Antibody response of inbred mouse strains to ordered tetrapeptides of tyrosine and glutamic acid attached to multichain polyalanine or polyproline. Tyr-Tyr-Glu-Glu is a major determinant of the random poly-(Tyr, Glu)-polyDLAla--polyLys

Carrier-dependent specificity of antibodies to a conserved peptide determinant of gp120

Amino acid residues 421-436 constitute a comparatively conserved determinant of gp120 that participates in the binding of host cell CD4 receptors by HIV-1. We compared the immunogenicity of synthetic Cys-gp120 (421-436) conjugated to KLH via the N terminal Cys residue (KLH-I) and gp120 (421-436) extended at its N terminus with a 15 residue tetanus toxoid T cell epitope (T-I) in non-autoimmune mice (BALB/cstrain) and Fas-defective autoimmune mice (MRL/lpr strain). Both immunogens elicited high titer Abs detected as the binding to gp120 (421-436) conjugated to bovine serum albumin (BSA-I) immobilized in ELISA plates. Abs from KLH-I immunized mice displayed binding to full-length gp120 but the Abs from T-I immunized mice did not. Proteins unrelated in sequence to gp120 did not bind the Abs. Soluble I and T-I failed to compete with immobilized BSA-I for binding to anti-KLH-I Abs, whereas these peptides inhibited anti-T-I Ab binding by BSA-I (rank potency order: BSA-I > T-I >> I). These results indicate the influence of the carrier protein on the specificity of Abs to synthetic I. Low level BSA-I and gp120 binding Abs were detected in sera from non-immunized MRL/lpr mice. Similar Ab binding titers and specificity profiles were evident in MRL/lpr and BALB/c mice following immunization with KLH-I and T-I, indicating that pre-existing immunity to gp120 in the former strain does not influence the magnitude or specificity of the Ab response.

Dichotomy between the T and the B cell epitopes of the synthetic polypeptide (T,G)-A--L

Studies with the well-characterized, synthetic, random-multichain polypeptide poly(LTyr,LGlu)-poly(DLAla)-poly(LLys) (T,G)-A-L) led to the discovery of determinant-specific genetic control of the immune response, as well as to other immunological phenomena. Moreover, the tetrapeptide TyrTyrGluGlu built on the same backbone ("(T-T-G-G)-A--L") was found to represent its major B cell epitope. We have recently shown that for interaction with major histocompatibility complex class II molecules and stimulation of T cells, (T,G)-A--L requires proteolytic processing and the resulting T cell epitopes are close to the N termini of the branched polymer's side chains. Thus, we were interested to elucidate the major T cell epitope of (T,G)-A--L, by using the ordered polypeptides (T-T-G-G)-A--L and (T-G-T-G)-A--L, in which only the two internal amino acids of the tetrapeptide attached to the side chains are switched. We established T cell lines to these antigens, and found that the ordered analog (T-T-G-G-)-A--L, which was defined as the B cell epitope of (T,G)-A--L, did not represent its T cell epitope, whereas (T-G-T-G)-A--L, to which only a minor anti-(T,G)-A--L Ab response was directed, was found to be its major T cell epitope. In addition, there was no cross-reaction between (T-G-T-G)-A--L and (T-T-G-G)-A--L at the T cell level, similar to the lack of cross-reaction of their antibodies. Analysis of the repertoire of the T cell receptors used by these lines revealed that the (T,G)-A--L and the (T-T-G-G)-A--L specific T cell lines were not restricted in their V alpha and V beta TCR usage, whereas the (T-G-T-G)-A--L-specific line was restricted by both V alpha and V beta T cell receptor gene products. This difference might be due to the thymus-independent characteristics previously described for the latter antigen.

Structural origin of the immunological diversity of two closely related tetrapeptides: CIDNP study of TyrTyrGluGlu and TyrGluTyrGlu epitopes

Photochemically induced dynamic nuclear polarization (photoCIDNP) measurements, specific for exposed tyrosine residues, have been applied to elucidate conformational differences responsible for the immunological diversity of the synthetic multichain copolymers, Tyr1Tyr2Glu3Glu4-poly-DL-Ala-poly-Lys and Tyr1Glu2Tyr3Glu4-poly-DL-Ala-poly-LS. These two copolymers are essentially identical in their molecular weight, size, shape and composition, and differ only in the order of the two internal amino acid residues within the sequence of the tetrapeptide epitopes. Nonetheless, previous studies have shown that the two macromolecules behave differently, as evidenced by their immunological and immunogenic properties. As immunogens they act under different genetic control mechanisms, and differ in their interactions with antigen presenting cells, T cells and B cells. Antibodies elicited against these two antigens do not cross react. The photoCIDNP measurements of these two polymers, intended to elucidate discrete structural differences controlling immune recognition, showed that in the TyrTyrGluGlu polymer, Tyr1 and Tyr2 rings are free, non-interacting and undergo fast internal rotation. Computed minimum energy conformations confirm these conclusions and indicate that Tyr1 and Tyr2 point to different regions in space. In TyrGluTyrGlu, however, CIDNP measurements give rise to one broad tyrosine 3,5 proton signal, the result of a strong Tyr1-Tyr3 hydrophobic interaction. These two tyrosine residues are thus close in space, and undergo slow internal rotation. These results are in agreement with the computed minimum energy conformations.

Imprint of thymic selection on autoreactive repertoires

We have focussed on the differences in origin and physiological properties of two classes of self-reactive T cells. Autoreactive T cells described in many laboratories are activated in the course of normal immune responses to foreign antigen. These T cells can be shown under well-defined conditions to be the direct progeny of antigen-stimulated precursors. This, together with evidence that their activation requirements can be distinguished from those of antigen-specific, MHC-restricted T cells, leads us to suggest that they represent a particular physiological state that recapitulates the conditions of thymic selection and is induced in many antigen-specific, MHC-restricted peripheral T cells as a result of normal antigen-dependent activation. Although it appears that the associated physiological properties can be stable in some in vitro maintained lines, it is possible that this is normally a transient state in vivo. Available evidence concerning the specificity of these T cells indicates only that they can be activated in the absence of any identifiable foreign antigen by class II MHC-syngeneic but not MHC-allogeneic stimulators. We have suggested that such T cells are specific for the same elements, possibly an association of MHC and other self-peptides (Singer et al. 1987), that are the basis for positive selection in the thymus. The properties of these autoreactive T cells need to be distinguished from those of T cells associated with autoimmune pathology. It is presumed that autoimmune T cells are directly activated in a resting state by specific self-peptides. Our interest in distinguishing these self-reactive T-cell populations has focussed on different predictions concerning the diversity of their associated self-reactive repertoires. The relative complexity of the immune repertoire expressed in autoreactive T cells expanded by positive selection and restimulated in the course of normal antigen-specific immune responses should be considerably greater than that of autoimmune T cells constrained by negative selection and a narrow window of escape from self-tolerance. We were greatly hindered in our initial efforts in this analysis by the considerable effort required to characterize any specific immune repertoire. A published technique employing poly(A) tailing (Frohman et al. 1988) did not work efficiently in our hands, although others (Loh et al. 1989) have apparently had some success. We describe above an alternative approach, linker-facilitated PCR, which we have employed for efficient repertoire analysis. Using this method we have been able to identify dominant utilization of the Va4 family in T cells specific for the synthetic peptide YYEELLKYYEELLK.(ABSTRACT TRUNCATED AT 400 WORDS)

Covalent linkage of the synthetic adjuvant MDP to the synthetic polypeptide (T,G)-A-L changes the specificity of the immune response at the T and B cell level

It is now well established that the synthetic molecule MDP (N-acetylmuramyl-L-alanyl-D-isoglutamine) can be a good adjuvant of immunity when covalently linked to antigen. The question raised in this work is whether conjugation of antigen to the immunomodulatory molecule MDP can modify the specificity of the antibodies and T cells induced following immunization. Using the well characterized synthetic polypeptide antigen, poly(L-Tyr,L-Glu)-poly(DL-Ala)--poly(L-Lys) [(T,G)-A--L], we show that immunization of C57B1/6 (H-2b) mice with MDP-(T,G)-A--L conjugate elicits at least two types of antibody directed against the poly(DL-Ala)--poly(L-Lys) (A--L) part of the antigen, and against new determinant(s) formed by MDP and a portion of the (T,G)-A--L molecule. Interestingly, the poly-(L-Try L-Glu) side chains thought to constitute the major antigenic determinants of the (T,G)-A--L molecule were not recognized. Lymph node cells from (T,G)-A--L immunized mice can be equally well stimulated in vitro by (T,G)-A--L or by MDP-(T,G)-A--L, whereas lymph node cells from MDP-(T,G)-A--L primed animals can be stimulated only when challenged by the conjugate used for immunization, and not by the free synthetic polypeptide (T,G)-A--L. The data presented here show that the coupling of a low mol. wt molecule such as MDP (mol. wt approx. 500) to an antigen can greatly modify the immune response directed against this antigen. Furthermore, (1) different antibody specificities are elicited depending upon whether the priming is done with free MDP and antigen or with MDP covalently linked to the antigen; (2) although still accessible on the conjugate, an epitope which represents the major antigenic determinant on the free polypeptide appears to be silent when presented on the conjugate; and (3) new determinant(s) formed by the chemical linkage of the polypeptide to the synthetic adjuvant are involved in the priming of T cells.

Serological analysis of idiotypic determinants on monoclonal antibodies specific to poly(Tyr,Glu)-poly(DLAla)--poly(Lys) and its ordered analogue (Tyr-Tyr-Glu-Glu)-poly(DLAla)--poly(Lys)

Anti-idiotypic sera (aIds) were raised in C57BL/6 mice against monoclonal antibodies (McAbs) which bind poly(Tyr,Glu)-poly(DLAla)--poly(Lys)--abbreviated to (T,G)-A--L--and (Tyr-Tyr-Glu-Glu)-poly(DLAla)--poly(Lys)--abbreviated to (T-T-G-G)-A--L--(nos. 103 and 160) and McAbs which react only with (T-T-G-G)-A--L (nos. 100 and 114). Anti-Id antibodies against 103 McAb reacted with (T,G)-A--L specific antibodies and specifically inhibited their binding to iodinated antigen. Similarly, conventional antibodies against the major idiotypes of (T,G)-A--L-specific antibodies inhibited the binding of 103 McAb to antigen. It is therefore suggested that 103 McAb shares major idiotypes with (T,G)-A--L-specific polyclonal antibodies of C3H.SW origin. Anti-Ids against 114 McAb also inhibited the binding of (T,G)-A--L-specific antibodies to antigen, but the binding of 114 McAb could not be inhibited by conventional aIds. Therefore, idiotypes of 103 and 114 McAbs define idiotypic determinants expressed on two different subpopulations of (T,G)-A--L-specific antibodies: those that carry major idiotypes and those which express idiotypic determinants other than the major one (minor Ids). Anti-idiotypic sera against McAbs nos. 100 and 160 reacted with the homologous idiotypes and not with the major idiotypes of (T,G)-A--L-specific antibodies. In addition to the aforementioned specificities we could define cross-reactive idiotypes (private) shared by McAbs nos. 100, 103 and 114 McAbs nos. 160 and 114. The analysis of idiotypes expressed on anti-(T,G)-A--L McAbs enabled the detection of new antigen binding site related idiotypic determinants in addition to the major idiotypes which were immunodominant in the polyclonal anti-(T,G)-A--L antibodies.

Fine specificity of antibodies to the synthetic polypeptide poly(L-tyrosine, L-glutamic acid)-poly(DL-alanine)--poly(L-lysine) and its ordered analogs as followed by solid-phase radioimmunoassay

The fine specificity of antibodies against (T,G)-A--L and its ordered analogs (T-T-G-G)-A--L and (T-G-T-G)-A--L was studied. Fifty percent of the antibodies against (T,G)-A--L are directed toward the T-T-G-G determinants and 19% against T-G-T-G-like determinants. The rest of the antibody response to (T,G)-A--L is directed against determinants which exist in (T,G)-A--L but are not cross-reactive with either T-T-G-G- or T-G-T-G-like determinants. Although (T-T-G-G)-A--L and (T-G-T-G)-A--L differ only in the sequence of tyrosine and glutamic acid in their side chains, no crossreactivity was observed between antibodies toward the two ordered polypeptide antigens.

Fine specificity and idiotypic expression of monoclonal antibodies directed against poly(Tyr,Glu)-poly(DLAla)--poly(Lys) and its ordered analogue (Tyr-Tyr-Glu-Glu)-poly(DLAla)--poly(Lys)

In order to study the repertoire of poly(Tyr,Glu)-poly(DLAla)--poly(Lys) [(T,G)-A--L] specific antibodies, monoclonal antibodies were prepared by fusing myeloma cells with spleen cells from C3H.SW mice immunized with (T,G)-A--L and boosted with (Tyr-Tyr-Glu-Glu)-poly(DLAla)--poly(Lys)](T-T-G-G)-A--L]. Eleven clones which secreted homogeneous antibodies were obtained. In general, two families of monoclonal antibodies were detected: those which bind exclusively (T-T-G-G)-A--L and those which bind both (T-T-G-G)-A--L and (T,G)-A--L. Analysis for idiotypic expression revealed that only two antibodies (clones no. 103 and 160), which were found to be similar in their fine specificity, cross-reacted with antibodies against the major idiotypes of (T,G)A--L specific antibodies. Guinea-pig antibodies against clone no. 160 reacted with the polyclonal (T,G)-A--L specific antibodies, whereas antibodies against 103 monoclonal antibodies did not react with C3H.SW anti-(T,G)-A--L antibodies, but did cross-react with four other monoclonal antibodies. It appears that the idiotypic determinants expressed on polyclonal (T,G)-A--L specific antibodies are heterogeneous, and consist of at least two serologically different idiotypes detected by clones no. 103 and 160.

Cellular analysis of specificity of antibodies and of delayed type hypersensitivity responses toward some structurally related synthetic antigens: boosting is determined by specificity of T cells

The crossreactivity between the random synthetic polypeptide antigen poly(Tyr,Glu)-poly(DLAla)--poly(Lys) [(T,G)-A--L] and its ordered-sequence analogs (Tyr-Tyr-Glu-Glu)-poly(DLAla)--poly(Lys) [(T-T-G-G)-A--L] and (Tyr-Glu-Tyr-Glu)-poly(DLAla)--poly(Lys) [(T-G-T-G)-A--L] at the level of humoral and cellular responses was studied. For delayed type hypersensitivity responses, (T,G)-A--L-activated T cells could be challenged with the homologous antigen as well as with the ordered analogs. T cells activated by (T-T-G-G)-A--L could be challenged with either the homologous antigen or with (T,G)-A--L but not with (T-G-T-G)-A--L. Similarly, no cross stimulation was observed between (T-G-T-G)-A--L-activated cells and (T-T-G-G)-A--L, whereas (T,G)-A--L could challenge the latter cells to mediate significant responses. Similar but not identical cross reactions were observed when primed spleen cells or lymph nodes were transferred to irradiated recipients that were boosted for the production of antibodies. In contrast to observations at the level of cellular responses, (T-G-T-G)-A--L-primed spleen or lymph node cells could not be boosted with (T,G)-A--L for the production of detectable amounts of antibodies, although boosting with the homologous antigen resulted in significant levels of (T-G-T-G)-A--L-specific antibodies. Transfer experiments in which mixtures of T and B cells, each primed to a different ordered polypeptide antigen, were injected into irradiated recipients showed that successful cooperation occurs provided that the boost is given with the T-cell-specific antigen. The antibodies produced were specific to the antigen used for B-cell priming. The T-cell-B-cell collaboration probably occurs through specific determinants that are shared between the two antigens in which the ordered peptides are attached to the same multichain polymer and that are recognized by both the T and the B cells.

The use of unideterminant fragments of ferredoxin in the genetic mapping of determinant specificity of the immune response

The ferredoxin (Fd) molecule is a small non-mammalian immunogenic protein containing 55 amino acid residues with only two major antigenic determinants located with the NH2-terminal heptapeptide and the COOH-terminal pentapeptide. Selective enzyme cleavages of Fd with either trypsin or carboxypeptidase A result in the inactivation of the antigenic determinants by the removal of a tripeptide at the NH2-terminal and two amino acid residues at the COOH-terminal, effectively leaving 52 and 53 amino acid fragments respectively, each containing a single antigenic determinant. Fd digested with both enzymes yielded a 50 amino acid peptide with both determinants inactivated. Purity of these digests was assessed using monoclonal antibodies in standard and antigen-blocking ELISAs. The doubly digested peptide had virtually no reactivity with anti-Fd sera, reconfirming that the central cysteine-rich region is serologically silent. It was found that the sum of the reactivities of the N- and C-determinant-bearing peptides as equal to that of the native Fd and that the ratio of the reactivities could be used to assess determinant selectivity in the response to Fd in congenic recombinant strains of mice. This method was used in mapping the determinant selectivity in the antibody response to the MHC of mice to the left of the I-B subregion. Use of the B10.HTT strain indicated that separate genes mapping to the same subregion code for the magnitude of the antibody response and the determinant selectivity of the response.

The specific binding of Listeria monocytogenes-immune T lymphocytes to macrophages. I. Quantitation and role of H-2 gene products

A system was developed to study the binding of Listeria monocytogenes-specific T cells to L. monocytogenes-pulsed macrophages as an analogue of the initial phase of T-cell activation: antigen recognition. Specific binding, demonstrable after a brief (1 h) contact, was quantitated by the depletion of L. monocytogenes-specific T-cell activity in the cells nonadherent to L. monocytogenes-pulsed macrophage monolayers. L. monocytogenes-specific T-cell function was measured by its ability to activate L. monocytogenes-pulsed macrophages, both to secrete a protein mitogenic for thymocytes and to effect nonspecific tumoricidal activity. These manifestations of T-cell function are known to be regulated by products of I region of the H-2 gene complex. Studies designed to determine the role of H-2 gene products in specific T-cell-macrophage binding have revealed the following. T cells bind specifically to syngeneic macrophages and poorly to allogeneic macrophages. The binding ability appears to map to the K end of the H-2 gene complex (K through I-E). At least two distinct populations of B6AF1 T cells with binding avidity for L. monocytogenes presented on parental macrophages can be identified. Finally, the binding of a given parental-reactive B6AF1 T-cell clone can be specifically inhibited by pretreatment of the antigen-pulsed B6AF1 binding macrophage with anti-H-2 (anti-Ia) antibodies reactive with the appropriate parental haplotype. These results strongly suggest that H-2 gene products play a direct role in mediating the specific binding of T cells to macrophages and imply that the antigen-dependent physical interaction between T cells and macrophages is the initial, and determining, event in some forms of H-2 gene control of immune reactivity.

Change in specificity of antibodies to a random synthetic branched polypeptide in mice tolerant to its ordered analogs

The crossreactivity between the random synthetic polypeptide antigen, (Tyr,Glu)-poly(DLAla)- -poly(Lys), and its ordered sequence analogs, (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(Lys) and (Tyr-Glu-Tyr-Glu)-poly(DLAla)- -poly(Lys), has been studied on the level of tolerance induction. Induction of tolerance to the random (Tyr,Glu)-poly(DLAla)- -poly(Lys) affected the response of the tolerant mice to the homologous antigen as well as to (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(Lys), which was shown previously to represent the major determinant of (Tyr,Glu)-poly(DLAla)- -poly(Lys). In contrast, these mice responded with high antibody titers to the hardly crossreacting (Tyr-Glu-Tyr-Glu)-poly(DLAla)- -poly(Lys). Mice tolerant to the ordered peptide antigen (Tyr-Glu-Tyr-Glu)-poly(DLAla)- -poly(Lys) did not respond to the homologous polypeptide; however, their immune response to either (Tyr-Glu)-poly(DLAla)- -poly(Lys) or (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(Lys) was not affected. Mice that were tolerant to (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(Lys) responded well to (Tyr-Glu-Tyr-Glu)-poly(DLAla)- -poly(Lys). Furthermore, these mice produced high antibody titers after immunization with the random (Tyr,Glu)-poly(DLAla)- -poly(Lys). However, the antibodies produced were not specific to the major determinant of (Tyr,Glu)-poly(DLAla)- -poly(Lys), namely, Tyr-Tyr-Glu-Glu, but were directed to minor determinants of the random polypeptide, including Tyr-Glu-Tyr-Glu, which are not immunopotent when nontolerant mice are immunized with (Tyr,Glu)-poly(DLAla)- -poly(Lys). Thus, whereas antigenic specificity reflects itself also at the level of tolerance induction, the animals that had been made tolerant are capable of responding to previously silent antigenic determinants.

Identification of different antigenic determinants within the synthetic multichain Co-polymer poly(LTyr,LGlu)-poly(DLAla) -- poly (LLys), (T,G)-A--L, as recognized by the chicken. II. Fine-specificities of the anti-(T,G) part of chicken anti-(T,G)-A--L antisera

Sera from three chickens obtained from a genetic high-responder inbred strain immunized with the multichain polypeptide poly(LTyr,LGlu)-poly-(DLAla)--poly(LLys) (T,G)-A--L) were analysed for possible restrictions in the fine-specificities of anti-(LTyr,LGlu) antibodies. A panel of synthetic hexa- and heptapeptides composed of L-Tyr and L-Glu residues linked to a C-terminal spacer tripeptide, and with L-Tyr as N-terminal, were used as inhibitors in a double-antibody radioimmunoassay. Results showed that all peptides tested possessed some inhibitional potential, although the percentage of displacement for the different sequences varied between 43% and 58%,20% and 56%, and 48% and 85%, respectively, for the three sera tested at a given inhibitor concentration. Different peptide sequences appeared as the most efficient inhibitor in the three sera tested. No simple relationship was found between substitution/elongation of inhibitor peptides and their inhibitional potential, as would have been expected from a simple conception of (T,G)-A--L possessing only one sequential determinant. Possible evidence for conformational determinants in the (T,G)-A--L antigen is discussed.

The nature and functions of specific immune response genes and their products

Antibodies produced by inbred mouse strains immunized with the random synthetic polypeptide poly (Tyr,Glu)-poly(DLAla)--polyLys denoted (T,G)-A--L were found to be specific mainly to the ordered peptide Tyr-Tyr-Glu-Glu. Low responder H-2k mice, upon immunization with either the random (T,G)-A--L or the ordered (T-T-G-G)-A--L coupled to methylated bovine serum albumin (MBSA), produce antibodies with comparable titers to those observed in high responder H-2b mice following immunization with the antigens alone or with their complexes with MBSA. A comparison of the above antibodies have led to the conclusion that low responder mice, upon immunization with the synthetic antigens complexed with MBSA, produce antibodies of the same specificity and quality as those of high responders (as shown by the isoelectric focusing technique) and they also have the same affinity and heterogeneity as antibodies of H-2b mice (measured by equilibrium dialysis and antigen binding capacity assay). Anti-idiotypic sera to anti-T,G)-A--L antibodies of C3H.SW (H-2b,Ig-1a) mice were raised in guinea pigs. C3H.SW anti-(T,G)-A--L antibodies from different pools cross reacted idiotypically. Anti-(T,G)-A--L antibodies of CWB (H-2b, Ig-1b) mice did not react with the anti-idiotypic serum suggesting linkage between the genes coding for idiotypes and allotypes. C3H/DiSn (H-2k, Ig-1a) anti-(T,G)-A--L antibodies elicited by immunization with (T,G)-A--L complexed to MBSA reacted with the anti-idiotypic serum to the same degree as C3H.SW anti-(T,G)-A--L antibodies, confirming the similarity between the high and low responder anti-(T,G)-A--L antibodies. C3H.SW (H-2b) mice as well as C3H/DiSn (H-2k) mice were found to be capable of producing an antigen specific factor from "educated" T cells which replaces the helper effect of T cells in the process of antibody production. On the other hand B cells of H-2k mice were not triggered by a factor of either high or low responder specific T cells. The activity of a C3H.SW (T,G)-A--L specific T cell factor was removed after passage on a Sepharose column coupled to the anti-idiotypic serum prepared against C3H.SW anti-(T,G)-A--L antibodies, suggesting similarity between the antigen specific T cell factor and the B cell recognition system. A (T,G)-A--L specific factor produced by C3H/DiSn (H-2k, Ig-1a) "educated" T cells reacted with the anti-idiotypic serum as well. Thus, C3H.SW high and C3H/DiSn low responder (T,G)-A--L specific T cell factors cross react at the level of their binding site for antigen.

Physicochemical studies of a branched polypeptide antigen: poly(L-Tyr,L-Glu)-poly(DL-Ala)--poly(L-Lys)

The synthesis of a branched polypeptide, poly(L-Tyr,L-Glu)-poly(DL-Ala)--poly(L-Lys), is described. Physicochemical investigations of the polymer by means of hydrogen-deuterium exchange, potentiometric titrations, and viscosity measurements indicate a non-ordered, flexible conformation in aqueous solution, depending on pH and salt concentration. A hysteresis phenomenon observed in the titrations is tentatively ascribed to interactions between the sidechains, and in accordance with observations from the infrared spectrum of the polymer it is suggested that rather slow conformational changes of the polymer molecules occur in aqueous solutions. The immunochemical implications of the physiochemical findings are discussed with special reference to the concept of sequential and conformational determinants.

T-lymphocyte-enriched murine peritoneal exudate cells. IV. Genetic control of cross-stimulation at the T-cell level

Antibodies raised against many structurally related antigens have been shown to cross-react extensively. Manifestations of T-cell immunity, on the other hand, appear to be more restricted in their ability to be elicited by cross-reacting antigens, although examples have been reported. This paper explores the nature of the cross-reactions at the T-cell level among the branched-chain copolymers (T,G)-A--L, (phi,G)-A--L, (H,G)-A--L, and G-A--L, as well as a related linear terpolymer, GAT, in a variety of mouse strains using the peritoneal exudate T-lymphocyte-enriched cells (PETLES) proliferation assay. (T,G)-A--L, (phi,G)-A--L, and GAT could cross-stimulate cells immune to the other two antigens, whereas (H,G)-A--L, (T,G)-Pro--L, and G-A--L showed no cross-stimulations. The extent of the cross-reactions varied with the mouse strain and was shown to be under the control of immune response genes. It was necessary for the strain to be able to respond to both the immunogen and the cross-reacting antigen, when used as an immunogen, in order for cross-stimulation to occur; however, this was not always sufficient. Several examples of unequal or one-way cross-reactions were found. In addition, the immune responses to (H,G)-A--L and (phi,G)-A--L showed no cross-reactions with the other antigen even though their Ir genes were both mapped to the K region or I-A subregion. The problem of accounting for such fine specificity of T-cell recognition in lieu of the genetic evidence demonstrating only Ir gene control of the response is discussed.

Identification of different antigenic determinants within the synthetic multichain co-polymer poly(Tyr,Glu)-polyAla--polyLys as recognized by the chicken. I. Significance of the polyAla--polyLys backbone and identification of poly-D-alanine as the antigenic determinant in backbone-directed responses

The multichain co-polymer poly(Tyr,Glu)-polyAla--polyLys, designated (T,G)-A--L, is normally thought to present only the poly(Tyr,Glu) sequences, designated (T,G), as antigenic determinants. Evidence is presented indicating that at least two different determinants in the (T,G)-A--L antigen are recognized by chickens. Studies in a partly inbred high-responder chicken strain reveal two major determinant systems: the (T,G) and the A--L in the (T,G)-A--L antigen. For one serum the antigenic determinant of the A--L backbone is shown to be a poly-D-alanine.

Role of antigenic structure in cell to cell cooperation

Two synthetic polypeptides which differ only in the order of amino acids in their NH2-terminal side chains, namely, (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(LLys) and (Tyr-Glu-Try-Glu)-poly(DLAla)- -poly(LLys), were found to be under different genetic control. By three different in vivo systems for thymus-derived cell depletion, it was demonstrated that (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(LLys), which represents the random poly(Tyr,Glu)-poly(DLAla)- -poly(Lys) in the pattern of immune responses and in the quality of antibodies they elicit, is thymus-dependent whereas (Tyr-Glu-Tyr-Glu)-poly(DLAla)-poly(LLys) does not require thymus-derived cell help for efficient antibody production. Therefore, the two ordered polypeptides which are similar chemically differ in parameters, not yet determined, which affect their capability to trigger bone marrow-derived cells.

Reconstitution of genetically regulated responses against random and ordered synthetic polypeptides by methylated bovine serum albumin as analyzed by isoelectric focusing

In previous publications it was shown by avidity measurements, cross-reactivity patterns and genetic analyses, that the tetrapeptide T-T-G-G is the immuno-dominant epitope of the synthetic polypeptide (T, G)-A--L. In the present study this close immunological relationship between the random multichain copolymer (T, G)-A--L and the ordered analogue (T-T-G-G)-A--L is extended by two additional criteria. First, the immune response against (T-T-G-G)-A--L in H-2k nonresponder mouse strains can be reconstituted to high antibody levels by complexing this antigen to methylated bovine serum albumin, as was tested earlier for (T,G)-A--L. The antibodies elicited upon reconstitution in both antigenic systems are directed mainly against the same determinant, T-T-G-G. Second, isoelectric focusing analysis of specific antisera developed with radiolabeled antigen revealed restricted 7 S IgG antibody populations in high responder and reconstituted high and low responder mice. The spectra were found to be of similar complexity in the (T,G)-A--L and in the (T-T-G-G)-A--L system. From these data it was concluded that the repertoires of specific B cells to T-T-G-G are very similar in high and low responder strains, and the defect in the H-2k low responder systems should be located at the level of T-B cell cooperation.

Determinants of antigenic molecules responsible for genetically controlled regulation of immune responses

The ability of mice bearing the H-2S haplotype to develop helper responses to the random copolymer of Glu,Ala while they developed suppressor responses to the terpolymer of Glu,Ala,Tyr suggested the crucial role of tyrosine in these peptides. On the basis of various considerations, it was postulated that many of the tyrosine residues in Glu,Ala,Tyr would be localized at the NH2-terminal end of the molecule. To verify this hypothesis, a block terpolymer composed of a short sequence of homopolymer tyrosine covalently bound to the random copolymer of Glu,Ala was synthesized. The present studies, using this block terpolymer, demonstrated that the chemical determinants stimulating helper and suppressor responses are distinct and can be present simultaneously in the same molecule. Thus, addition of COOH-terminal tyrosine residues to the Glu,Ala polypeptide converted this immunogenic molecule to an immunosuppressive molecule in mice bearing the H-2S haplotype. The mechanism by which these short sequences of tyrosine influence H-2-linked immune responses remains to be determined.

Amino acid sequence studies on the branched, synthetic polypeptide antigens of the immune response- 1 gene system

Three immunogens with side chains of random amino acid sequence, poly (L Phe, l glu)-poly (DL Ala)--poly (L Lys) [(Phe, G)-A--L 223], poly (L Tyr, L Glu)-poly (DL Ala)--poly (L Lys) [(T, G)-A--L 509] and (T, G)-A-L 52, as well as two immunogens with side chains of defined amino acid sequences, GGT-A--L and TG-A--L, were sequenced using a Beckman automated sequenator. Despite the lack of a unique amino acid sequence for the amino terminus, reasonable results for the sequence studies were obtained using the Edman reaction. GGT-A--L and TG-A--L had 70% and 80% of their side chains respectively, with the desired sequence. The three compounds of random amino acid sequence were found to contain a large proportion of their A--L side chains unsubstituted. The side chains had a much greater probability of terminating in the aromatic amino acid than in the glutamic acid. The distribution of the length of side chains and their amino acid sequences was completely heterogeneous.

Genetic control of the immune response: ability of antigens of defined amino acid sequence to be recognized by the Ir-1 gene system

Mice were injected with a series of (T,G)-A--L[poly (L Tyr, L Glu)-poly DL Ala)--poly (L Lys)]-like compounds with side chains of homogeneous sequences: T-A--L, GT-A--L, GGT-A--L, and TG-A--L. T-A--L was not immunogenic. However, T-A--L was able to bind antibodies to (T, G)-A--L 509, and this binding could not be blocked by A--L. When complexed with bovine serum albumin, T-A--L, was immunogenic in both responder and nonresponder strains of mice. GT-A--L and GGT-A--L were both immunogenic and elicited the characteristic responder-nonresponder difference induced by (T,G)-A--L. TG-A--L was also immunogenic, but there was considerable overlap in the response of responder and nonresponder strains. On the average, responder mouse serum had a slightly higher antigen-binding capacity than nonresponder mouse serum. In contrast to antibodies against GGT-A--L, antibodies against TG-A--L bound heterologous antigens poorly. These data, along with the results of other investigators, are consistent with the hypothesis that there are multiple Ir- 1 genes which recognize different sequences. The specificity of the Ir- 1 genes is extraordinary. The polypeptides TG-A--L, TGTG-A--L and GTTG-A--L do not appear to be recognized by these genes.