A clonal deletion model for Ir gene control of the immune response

Borrelia Infection in Bank Voles Myodes glareolus Is Associated With Specific DQB Haplotypes Which Affect Allelic Divergence Within Individuals

The high polymorphism of Major Histocompatibility Complex (MHC) genes is generally considered to be a result of pathogen-mediated balancing selection. Such selection may operate in the form of heterozygote advantage, and/or through specific MHC allele–pathogen interactions. Specific MHC allele–pathogen interactions may promote polymorphism via negative frequency-dependent selection (NFDS), or selection that varies in time and/or space because of variability in the composition of the pathogen community (fluctuating selection; FS). In addition, divergent allele advantage (DAA) may act on top of these forms of balancing selection, explaining the high sequence divergence between MHC alleles. DAA has primarily been thought of as an extension of heterozygote advantage. However, DAA could also work in concert with NFDS though this is yet to be tested explicitly. To evaluate the importance of DAA in pathogen-mediated balancing selection, we surveyed allelic polymorphism of MHC class II DQB genes in wild bank voles (Myodes glareolus) and tested for associations between DQB haplotypes and infection by Borrelia afzelii, a tick-transmitted bacterium causing Lyme disease in humans. We found two significant associations between DQB haplotypes and infection status: one haplotype was associated with lower risk of infection (resistance), while another was associated with higher risk of infection (susceptibility). Interestingly, allelic divergence within individuals was higher for voles with the resistance haplotype compared to other voles. In contrast, allelic divergence was lower for voles with the susceptibility haplotype than other voles. The pattern of higher allelic divergence in individuals with the resistance haplotype is consistent with NFDS favouring divergent alleles in a natural population, hence selection where DAA works in concert with NFDS.

Is allograft rejection a clue to the mechanism promoting MHC polymorphism?

Extreme polymorphism at MHC loci is generally thought to be maintained by natural selection at a population level. Because allelic MHC molecules differ in their influence on the immune response, polymorphism ensures that the response repertoire is broad and that the group survives microbial challenge. Here Leif Anderson and his colleagues propose a different view, based on the observation that certain pathogens passively acquire MHC antigens from their primary host and carry these antigens into subsequent hosts. An immune response to the pathogen may depend on recognition of the non-self MHC antigens.

Induction of tolerance in autoimmune diseases by hematopoietic stem cell transplantation: getting closer to a cure?

Hematopoietic stem cells (HSCs) are the earliest cells of the immune system, giving rise to B and T lymphocytes, monocytes, tissue macrophages, and dendritic cells. In animal models, adoptive transfer of HSCs, depending on circumstances, may cause, prevent, or cure autoimmune diseases. Clinical trials have reported early remission of otherwise refractory autoimmune disorders after either autologous or allogeneic hematopoietic stem cell transplantation (HSCT). By percentage of transplantations performed, autoimmune diseases are the most rapidly expanding indication for stem cell transplantation. Although numerous editorials or commentaries have been previously published, no prior review has focused on the immunology of transplantation tolerance or development of phase 3 autoimmune HSCT trials. Results from current trials suggest that mobilization of HSCs, conditioning regimen, eligibility and exclusion criteria, toxicity, outcome, source of stem cells, and posttransplantation follow-up need to be disease specific. HSCT-induced remission of an autoimmune disease allows for a prospective analysis of events involved in immune tolerance not available in cross-sectional studies.

HLA-A2.1/K(b) transgenic murine dendritic cells transduced with an adenovirus encoding human gp100 process the same A2.1-restricted peptide epitopes as human antigen-presenting cells and elicit A2.1-restricted peptide-specific CTL

HLA-A2.1/K(b) transgenic mice (A2.1/K(b) mice) were used to investigate the processing of human gp100 melanoma antigen by murine antigen presenting cells (APC). Bone marrow-derived dendritic cells (DC) from A2.1/K(b) mice were transduced with adenovirus encoding human gp100 (Ad2/hugp100v2). The Ad2/hugp100v2-transduced DC express human gp100, as documented by immunoperoxidase staining. Flow cytometric analysis demonstrates that Ad vector transduction does not downregulate expression of several markers, including MHC class I. We show that Ad2/hugp100v2-transduced DC are recognized by peptide-specific, A2.1-restricted CTL, suggesting correct processing and presentation of the hugp100 antigen by murine DC. To assess dominance among the various A2.1-restricted epitopes encoded by hugp100, A2.1/K(b) transgenic mice were immunized with Ad2/hugp100v2-transduced DC. Resulting effector cytotoxic T lymphocytes (CTL) were assayed for peptide specificity using a panel of six synthetic peptides known to encode A2.1-restricted epitopes of human gp100 (denoted G154, G177, G209, G280, G457, G476). CTL obtained from Ad2/hugp100v2-transduced DC immunized A2.1/K(b) mouse lysed target cells presenting five of the six epitopes, supporting the observation that murine cells correctly process the hugp100 antigen. The immunogenicity of individual gp100 epitopes correlates with their binding affinity to A2.1. CTL generated from A2.1/K(b) mice immunized with Ad2/hugp100v2-transduced DC also specifically recognize A2.1(+)/gp100(+) human melanoma cells. These data suggest that murine APC process and present the same set of HLA-restricted peptides, similar to human APC. HLA transgenic mice serve as a useful model system to study class I-restricted epitopes of human tumor-associated antigens.

Assessment of the Role of Determinant Selection in Genetic Control of the Immune Response to Insulin in H-2b Mice

The immune response to insulin is regulated by MHC class II genes. Immune response (Ir) gene-linked low responsiveness to protein Ags can be mediated by the low affinity of potential antigenic determinants for MHC molecules (determinant selection) or by the influence of MHC on the functional T cell repertoire. Strong evidence exists that determinant selection plays a key role in epitope immunodominance and Ir gene-linked unresponsiveness. However, the actual measurement of relative MHC-binding affinities of all potential peptides derived from well-characterized model Ags under Ir gene regulation has been very limited. We chose to take advantage of the simplicity of the structure of insulin to study the mechanism of Ir gene control in H-2b mice, which respond to beef insulin (BINS) but not pork insulin (PINS). Peptides from these proteins, including the immunodominant A(1–14) determinant, were observed to have similar affinities for purified IAb in binding experiments. Functional and biochemical experiments suggested that PINS and BINS are processed with similar efficiency. The T cell response to synthetic pork A(1–14) was considerably weaker than the response to the BINS peptide. We conclude that the poor immunogenicity of PINS in H-2b mice is a consequence of the T cell repertoire rather than differences in processing and presentation.

The antibody repertoire in infection and vaccination with Dictyocaulus viviparus: heterogeneity in infected cattle and genetic control in guinea pigs

The antigen recognition profiles of serum antibody from calves infected or vaccinated with irradiated Dictyocaulus viviparus larvae were analysed by immunoprecipitation of radio-iodinated in vitro-released excretory-secretory materials from live adult parasites. Immunoprecipitates were analysed by SDS-PAGE and considerable heterogeneity in antigen recognition between individual animals was observed, regardless of infection regimen. This heterogeneity was also found to occur amongst outbred guinea pigs infected with the parasite and permitted an examination of the genetics of the effect using inbred guinea pigs (Strains 2 and 13). The antibody repertoires of the two strains were distinct, with only slight variation occurring between individuals within a strain. Previous work on nematode infections in rodents has demonstrated a role for the major histocompatibility complex (MHC) in the control of the immune repertoire. If this, as is probable, holds for the guinea pig, then it can be ascribed to the MHC Class II region because Strain 2 and Strain 13 bear identical Class I alleles but disparate Class II alleles. Whilst there is no evidence to date that the efficiency of vaccination of cattle is influenced by genetic factors, the operation of vaccines based on a single or a few molecularly cloned parasite antigens might be seriously compromised by the kind of genetic restriction to the immune repertoire described here.

Nonresponsiveness to an immunodominant Epstein-Barr virus-encoded cytotoxic T-lymphocyte epitope in nuclear antigen 3A: implications for vaccine strategies

An immunodominant Epstein-Barr virus (EBV)-encoded cytotoxic T lymphocyte (CTL) epitope has been mapped to the EBV nuclear antigen 3A. The epitope, represented by the peptide sequence AWNAGFLRGRAYGLD (hereafter termed AWNA), is restricted through the HLA-B8 allele and is expressed by type A but not type B-infected transformants. Herein, we show that EBV-specific memory CTLs from an HLA-B8+ healthy virus carrier, JS, did not respond in vitro to AWNA, even though that individual's endogenously infected transformants processed and presented the natural equivalent of this peptide to AWNA-specific CTLs from another B8+ individual. Instead, an epitope, represented by the peptide sequence QLSDTPLIPLTIFVGENTGV, was the dominant EBV-specific CTL epitope in donor JS. This epitope mapped to EBV nuclear antigen 2A, was restricted by an HLA-A2 subtype, and specifically associated with type A strains of EBV. No AWNA-specific CTL precursors were detected by limiting dilution analysis of peripheral blood mononuclear cells from donor JS whereas the precursor frequency of AWNA-specific CTLs from a responder donor, LC, was estimated at 1:4500. The presentation in vivo of an immunogenic epitope-HLA antigen complex is clearly insufficient to guarantee an effective memory CTL response to that foreign epitope. Thus, vaccination strategies based on peptides inducing CTL responses may need to take into account not only the polymorphism of HLA antigens but also possible allelic variation in the repertoires of T-cell receptors.

Immunogenicity of B chain in insulin responder and nonresponder mice

The potential immunogenicity of insulin B chain in beef insulin low-responder H-2k,a and high-responder H-2b,d mice was examined using lymph node proliferation assays. Oxidized B chain was immunogenic in H-2k,a, but not H-2b,d, mice. The T cell population recognized a determinant in OX-B chain associated with I-Ak. These cells did not respond to intact insulin, suggesting that the B chain determinant was not available to I-Ak during immunologic processing of insulin. Responses were observed in H-2k and H-2d, but not H-2b, after immunization with reduced and carboxyamidomethylated-insulin which contains equimolar A chain and B chain. These responses were I-A-restricted and heterogeneous, with reactivity to A chain and B chain determinants. In each case, little or no cross-reactivity was observed between RCAM-insulin and intact insulin. Furthermore, T cell populations induced in H-2k mice selectively recognized OX-B chain or RCAM-B chain, which differ in chemical modification of the thiols of Cys B7 and Cys B19. Similarly, RCAM-BINS-immune T cells from H-2d did not react to OX-B chain. These results indicate that derivatization of the cysteine thiols, through disulfide bonds, oxidation, or carboxyamidomethylation, radically affects T cell recognition of insulin B chain.

The specificity of the antibody response to internal antigens of Ascaris: heterogeneity in infected humans, and MHC (H-2) control of the repertoire in mice

Children from an area of Africa endemic for the large roundworm of humans, Ascaris lumbricoides, were found to vary considerably in the specificity of their serum IgG response to the internal antigens of the parasite. This was particularly noticeable for responses to a 14-kD protein (ABA-1) of the parasite that has previously been shown to be the subject of a strong IgE antibody response in infected animals. The possibility that this heterogeneity in immune repertoire has a genetic basis was explored in inbred mice infected with Ascaris suum. This showed that no strain responded to all the potential antigens, that the recognition profiles of strains bearing independent haplotypes were unique, and only H-2-identical strains had responses of similar specificities. Major histocompatability complex (MHC) restriction was confirmed using H-2-congenic animals on BALB and B10 backgrounds, which responded according to their H-2 haplotype. It is likely, therefore, that it is the MHC which controls the repertoire to Ascaris antigens in infected people. If this is so, then there will be implications for immunopathology associated with ascariasis, and possibly also for resistance and susceptibility to infection.

A single amino acid interchange yields reciprocal CTL specificities for HIV-1 gp160

For the IIIB isolate of human immunodeficiency virus type-1 (HIV-1), the immunodominant determinant of the envelope protein gp160 for cytotoxic T lymphocytes (CTLs) of H-2d mice is in a region of high sequence variability among HIV-1 isolates. The general requirements for CTL recognition of peptide antigens and the relation of recognition requirements to the natural variation in sequence of the HIV were investigated. For this purpose, a CTL line specific for the homologous segment of the envelope from the MN isolate of HIV-1 and restricted by the same class I major histocompatibility (MHC) molecule (Dd) as the IIIB-specific CTLs was raised from mice immunized with MN-env-recombinant vaccinia virus. The IIIB-specific and MN-specific CTLs were completely non-cross-reactive. Reciprocal exchange of a single amino acid between the two peptide sequences, which differed in 6 of 15 residues, led to a complete reversal of the specificity of the peptides in sensitizing targets, such that the IIIB-specific CTLs lysed targets exposed to the singly substituted MN peptide and vice versa. These data indicate the importance of single residues in defining peptide epitopic specificity and have implications for both the effect of immune pressure on selection of viral mutants and the design of effective vaccines.

Genetic control of the immune repertoire in nematode infections

Mammals vary considerably, both within and between species, in the way in which their innate and adaptive immune systems respond to infections. An understanding of the processes involved in such variability will not only contribute to explaining heterogeneity in susceptibility and pathology, but will also be relevant to vaccination. This will be particularly important for the new generation of vaccines that are likely to be composed of one or a few cloned or synthesized antigens. For helminth infections, this could have particular relevance to hypersensitivity responses. The adaptive immune response is fundamentally constrained by the genetic constitution of an individual, and the need to avoid reactivity to self. This will have important implications for the dynamic relationship between host defences and parasite evasion mechanisms at both physiological and evolutionary levels. In this review, Malcolm Kennedy examines the genetic control of the specificity of the immune response to nematode infections, and in particular, the role of the major histocompatibility complex.

Elimination of self-tolerogen turns nonresponder mice into responders

Two sets of genes control the immune response of H-2d mice to the synthetic antigen poly(Glu50Tyr50) (GT). One set involves class II major histocompatibility complex (Mhc) loci encoding an Ad product that serves as a recognition context to GT-reactive helper T cells (Th). The other one is a background gene, the product of which, in association with the same Mhc-restricting element, mimics the GT/Ad complex. Mice expressing the GT-mimicking background-encoded structure (Imgt), which is preferentially displayed on B lymphoblasts, do not respond to GT as a consequence of self-tolerance. On the other hand, elimination of cells bearing Imgt renders these mice responsive to GT, demonstrating that tolerance to self can impoverish the immune system. Imgt is probably not identical to GT, but resembles it in the way it forms complexes with Ad molecules of Mhc.

Indomethacin augments in vitro proliferative responses of Lewis rat lymphocytes to myelin basic protein. Implications for experimental autoimmune encephalomyelitis

Indomethacin (IM), a specific inhibitor of prostaglandin (PG) synthesis, and PGE2 were studied in terms of their ability to modulate in vitro immune responses associated with experimental autoimmune encephalomyelitis (EAE) in Lewis rats. Lymphoid cells from either the spleens or the draining lymph nodes of myelin basic protein (MBP)-sensitized rats exhibited in vitro immune responses which were enhanced in the presence of IM. Specifically, IM enhanced (i) guinea pig MBP (GPMBP)- and rat MBP (RMBP)-stimulated lymphocyte proliferation, (ii) background proliferation, and (iii) interleukin 2 (IL-2)-stimulated proliferation. Conversely, PGE2 inhibited both GPMBP- and IL-2-stimulated proliferation of MBP-sensitized lymphocytes. Together, these results indicate that PGs secreted by cultured lymphoid cells can directly mitigate MBP- or IL-2-stimulated lymphocyte proliferation. Furthermore, the observation that IM and PGE2 modulate in vitro responses of MBP-specific lymphocytes may provide insight into how the in vivo administration of IM potentiates the severity of EAE (H. Ovadia and P.Y. Paterson, Clin. Exp. Immunol. 49, 386, 1982) and how PGs may be involved in the spontaneous remission of EAE in rats.

Fractionation of T cell subsets on Ig anti-Ig columns: isolation of helper T cells from nonresponder mice, demonstration of antigen-specific T suppressor cells, and selection of CD-3 negative variants of Jurkat T cells

In the present experiments we have explored the possibilities of a modified immunoadsorbent technique to select for (1) mutagenized T cell receptor (Tcr) negative variants of Jurkat T lymphoma cells and (2) purified CD-4+ or CD-8+ T lymphocytes. The basic principle was to make large numbers of immunoglobulin (Ig) negative T cells Ig+ by T cell subset-specific monoclonal antibodies (mAb), and to select such cells on Ig anti-Ig columns. Our results demonstrated that Thy-1+, Fc receptor positive, antigen-specific T cells regulate the immune response in mice nonresponders to pork insulin, and the "autologous" mixed lymphocyte reaction. In addition, the immunoadsorbent method very efficiently selects Tcr/CD-3- variants from mutagenized Jurkat cell populations incubated with anti-CD3 mAb. The described method is easy and quick and can fractionate large numbers of cells; it is the "poor-man's cell sorter." The most important finding is the demonstration of antigen-specific Thy-1+, CD-8+, and Fc receptor+ T suppressor cell that apparently react with antigen in a non-major histocompatibility complex-restricted manner.

Why peptides? Their possible role in the evolution of MHC-restricted T-cell recognition

The peptide-presenting function of major histocompatibility complex (MHC) molecules permits pathogenic microorganisms to evade the host's immune system in two different ways: first, by escape of pathogen-derived antigenic peptides from presentation, and second, by molecular mimicry, that is resemblance between MHC-bound self and foreign peptides. These two mechanisms could have served as selective pressures in the evolution of the MHC. In this article, Zoltan Nagy and colleagues propose that escape from presentation selects for one or a few MHC molecules with the capacity to bind a broad range of different peptides. In contrast, molecular mimicry is considered to be the driving force for MHC diversification, that is it increases the number (polymorphism) and selectivity of peptide-binding sites.

Specific immune responses restored by alteration in carbohydrate chains of surface molecules on antigen-presenting cells

Two class I major histocompatibility (MHC) mutant mouse strains, H-2bm14 and H-2bm6, differ from the strain of origin C57BL/6 (B6, H-2b) in one and two amino acids of the H-2Db and H-2Kb molecule, respectively. The bm14 Db mutation results in specific failure of female bm14 mice to generate a cytotoxic T lymphocyte (Tc) response to the male-specific antigen H-Y. The allospecific Tc response of CD8+ B6T cells against bm6 Kb mutant spleen cells, in contrast to that against other Kb mutants, is absolutely CD4+ T helper cell dependent. Purified CD8+ T cells completely fail to respond. We now report that the inability to mount these specific immune responses is restored by the use of dendritic cells (DC) as antigen-presenting cells (APC). Comparison of MHC expression on various types of APC by cytofluorimetry and quantitative immunoprecipitation showed very high expression of class I and class II MHC molecules on DC. Strikingly, examination of class I and class II molecules by isoelectric focusing revealed qualitative differences as well. We show that the surface MHC class I molecules of DC are present in greater quantity and carry on average fewer sialic acids than the same molecules isolated from other APC types such as spleen cells, lipopolysaccharide blasts or concanavalin A blasts. That sialic acids on cell surface molecules, including MHC, may play a role in antigen presentation is suggested by our finding that removal of sialic acids, by neuraminidase, can restore specific responses to nonresponder APC as well.

Unresponsiveness to a foreign antigen can be caused by self-tolerance

In mice, two sets of genes govern the immune response to the synthetic antigen GT. One maps to the major histocompatibility complex and behaves like a typical immune response gene. The second is a background gene encoding a cell surface structure found on B cells. Mice which express, and are therefore tolerant of, one form of this structure do not respond to GT. Thus, tolerance of self generates holes in the T-cell repertoire, partially crippling the immune system.

The murine T-lymphocyte response to tyrosine-azobenzenearsonate. Characteristics of a low responder haplotype T-cell clone

An I-Ab-restricted, L3T4+ Ly2- T-cell clone, 5R-4F3, specific for ABAtyr was established in culture from a B10.A(5R) mouse. Since b haplotype mice respond weakly to ABAtyr compared to other haplotypes, this is a candidate clone of low responder phenotype. In support of this contention, 5R-4F3 grew very poorly under conditions that supported the vigorous growth of E beta bE alpha k-restricted T-cell clones from the same mouse. The I-A (low responder) and I-E (high responder) restricted T-cell clones also differed in their responses to apc pre-pulsed with antigen, compared to apc with antigen present continuously during culture. The low and high responder clones responded comparably to IL-2. Attempts to elevate the response of C57BL/6 mice to ABAtyr in vivo by injecting them with human recombinant IL-2 and antigen together were only partially successful: C57BL/6 mice treated in this way showed a 3-5-fold increase in their proliferative responses to ABAtyr, which was at best only one quarter of the level of response shown by high responder A/J mice to the same antigen dose.

The influence of MHC gene products on the generation of an antigen-specific T-cell repertoire

We have previously described the B10.A pigeon cytochrome c-specific response in terms of clonal phenotypes and T-cell receptor (TcR) gene usage. All B10.A T-cell clones studied respond to antigen in association with syngeneic B10.A APCs and cross-react to antigen in association with one or two allogeneic variants of the I-E-encoded MHC molecules. In congenic strains of mice expressing these allogeneic MHC alleles [B10.A(5R) and B10.S(9R)], pigeon cytochrome c-specific T cells exhibit very similar MHC cross-reactivities. Our goal was to determine whether the same MHC cross-reactive T-cell clones were expressed in each appropriate strain, or whether each T-cell repertoire was unique. The results indicate that identical V alpha-J alpha and V beta-J beta combinations were expressed by the major pigeon cytochrome c-specific response phenotype in B10.A and B10.A(5R) mice. Previous functional data supports this overlap in expressed T-cell clones. B10.A and B10.S(9R) mice exhibit similar response phenotypes to pigeon cytochrome c but express distinctly different TcR genes. The results of these studies support the existence of at least two different mechanisms in determining MHC-linked immune response polymorphisms.

The functional link between the immune suppression gene and Mhc class II molecules

The immune response to bovine insulin (BI) in the rat is controlled by the major histocompatibility complex (Mhc)-linked immune response gene (Ir-BI) and immune suppression gene (Is-BI). In the present study, we investigated the low responsiveness to BI in the WKAH rat (RT1k) and attempted to explore the functional link between Is-BI and Mhc class II molecules. Lymph node cells (LNC) from the low responder (WKAH) rats responded well to BI when a large amount of antigen was added to the culture in vitro or after OX8-bearing (OX8+) T cells were eliminated. These LNC, after the elimination of OX8+ cells, could show the RT1.Dk-restricted proliferative response upon in vitro challenge with BI, BI-B chain, or pork insulin. In addition, OX8+ T cells, which were activated with BI and antigen-presenting cells (APC) in vitro, suppressed the anti-BI response of W3/25-bearing proliferating T cells from BI-immunized rats. The results have demonstrated that proliferating T-cell repertoires do exist to BI, which recognize BI-B chain in the context of RT1.Dk molecules in the WKAH rat, and that the state of low responsiveness is mediated to a great extent by antigen-specific OX8+ suppressor T (Ts) cells. Furthermore, the elimination of APC or the addition to RT1.Bk-specific monoclonal antibody in the in vitro secondary activation culture of Ts cells diminished the suppressive activity of OX8+ Ts cells. In the induction phase of Ts cells it therefore seems to be necessary for these cells to recognize BI together with RT1.Bk molecules on APC.

Helper T-cell clones that recognize autologous insulin are stimulated in nonresponder mice by pork insulin

Murine antibody responses to various species of insulin are under major histocompatibility complex-linked Ir gene control. Beef insulin differs from pork insulin by only two amino acids in the A-chain loop, yet strain C57BL/10 (B10) mice produce insulin-specific antibodies after immunization with beef insulin and fail to produce antibody after stimulation with pork insulin. Nevertheless, pork insulin primes helper T cells in B10 mice that can be demonstrated if insulin-specific Lyt-1-, -2+ suppressor T cells are removed. Not only do the pork insulin-primed helper and suppressor T cells cross-react with autologous insulin, but also rat insulin (the amino acid sequence of which is identical to mouse insulin) elicits functionally identical helper and suppressor T cells. In this report, we demonstrate that in B10 mice the frequency of helper T cells stimulated by pork insulin is equivalent to that stimulated by beef insulin and that helper T-cell clones induced by beef and pork insulin are major histocompatibility complex-restricted T cells that proliferate, produce lymphokines, and provide helper activity after activation. These helper T-cell clones exhibit different antigenic fine specificities: beef insulin-induced clones respond to beef insulin but not pork or autologous insulin, whereas pork insulin-induced clones cross-react with all species of insulin tested, including rat insulin. In addition, the helper activity of cloned pork insulin-specific T cells is abrogated by pork insulin-primed suppressor T cells. These data support the hypotheses that Ir gene control of antibody responses to certain antigens involves mechanisms used for maintenance of self-tolerance.

A compartment of effector helper and suppressor T cells in the normal mouse thymus

We have recently described an autonomously activated set of T cells in the spleens of normal and "antigen-free" mice which display effector T helper (TH) or T suppressor (TS) activities; we describe here an intrathymic effector T-cell compartment which directly helps or suppresses B-cell responses and appears to be distinct from the peripheral set of effector cells. Splenic effector T cells do not represent recent thymic migrants (because adult thymectomized mice have unaltered levels of effector TH and TS cells in the spleen), nor do intrathymic effector T cells represent circulating peripheral T cells (since thymic effector T cells are B2A2+, while splenic effector T cells are B2A2-). Furthermore, effector TH cells within the two compartments exert differential effector activities: splenic effector TH cells induce B cells to both proliferation and maturation, while thymic effector TH cells are defective in activating B-cell maturation. The present findings extend our studies on "natural" lymphocyte activities in the normal immune system, revealing the existence of two apparently distinct effector T-cell compartments. The potential significance of the intrathymic set of effector cells in repertoire selection is considered.

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.

Immune suppression genes control the anti-F antigen response in F1 hybrids and recombinant inbred sets of mice

The immune response to the liver protein F antigen which, in the mouse, occurs in two allelic forms, is under sharp immunogenetic control in that only mice that possess the Ak molecule can respond to allo-F antigen. This response has been studied in a number of F1 hybrids between inbred strains and with recombinant inbred lines all of which express Ak, and which thus enable immune suppression effects to be detected. In the AKXL and AKXD sets the hybrids with CBA are responders if H-2k/H-2k, and usually nonresponders if H-2k/H-2b or H-2k/H-2d. Although this may be due to gene dosage effects, this cannot be the explanation for the low responsiveness of the H-2k/H-2b relative to the H-2k/H-2d mice found in CBA x BXD hybrids. For this, and other reasons, it seems likely that low responsiveness in any mouse possessing a responder Ak allele is due to suppression, and that this is mediated by the immune suppression effects of the non-H-2k haplotype. These H-2-mediated effects can be modified, both positively and negatively, by background genes. Thus, of the ten H-2k/H-2d members of the CBA x AKXD cross, seven are low responders and three are high responders. No other typed marker has the same strain distribution pattern at present. Major unresolved questions, therefore, concern the location and mechanism of action of the background genes and the mechanism of action of the H-2 immune suppression genes.

Analysis of T cell responses to poly-L(GluLys) at the clonal level. I. Presence of responsive clones in nonresponder mice

The synthetic random copolymer of L-glutamic acid and L-lysine (GL) is weakly or nonimmunogenic in all inbred strains of mice. Theories proposed to account for nonresponsiveness to GL include a deficient T cell repertoire, failure of antigen-presenting cells to present the antigen and/or the presence of suppressor cells. In this study we examine mechanisms for nonresponsiveness to GL. We demonstrate the existence of GL-reactive T cells which can be isolated with a relatively high frequency. These clones, which were derived following immunization of H-2d mice with poly(LGluLLysLTyr), also respond to several GL-containing polypeptides including the terpolymers of GL with phenylalanine, alanine (GLA) or leucine. Although recognition of GLA by heterogeneous T cell populations usually occurs in association with I-A determinants, these clones recognize GLA, as well as the other GL-containing polymers, in association with I-E determinants. Analysis of the antigen and alloreactivity patterns of these clones indicated that they expressed distinct antigen receptors. These studies imply that the T cell repertoire of "nonresponder" H-2d mice includes multiple GL-reactive T cell clones and that the antigen-presenting cells of these mice are effective in processing and presenting GL.

Possible mechanisms by which the H-2Kbm3 mutation may decrease cytotoxic T-lymphocyte recognition of vesicular stomatitis virus nucleoprotein antigen

Spleen cells from C57BL/6 (B6) mice generate a strong in vitro cytotoxic T-lymphocyte (CTL) response specific for vesicular stomatitis virus (VSV). Spleen cells from VSV-primed B6-H-2bm3 (bm3) mice, which have a mutation in H-2Kb, require approximately 10-fold more UV-inactivated VSV to generate in vitro secondary anti-VSV CTL, compared with spleen cells from primed B6 mice. Anti-VSV CTL elicited in both bm3 and B6 mice are primarily specific for the viral nucleocapsid protein (N protein), as demonstrated by using recombinant vaccinia viruses that express the VSV N protein. bm3 CTL were found to exhibit only a very low level of lytic activity when tested against autologous VSV-infected concanavalin A spleen cell blasts as well as several H-2b tumor cell lines. The weak anti-VSV response of bm3 CTL was found to be the result of a combination of inefficient recognition of VSV-infected target cells and decreased elicitation of secondary effector cells. VSV-infected bm3 target cells were not killed as well as B6 targets by either bm3 or B6 effectors. This is because of the inefficient recognition of targets, as demonstrated by the fact that VSV-infected bm3 cells were unable to competitively inhibit the lysis of VSV-infected B6 target cells by either bm3 or B6 effectors. By using cells from recombinant mice, it was shown that the CTL response restricted by H-2Kb was low in the bm3 mice, compared with that of the B6 mice. However, the H-2Db-restricted CTL activity was similarly low in both the B6 and bm3 mice. The possibility that the low response to VSV-infected bm3 cells is caused by differences between the bm3 and B6 cells in expression of either viral antigens or H-2K was investigated by radiolabeling and immunoprecipitation. VSV-infected B6 and bm3 cells were found to express equivalent levels of both viral antigens and H-2K. These results indicate that the bm3 mutation alters a functional site on the H-2Kb molecule that is involved in the recognition of VSV-infected cells. The observation that elicitation of bm3 CTL can occur at high antigen doses further suggests that the bm3 mutation results in a lower affinity of H-2K either for viral antigen or for receptor sites on the CTL.

Synthetic peptides and beta-chain gene rearrangements reveal a diversified T cell repertoire for a lambda light chain third hypervariable region

Twelve L3T4+ Ly-2.2- subclones, derived from 4 independent BALB/c T cell lines, responded to a combination of the I-Ed molecule and a synthetic peptide corresponding to residues 91-108 of the lambda light chain from BALB/c myeloma protein M315 (alpha, lambda 2). Peptide analogues in which the mutated residues Arg95 or Asn96 were exchanged with the corresponding germ-line-encoded Ser95 or Thr96 had an abolished or greatly reduced capacity to stimulate T cell clones. However, responses of subclones to an analogue where the mutated Phe94 was substituted with the germ-line-encoded Tyr94 revealed three specificity patterns: 5 clones reacted only with the lambda 2(315) peptide, 6 clones responded equally well to both peptides and a single clone reacted better with the Tyr94 analogue. Analysis of the T cell receptor beta-chain gene rearrangements disclosed 7 distinct rearrangements, identical rearrangements only being found for subclones originating from the same line. At least 3 different V beta genes were used. Subclones with identical or nearly identical peptide specificity, major histocompatibility complex-restriction and alloreactivity could differ in their V beta or J beta gene segment utilization.

Genetic influence on the antibody response to antigens of Schistosoma mansoni in chronically infected mice

Immunoprecipitations of in vitro translation products of mRNA from adult Schistosoma mansoni worms with sera from chronically infected mice of 12 inbred strains reveal a strain-dependent heterogeneity in the antibody responses to schistosome antigens. Of the strains tested the response to the 86K antigen was restricted to mice of haplotypes H-2d H-2k, and H-2a while the 14K antigen was only recognized by H-2k mice. Responses to other antigens revealed the influence of non-H-2 genes on the antibody response although no clear correlation was apparent between the antigens recognized and the non-H-2 genes of the strains. Both dominant and recessive responses towards individual antigens were seen in F1 animals. Some of these results support the cross tolerance model of Ir gene function.

The role of IL-2 and T4+ cells in the generation of human influenza virus-specific CTL activity

Stimulation of human peripheral blood lymphocytes (PBL) with influenza A virus leads to the generation of virus-specific cytotoxic T lymphocyte (CTL) activity as well as natural killer (NK)-like activity. In this study, we show that exogenous IL-2 augments the in vitro generation of virus-specific CTL activity, only when added some days after the initiation of the culture. Apparently, the endogenously produced IL-2 can be a limiting factor in the in vitro generation of CTL activity. The increase of influenza virus-specific CTL activity after addition of exogenous IL-2 does not affect the restriction pattern of the CTL response. So, the preferential use of certain HLA antigens as restriction elements is not due to a limiting amount of endogenously produced IL-2. Depletion of T4+ cells completely abrogates the generation of virus-specific CTL activity. Addition of exogenous IL-2 to T4+-cell-depleted cultures fully restores the generation of HLA-restricted virus-specific CTL activity. We conclude that in the in vitro generation of virus-specific CTL activity in bulk cultures of human PBL the sole function of T4+ cells in human virus-specific CTL generation is the production of IL-2, no cognitive cell interaction of T8+ CTL precursors with T4+ cells is required, and in bulk cultures T8+ cells themselves are not able to produce sufficient amounts of IL-2 to ascertain the maturation of virus-specific CTL precursors into cytolytic T cells. Finally, we show that exogenous IL-2 also has a stimulatory effect on the NK-like or lymphokine-activated killer activity, which is always concomitantly induced in virus-specific CTL generation cultures, but has no influence on the levels of IFN produced in such cultures.

Antigenic requirements for T-cell activation: reconstitution of a functional antigen from an inactive peptide portion of an antigen conjugated to protein carriers

The structural features of an antigenic peptide required for T-cell activation were examined by a novel approach: an active antigen was constructed from an inactive peptide portion of the original antigen by conjugating it to various proteins. An eicosapeptide, peptide 8, representing residues 103-112 of the tobacco mosaic virus protein (TMVP), was utilized as the model antigen for these studies. While peptide 8 was able to stimulate, in vitro, T-cells from peptide 8 primed mice, synthetic peptides representing various portions of peptide 8 were unable to activate these cells. Although the amino-terminal undecapeptide of peptide 8 (residues 93-103 of TMVP) was unable to activate T-cells from peptide 8 primed mice, conjugates which consisted of this undecapeptide coupled to certain proteins were capable of inducing antigen-specific proliferation of these T-cells. These results identify two structural antigenic features essential for T-cell activation: a T-cell-recognizable epitope within the amino-terminal undecapeptide of peptide 8 and a second region provided by the carboxy-terminal half of peptide 8 or by protein carriers. Potential roles for this second region include providing a site for antigen interaction with Ia molecules on the antigen-presenting cell or, alternatively, providing amino acids important in stabilizing the binding of the T-cell antigen receptor. The results suggest that the recognition of this second region exhibits only a limited specificity.

Ir gene expression on T cells: effect of a monoclonal antibody directed against I region-controlled determinants on T cells

A monoclonal antibody directed at an I region-controlled epitope uniquely expressed on T cells (Iat) was studied for its in vivo effect on the antibody response under the control of an Ir gene. The antibody was produced by a hybridoma made from A.TH spleen cells immune to A.TL (anti-Ik), that was selected for its reactivity with T but not B cells and macrophages, and thus was designated as anti-IatK. The injection of this anti-Iatk into H-2k, H-2b and H-2k X bF1 mice resulted in the suppression of antibody response to poly-L-(His,Glu)-poly-D,L-Ala--poly-L-Lys [(H,G)-A--L] in H-2k and F1 mice but not that to poly-L-(Tyr,Glu)-poly-D,L-Ala--poly-L-Lys [(T,G)-A--L] both in H-2b and F1 mice. The adoptive cell transfer of the combinations of anti-Iatk- or normal mouse serum-treated T and B cells into irradiated hosts demonstrated that anti-Iatk primarily affected (H,G)-A--L-specific helper T cells but not B cells and macrophages, resulting in the specific elimination of the antibody response. Suppressor T cells were not induced by the treatment with anti-Iatk. The antibody specifically eliminated the (H,G)-A--L-specific but not (T,G)-A--L-specific helper T cells in F1 spleen cells that had been primed with both (H,G)-A--L and (T,G)-A--L. The results indicated that anti-Iatk affected the H-2k-associated Ir gene function born by T cells but not by antigen-presenting cells, which was expressed on F1 helper T cells with apparent exclusion of the other allele, and implied that the Iat antigen on helper T cells is one of the sites of expression of Ir genes.

The cytotoxic T cell response to the male-specific histocompatibility antigen (H-Y) is controlled by two dominant immune response genes, one in the MHC, the other in the Tar alpha-locus

The genetic control of the cytotoxic T-cell response to the male histocompatibility antigen, H-Y, was analyzed in BALB/cKe(C) and SJL/J(J) which are both nonresponders. However, the (C X J)F1 hybrid is a responder. Therefore, two dominant complementing genes are involved. Analysis of a set of (C X J) recombinant inbred (RI) lines reveals that these two complementing gene products are a restricting element (R) encoded by the H-2 (MHC) locus on chromosome 17 and a subunit of the T-cell receptor (anti-R) encoded by the Tar alpha-locus on chromosome 14. The order and orientation of gene segments within the Tar alpha-locus has also been established relative to the chromosome 14 marker, Es-10. The existence of two RI strains which are recombinant at chromosome 14 has made it possible to determine that this order is Es-10--v alpha-1--v alpha-2--[C alpha--Np-2]--centromere. The implications of these data for the antigen-specific regulation of immune responsiveness are discussed in terms of the dual recognitive-single receptor model.

Proliferative responses of T cells from SJL----F1 and F1----SJL bone marrow chimeras to SJL lymphoma cells

RCS tumor cells induce marked proliferation of syngeneic SJL T cells in vivo and in vitro. Certain F1 hybrids of SJL mice give high proliferative responses to gamma-RCS, while other F1 hybrids give low responses. SJL----"non-responder" F1 and "non-responder" F1----SJL semiallogeneic bone marrow chimeras were prepared to study how the host environment affects the ability of T cells to give a proliferative response to gamma-RCS. The results indicate that T cells educated in an SJL host become responsive to RCS cells, while T cells educated in an (SJL X BALB/c)F1 host become unresponsive. This finding applies to both thymus and lymph node T cells. The unresponsiveness in F1 mice is not due to suppressor cells, since added F1 cells do not affect the proliferative response of SJL cells to gamma-RCS. Instead, it appears that RCS-specific T cells are either deleted in (SJL X BALB/c)F1 mice, or expanded in SJL mice as they develop. These findings are discussed in relation to the specificity of the responding T cells, for LPS activated syngeneic B cell blasts as well as RCS cells, and to the presence of a "leaky" thymus barrier in SJL mice for B cells.

One I region restriction determinant can associate with multiple antigenic epitopes

Studies presented in this paper show that T cell clones recognizing different epitopes of multideterminant antigens can be restricted by the same I-A molecule. These data further support the concept that a single I-A restriction site can present more than one antigenic epitope. This concept was supported by data on the proliferation of T cell clones reactive with either poly(L-Glu60, L-Ala30, L-Tyr10)n(GAT) or poly(Tyr, Glu)-poly D,L-Ala--poly Lys [(T,G)-A--L] which recognized different epitopes on these multideterminant antigens. Two clones recognizing different epitopes on the same multideterminant antigen can be blocked by the same monoclonal anti-I-A antibody. Additionally, the mutation in the Abm12 chain utilized in [B6.C-H-2bm12(bm12) X B10.A(4R)]F1 mice can affect the restriction determinant of clones recognizing different antigenic epitopes. These results suggest that in the strictest sense, the determinant selection theory is not tenable and would support the concept that T cell specificity is controlled by the T cell repertoire.

Dominant suppressive effect of the silent Eb alpha allele on an in vivo T helper cell response under Ed beta Ed alpha region-linked immune response gene control

Previous adoptive spleen cell transfer experiments have demonstrated that an immune response (Ir) gene linked to the Ed beta Ed alpha region allows BALB/c T helper lymphocytes (Th) to respond to an idiotope on the V lambda 2(315) fragment of isologous myeloma protein M315. BALB.K (H-2k) and BALB.B (H-2b) do not respond to V lambda 2(315). While (H-2d X H-2k)F1 hybrids have been shown to be responders, it is now demonstrated that (H-2d X H-2b)F1 hybrids are low responders. By crossing BALB/c with various H-2 recombinants on B10 background and probing Th responsiveness to V lambda 2(315) in these F1 hybrids, the dominant suppressive gene of the H-2b haplotype is mapped to Eb alpha Sb. It is argued that the suppressive gene is Eb alpha, which is a silent allele. A likely explanation for the suppressive effect of the Eb alpha allele is that reduced amounts of Ed beta: Ed alpha restriction elements are present on antigen-presenting cells of (H-2d X H-2b)F1 hybrids because only one E alpha gene is functional in such mice. The present report extends previous in vitro findings from other laboratories to the in vivo situation and suggests that silent alleles for class II molecule chains may profoundly affect certain immune responses of individuals heterozygous for the silent allele.

Distinct recognition phenotypes exist for T cell clones specific for small peptide regions of proteins. Implications for the mechanisms underlying major histocompatibility complex-restricted antigen recognition and clonal deletion models of immune response gene defects

Using synthetic peptides as antigens, it was found that T cell clones of a given haplotype specific for 13-16 amino acid peptides could be clearly distinguished by the varied influence of amino acid substitutions on recognition. This was true for different antigenic determinants within peptides 81-96 and 74-86 of hen egg-white lysozyme, recognized in the context of the I-Ab and I-Ak molecules, respectively. Considerable complexity was demonstrated in the induced T cell repertoire specific for apparently single determinants, which implies that diversity of T cell recognition approaches that for B cells. The implications of the degeneracy of T cell recognition are discussed in the context of mechanisms through which Ia molecules restrict recognition and theories of Ir gene defects.

Analysis of immunological tolerance to major histocompatibility complex antigens. I. High frequencies of tolerogen-specific cytotoxic T lymphocyte precursors in mice neonatally tolerized to class I major histocompatibility complex antigens

Injection of (CBA X A)F1 cells into neonatal CBA mice rendered them tolerant to skin grafts of (CBA X A)F1 origin. Limiting dilution analysis revealed a very low frequency of tolerogen-inducible cytotoxic T lymphocyte precursors (CTL-P) in spleens of tolerant mice. Two in vitro procedures allowed, however, the induction of tolerogen-specific CTL-P of high frequencies in tolerant mice: (a) the "by-pass" activation of spleen cells from tolerant mice by concanavalin A under short-term bulk culture conditions followed by culture of limiting numbers of activated responder cells, and (b) absorption of spleen cells from tolerant mice on monolayers of tolerogen-activated T cells from normal syngeneic mice. Furthermore, spleen cells from tolerant mice, recently challenged with a tolerogen-bearing skin graft, specifically suppressed the activation of tolerogen-reactive splenic CTL-P from normal CBA mice under limiting dilution conditions. These data confirm the presence of tolerogen-specific CTL-P of high frequency in tolerant mice and suggest their functional inactivation through a suppressive mechanism.