A cellular basis for genetically controlled immunologic unresponsiveness in mice: tolerance induction in T-cells

Regulatory T cell-mediated transplantation tolerance

The existence of naturally occurring regulatory T cells in normal hosts and their pivotal role in maintaining both auto- and allo-tolerance have direct implications on the therapy of autoimmune disorders and for achieving immunosuppression-free allotransplantation. Among the various forms of regulatory T cells described, CD4(+)CD25(+) T cells have emerged as one of the most potent tolerogenic subsets. In this review, we discuss the molecular basis of development and function of these regulatory T cells and their potential role in the context of chronic lung allograft rejection.

Isolation of antigen-specific T cell clones from nonresponder mice

The mechanisms responsible for major histocompatibility complex (MHC)-linked unresponsiveness are still poorly understood. Here we examine the cellular events that follow when B10. A mice are immunized with cow insulin, an antigen to which they make no apparent immunologic response. Despite the fact that there is no detectable antibody or T cell proliferative response to cow insulin, we have been able to clone out responding T cells after priming and restimulating in vitro with this "nonimmunogenic" antigen. These cells are L3T4+, and co-recognize specific antigen and class II MHC gene products. The data demonstrate that "nonresponder" mice to cow insulin have both the capacity to present antigen and T cells capable of recognizing that antigen. The diversity within this population was investigated by analyzing various parameters of cellular activation. These include fine specificity of both antigen and MHC recognition, as well as recognition of allogeneic MHC and M1s determinants. In addition, the antigen-presenting cell requirements were studied. The results demonstrate that this population comprise a surprisingly heterogeneous group in terms of its repertoire of receptors.

Accessory cells and T cell activation. The relationship between two components of macrophage accessory cell function: I-A and IL1

Accessory cells are required for the activation of helper T cells. We have examined two characteristics of accessory cells, their expression of I-A, and their ability to release IL1. We provide evidence that these two properties are related, and postulate that membrane I-A molecules participate in the pathway leading to IL1-release. Experimental results are described relating I-A to IL1-release as follows: 1. In vitro-educated Ly1 T cells stimulate IL1-release from M phi; this process is H-2-restricted and blocked by anti-I-A antibodies. 2. H-2-restriction between T cells and M phi is overcome in the presence of ConA, but this unrestricted interaction is also blocked by anti-I-A. 3. LPS stimulation of IL1-release is blocked by anti-I-A. These findings suggested an active role for I-A molecules on IL1-producing cells. We next describe a series of experiments designed to assess the requirements for I-A versus IL1 during T cell activation. In a number of experimental systems, T cells demonstrated a requirement for I-A-recognition, but none that could not also be satisfied by IL1: 1. Generation of helper T cells in allogeneic chimeras. 2. Proliferation of KLH-primed lymph node cells. 3. Proliferation of KLH-primed lymph node cells from chronically anti-I-A-suppressed mice. 4. Proliferation of GAT-primed lymph node cells from nonresponder mice. These findings suggest that for many kinds of T cells (not necessarily all) the apparent requirement for I-A-recognition is primarily involved in stimulating IL1-release from accessory cells.

Immunoregulation of lysozyme-specific suppression. I. Induction and suppression of delayed-type hypersensitivity to hen egg-white lysozyme

Subcutaneous immunization with hen egg-white lysozyme (HEL) in complete Freund's adjuvant induces, both in antibody responder and nonresponder mice, a classical delayed-type hypersensitivity (DTH) reaction evaluated as footpad swelling. This response can be specifically transferred to naive recipients by Lyt-1+2- T cells and passive transfer is restricted by genes mapping in or to the left of the I-A region of the H-2 complex. Fine antigenic specificity analysis shows that HEL-primed T cells mediating DTH recognize ring-necked pheasant egg-white lysozyme, a lysozyme closely related to HEL, but fail to respond to human lysozyme, differing from HEL at 40% amino acid residues. Complete cross-reactivity between native and denaturated (reduced and carboxymethylated) HEL is exhibited by T cells involved in the DTH response. Subcutaneous injection of HEL coupled to spleen cells is also able to induce antigen-specific and genetically restricted DTH responses whereas the same cells administered by i.v. or i.p. route induce predominantly suppressor T cell activation. These suppressor T cells specifically inhibit the induction phase of DTH reactivity to HEL.

Two genes in the major histocompatibility complex control immune response

Sixty-four (57.6%) of 111 cancer patients with cerebrospinal fluid cytology positive for malignant cells had cranial computed tomographic (CT) scans within 2 weeks before or after a lumbar puncture. Twenty-two (34.3%) of the 64 had abnormal CT findings indicative of leptomeningeal metastasis: (1) sulcal-cisternal enhancement, (2) ependymal-subependymal enhancement, (3) widened irregular tentorial enhancement, or (4) communicating hydrocephalus. Thirteen (59.6%) of these 22 patients had associated parenchymal metastases. Recognition of leptomeningeal disease may alter the management of patients with parenchymal metastases. Communicating hydrocephalus in cancer patients should be considered to be related to leptomeningeal metastasis until proven otherwise.

Mechanisms of genetic control of immune responses. I. Evidence for distinct multi-step helper T-cell pathways in cellular and humoral responses to GAT

We examined multiple genetically regulated humoral and cell-mediated immune (CMI) responses to poly( glu60ala30tyr10 ) (GAT) using a panel of mouse strains. We show that assignment of responder/nonresponder status depends upon the assay method. In addition, two distinct categories of nonresponder mice were found: (1) those which are unresponsive by all parameters tested (H-2q and H-2s haplotypes) and (2) those which are partially nonresponsive [H-2bm12 mutant strain--a low/nonresponder by splenic plaque-forming cell (PFC) and delayed-type hypersensitivity (DTH) responses, but exhibits B6 parental levels of high GAT-specific T-cell proliferation ( Tprlf ) and interleukin-2 production]. The distinction between these two nonresponder types was confirmed by complementation tests in which significant GAT-specific PFC and DTH responses were seen in (H-2q X H-2bm12)F1 hybrids, but not in (H-2q X H-2s)F1 hybrids. Suppressor T cells (Ts) also play a selective role in nonresponsiveness to GAT. Cyclophosphamide treatment of nonresponders (to eliminate Ts activity) as well as immunization with GAT coupled to the immunogenic carrier MBSA result in the development of GAT-specific humoral, but not CMI responses. Our results indicate that the T cell is the cellular site of Ir gene expression and that Tprlf responses do not correlate with functional helper T-cell activity and suggest distinct, multi-step Th/Ts regulatory pathways in the development of humoral and CMI effector functions.

Cell-free translation of a biologically active, antigen-specific suppressor T cell factor

In vitro synthesis of an antigen-specific T cell suppressor factor (TsF) has been accomplished by using partially purified poly(A)-containing RNA in a rabbit reticulocyte lysate cell-free translation system. The poly(A)-containing mRNA was isolated from a cloned T cell hybridoma that constitutively produces a TsF specific for the synthetic polypeptide antigen poly-(LGlu60LAla30LTyr10) (GAT). The RNA was fractionated by size and translated in vitro. The 16S RNA fraction stimulated synthesis of a biologically active protein that specifically suppressed both the GAT-specific antibody response by spleen cells in vitro and the proliferation response to GAT by lymph node T cells from GAT-primed mice. Further, the suppressor factor had a binding site for GAT, a determinant encoded by the I subregion of the major histocompatibility complex (MHC), and an apparent Mr 19,000 estimated by functional assays on protein separated by NadodSO4/polyacrylamide gel electrophoresis. These results indicate that virtually no posttranslational modifications (other than proteolytic cleavage) are necessary to obtain biologically active TsF. Hence, the presence of carbohydrate or other chemical groups does not contribute to either the serological properties of GAT-TsF or its biological properties.

Purification and characterization of a monoclonal T-cell suppressor factor specific for poly(LGlu60LAla30LTyr10)

A monoclonal T-cell-derived suppressor factor specific for the terpolymer poly(LGlu60LAla30LTyr10) produced by the T-cell hybridoma 258 C4.4, was purified to homogeneity. This was accomplished by fractionation of the culture medium by using a combination of affinity chromatography and reverse-phase and ion-exchange high-performance liquid chromatography. The purified factor is composed of a single Mr 24,000 polypeptide chain, and the homogeneous protein maintains the ability to suppress antibody and T-cell proliferative responses to poly(LGlu60LAla30LTyr10) specifically. The specific activity of pure suppressor factor is calculated to be 8 X 10(7) units/micrograms.

Genetic control of the immune response to collagen. I. Quantitative determination of response levels by multiple I-region genes

The antibody response in mice to type I calf skin collagen is quantitatively determined by genes with map to the I region of the H-2 histocompatibility complex. The use of H-2 recombinant B10 congenic strains of mice reveals that a gene in the IA subregion and a gene to the right of the IA subregion affect responsiveness. To examine complementation patterns in the antibody response to collagen, five B10 congenic strains, each bearing an independent H-2 haplotype, were intercrossed to obtain nine hybrid strains heterozygous at the H-2 locus. In five combinations heterozygous progeny produced significantly greater antibody responses than those observed for the homozygous parental strains. Two low responder haplotypes, H-2k and H-2d, were shown to be qualitatively different. Mice of these haplotypes show a different dose--response pattern and a different phenotypic pattern of inheritance with respect to the high responder H-2b haplotype. Complementation effects found in F1 hybrid mice derived from H-2 recombinant parental strains indicate that high responsiveness, controlled by an IA6 subregion gene, can be influenced by an interaction between an IAk subregion gene and an ICd subregion gene on different chromosomes. These data are consistent with the possibility that there exist two or more I region genes that have distinct functions and can interact to affect the levels of immune responsiveness.

Behaviour of human immunoregulatory cells in culture. I. Variables requiring consideration for clinical studies

The suppressor function of lymphocytes stimulated with concanavalin A (Con A) provides a potential method for examining disorders of immunoregulation. Clinical application, however, requires definition of the culture conditions that influence the expression of normal suppressor cell activity. In the present studies culture conditions were modified until a sensitive assay for non-specific suppressor cell function was reproducible utilizing the response to varying doses of phytohaemagglutinin (PHA) as an indicator system. Practical conclusions included (1) that sensitivity was not lost if the suppressor cells and responder cells were allogenic; (2) that fresh responder cells were as sensitive as precultured responder cells; (3) that a wide range of Con A concentrations could induce suppressor activity; and (4) that the sensitivity of the assay was much enhanced by using suboptimal mitogen doses of PHA. Twelve percent of normal subjects gave false negative results but these could be avoided by studying cells at more than one time point after stimulation with Con A. Cells resting in culture for 7 days could be induced to suppress after stimulation with Con A and these suppressor cells were very sensitive to pharmacological doses of dexamethasone. Studies utilizing different times of cell pre-incubation before Con A stimulation and different periods of exposure to Con A revealed fluctuation in the induction of suppression that may represent alternating periods of suppression and amplifying activity among stimulated cells in vitro. Such variations will need to be taken into account in the application of this type of assay to clinical studies seeking disordered immunoregulation.

Idiotypic analysis of antibodies against the terpolymer L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT). IV. Induction of CGAT idiotype following immunization with various synthetic polymers containing glutamic acid and tyrosine

The immune responses of all inbred strains of mice specific to the synthetic terpolymer poly(LGlu60LAla30LTyr10), referred to as GAT10, are characterized by the presence of anti-GAT antibodies which share a common (CGAT) idiotype. In this report, we describe the ability of the synthetic polymers, LGlu33LAla33LTyr33, LGlu51-LAla34LTyr15 and poly-L(Tyr, Glu)-DLAla--LLys [(T,G)-A--L] to induce antibodies with CGAT idiotypic specificities. All of these polymers contain "GT"-related determinants. Following immunization with these polymers, antisera from responder mice bind the corresponding 125I-labeled antigen and 125I-labeled poly(LGlu50LTyr50) or GAT10. These antisera shared the CGAT idiotype which is associated with the antibody fraction with binding specificity for GAT10. Collectively, the present results indicate that GT-related determinants are required for the induction of the CGAT idiotype. Moreover, since the immune responses to these synthetic polymers are under distinct H-2-linked immune response (Ir) gene control, a mouse strain can be nonresponder to one polymer and responder to another; in this case, only the latter polymer induces CGAT idiotype. Thus, although the immune responses of inbred strains of mice to different polymers are under distinct Ir gene control, the antibody responses can be idiotypically related.

Stimulation of specific suppressor T cells in newborn responder mice by the terpolymer L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT)

The effects of immunization with the terpolymer of L-glutamic acid60-L-alanine40-L-tyrosine10 (GAT), the copolymers of L-glutamic acid60-L-alanine40 (GA) and of L-glutamic acid50-L-tyrosine50 (GT), were compared in adult and newborn BALB/c and BALB.B mice. as expected, BALB/c (H-2d) and BALB.B (H-2b) adult mice were responders to GAT and GA and nonresponders to GT, which induced suppressor T cells in BALB/c but not in BALB.B mice. in contrast, newborn mice expressed different phenotypes. Two-week-old mice developed responses to GAT, GA and GT-complexed methylated bovine serum albumin, but immunization at birth with these copolymers induced a cross-reactive tolerance in both strains. Neonatal GAT tolerance could be transferred in adult and involved suppressor T cells in the two inbred strains, whereas the GT-specific immune suppression was not demonstrable in newborn BALB/c mice. The significance of these data to our understanding of the regulation of specific immune response and tolerance is discussed.

In vivo effects of anti-Ia alloantisera. I. Elimination of specific suppression by in vivo administration of antisera specific for I-J controlled determinants

The in vivo effects of intravenous administration of alloantisera directed to I-J subregion coded determinants were investigated. In confirmation and extension of our previous results, anti-I-Jk [B10.A(3R) anti-B10.A(5R)] and anti-I-Js ([B10.A(3R) X B10.S(9R)]F1 anti-B10.HTT) antisera, when administered in 1 to 10 microliter amounts at the time of immunization, led to twofold increases in the IgM and IgG plaque-forming cells (PFC) responses to suboptimal doses of sheep erythrocytes in A/J (I-Jk) and SJL (I-Js) mice, respectively. To assess whether this immunopotentiation was due to a decrease in specific suppression, experiments were carried out using the polypeptide antigens random linear terpolymer of L-glutamic acid60, L-alanine30, and L-tyrosine10 (GAT) and random linear copolymer of L-glutamic acid50-L-tyrosine50 (GT), since administration of GAT to the nonresponder strain SJL, or GT to the nonresponder strain CBA fails to induce a primary PFC response and stimulates specific suppressor T cells able to prevent PFC responses to subsequent challenge with the immunogens GAT-methylated bovine serum albumin (MBSA) or GT-MBSA, respectively. The current study demonstrates that CBA (I-Jk) mice given 100 microgram GT in Maalox-pertussis adjuvant on day 0, and 10 microliter anti-I-Jk antiserum i.v. on days 0, 1, and 2, develop a significant primary specific PFC response on day 7. A similar responsiveness to 10 microgram GAT is found in SJL mice treated with 10 microliter anti-I-Js antiserum for 3 days. This same active anti-I-Js antiserum does not permit CBA mice to respond to GT, demonstrating the specificity of the anti-I-J effect. These data suggest that anti-I-J antiserum treatment at the time of antigen administration reduces suppressor responses to GAT or GT, permitting primary PFC responses. To directly demonstrate such an effect on suppressor activity, SJL or CBA mice treated, respectively, with GAT or GT to induce suppressor cells active on GAT-MBSA or GT-MBSA responses after adoptive transfer to normal syngeneic recipients were also given anti-I-J antisera (10 microliter/day) for 3 days, at which time their spleen cells were tested for suppressive activity upon transfer. Cells from such treated mice failed to show detectable suppressive activity upon transfer to syngeneic recipients challenged with GAT-MBSA or GT-MBSA, confirming the hypothesis of an in vivo effect of anti-I-J antiserum on suppressor activity.

The kinetics of IgG and IgM antibody-forming cells in ACI and F344 rats immunized with poly(glu52lys33tyr15)

The cellular kinetics of antibody production in high and low responder rats immunized with poly(Glu52Lys33Tyr15) or with poly(Glu52Lys33Tyr15)/MeBSA were characterized: serum antibody and IgG and IgM antibody-forming cells in the spleen and in selected lymph nodes were assayed in male and female rats following immunization by several routes. Aggregation of the antigen with MeBSA enabled the poorly responding F344 rats to produce antibody, which was almost exclusively IgG. High responder ACI rats, under the same conditions, produced antibody of both IgG AND IgM classes. These data suggest that in low responders one defect, possibly at the T-cell level, can be overcome by aggregation but that a second defect, involving the regulation of IgM production, still exists.

In vitro studies on H-2 linked unresponsiveness to synthetic polypeptide antigens. II. Induction of suppressor cells in both responsive and unresponsive mice to (T,G)-A-L and GAT;

Antigen-specific T-suppressor cells can be induced in vitro from unprimed lymphoid cells of high responder (C57BL/10) and low responder (B10.Br, B10.A, CBA) mice to (T,G)-A-L and high responder (B10, B10;A) and non-responder (B10.G, DBA/1) mice to GAT10. The suppressor cells induced from high and low or non-responder mice appear identical in efficiency, in the antigen concentration required for induction and in their induction kinetics.

In vitro studies on H-2 linked unresponsiveness. 1. Normal helper cells to (T,G)-A-L and GAT in low and non-responder mice

Lymphoid cells from unprimed high responder (C57BL/10) and low responder mice (B10.Br, B10.A, CBA) to (T,G)-A-L and high responder (B10, B10.A) and non-responder (B10.G, DBA/I) mice to GAT can be induced to form antigen specific T-helper cells in vitro under identical culture conditions. The helper cells induced from high and low or non-responder mice appear to be identical in efficiency, antigen concentration requirement for induction and induction kinetics.

A new I subregion (I-J) marked by a locus (Ia-4) controlling surface determinants on suppressor T lymphocytes

In an accompanying publication we show that a subpopulation of T lymphocytes, which includes allotype suppressor T cells, selectively expresses I-region determinants. In this report, we show that these determinants are controlled by a new locus, Ia-4. Unlike the classically defined Ia antigens, they are not found on B lymphocytes. Antibody against Ia-4 determinants cannot be detected by conventional dye exclusion cytoxicity assays, suggesting that they are present on a small subpopulation (less than 10%) of peripheral T lymphocytes. The Ia-4 locus marks a new I subregion, provisionally designated I-J. This chromosomal segment is defined by the crossover positions in strains B10.A(5R) (K-end boundary) and B10.HTT (D-end boundary), and maps between the I-B and I-C subregions.

Heterogeneity of murine regulatory T cells. I. Subpopulations of amplifier and suppressor T cells

Immunization of C3H/HeJ mice with 4 X 10(9) SRBC yields a whole splenic T-cell population which can, upon transfer, specifically suppress recipient direct and indirect plaque-forming cells (PFC) responses to sheep erythrocytes (SRBC). Discontinuous bovine serum albumin density gradient fractionation of these T cells demonstrated a population of low density T cells which augmented and a population of high density T cells which suppressed recipient responses irrespective of the number of T cells transferred. Moreover, infusion of admixtures of low and high density cells resulted in intermediate regulatory functions which could be predicted by knowing the regulatory capacity of each population alone. In addition to heterogeneity existing among regulatory T cells as regards amplification and suppression, it appeared that heterogeneity existed within the suppressor T population. Thus, T cells capable of inhibiting direct PFC could be distinguished from those suppressing indirect PFC by their differential localization in peripheral lymphoid tissue, differences in the dissipation of suppressive influences during incubation at 37 degrees C, and by differences in the possible requirement for adherent cell populations. While the relative frequency of both low density amplifier and high density suppressor cells increased with the dose of SRBC used for their induction, it appeared that suppressor cells might be generated in response to feedback signals from amplifier cells. These studies indicate that further delineation of heterogeneity existing within suppressor populations may be helpful in defining mechanisms required for the induction and manifestation of suppressive regulatory forces.

Liver disease--a prominent cause of serum IgE elevation

Serum IgE concentrations were elevated in thirty-seven out of sixty-seven patients (55%) with acute or chronic liver disease of widely differing aetiology. The mean IgE concentrations in these patients showed an eight-fold increase above that observed in control subjects. Increased IgE levels in patients with liver disease occurred in the absence of eosinophilia, clinical evidence of atopy or other known causes of IgE elevation. No IgE-containing plasma cells were detected in the liver biopsies from thirty-two of the sixty-seven patients tested. Peripheral blood T cells were significantly decreased from normal in the patients with liver disease, but no correlation emerged between serum IgE levels and absolute peripheral blood T-cell numbers. These findings emphasize the importance of liver disease as a significant cause of serum IgE elevation.

Genetic control of specific immune suppression. I. Experimental conditions for the stimulation of suppressor cells by the copolymer L-glutamic acid50-L-tyrosine50 (GT) in nonresponder BALB/c mice

In the present studies we have confirmed that the random copolymer of L-glutamic acid50-L-tyrosine50 (GT) fails to induce an antibody response in a large number of inbred strains of mice. Nevertheless, GT complexed to methylated bovine serum albumin (MBSA) elicits a GT-specific IgG PFC response in vivo. Furthermore, injection of BALB/c mice with 10 to 100 mug of GT specifically decreases their ability to develop anti-GT PFC responses to a subsequent challenge with GT-MBSA. GT-specific tolerance can be transferred to normal, syngeneic recipients by spleen cells or thymocytes of GT-primed animals. These results indicate that the stimulation of suppressor cells can be observed in nonresponder mice with another synthetic polypeptide besides GAT. Various parameters of GT-specific immunosuppression in BALB/c mice are described. The application of these techniques to the study of the genetic factors controlling the stimulation of specific immune suppression is discussed.

Lymphocyte surface immunoglobulins

Immunoglobulins have been isolated from the surface of B (bone marrow-derived) and T (thymus-derived) lymphocytes. Two types of membrane immunoglobulin occur on B lymphocytes; one type resembles the 200,000-dalton subunit of IgM, the second possesses a heavy chain electrophoretically distinct from mu chain and does not correspond to any of the known classes of mouse immunoglobulins. It might correspond to human sigma chain. T lymphocytes possess only one type of surface immunoglobulin. This molecule has a mass of approximately 200,000 daltons and contains light chains and heavy chains similar to, but not identical to, mu chains. Evidence now exists that surface IgM-like immunoglobulins of B lymphocytes and T lymphocytes activated to certain antigens can bind specifically to antigen. These observations suggest that surface immunoglobulin functions as a receptor for antigen on B cells and at least on some T cells. The mechanisms by which combination of antigen with surface immunoglobulin initiate differentiation remain to be determined.

A disquisition on suppressor T cells

The main points that I have put forth are that: (1) suppressor T cell activity cannot be explained as simply being too much help; (2) feedback signals from target cells are of crucial importance in determining and maintaining the activity of suppressor T cells; (3) whenever T cells are triggered by antigen, suppression occurs. Immune responses only occur when countermanding signals are also generated. Both intrinsic and extrinsic adjuvanticity is the operational production of countermanding signals; (4) memory T cells are qualitatively different from normal T cells in their sensitivity to feedback signals and also in their susceptibility to suppression; (5) mature thymus dependent B cells cannot be rendered tolerant by the direct action of antigen, while immature and thymus independent B cells can; (6) the mechanism of suppression induced by exogenously administered antigens and that by normal differentiation products (i.e.: GVH; allotypes), is different; (7) generation of suppressor cells requires or results from complex interactions between subpopulations of cells, making it impossible under present conditions to determine which cell is doing what and to which; (8) further work is required before a full understanding of the importance, mechanism of action and other aspects of suppressor T cell function can be fully understood.

Fine specificity of the H-2 linked immune response gene for the gallinaceous lysozymes

An immune response (Ir) gene is described which controls the ability of mice to respond to seven very closely related gallinaceous egg white lysozymes (GEL). This Ir-GEL gene locus is linked to the major histocompatibility locus of the mouse and operates at the level of the T cell. Responsiveness to the nonimmunogenic prototype hen egg white lysozyme (HEL) is dominant and is unrelated to age or sex of the animals, or to dose of protein administered. Ninety percent of C57BL/6 mice are absolute nonresponders to the nonimmunogenic lysozymes in complete Freund's adjuvant. The remaining mice exhibit severely restricted responses, with different anti-HEL clonotypes appearing in individual mice. The fine specificity of the Ir-GEL locus is evident in the discrimination of as few as two amino acid differences in a single region of the lysozyme molecule. This very precise distinction determines whether there will, or will not, be any response to the multideterminant molecule.

Genetic control of the murine cell-mediated immune response in vivo. I. H-2-linked responsiveness to the terpolymer L-glutamic acid-60-L-alanine-30-L-tyrosine-10

Various inbred and congenic strains of mice were immunized with the linear terpolymer L-glutamic acid-60-L-alanine-30-L-tyrosine-10 (GAT). Using a radioisotopic footpad assay to measure cell-mediated immunity in vivo, mice with H-2-a, H-2-b, H-2-d, and H-2-k histocompatibility alleles showed a positive reaction, whereas mice with H-2p and H-2-s alleles failed to respond. The ability of "responder" lymphocytes to show an immune response resides in the thymus-derived (T) lymphocyte population. Unfractionated spleen cells from H-2-q nonresponder mice, on transfer, showed no reactivity, whereas T-cell-enriched preparations were active.

Antigen-induced proliferative response to murine thymus cells in vitro

Thymus cells from 5- to 6-week-old normal (unimmunized) BALB/c mice showed an increased incorporation of [(3)H]thymidine in the presence of 2,4-dinitrophenyl-bovine serum albumin, fluorescein-bovine serum albumin, and bovine serum albumin (BSA) in tissue culture. The concentrations of antigen (BSA and haptenated proteins) required for stimulation were approximately 25- to 50-fold higher than those of the nonspecific mitogen, concanavalin A. In contrast to the stimulation by concanavalin A, which was maximal at 24 to 72 h, the stimulation by antigen was most marked earlier in the culture period (6 to 24 h). The BSA response was diminished to a statistically significant degree (especially at low BSA concentrations) in thymocytes from animals injected 72 h previously with BSA, indicating that the stimulation is immunologically specific.

Genetic control of immune responses in vitro. V. Stimulation of suppressor T cells in nonresponder mice by the terpolymer L-glutamic acid 60-L-alanine 30-L-tyrosine 10 (GAT)

In recent studies we have found that GAT not only fails to elicit a GAT-specific response in nonresponder mice but also specifically decreases the ability of nonresponder mice to develop a GAT-specific PFC response to a subsequent challenge with GAT bound to the immunogenic carrier, MBSA. Studies presented in this paper demonstrate that B cells from nonresponder, DBA/1 mice rendered unresponsive by GAT in vivo can respond in vitro to GAT-MBSA if exogenous, carrier-primed T cells are added to the cultures. The unresponsiveness was shown to be the result of impaired carrier-specific helper T-cell function in the spleen cells of GAT-primed mice. Spleen cells from GAT-primed mice specifically suppressed the GAT-specific PFC response of spleen cells from normal DBA/1 mice incubated with GAT-MBSA. This suppression was prevented by pretreatment of GAT-primed spleen cells with anti-theta serum plus C or X irradiation. Identification of the suppressor cells as T cells was confirmed by the demonstration that suppressor cells were confined to the fraction of the column-purified lymphocytes which contained theta-positive cells and a few non-Ig-bearing cells. The significance of these data to our understanding of Ir-gene regulation of the immune response is discussed.

Genetic control of immune responses in vitro. 3. Tolerogenic properties of the terpolymer L-glutamic acid 60-L-alanine30-L-tyrosine10 (GAT) for spleen cells from nonresponder (H-2s and H-2q) mice

Although nonresponder, H-2(s) and H-2(q), mice fail to develop GAT-specific PFC responses to GAT, they do develop GAT-specific PFC responses when stimulated by GAT complexed to an immunogenic carrier such as methylated bovine serum albumin. The studies described in this paper show that injection of nonresponder mice with GAT specifically decreases their ability to develop anti-GAT PFC responses to a subsequent challenge with GAT-MBSA. Addition of GAT to cultures of spleen cells from nonresponder mice also prevents development of the GAT-specific PFC responses stimulated by GAT-MBSA. Thus, interaction of nonresponder spleen cells with GAT leads to the induction of unresponsiveness in vivo and in vitro. Various parameters of the tolerance induction have been investigated and described. A comparison of the effects of GAT on B cells indicates that nonresponder B cells are more readily rendered unresponsive by soluble GAT than are responder B cells. The significance of these data for our understanding of Ir gene regulation of the immune response is discussed.

Immunological tolerance in bone marrow-derived lymphocytes. 3. Tolerance induction in primed B cells by hapten conjugates of unrelated immunogenic or "nonimmunogenic" carriers

The present studies were designed to probe the role(s) of T cells in preventing or altering tolerance induction in hapten-specific B cells. This was accomplished by using hapten conjugates of normally immunogenic heterologous carriers to selectively inhibit 2,4-dinitrophenyl (DNP)-primed B cells in adoptive transfer experiments in vivo. The data provide strong indications that one critical role of T-cell participation in humoral responses to antigens is to circumvent the development of a tolerogenic signal that, in the absence of such T-cell function, might otherwise ensue after binding of the antigenic determinants by specific precursor B lymphocytes.