in the context of lymphocyte repertoire selection.     

Uniformity in the clonal repertoire for the immune response to phosphorylcholine in mice.

A comparison of the clonal nature of the immune response to phosphorylcholine (PC) was made in nine different inbred mouse strains. Quantitative idiotypic analysis showed that anti-PC antibodies from each strain were composed of antibodies bearing binding-site idiotypic determinants indistinguishable from two different BALB/c myeloma proteins, T15 and M511. Idiotypic determinants of two other PC-binding proteins, M167 and M603, were not detected. Isoelectric focusing of the light (L) chains verified the presence of antibodies similar to T15 and M511 in each strain and indicated the presence of two additional antibodies, one of which has an L chain which cofocuses with M603. Fractionation of anti-PC antibody with anti-idiotypic antibody showed that immunoglobulins bearing T15 and M511 idiotypic determinants are separate and contain L chains that are unifore and resemble those of T15 and M511, respectively. Thus, these mice which differ genetically at multiple loci including the heavy chain allotype complex locus each possess, at least in part, an equivalent set of clonotypes specific for PC. This indicates that the genes encoding these antibodies must be contained in the germ line.     

Idiotype suppression by maternal influence.

In BALB/c mice, antibodies to the alpha-(1-3) glucosidic linkage of some dextrans (Dex) carry the idiotype of the BALB/c myeloma protein J558. Both specific antibody and idiotype are inherited in a dominant fashion, linked to the immunoglobulin (Ig) (heavy chain) allotype Igla of BALB/c mice (Eur. J. Immunol. 1975. 5: 775). In F1 hybrid mice from the parent strains SJL and BALB/c, we were able to suppress the expression of anti-Dex antibodies by immunizing prospective SJL mothers to the J558 idiotype. The state of suppression in the progeny was ascertained by immunization with Dex, and tests for the following were carried out: (a) antibodies specific for Dex; (b) inhibition of such antibodies (if present) by antiidiotypic serum to protein J558; (c) presence of the J558 idiotype; and (d) concentration of lambda1 chains (which are associated with the 558 idiotype) in the serum. SJL mothers, once immunized, conferred suppression upon several successive litters, spanning a period of 4-5 months. Suppression in F1 progeny animals lasted for 16 weeks or more. Spleen cells from suppressed F1 mice which had neither been treated with Dex nor with J558 protein, were able to confer suppression to further F1 newborn mice.     

Idiotypic profile of the response to phosphorylcholine induced in the absence of the homologous antigen

In the absence of the homologous antigen, an anti-phosphorylcholine (PC) plaque- forming cell (PFC) response has been induced in vitro which is restricted to the TEPC 15 idiotype (T15). Anti-T15 antibodies were used to focus either the keyhole limpet hemocyanin (KLH) or the fowl gamma-globulin (FGG) carrier molecules on the membrane of B cells carrying the T15 idiotype on their immunoglobulin receptors; thereafter, these cells were allowed to cooperate in vitro for 5 days with T cells primed to the appropriate carrier molecule. A response, virtually 100% T15⁺, could be induced both in normal BALB/c and in T15 neonatally suppressed mice which had lost the T15 ⁺ clonal dominance. The magnitude of this response is comparable to that obtained in the presence of the PC antigen. The role of the membrane-bound immunoglobulin receptor (sIg) in the expression of different anti-PC clones was also investigated. We have focused either the KLH or the FGG carrier molecules on the membrane of B cells via anti-H-2 antibodies and then cultured these cells for 5 days with the appropriate carrier-specific T cells. Under these conditions, B cells are activated in the absence of interaction at the sIg. The idiotypic profile of the anti-PC PFC obtained with the anti-H-2-mediated activation was then compared with the profile of the anti-PC response obtained in the presence of PC antigen. Since similar idiotypic profiles were obtained in both cases, it can be excluded that sIg plays a direct role in favoring the expression of T15⁺ over T15^? anti-PC clones.     

Absence of an antigen-specific helper T cell required for the expression of the T 15 idiotype in mice treated with anti-mu antibody

T-dependent anti-phosphorylcholine (PC) plaque-forming cell (PFC) responses were studied in BALB/c mice. Helper T cells derived from normal, carrier-primed donors induced anti-PC PFC responses dominated by the T15 idiotype. Helper T cells derived from carrier-primed mice that had been treated from birth with anti-μ antibody, so that they were lacking B cells and circulating antibody bearing the T15 idiotype, also provided helper cell function for the anti-PC antibody response. In contrast to the response induced by helper T cells from normal mice, T helper cells from μ-suppressed mice induced an anti-PC antibody response which was mainly non- T15 in character. The failure to induce antibody formation by T15⁺ B cells was not due to suppressor cells but rather to the lack of an Lyt-1⁺ helper T cell population which is necessary for predominant T15 production. This latter cell population was shown to be present in carrier-primed normal but missing or diminished in carrier- primed anti-μ-treated BALB/c mice. It required carrier priming for the expression of its helper function, but its function did not require the antigen (carrier) to be physically linked to the hapten. From this, we conclude that dominant production of the T15 idiotype involves the synergistic activity of two antigen-specific helper T cells. The helper cell population which is required for predominant T15 production is greatly diminished in mice treated with anti-μ antibody from birth. Hence, the production of circulating T15⁺ antibody induced by environmental antigens or the appearance of T 15-bearing B cells would appear to be required for the induction of helper T cells which enhance T15⁺ anti-PC antibody synthesis.     

T-cell enforced invariance of the antibody repertoire in the immune response against a bacterial carbohydrate antigen

The humoral response against the bacterial polysaccharide antigen alpha(1-->3) dextran (Dex) is controlled by J558 idiotype-(Id) specific T cells. These T cells of which the cell clone 178-4 Ts is a representative by all relevant criteria, recognize J558 Id-bearing B cells in an I-Ed-restricted manner. Costimulation via CD28/B7-1 but not via CD40/CD40L leads to T-cell activation. These T cells do not only suppress B cells producing the immunoglobulin (Ig)G3 isotype but also support the survival and clonal expansion of J558 Id positive B cells both in vivo and in vitro. This T-cell mediated dominance of the J558 idiotype limits the appearance of antibodies carrying other more diverse idiotypes which appear in immunized BALB/c nu/nu mice where no regulatory T cells occur. This T-cell mediated antibody invariance could be a strategy of the immune system responding to highly conserved antigens like polysaccharides, different from those against protein antigens, where diversity is assumed to be the basis for a successful response.