Variant-specific monoclonal and group-specific polyclonal human immunodeficiency virus type 1 neutralizing antibodies raised with synthetic peptides from the gp120 third variable domain

The third variable (V3) domain of the human immunodeficiency virus type 1 (HIV-1) external membrane glycoprotein gp120 is of crucial importance in eliciting neutralizing antibodies in infected persons. Polyclonal (PAb) and monoclonal (MAb) antibodies directed against selected epitopes in the V3 domain are valuable tools for analysis of the involvement of such sequences in neutralization and for definition of the relation between amino acid variability and immunological cross-reactions. The aim of this study was to obtain such site-specific antibodies. By using synthetic peptides derived from the V3 domain, a group-specific neutralizing PAb, two high-affinity HIV-1 IIIB neutralizing MAb, and two nonneutralizing MAb were raised. A 15-amino-acid peptide overlapping the tip of the V3 domain of HIV-1 MN was used to produce a rabbit PAb (W0/07). This PAb inhibited syncytium formation induced by HIV-1 IIIB and four field isolates. A similar IIIB-derived peptide was used to generate two murine immunoglobulin G1 (IgG1) MAb (IIIB-V3-13 and IIIB-V3-34). Pepscan analysis mapped the binding site of IIIB-V3-34 to the sequence IRIQRGPGR. The Kds of IIIB-V3-13 and IIIB-V3-34 for gp120 were 6.8 x 10(-11) and 1.6 x 10(-10) M, respectively. These MAb neutralized IIIB but not MN and inhibited syncytium formation induced by IIIB. They are applicable in enzyme-linked immunosorbent assays, immunocytochemistry, and flow cytometry. A peptide covering the left base of the V3 domain was used to generate two murine IgG1 MAb (IIIB-V3-21 and IIIB-V3-26). The binding site of IIIB-V3-21 was mapped to the sequence INCTRPN. These MAb did not neutralize HIV-1 and did not inhibit syncytium formation. This study supports the notion that HIV-1 neutralizing antibodies suitable for multiassay performance can be obtained with synthetic peptides and that high-affinity MAb can be generated. Such site-specific antibodies are useful reagents in the analysis of HIV-1 neutralization. In addition, the cross-neutralization of different viral strains by PAb generated through single-peptide immunization is directly relevant to vaccine development.

Characterization of the binding of radioiodinated hybrid recombinant IFN-alpha A/D to murine and human lymphoid cell lines

The hybrid recombinant human interferon (IFN) rIFN-alpha A/D was radioiodinated. Specific binding of [125I]rIFN-alpha A/D was observed with both human and murine cell lines. The binding of [125I]rIFN-alpha A/D to human Daudi cells had similar characteristics to the previously described binding of [125I]rIFN-alpha A or -alpha 2. The following lines of evidence demonstrated that [125I]rIFN-alpha A/D bound with high affinity to the same receptor on murine cells as murine IFN-alpha and -beta: (i) the binding of [125I]rIFN-alpha A/D to murine LBRM cells was inhibited to a similar extent by natural murine IFN-alpha, natural murine IFN-beta, and rIFN-A/D; (ii) the Kd (approximately 2 X 10(-10) M) obtained from both competition experiments and saturation binding experiments with [125I]rIFN-alpha A/D was comparable to the previously reported Kd for the binding of natural murine IFN-alpha and -beta to other murine cell lines; (iii) the size of the cross-linked [125I]rIFN-alpha A/D receptor complex formed on murine LBRM cells was similar to the previously reported cross-linked complex formed after binding radioiodinated natural murine IFN-beta to other murine cell lines. Due to the current lack of readily available recombinant murine IFN-alpha or -beta for radiolabeling and the previously demonstrated biological activity of rIFN-alpha A/D on murine cells, [125I]rIFN-alpha A/D should prove to be a useful reagent for further studies of murine IFN receptors.

Arsonate-specific murine T cell clones. III. Correlation between clonotype expression and fine specificity for analogs of L-tyrosine-p-azobenzenearsonate

Despite recent advances in our understanding of T cell antigen receptor structure, relatively little is known about the role of this receptor in MHC-restricted antigen recognition. To study this problem, we have developed a panel of ABA-Tyr-reactive, I-Ak-restricted T cell clones that differ in their ability to recognize structural analogs of ABA-Tyr. Three fine specificity groups have been defined. In each group, ABA-Tyr elicited the strongest response of any of the antigens tested. Group I clones responded to ABA-conjugated hydroxyphenyl-ethanol (ABA-HPE). Group II clones responded to ABA-conjugated hydroxyphenyl-methanol (ABA-HPM) but not to ABA-HPE, and group III clones responded only to ABA-Tyr. These studies show that differences as small as a single methylene group can dramatically affect fine specificity. Because these clones are all I-Ak-restricted, it was possible to correlate receptor serology with fine specificity. To this end, monoclonal anti-clonotypes were made against clone 16-F2 from group I and used to study the relationship between fine specificity and clonotype expression. A panel of 15 T cell clones studied with four anti-clonotype antibodies showed a strict correlation between clonotype expression and fine specificity. Taken together, these data suggest that the structure recognized by the anti-clonotype antibodies is a determinant of receptor fine specificity.

Arsonate-specific murine T cell clones. III. Correlation between clonotype expression and fine specificity for analogs of L-tyrosine-p-azobenzenearsonate

Despite recent advances in our understanding of T cell antigen receptor structure, relatively little is known about the role of this receptor in MHC-restricted antigen recognition. To study this problem, we have developed a panel of ABA-Tyr-reactive, I-Ak-restricted T cell clones that differ in their ability to recognize structural analogs of ABA-Tyr. Three fine specificity groups have been defined. In each group, ABA-Tyr elicited the strongest response of any of the antigens tested. Group I clones responded to ABA-conjugated hydroxyphenyl-ethanol (ABA-HPE). Group II clones responded to ABA-conjugated hydroxyphenyl-methanol (ABA-HPM) but not to ABA-HPE, and group III clones responded only to ABA-Tyr. These studies show that differences as small as a single methylene group can dramatically affect fine specificity. Because these clones are all I-Ak-restricted, it was possible to correlate receptor serology with fine specificity. To this end, monoclonal anti-clonotypes were made against clone 16-F2 from group I and used to study the relationship between fine specificity and clonotype expression. A panel of 15 T cell clones studied with four anti-clonotype antibodies showed a strict correlation between clonotype expression and fine specificity. Taken together, these data suggest that the structure recognized by the anti-clonotype antibodies is a determinant of receptor fine specificity.

Multistep transformation by defined fragments of herpes simplex virus type 2 DNA: oncogenic region and its gene product

Diploid Syrian hamster embryo cells transfected with Bgl II C fragment of herpes simplex virus type 2 DNA acquired a neoplastic phenotype. Cultures transfected with its left-hand 64% subclone EcoRI/HindIII fragment AE (0.419-0.525 map unit) grew into established but nontumorigenic lines. Transfection of EcoRI/HindIII AE-immortalized cells with a 4.4-kilobase Sac I/BamHI subfragment within BamHI E (0.554-0.584 map unit; overlaps the right-hand 16% of Bgl II C) converted them to tumorigenicity. The 4.4-kilobase subfragment encodes a 144-kDa protein immunologically and structurally similar to an infected cell protein designated ICP 10. DNA extracted from cells transformed with the 4.4-kilobase subfragment exhibited discrete hybridizing bands homologous to BamHI E fragment. Monoclonal antibody to ICP 10 precipitated a 144-kDa protein from the transformed cells and stained them in immunofluorescence. A tumor derivative established with the transformed cells did not stain with this antibody, but approximately equal to 25% of the cells stained with a monoclonal antibody to c-myc protooncogene products.

Isolation of monoclonal antibodies specific for human c-myc proto-oncogene product

Six monoclonal antibodies have been isolated from mice immunized with synthetic peptide immunogens whose sequences are derived from that of the human c-myc gene product. Five of these antibodies precipitate p62c-myc from human cells, and three of these five also recognize the mouse c-myc gene product. None of the antibodies sees the chicken p110gag-myc protein. All six antibodies recognize immunoblotted p62c-myc. These reagents also provide the basis for an immunoblotting assay by which to quantitate p62c-myc in cells.

Idiotypic properties of the murine anti-arsonate antibody response: B- and T-cell influences

In a previous report characterizing the arsonate (ABA)-specific plaque-forming cell (PFC) responses of A/J mice induced by ABA-KLH, two interesting characteristics of the idiotypic (Id) profile were noted: (1) an apparent Id selectivity in the isotype switch since the earliest appearing IgG PFC in the primary response were significantly more "cross-reactive Id" (CRI)-dominant than the IgM PFC population, and, (2) a temporal waning of CRI dominance with time among IgG PFC, from 75-100% CRI+ PFC to about 25-45% CRI+ PFC in secondary responses. Experiments were performed to determine whether these effects are largely attributable to T or to B cells. Mice were immunized with a T-independent (TI) form of ABA (ABA-Brucella abortus) and apparent Id selectivity was observed; the earliest IgG PFC averaged 75% CRI+ while IgM PFC were only 39% CRI+. Due to the TI nature of the Ag, this provides suggestive, but not conclusive, evidence that the Id asymmetry in the isotype switch may be attributable to the direct interaction of Ag with B cells. Other studies addressed the temporal shift in CRI dominance. First, it was found that preexposure of mice to either KLH or to ABA (on an irrelevant carrier) resulted in diminished CRI dominance in subsequent "primary" responses to ABA-KLH. Secondly, adoptive transfer experiments with B and T cells from virgin mice (Bv, Tv) or ABA-KLH-primed mice (Bp, Tp) showed that recipients of Bv + Tp or Bp + Tv generated anti-ABA PFC responses with intermediate CRI levels. The Tv cells had some preferential tendency to activate CRI+ clones in the Bp population. The results demonstrate that CRI levels are jointly determined by the immune status of both B and T cells. A simple model is offered which accounts for early Id dominance and its gradual decline and has as its central postulate the assumption that CRI+ B cells in the virgin ABA-specific repertoire have an affinity advantage over CRI- clones.

Antibodies to the scrapie protein decorate prion rods

Scrapie is a degenerative, transmissible neurologic disease of sheep and goats which occurs in the absence of any detectable host immune response. Antibodies to the scrapie agent have been produced after immunization of rabbits with either scrapie prions or the prion protein, PrP 27-30, purified from infected hamster brain. Immunoreactivity of the antisera was assessed by dot and Western immunoblots with purified prions and PrP 27-30. Antibodies raised against infectious prions were more immunoreactive with native than denatured preparations, whereas those raised against PrP 27-30 were more reactive with denatured prion preparations. As determined by second antibody-colloidal gold, both antisera were found to decorate scrapie prion rods in purified preparations. Antibodies to cellular filamentous proteins failed to react with PrP 27-30 or the scrapie prion rods; conversely, antibodies to PrP 27-30 did not exhibit immunoreactivity with cellular filamentous proteins. The monospecificity of the rabbit antiserum raised against PrP 27-30 was established by its reactivity after affinity purification. The purified antibodies reacted with PrP 27-30 on Western blots and with the prion rods. Considerable evidence indicates that the scrapie rods are aggregates of infectious prions; the findings presented here provide an immunologic demonstration that PrP 27-30 is a structural component of the prion rods.

Antibodies to the scrapie protein decorate prion rods

Scrapie is a degenerative, transmissible neurologic disease of sheep and goats which occurs in the absence of any detectable host immune response. Antibodies to the scrapie agent have been produced after immunization of rabbits with either scrapie prions or the prion protein, PrP 27-30, purified from infected hamster brain. Immunoreactivity of the antisera was assessed by dot and Western immunoblots with purified prions and PrP 27-30. Antibodies raised against infectious prions were more immunoreactive with native than denatured preparations, whereas those raised against PrP 27-30 were more reactive with denatured prion preparations. As determined by second antibody-colloidal gold, both antisera were found to decorate scrapie prion rods in purified preparations. Antibodies to cellular filamentous proteins failed to react with PrP 27-30 or the scrapie prion rods; conversely, antibodies to PrP 27-30 did not exhibit immunoreactivity with cellular filamentous proteins. The monospecificity of the rabbit antiserum raised against PrP 27-30 was established by its reactivity after affinity purification. The purified antibodies reacted with PrP 27-30 on Western blots and with the prion rods. Considerable evidence indicates that the scrapie rods are aggregates of infectious prions; the findings presented here provide an immunologic demonstration that PrP 27-30 is a structural component of the prion rods.

Arsonate-specific murine T cell clones. II. Delayed-type hypersensitivity induced by P-azobenzenearsonate-L-tyrosine (ABA-Tyr)

To study T cell idiotype expression at the functional level, we developed a hapten-specific delayed-type hypersensitivity (DTH) system by which we avoid the complication of anti-hapten antibody and which is specific only for the immunizing hapten, and not for conjugate specific determinants. Immunization with ABA-Tyr and challenge with ABA diazonium induced footpad swelling with the characteristics of DTH. Anti-ABA antibodies did not contribute to this reaction, as they were undetectable in mice immunized with ABA-Tyr. Furthermore, this ABA-Tyr-specific DTH was under Ir gene control identical to that reported for ABA-Tyr-specific lymphocyte proliferation. All mouse strains tested responded to ABA-Tyr except those of the b haplotype across the entire Ia region. In contrast, contact sensitivity induced by ABA diazonium was not under apparent Ir gene control, probably reflecting 1) different specificities of the induced T cells and 2) the production of anti-ABA antibodies that contribute to the footpad swelling via an Arthus reaction. Having shown that ABA-Tyr can induce T cells mediating DTH, we then examined ABA-Tyr-reactive T cell clones, propagated in vitro, for their ability to mediate DTH. Such clones elicited a response identical to that seen with in vivo immunization with respect to dose dependency, I-Ak restriction, and antigen specificity.

Arsonate-specific murine T cell clones. II. Delayed-type hypersensitivity induced by P-azobenzenearsonate-L-tyrosine (ABA-Tyr)

To study T cell idiotype expression at the functional level, we developed a hapten-specific delayed-type hypersensitivity (DTH) system by which we avoid the complication of anti-hapten antibody and which is specific only for the immunizing hapten, and not for conjugate specific determinants. Immunization with ABA-Tyr and challenge with ABA diazonium induced footpad swelling with the characteristics of DTH. Anti-ABA antibodies did not contribute to this reaction, as they were undetectable in mice immunized with ABA-Tyr. Furthermore, this ABA-Tyr-specific DTH was under Ir gene control identical to that reported for ABA-Tyr-specific lymphocyte proliferation. All mouse strains tested responded to ABA-Tyr except those of the b haplotype across the entire Ia region. In contrast, contact sensitivity induced by ABA diazonium was not under apparent Ir gene control, probably reflecting 1) different specificities of the induced T cells and 2) the production of anti-ABA antibodies that contribute to the footpad swelling via an Arthus reaction. Having shown that ABA-Tyr can induce T cells mediating DTH, we then examined ABA-Tyr-reactive T cell clones, propagated in vitro, for their ability to mediate DTH. Such clones elicited a response identical to that seen with in vivo immunization with respect to dose dependency, I-Ak restriction, and antigen specificity.

Idiotype connectance in the immune system. II. A heavy chain variable region idiotope that dominates the antibody response to the p-azobenzenearsonate group is a minor idiotope in the response to trinitrophenyl group

We describe the recurrence of a cross-reactive idiotope (CRIAD8) in antibody responses to different epitopes, and explore factors leading to its dominance in some responses, but not others. Serological and genomic DNA analyses showed that CRIAD8 is a marker of the CRIa heavy chain variable region (VH) that encodes the majority of anti-p-azobenzenearsonate (anti-ABA) antibodies. The independence of CRIAD8 from any particular light chain or antigen specificity was underscored by the fact that we could isolate hybridomas that secrete antitrinitrophenyl (TNP) antibodies expressing CRIAD8, with lambda 1 light chains. CRIAD8 is dominant in anti-ABA responses, recurrent but nondominant in anti-TNP and anti-chicken gammaglobulin responses, and is virtually absent in other antihapten responses, including that to p-azobenzenephosphonate (ABP), which contains an ABA-cross-reactive component (approximately 5-40%). Dominance in the anti-TNP response could not be achieved by immunization with doubly haptenated TNP-ABA-KLH (keyhole limpet hemocyanin), where the anti-ABA response was dominated by CRIAD8. These observations suggest that, while the CRIAD8 VH region is necessary for idiotypic dominance, it is not sufficient. Apparently, an additional specificity is required. Since immunization with ABA calls up anti-ABP antibodies that express CRIAD8, but not vice versa, it is possible that the additional specificity is ABA itself. This possibility imposes a new constraint on the specificity of the putative idiotype-specific regulation that may establish dominance in the CRIa system.

Isolation of monoclonal antibodies specific for products of avian oncogene myb

We isolated a series of monoclonal antibodies which were raised against a bacterially expressed protein, bp37v-myb, and coded for by part of the avian v-myb gene. These monoclonal antibodies recognized a range of antigenic specificities on bp37v-myb, and this was reflected in their differing specificities for the gene products of the v-myb, c-myb, and E26 viral oncogenes. One monoclonal antibody recognized, in addition to the v-myb and c-myb gene products, a conserved nuclear protein found in all tested cells. We describe the characterization of these monoclonal antibodies.

The anatomy of an antigen molecule: functional subregions of L-tyrosine-p-azobenzenearsonate

The structural components of antigen molecules that interact with class II major histocompability complex (MHC) molecules on antigen-presenting cells (APCs) (agretopes) and with antigen receptors of T-lymphocytes (epitopes) in class II restricted T-cell responses have not been precisely defined. This issue was addressed here using murine T-cell clones specific for the simple immunogen L-tyrosine-p-azobenzenearsonate (ABA-tyr) and a series of analogs of the homologous antigen. Two experimental approaches were used. First, APCs were pulsed with analogs and used to stimulate T-cell proliferation. The patterns of stimulation segregated the clones into two specificity groups and indicated that the epitope recognized by the T-cell included the arsonate group and elements in the side chain of tyrosine. Furthermore, the clones manifest different sensitivities to antigen. Second, non-stimulatory analogs were used to block the presentation of ABA-tyr in an effort to define the agretope. Compounds containing the azophenyl group blocked presentation of ABA-tyr in a dose-dependent fashion, whereas p-arsanilic acid and L-tyrosine were ineffective. The blocking was specific inasmuch as the compounds had no effect on the antigen-induced proliferative responses of giant keyhole limpet hemocyanin (KLH) or hen egg white lysozyme (HEL)-reactive T-cell clones. The blocking pattern indicated that the feature required for productive association with the APC centered on the planar structure of the azo-linked aromatic rings, with little or no contribution from either the arsonate moiety or the tyrosyl side chain. We propose that this structure forms an agretope for this family of compounds.

Differential induction of help and suppression in mice by bifunctional antigens administered via different routes

Bifunctional antigens composed of one L-tyrosine-p-azobenzenearsonate (Tyr-ABA) carrier epitope and one dinitrophenyl (DNP) haptenic epitope separated by 6-aminocaproyl or polyprolyl spacers induced weak IgM anti-DNP plaque-forming cell (PFC) responses in the spleens of mice immunized intraperitoneally, without detectable IgG PFC. However, the same antigens introduced into the footpads induced IgG PFC responses in the draining lymph nodes which rose to levels greater than 100/10(6) viable lymphocytes. Moreover, the response in the lymph nodes to booster injections of antigen was characteristic of secondary T-dependent antibody responses, whereas the splenic secondary response simply mirrored the primary. The magnitude of the IgG PFC response was influenced by the size of the spacer and by the strain of mice, although genetic control did not map to the major histocompatibility complex. Prior i.p. immunization suppressed the IgG response to subsequent immunization in the footpads. This suppression could be transferred to normal syngeneic recipient mice with spleen cells from suppressed donors. Suppressor activity was eliminated by treating the spleen cells with anti-Thy-1 antibody prior to transfer, establishing the T-cell dependency of suppression. Suppression was also induced by Tyr-ABA itself, but not by DNP-lysine, indicating the epitope specificity of the suppressor cells. Thus, bifunctional antigens induce dominant suppression in the spleen but significant help in lymph nodes.

Idiotype profile of an immune response. II. Reversal of the relative dominance of major and minor cross-reactive idiotypes in arsonate-specific T-independent responses

Two different cross-reactive idiotype (CRI) groups are distinguishable in the Ab response of A/J mice to the p-azobenzenearsonate (ABA) hapten: CRIA and CRIm. These two groups showed distinct patterns of relative dominance in the ensuing response depending on whether the inducing Ag was a T cell-dependent (TD) form of ABA, such as ABA-KLH or ABA-CGG, or a T-independent type 1 (TI-1) form, such as ABA-Brucella abortus or ABA-lipopolysaccharide (LPS), and on whether the response was elicited in vivo or in vitro. The CRI+ component of primary in vivo plaque-forming cell (PFC) responses to TD ABA Ags was largely (greater than 90%) CRIA+ as was, to a slightly lesser extent (greater than 75%) the CRI+ portion of secondary or hyperimmune serum Ab or PFC responses to the same Ags. In contrast, in vivo primary and hyperimmune PFC responses to ABA-Bru or ABA-LPS showed a significantly lower CRIA/CRI ratio, averaging 0.5-0.6, with some individual mice giving figures as low as 0.2, indicating predominance of CRIm over CRIA. Serological analysis of hyperimmune anti-ABA Abs from a group of 5 A/J mice immunized with ABA-Bru gave a figure of less than 0.5 for the CRIA/CRI ratio. The most striking disparity from the TD pattern was seen in primary in vitro PFC responses to the TI ABA Ags; here ratios of less than 0.2 were generally seen. Since T cell removal did not alter the Id pattern in the TI responses, CRIA-specific Ts cells do not account for the weak expression of CRIA in such responses. We propose a model that explains these results on the basis of differential expression of IdX dominance by two distinct B cell subpopulations--equatable to the Lyb-5+ and Lyb-5- B cell subsets--along with differential relative activation of these subsets in different types of responses. Examination of anti-ABA PFC responses of F1 progeny of CBA/N and A/J mice to ABA-Bru lends support to this hypothesis since CRIA expression was significantly lower in mice with the xid defect.

Idiotype connectance in the immune system. I. Expression of a cross-reactive idiotype on induced anti-p-azophenylarsonate antibodies and on endogenous antibodies not specific for arsonate

A new cross-reactive idiotope family (CRIAD8) is described that contains subpopulations of antibodies binding to different epitopes. One subpopulation occurs naturally in normal sera from strain A mice, is found mainly on IgG2 and IgG3 subclasses, does not bind p-azobenzenearsonate (ABA)+, does not express CRI5Ci, and can be selectively stimulated by low doses of antiidiotype antibody (AD8). The second subpopulation is not found in normal serum, binds ABA, is found on all IgG subclasses, expresses CRI5Ci, and is selectively stimulated by ABA-conjugated proteins. Since CRIAD8 was found on both subpopulations of antibody, and since each subpopulation could be selectively expanded, it was possible to study the effect that expansion of the ABA- CRIAD8+ set had on subsequent responses elicited by ABA-keyhole limpet hemocyanin (KLH) in the ABA+ CRIAD8+ set. In these experiments, prior immunization with AD8 restricted the subsequent response of the ABA+ CRIAD8+ set to ABA-KLH. Furthermore, only those doses of AD8 that stimulated the ABA-CRIAD8+ set reduced the responsiveness of the ABA+ CRIAD8+ set to ABA-KLH, suggesting that the two phenomena are causally related. These findings argue that CRIAD8 correlates well with a regulatory idiotope and that immune responses by lymphocyte clones that have different antigen-binding specificities can affect one another as a result of their sharing such an idiotope. These results strongly favor a network organization of the immune system.

Arsonate-specific murine T cell clones. I. Genetic control and antigen specificity

The antigen-induced proliferative response of lymph node cells (LNC) from mice sensitized to the monofunctional antigen L-tyrosine-p-azobenzenearsonate (ABA-Tyr) was used to monitor genetic control. All strains tested mounted significant responses, but those that were H-2(b) at both the I-A and I-E loci [B10., B6., B10.A(18R), A.BY, and C3H.SW] gave consistently weaker responses than other haplotypes. The F(1) progeny of matings between high and low responder phenotype parents (DBA/2 and B6, respectively) were high responders, establishing the dominance of the responder trait. Proliferative responses of LNC to ABA-Tyr were blocked by the appropriate anti-Ia monoclonal reagents. For example, B10.A(4R) LNCI (I-A(k), I-E(b)) were blocked by anti-I-A(k), whereas B10.A(3R) LNC (I-A(b), I-E(k)) were blocked by anti-I-E(k). Long-term cultures of T cell lines specifically reactive to ABA-Tyr were established from LNC of A/J mice immunized with ABA-Tyr and were cloned by limiting dilution. The proliferative responses to ABA-Tyr of 14 out of 15 clones tested were I-A restricted on the basis of activation by antigen-presenting cells from appropriate recombinant strains and the blocking activity of the monoclonal anti-Ia antibodies. The response of the other clone was I-E restricted. The fine antigen specificity of the clones was studied using structural analogs of the homologous antigen to induce proliferation. The clones could be divided into three types with respect to responsiveness to ABA-histidine (ABA-His). One group responded about equally well to ABA-His and ABA-Tyr. A second set responded less strongly to ABA-His than to ABA-Tyr, while the third showed no response above background to ABA- His. In all instances, the ABA-His-responding clones discriminated exquisitely between the 2-azo and 4-azo histidine isomers, responding only to the 4-azo compound. These T cell clones provide extremely useful tools for studies of T cell specificity, antigen recognition and lymphoid cell interaction systems.

Idiotype profile of an immune response. I. Contrasts in idiotypic dominance between primary and secondary responses and between IgM and IgG plaque-forming cells

The primary response of A/J mice to p-azobenzenearsonate-keyhole limpet hemocyanin (ABA-KLH) was investigated. A day-by-day analysis at the plaque- forming cell (PFC) level was performed, with inhibition by anti-cross- reactive idiotype (CRI) serum to determine percentage of CRI(+) PFC. A regular pattern in the dynamics of Id (idiotype) dominance was observed. Just as in the NP-b and NP-a systems (9, 12), the major Id (CRI) is more dominant in primary than in secondary or hyperimmune responses. This trend is more apparent in IgG PFC which are generally 80-95 percent CRI(+) at day 10 in the primary response but only 30-40 percent CRI(+) at day 10 in secondary or hyperimmune responses. A somewhat different pattern is seen with IgM PFC. These may reach a peak of 85 percent CRI(+) in the primary response, but secondary or hyperimmune IgM PFC, which are lower in numbers than IgG PFC, remain high in CRI content at approximately 70 percent. The PFC data on extent of id dominance in secondary or hyperimmune responses is fully compatible with previously reported serological data by others. Analysis of IgG PFC by hapten inhibition indicated that heterogeneity was in the order secondary PFC {greater than} primary PFC {greater than} hybridoma AK-2.2 PFC with H(75)/H(25) values of 22.9, 6.2, and 2.7, respectively; where H(75) and H(25) are the hapten concentrations required to give 75 percent and 25 percent of inhibition of PFC, respectively. Hapten inhibition data also suggested that secondary IgG PFC were 10 times higher in median binding avidity for ABA-L-tyrosine than primary IgG PFC. The kinetic analysis strongly indicated that CRI(+) IgM PFC were preferentially switched to IgG PFC in the primary response. In both studies, the CRI content of the earliest-appearing IgG PFC was significantly higher than that of IgM PFC on that day. For example, in one case IgM PFC were 60 percent CRI + on day 6 whereas IgG PFC were 100 percent CRI(+). The high Id dominance and selective isotype switching may have either a B or a T cell basis.

Antigen structural requirements for immunoglobulin isotype switching in mice

L-Tyrosine-p-azobenzene-p-arsonate (RAT) is immunogenic and serves as a carrier for anti-hapten antibody responses in guinea pigs, rats, and mice. However, the murine anti-N-2,4-dinitrophenyl (DNP) plaque-forming cell (PFC) response to the bifunctional antigen 2,4-dinitrophenyl-6-amino-caproyl-L- tyrosine-p-azobenzene-p-arsonate (DNP-SAC-RAT; or BI-1) is extremely weak (2,000-4,000 PFC/spleen) and exclusively IgM in both primary and secondary responses. The 6-amino-caproyl group serves as a spacer in this antigen between the DNP haptenic and RAT carrier epitopes. In view of recent evidence indicating that different T helper cells synergize for optimal antibody responses, a trifunctional antigen, N-2,4- dinitrophenyl-6-amino-caproyl-L-tyrosine-p-azobenze-p-arsonate-(proline)9-L- tyrosine-p-azobenzene-p-arsonate (DNP-SAC-RAT-PRO(9)-RAT; or TRI), was prepared to investigate the effect of adding a second RAT epitope to BI-1. The nonaproline spacer between the two RAT epitopes in TRI is assumed to be a rigid rod of approximately 28 A. TRI induced about twice as many PFC as BI-1 in primary responses of A/J mice, and induced both IgM and IgG PFC in secondary responses. Furthermore, TRI induced IgG PFC responses in mice primed with p-azobenzene-p-arsonate-keyhole limpet hemocyanin, BI-1, or RAT, whereas boosting with BI-1 failed to induce IgG PFC, even in mice primed with TRI. These findings indicate that the minimum antigen structural requirements for inducing IgG PFC in mice are two carrier epitopes and one haptenic epitope. In addition, priming with a mono-epitope carrier (RAT) is sufficient preparation for IgG responses to a trifunctional immunogen. Because TRI differs from BI-1 by the (proline)(9) spacer as well as the additional RAT epitope, two other compounds, N-2,4-dinitrophenyl-6-amino- caproyl-(proline)(9)-L-tyrosine-p-azobenzene-p-arsonate (DNP-SAC-PRO(9)-RAT; or BI-2) and N-2,4-dinitrophenyl-6-amino-caproyl-(proline)(9)-L-tyrosine-p- azobenzene-arsonate (DNP-SAC-RAT-PRO(10); or BI-3), were prepared to evaluate the possible role of the spacer in the observed responses. BI-2, but not BI-3, induced IgG as well as IgM PFC in TRI-primed mice. However, BI-2 failed to induce IgG responses in RAT-primed mice, indicating that TRI and BI-2 were not equivalent immunogens. Because anti-prolyl antibodies had been found in guinea pigs immunized with N-2,4-dinitrophenyl-(proline)10-L-tyrosine-p- azobenzene-p-arsonate (DNP-PRO(10)-RAT), it seemed possible that priming with TRI might induce anti-prolyl antibodies, which, in turn, could cross-link BI-2 molecules into aggregates containing at least two carrier epitopes. To help resolve this question, mice were immunized with acetyl-(proline)10-L- tyrosine-p-azobenzene-p-arsonate and boosted with BI-2. IgG PFC responses were detected, suggesting that anti-prolyl antibodies were indeed responsible, because priming with RAT and boosting with BI-2 did not induce IgG formation. Accordingly, the observations that IgG responses in RAT-primed mice were induced only by TRI and not by any of the bifunctional antigens indicate that two carrier epitopes per antigen molecule are indeed required for IgG induction. They also provide indirect evidence for synergistic help in the switching of immunoglobulin isotypes.

The role of immunoglobulin receptors and T cell mediators in B lymphocyte activation. I. B cell activation by anti-immunoglobulin and anti-idiotype reagents

The possibility that the failure of anti-mouse immunoglobulin (Ig) antibody to induce antibody synthesis by B cells might be due to reversible receptor blockade was investigated. Murine spleen cells were cultured for 3 days in the presence of minute quantities of intact of (Fab') fragments of rabbit anti-mouse Ig antibody. Thereafter, the cells were washed and either trypsin treated or not before reculturing for 18 hr. Only cells that had been trypsinized after culturing with either intact or fragments of anti-Ig gave a vigorous polyclonal antibody response. This response was extremely T dependent, since T cells or culture supernatants from Con A-activated T cells were required for the B cell response. Moreover, anti-delta was much more effective than anti-mu in inducing antibody synthesis. Finally, the use of three different anti-idiotypic antisera rather than anti-Ig reagents selectively activated the specific idiotype in each instance. The findings demonstrate that anti-Ig reagents can potentiate the response of B cells to signals delivered by T cells.

The role of immunoglobulin receptors and T cell mediators in B lymphocyte activation. I. B cell activation by anti-immunoglobulin and anti-idiotype reagents

The possibility that the failure of anti-mouse immunoglobulin (Ig) antibody to induce antibody synthesis by B cells might be due to reversible receptor blockade was investigated. Murine spleen cells were cultured for 3 days in the presence of minute quantities of intact of (Fab') fragments of rabbit anti-mouse Ig antibody. Thereafter, the cells were washed and either trypsin treated or not before reculturing for 18 hr. Only cells that had been trypsinized after culturing with either intact or fragments of anti-Ig gave a vigorous polyclonal antibody response. This response was extremely T dependent, since T cells or culture supernatants from Con A-activated T cells were required for the B cell response. Moreover, anti-delta was much more effective than anti-mu in inducing antibody synthesis. Finally, the use of three different anti-idiotypic antisera rather than anti-Ig reagents selectively activated the specific idiotype in each instance. The findings demonstrate that anti-Ig reagents can potentiate the response of B cells to signals delivered by T cells.

A hemolytic plaque assay for activated murine T cells

In an earlier report, it was shown that murine spleen cells cultured with concanavalin A (Con A) released into the culture supernatants helper and suppressor substances for antibody production. The present communication describes the production of rabbit antisera against culture supernates from Con A-activated spleen cells and their use in a plaque assay for mitogen-activated T cells. The plaque assay, utilizing SRBC to which Staphylococcal protein A had been coupled, the developing anti-supernatant antiserum and guinea pig complement, readily detected secreting T cells. The T-cell nature of the plaque-forming cells (PFC) was established principally by the following: (a) the majority of lymphocytes in the centers of plaques were Thy-1-positive by fluroescence; (b) spleen cells depleted of B cells by incubation in plastic dishes coated with rabbit anti-mouse Ig antibody gave greatly enriched PFC responses; (c) anti-Thy-1 and anti-Lyt-2.2 treatment of spleen cells almost completely depleted PFC; (d) T-cell mitogens (Con A and phytohemagglutinin) but not B-cell mitogens (lipopolysaccharides) induced PFC responses; (e) T cells maintained in culture for 10 d with Con A and T-cell growth factor yielded PFC. Kinetic and dose response studies showed that high doses of mitogen induced rapidly appearing T-PFC and the responses peaked at day 1--2 of culture. Lower doses of mitogen-induced PFC required longer periods of incubation for detection, indicating that cell activation and secretion may be different dose-dependent activities of mitogens. Another noteworthy finding was that the antiserum reacted with surface antigens of T-PFC, indicating that secreted products are expressed on the membranes of T cells, offering the possibility of isolating populations of cells with specific secretory potential. Although the precise nature of the T-cell products detected by the antiserum used in this assay are unresolved, 10% of the target-cell-adherent population from spleen cells of BALB/c mice sensitized to L929 cells formed plaques. This suggests that the antiserum has significant activity against the products of cytotoxic T cells, a finding which accords with the activity of anti-Lyt-2.2 serum against mitogen-induced T-PFC. The method clearly offers new possibilities for the analysis of T cells and their products and should provide an important approach to the clonal analysis of lymphokine production.

Rosette formation between murine lymphocytes and erythrocytes. A new locus in the H-2 region

More than 5% of murine splenic lymphocytes form rosettes with syngeneic erythrocytes. This property was maximally expressed when the lymphocytes were cultured for 24 h before rosetting. About 70% of the rosetting lymphocytes were B cells and 30% were T cells on the basis of surface immunoglobulin and the Thy-1-antigen. Capping surface immunoglobulin had no effect on the capacity of lymphocytes to form rosettes, indicating that the receptor in question was not immunoglobulin. The capacity of lymphocytes to form rosettes with erythrocytes from other strains of mice was H-2 restricted. Extensive pairings of congenic and recombinant strains as donors of lymphocytes and erythrocytes showed that none of the known loci within the H-2 region-controlled rosetting. The involvement of regions on chromosome 17, telomeric or centromeric to H-2, was also excluded. The data were only compatible with the conclusion that this form of self-recognition is associated with a new locus (or loci) mapping between H-2G and H-2D.

Radionuclide kymography for the assessment of regional myocardial wall motion

Regional myocardial wall motion is usually evaluated qualitatively from ECG-gated end-systolic and end-diastolic blood-pool images. Radionuclide kymography, which displays a one-dimensional scintigraphic image in time, synchronized with the electrocardiogram, provides a method to quantitate this motion. The technique is analogous to M-mode ultrasound in that one dimension is displayed as a function of time, but the activity distribution is displayed in place of acoustic interfaces. The motion of regional myocardial segments can be measured from multiple kymographic projections across the cardiac blood pool, after equilibration of a radioactive tracer. Radionuclide kymography is potentially better quantitatively than gated blood-pool imaging and is not hindered by viewing windows as are single- and multiple-transducer ultrasonography. Regional wall motion determined from radionuclide kymography correlated well with that determined from contrast left ventriculography in a series of patients. Since the kymographic sweep is initiated by the R wave of the ECG and proceeds continuously throughout the cardiac cycle, the temporal sequence of regional myocardial contraction can be directly assessed and related to corresponding portions of the ECG.

Purification of functional, determinant-specific, idiotype-bearing murine T cells

Strain A/J mice immunized with azobenzenearsonate (ABA)-mouse IgG conjugates develop suppression for anti-trinitrophenyl(TNP) responses to doubly conjugated (ABA,TNP) proteins. This suppression is specific for the ABA epitope and is mediated by T cells in cell transfer experiments. ABA-binding T cells from suppressed animals were purified by a two-stage procedure in which B cells were removed from spleen cell populations by adherence to plastic surfaces coated with anti-mouse Ig antibody, followed by binding the nonadherent population (more 95 percent Thy-1-positive) to surfaces coated with ABA-protein conjugates. Approximately 90 percent of the cells recovered by temperature-dependent elution from the ABA plates (similar to 2 percent of the spleen cells) bound antigen immediately afterward, and up to 50 percent of the cells bound anti-cross-reactive idiotype antibody. On the other hand, the nonadherent T-cell population was completely negative in the antigen- binding and idiotype assays. Another distinguishing feature of the two T-cell populations was that 78 percent of the adherent cells, but only 2 percent of the nonadherent cells, were Ia positive, although the specific I-region marker(s) expressed on the cells was not identified. The biological function of the antigen-binding T cells was investigated using a standard cell transfer protocol. Suppressor cells were enriched in the adherent population by a factor of at least 25, establishing that functional, epitope-specific, idiotype-bearing T cells can be significantly purified by this procedure. Note Added in Proof. We have recently isolated two types of ABA-binding molecules biosynthetically labeled with (35)S-methionine from NP-40 lysates of purified antigen-specific T cells. The molecules were purified by adsorption onto an ABA-Sepharose immunoadsorbent followed by elution with 9 M urea. Autoradiograms of SDS-PAGE of the eluates revealed components with tool wt of approximately 60,000 and 33,000 dahons. These molecules were not present in eluates from a bovine IgG-Sepharose control immunoadsorbent and thus represent specific ABA-binding products synthesized by T cells.

T-lymphocyte activation by immunogenic determinants

Synthetic antigens have been of great value in elucidating the relationships between antigen structure and lymphocyte activation. The compound RAT behaves as a monofunctional antigen in guinea pigs and mice, inducing T-lymphocyte responses without appreciable circulating antibody, although the ABA-specific B cell population is expanded by immunization with the monovalent molecule. On the other hand, bifunctional antigens composed of one RAT moiety serving as a carrier and a second chemical group, either identical to or different from RAT, serving as a hapten, induced antibody responses. In such responses, T cell specificity was always directed against the RAT component. Using symmetrical bifunctional antigens with rigid or flexible spacers between the two determinants, marked differences in structural requirements for cell triggering, assessed by antigen-induced lymphocyte proliferation, and for cell cooperation, determined by antibody formation, were found. Rigidly spaced bifunctional antigens serve admirably for cooperation but poorly for T cell activation, underscoring the advantage of two-point binding for the latter.

Activation of B cell subsets by T-dependent and T-independent antigens

The capacity of the trinitrophenyl haptenic group coupled to a series of chemically dissimilar carriers to cross-stimulate putative T-dependent and T-independent B-cell subpopulations was determined by using an in vitro limiting dilution technique to generate primary IgM responses. TNP-Ficoll and TNP-dextran, two T-independent antigens with little or no polyclonal mitogenicity, stimulate the same population of anti-TNP precursors, which is distinct from the precursor population activated by TNP-LPS, a T-independent polyclonal mitogen, or by TNP-HRBC, a T-dependent antigen. TNP-LPS and TNP-HRBC activate the same precursor population, indicating that LPS can substitute for the T cell signal in T-dependent B-cell responses, whereas nonmitogenic T-independent antigens cannot. However, the cumulative evidence from this and other laboratories suggests that LPS and T-dependent antigens activate B cells by different mechanisms. TNP conjugates of Ficoll and dextran, which are relatively poor inducers of polyclonal B cell activation, induced larger anti-TNP clones than did TNP-LPS, a strong polyclonal mitogen. Macrophages are required for the anti-TNP-Ficoll/anti-TNP-dextran response, whereas, a similar requirement has not been shown for the anti-TNP-LPS response. Thus, macrophages may function as polyclonal B cell activators in T-independent responses. Experiments in which TNP was coupled directly onto the macrophage surface support this hypothesis. B-cell heterogenity in T-dependent responses is suggested by experiments using the C3 receptor as a marker for functional subpopulations of B cells. Murine T cells cooperate with B cells that carry a receptor for C3 and with at least some B cells which lack the C3 receptor in a primary in vitro antibody response. In vitro culture experiments using populations of B cells fractionated on the basis of the C3 receptor showed that CR+ cells were unable to make T-dependent antibody responses in the presence of anti-C3 antibody, whereas the response of CR- B cells was unaffected. Using irradiated, carrier-primed spleen cells from B10.A mice as a source of helper cells for B cells derived from various congenic strains in an in vitro primary IgM response to TNP-KLH, CR+ B cells cooperated across haplotype differences in the I region of the MHC, whereas CR- B cells did not. Preliminary mapping experiments for the genetic restriction of CR- B cells suggest complementation between the I-A and I-C subregions of the MHC. These findings tentatively suggest the existence of alternative cooperative pathways between T cells and B cell subpopulations.

Carrier-directed anti-hapten responses by B-cell subsets

The capacity of the trinitrophenyl (TNP) haptenic group, coupled to a series of chemically dissimilar carriers, to cross-stimulate putative T- dependent and T-independent murine B-cell subpepulations was determined by using an in vitro limiting dilution technique to generate primary IgM responses. It was found that TNP-Ficoll and TNP-dextran, two T- independent antigens with little or no polyclonal mitogenicity, stimulate the same population of anti-TNP precursors, which is distinct from the precursor population activated by TNP-bacterial lipopolysaccharide (LPS), a T-independent polyclonal mitogen, or TNP-horse erythrocytes (HRBC), a T-dependent antigen. On the other hand, TNP-LPS and TNP-HRBC activate the same precursor population, indicating that LPS can substitute for the T- cell signal in T-dependent B-cell responses, whereas nonmitogenic T- independent antigens cannot. However, the cumulative evidence from this and other laboratories strongly indicates that LPS and T-dependent antigens activate B cells by different mechanisms. Of particular interest, LPS is incapable of activating B cells responsive to weakly- or nonmitogenic T-independent antigens. Based on clonal burst size, T-dependent antigens are capable of inducing greater antigen-specific B-cell proliferation than T-independent antigens. However, TNP conjugates of Ficoll and dextran, which are relatively poor inducers of polyclonal B-cell activation, induced larger anti-TNP clones than did TNP-LPS, a strong polyclonal mitogen. The findings reinforce the evidence favoring existence of multiple B- cell subpopulations with distinctive activation pathways. They also strengthen the proposition that a given B-cell subset can be activated by more than one mechanism.

Complement-dependent and -independent pathways of T cell-B cell cooperation

BDF1 mice treated with CoV had markedly reduced levels (less than 20%) of native serum C3 32 hr later, whereas the frequency of splenic CR+ cells was normal. CoV treatment before immunization reduced the IgM PFC response to a T-dependent antigen (TNP-SRBC) by more than 60%. Inclusion of highly specific anti-C3 antibody had no effect on the T-dependent IgM response of CR- B cells. The residual PFC responses in cultures of unfractionated spleen cells treated with anti-C3 could be largely or completely accounted for by CR- B cells in the cultures. The effect of anti-C3 antibody was not due to cytotoxicity. These data collectively indicate that the effect of CoV on T-dependent antibody responses is due to decreased C3 in serum rather than to interaction of C receptors directly with CoV or with C3 cleavage products. They suggest the existence of at least two distinct pathways of T-B cooperation, one in which C3 is an obligatory participant and another in which it may be uninvolved.

Murine B-cell subpopulations responsive to T-dependent and T-independent antigens

Strain A/J mice made secondary indirect plaque-forming cell (PFC) responses to azobenzenearsonate (ABA) conjugates of giant keyhole limpet hemocyanin (KLH), a thymic-dependent antigen, but not to conjugates of Ficoll, a T-independent antigen. ABA-Ficoll was also unable to elicit a response in animals primed with ABA-KLH, which have an expanded anti-ABA memory cell pool. On the other hand, ABA-Ficoll rendered mice unresponsive to ABA-KLH when administered before priming or boosting with the T-dependent immunogen. Hence, the T-independent antigen was able to tolerize but unable to trigger B-memory cells responsive to the T-dependent antigen. A/J mice immunized with dinitrophenyl conjugates of Ficoll or bovine IgG (BGG) made vigorous IgM and IgG PFC responses. PFC responses to ABA-KLH and 2,4-dinitrophenyl (DNP)-BGG were abrogated by depleting mice of C3 with cobra venom factor, whereas the IgM and IgG PFC responses to DNP-Ficoll were unaffected. B lymphocytes were fractionated on the basis of receptors for C3 and the subpopulations were assayed for in vitro PFC responses to DNP-Ficoll. Very little response was obtained from complement receptor lymphocyte [CRL(+)] B cells, whereas CRL(-) cells were more responsive than unfractionated B cells. Both populations responded to a polyclonal B-cell mitogen (lipopolysaccharide). On the other hand, the in vitro PFC response to a T-dependent antigen (sheep erythrocytes) correlated with the presence of CRL(+) B cells in the cultures. However, a minor component of this response, sensitive to anti-Thy-1 serum, was made by CRL(-) B cells, indicating the existence of subpopulations of T-dependent B cells with different signalling requirements. The results suggest that most B cells responsive to T-dependent antigens possess receptors for C3 and that C3 plays an obligatory role in the response of these cells. A distinct subpopulation of B cells which lack C3 receptors respond to T-independent antigens. The precursors of PFC for the ABA epitope reside largely or exclusively in the CRL(+) compartment in A/J mice, whereas precursors for the DNP determinant are found in both compartments.

Thallium-201: scintillation camera imaging considerations

Modulation transfer functions, line spread functions, and energy spectra were obtained for an Anger scintillation camera using three different collimators and commercially produced 201Tl. Images of a thyroid phantom were obtained using these collimators. For each of the three collimators, line spread functions and modulation transfer functions were obtained for both the 75-keV x-ray and 167-keV gamma photon of 201Tl. Although the intrinsic resolution of the scintillation camera is superior when imaging with the 167-keV gamma photon, system performance was superior when the 75-keV x-ray was imaged. Contamination form 202Tl, which emits abundant 439-keV gamma photons, degraded images taken at 167 keV because of septum penetration. At 75 and 167 keV the converging collimator yielded the best system performance. Imaging time was significantly shorter using the 75-keV x-rays.