Ir Gene Research Articles

Identification of suppressor T cells in virgin non-responder spleen cells responsible for primary unresponsiveness to L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT).

T cell subsets that regulate antibody responses to L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT) in mice that are Ir gene non-responders have been further characterized. We previously defined several T cell subsets in GAT-primed non-responder mice. The Lyt-2+ suppressor-effector T cells suppress responses to GAT and GAT complexed to methylated BSA (GAT-MBSA). The Lyt-1+ cell population is complex and can be separated into I-J- Th cells, which support responses to GAT and GAT-MBSA. After priming, the Lyt-1+, I-J+ cell population contains suppressor-inducer cells that activate precursors of suppressor-effector cells to suppress responses to GAT and GAT-MBSA as well as Ts cells that directly inhibit responses to GAT but not GAT-MBSA. By contrast, the Lyt-1+ cells from virgin mice contain only cells that directly suppress responses to GAT but not GAT-MBSA. The major question addressed in the present studies was whether the Lyt-1+, I-J+ Ts cells in virgin and primed mice and the suppressor-inducer cells in GAT-primed mice were functionally and serologically distinct subsets. The studies used mAb and panning procedures to separate cell populations and inhibition of PFC cell responses to functionally define the activity of the cell populations. We used the following two mAb that were raised by immunizing rats with GAT-specific suppressor factors: 1248A4.10 (known to react with suppressor-inducer cells) and 1248A4.3, another reagent from the same fusion. Lyt-1+ cells from virgin spleens contained Ts cells that were A4.10-, A4.3+ and no suppressor-inducer T cells, whereas Lyt-1+ cells from GAT-primed spleens contained Ts cells that were A4.10-, A4.3+ as well as A4.10+, A4.3- suppressor-inducer cells. Thus, the Lyt1+, I-J+ cell subset can be divided into two functionally and serologically distinct subsets, direct Ts cells (1248A4.3+), which suppress responses to GAT but not GAT-MBSA, and GAT-primed suppressor-inducer T cells (1248A4.10+).

Two distinct mechanisms account for the immune response (Ir) gene control of the T cell response to pigeon cytochrome c.

Previous experiments have demonstrated that the immune response of MHC congenic mice to pigeon cytochrome c is under Ir gene control. Expression of I-E-encoded gene products influences both the magnitude and fine specificity of the Th cell response to pigeon cytochrome c and phylogenetic derivatives. Results of those experiments implicate both determinant selection and repertoire selection as mechanisms of Ir gene control in this system. In this report we have compared the TCR expressed in pigeon cytochrome c-reactive Th cells from B10.A(I-Ek), B10.A(5R) (I-Eb), and B10.S(9R) (I-Es) mice. The B10.A(5R) strain is a low responder to pigeon cytochrome c, but in response to moth cytochrome c this strain produces T cells which respond to pigeon or moth cytochrome c on B10.A APC. These cells are phenotypically identical to the predominant clonal phenotype seen in the B10.A response to pigeon cytochrome c. In this report, we show that the B10.A and B10.A(5R) pigeon cytochrome c-reactive T cells express essentially identical T cell receptors. These results, coupled with recent studies reporting a relatively low affinity for I-Eb molecules by pigeon cytochrome c peptides compared with moth cytochrome c peptides, strongly argue that the immune response defect in the B10.A(5R) strain is due to a defect in Ag presentation (determinant selection). In contrast, B10.A and B10.S(9R) strains are high responders to pigeon cytochrome c. Both strains produce T cell clones which are capable of responding to cytochrome c presented by either B10.A or B10.S(9R) APC in vitro. We show that, even in T cells with this MHC restriction degeneracy, the TCR expressed in the two strains are different. Because the APC of both strains can clearly present the cytochrome c Ag, we conclude that the differential expression of the TCR in the responses is due to a T cell repertoire selection difference in the two strains. Thus, for the response to one Ag in three MHC congenic strains, there exists evidence that both determinant selection and repertoire selection can be mechanisms of Ir gene control of an immune response.

An immunodominant epitope of the human immunodeficiency virus envelope glycoprotein gp160 recognized by class I major histocompatibility complex molecule-restricted murine cytotoxic T lymphocytes.

Because cytotoxic T lymphocytes (CTL) may be important for preventing direct cell-to-cell transmission of human immunodeficiency virus (HIV), the agent responsible for acquired immunodeficiency syndrome, we have begun to investigate the epitope specificity and immune response (Ir) gene control of anti-HIV CTL responses in experimental animals. Mice were infected with a recombinant vaccinia virus expressing the HIV gp160 envelope gene, and the primed lymphocytes were restimulated in vitro with a transfected histocompatible cell line expressing the same gene. Our results show that H-2d mice are CTL high responders and H-2k mice are low responders to the HIV gp160 envelope protein under these conditions. Moreover, the H-2d mice respond predominantly to a single immunodominant site represented by a 15-residue synthetic peptide conforming to the amphipathic alpha-helix model of T-cell epitopes and seen by CD4- CD8+ CTL in association with the Dd class I major histocompatibility complex (MHC) molecules. The facts that CTL responses were detected in the context of only one of four class I MHC molecules tested and that the response was limited predominantly to a single epitope indicate that the CTL repertoire elicited by the HIV envelope protein in association with murine class I MHC molecules may be very limited. In addition, this epitope occurs in a highly variable segment of the envelope protein. This puts constraints on the use of a single peptide sequence from this region in a vaccine, as such a vaccine would have to be polyvalent. Nevertheless, this same variability suggests that this region may be under selective pressure from human CTL, and therefore that this site may be immunodominant in humans as well as mice and so of clinical importance in vaccine development.

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.

Antigenic competition in the immune response against protein mixtures: Strain-specific non-immunogenicity of Escherichia coli antigens

Antigenic competition is argued to impair the immune response on the level of accessory cell-dependent antigen presentation to responsive T-cells (regulated by MHC encoded Ir gene products). A possible influence of these mechanisms on in vivo immunization with antigen mixtures was investigated by using cytoplasmic extracts of four different strains of Escherichia coli as antigen sources for immunizing rabbits. The immune response against these antigen mixtures was tested by crossed immune electrophoresis (CIE) and immunoblotting (IB) in a homologous system (a given antigen extract of one strain against the corresponding antisera) and in the heterologous system (antigen extract of one strain against the antisera of different other strains). Several proteins were non-immunogenic in the extract of one strain but elicited good antibody responses in other strains. One of the strain-specific non-immunogenic proteins was purified and revealed a normal immune response upon immunization. The data suggest that different antigenic competition effects are induced by different protein compositions of antigen mixtures. This strain-specific competition seems to determine the immunogenicity of certain molecules (and not only the immunogenic properties of the molecules themselves). Furthermore this method offers a practical approach to increase the antibody production against weak immunogens in antigen mixtures.

Processing of a minimal antigenic peptide alters its interaction with MHC molecules

Before their recognition by T lymphocytes, protein antigens generally require processing by antigen-presenting cells. In a poorly understood series of events, the protein antigen is internalized, transformed and re-expressed on the surface of the antigen-presenting cell in association with gene products of the major histocompatibility complex (MHC). Small peptides derived from the native protein can be recognized in the absence of antigen processing, suggesting that processing involves proteolytic degradation. These peptides are thought to mimic the naturally produced peptide fragment. We describe here a synthetic peptide antigen of this type which does not require processing but which is nevertheless further processed by splenic antigen-presenting cells. Interestingly, this processing event specifically alters the interaction of the peptide with the class II MHC (Ia) molecule, markedly affecting both its potency as an antigen in vitro and its immunogenicity in vivo (IR gene control).

Cytotoxic T lymphocyte response to minor H-43a alloantigen in H-43b mice. Privileged H-2Kb restriction to the response is not due to immunodominance or epistatic effect but due to Ir gene function of H-2Kb itself.

Previous study demonstrated that anti-H-43a cytotoxic T lymphocyte (CTL) response of H-43b CWB (H-2b) stain carrying non-major histocompatability complex (MHC) genes of C3H and F1 strains raised by crossing CWB with various H-43b strains was restricted exclusively by self H-2Kb (Kb). In the present study, newly produced C3W strain (H-2k, H-43b), which is H-43-congenic to C3H/HeN (H-2k, H-43a), was used as H-43b mice, and possibility of immunodominance of Kb was examined. No anti-H-43a CTL response could be induced in C3W strain and F1 strains raised by crossing C3W with other H-43b strains not carrying Kb. Thus, the possibility of immunodominance of Kb over the other MHC class I alleles could not be supported. We also examined possibility of epistatic effect of I region genes and non-MHC genes on the Kb restriction. (C3W x C57BL/6)F1(I-Ak/b) and (C3W x B6.CH-2bm12)F1(I-Ak/bm12)mice showed equally anti-H-43a CTL response restricted exclusively by self Kb, and (C3W x B10.MBR)F1(Ik/k) mice also showed anti-H-43a CTL response restricted solely by self Kb. Cold target competition experiments demonstrated that H-43b C57BL/10 or A.BY mice, which do not have non-MHC genes of C3H mounted anti-H-43a CTL response restricted solely by self Kb. Thus, no relation of I region genes or non-MHC genes to the Kb restriction was shown. All the results indicate that H-43b mouse strains, including F1, can not achieve anti-H-43a CTL response unless they carry Kb allele. Notably, (C3W x C57BL/6)F1 mice mounted self Kb-restricted anti-H-43a CTL response, whereas (C3W x B6.CH-2bm1)F1 mice carrying mutated Kb could not mount anti-H-43a CTL response at all. These findings indicate strongly that Kb itself is classical Ir gene of anti-H-43a CTL response and directs self Kb restriction of the response.

Are idiotypic peptides from variable domains critical for T-dependent production of rheumatoid factors?

Studies from this laboratory have indicated that isologous myeloma protein 315 (M315, isotype IgA, lambda 2) elicits T helper cells which recognize processed forms (peptides) of its V-domains and that recognition is controlled by H-2 linked immune-response (Ir) genes (J Exp Med 1982; 155:1587-96; Eur J Immunol 1986; 16:889-93). We now report that adjuvant-free soluble M315, particularly the mildly reduced and alkylated form, stimulates a T-dependent antibody response mainly specific for M315's paired V-domains. A small subset of the antibodies appeared to recognize the C-region of IgA, thus being analogous to rheumatoid factors (RF). On the basis of these observations, we propose that one pathway to RF production depends on T helper cells that interact directly with RF-producing B cells across peptide-MHC bridges. These peptides are envisaged to be derived from hypervariable regions of IgG V-domains, and they are therefore called "idiotypic peptides". This hypothesis assumes that the number of different idiotypic peptides is so large that the immune system has not developed tolerance to all of them.

In vivo effects of antibodies to immune response gene products. II. Suppression of humoral immune responses with monoclonal anti-I-A is due to suppressor cells.

The I region of the murine major histocompatibility complex (H-2) encodes two cell surface glycoprotein complexes (Aα:Aβ and Eα:Eβ) which exert profound control over many immunologic reactions including humoral and cellular responses to a variety of antigens, i.e., Ir gene effects, stimulation in mixed lymphocyte reaction, graft versus host disease, antigen presentation to T cells by macrophages, collaboration between T and B cells and determination of T cell help or suppression [1-13]. In the past few years, several laboratories have reported that antibodies directed against I region gene products (anti-la) are effective in modulating immune responses both in vitro and in vivo [14-32, 48-51]. The ability of anti-la antibodies to alter immune responsiveness was attributed to their interaction with macrophage la antigens, thus masking or sterically hindering la epitopes involved in antigen presentation [16,17, 33-35]. However, other reports have suggested that additional mechanisms may be involved [28, 36-...

Genetic control of immune response: New concepts and old misconceptions

A common misconception about the genetic control of the immune response is that it concerns a few selected antigens. In fact, the immune response to any antigen recognized by T-lymphocytes is genetically controlled. To be able to demonstrate this control is another matter: needed are nonresponders to a particular antigen that can pass nonresponsiveness to their progeny. Only then, by mating responders with nonresponders and following the segregation of responsiveness among the progeny, can it be shown that a gene or genes are responsible for the difference in the phenotype. Another misconception is that the genetic control of immune response is exerted primarily or exclusively by the genes belonging to the major histocompatibility complex of a species (Fig. 1). Probably a large number of immune response genes map outside the Mhc. Only a few of these genes have been identified, possibly because immunologists are too preoccupied with the Mhc-associated Ir genes. Some non-Mhc genes function at the B-lymphocyte level, 1 others at the T cell receptor level, 2 and still others at the level of the macrophage? The Mhc-associated Ir genes are, however, the only Ir genes for which the mechanism of action is known. The third misconception is that the Mhc-associated Ir genes all map in the class II region, therefore sometimes referred to as the Ir or I region. This misconception has historical roots in that the class II-associated Ir genes were the first Ir genes discovered. 4,5 The discovery of class I-associated Ir genes was made more than 10 years later 6 in a form that some immunologists still do not take for what it is. I shall return to this point later. What are the Mhc-associated Ir genes? And what is the mechanism of their action? The answer to these two

Ir gene influence on DNP-specific B-memory-cell formation.

It is well known that Ir genes control the antibody production. To investigate whether they also influence B-memory-cell generation, CBA mice (nonresponders) were primed with dinitrophenyl-poly-(L-tyr,L-glu)-poly-(D,L-ala)-poly-(L-lys)-DNP-TGAL conjugate. At the same time animals were injected with ovalbumin (OVA) to activate OVA-specific T helpers. Two to four weeks later animals were challenged with DNP-OVA conjugate and the number of IgG-producing B cells was determined. The data presented indicate that carrier-specific MHC-restricted T helpers are not required for B-memory-cell generation. It is concluded that the defect of IgG response to DNP-TGAL in CBA mice is caused by a block in the maturation of memory cells to antibody-producing cells.

Genetic control of immune response to staphylococcal exfoliative toxin A in mice.

Different inbred and congenic resistant strains of mice were immunized with staphylococcal exfoliative toxin A (ETA). In antibody responses measured in sera of mice by a passive hemagglutination technique, A/J, DBA/2, BALB/c, B10A, B10D2, B10S, and A.SW were high responders. C57BL/10 (B10), A.BY, and DBA/1 were low responders. The congenic C3H/HeJ and C3H.SW mice were, respectively, high and low responders. The observation that the immune responses of the mice to ETA were closely linked with the haplotypes of their H-2 complexes suggests the existence of an H-2-linked immune response (Ir) gene coding for the production of humoral antibodies to ETA. Four B10A recombinants were used to map this gene within the H-2 complex. The finding that B10A(2R) and B10A(4R) were high responders, whereas B10A(3R) and B10A(5R) were low responders, indicates that the gene controlling antibody response to ETA is located in the I-A subregion or the H-2K end within the H-2 complex. We wish to propose the name Ir-ETA for this gene. The function of Ir-ETA seems to be at least related to antigen recognition at the T-lymphocyte level. Neonatal mice are generally susceptible to ETA regardless of their H-2 haplotypes. However, the neonatal mice born to a high-responder mother immunized with ETA were resistant to the subcutaneous challenge of ETA, but those born to an immunized low-responder mother were susceptible to the challenge. This result suggests that if the mother is a high responder to ETA and is effectively immunized with ETA, the maternal immunity makes it possible to neutralize this toxin in neonatal mice.

Inverse Ir gene control of the antibody and T cell proliferative responses to human basement membrane collagen.

The immune response to pepsin-soluble human basement membrane-derived type IV collagen in mice has been characterized. Both T cell proliferative and antibody responses have been shown to be under major histocompatibility complex (MHC)-linked Ir gene control in inbred and MHC congenic mice. However, unlike previous examples studied, this response shows a separation of these two types of immunologic responsiveness. Only mice having I-As give potent in vitro T cell proliferative responses to type IV collagen whereas all mice except those having I-As give high antibody responses to this antigen. In (I-As X I-Anon-s) F1 mice, the T cell proliferative response was dominant, whereas antibody responses were markedly reduced compared with the responder parent. Given the recent demonstration that class II MHC-restricted, L3T4+ T cells can be divided into two sets, one of which helps for antibody responses and the other of which produces interleukin 2 and can also suppress such responses, it seems likely that these data can be accounted for on the basis of differential activation by this antigen of these two cell sets in mice of different MHC genotypes.

T-cell-receptor beta- and I-A beta-chain genes of normal SWR mice are linked with the development of lupus nephritis in NZB x SWR crosses.

The incidence of nephritis in autoimmune New Zealand Black (NZB) mice is low, but when they are crossed with normal SWR mice, almost 100% of the female F1 hybrids (SNF1) develop lethal glomerulonephritis. To define the contribution of the normal SWR strain to the development of nephritis, we analyzed the association of the I-A beta-chain gene of Ia-encoding region, the T-cell-receptor beta (TcR beta)-chain gene, and immunoglobulin heavy-chain allotype (IgH) with the development of lupus nephritis in 165 NZB X SWR crosses. We found that genes linked to the TcR and Ir gene loci of the normal SWR mice interacted with NZB-derived genes, leading to the development of accelerated and severe nephritis in the NZB X SWR crosses.

Immune responsiveness to Ambrosia artemisiifolia (short ragweed) pollen allergen Amb a VI (Ra6) is associated with HLA-DR5 in allergic humans.

The relationship between HLA type and specific immune responsiveness toward ultrapure Ambrosia artemisiifolia (short ragweed) pollen allergen Amb a VI (Ra6) was explored in a genetic-epidemiologic study of groups of 116 and 81 Caucasoid subjects who were skin-test positive (ST+) toward common environmental allergens. Specific immune responsiveness to Amb a VI was assessed by measuring serum IgE and IgG antibodies (Abs) by double Ab radioimmunoassay in both ST+ groups. Significant associations were found between IgE Ab responsiveness to Amb a VI and the possession of HLA-DR5; P values for the two groups were, respectively, 7 X 10(-7) and 1 X 10(-3) by nonparametric analyses, and 4 X 10(-11) and 5 X 10(-8) by parametric analyses. The levels of significance for the associations between HLA-DR5 and IgG Ab responsiveness were highly dependent on the extent of ragweed immunotherapy (Rx) within the patient group; by parametric statistics, the associations were 10(-11) for the group that had received relatively little Rx and 2 X 10(-3) for the group that had received more intensive Rx. These results provide further striking evidence for the existence of specific HLA-linked human Ir genes involved in responsiveness toward inhaled allergens and illustrate the usefulness of the allergy model in studies of the genetic basis of human immune responsiveness. Extension of these studies to investigation of structure-function relationships involved in antigen recognition by Ia molecules and the T-cell receptor will lead to a better understanding of human susceptibility toward immunologic diseases.

Turning (Ir gene) low responders into high responders by antibody manipulation of the developing immune system.

The ability of helper T cells directed against trinitrophenyl-modified syngeneic spleen cells to recognize low-hapten densities on target cells is under major histocompatibility complex-linked Ir gene control. Thus, BALB/c (H-2d) mice are low responders while H-2 congenic BALB.C3H (H-2k) mice are high responders. Immunization of adult BALB/c mice with the monoclonal antibody F6(51), directed to shared idiotopes by anti-trinitrophenyl antibodies and clonal receptors on anti-trinitrophenyl-self helper T cells, leads to the production of high titers of circulating idiotype, has no influence on helper T cell idiotypic profiles, but shifts to a high-responder phenotype the ability of helper T cells to recognize low-hapten densities. These effects on Ir gene phenotype are even more striking in untreated progenies from F6(51)-immunized BALB/c females, which are better responders than genetically high-responder BALB.C3H mice, although completely different in the expression of the F6(51)-defined clonotype. The general significance of these findings on Ir gene-directed T-cell repertoire selection is discussed, for they constitute formal evidence against antigen-presentation as a mechanism of Ir gene effects and strong support for the importance of maternal influences on the development of T-cell repertoires.

HLA-DQ is epistatic to HLA-DR in controlling the immune response to schistosomal antigen in humans.

Antigens that produce an antibody response in some members of a species may fail to do so in others. The response to an antigen is controlled by a gene termed the immune response (Ir) gene, which is transmitted as a single dominant trait. We have provided evidence for similar immune suppression (Is) genes which control non-responsiveness through the antigen specific suppressor T cell. The non-responsiveness is also dominantly inherited and the Is genes are linked to the histocompatibility (HLA) antigen system. Here we report that the HLA-DR2 molecule from a non-responder haplotype (HLA-Dw12-DR2-DQwl) is required for the proliferative T cell response to schistosoma japonicum (Sj) antigen, as a restriction element, indicating that the HLA-DR2 is the product of the Ir gene, and that the HLA-DQwl molecule of the non-responder haplotype is important in the antigen-specific suppression of the response to this antigen, suggesting that it is the product of the Is gene. We therefore conclude that the HLA-DR and DQ molecules, which are controlled by the distinct genes in the MHC multigene family, regulate immune response and immune suppression and that the gene for HLA-DQ is epistatic to that for HLA-DR in controlling the immune response to schistosomal antigen in humans.

The virulence of Trypanosoma congolense can be determined by the antibody response of inbred strains of mice.

Three inbred strains of mice, BALB/c, C57Bl/6 and CBA/J were infected with three clones of Trypanosoma congolense, DIND/3.1, SAM/28.1 and KAR/57.1, which were obtained from three different stocks. DIND/3.1 was of high virulence for BALB/c and CBA/J but of negligible virulence for C57Bl/6. SAM/28.1 was of high virulence and KAR/57.1 of negligible virulence for the three strains of mice. In each case, high virulence was correlated with a late, transient and low titre protective antibody response measured by complement mediated lysis of live organisms. Negligible virulence was correlated with an early, high titre protective antibody response. Suppression of the antibody response by sub-lethal irradiation or cyclophosphamide treatment of the host turned a trypanosome infection of negligible virulence into one of high virulence. In mice with mixed infections it was shown that highly virulent trypanosomes did not influence the course of infection and antibody response to trypanosomes of negligible virulence and vice-versa. The relationship of total antigen mass to the kinetics of the antibody response suggests that 1000- to 10,000-fold less antigen is required in good responder than in bad responder mice to trigger the immune response. Thus the virulence of T. congolense can be determined by the antibody response of inbred strains of mice. The specificity and dose dependency of this antibody response seem to implicate the involvement of Ir genes.

Arsonate-specific murine T cell clones. IV. Properties of I-E- and I-A-restricted clones.

The T cell antigen L-tyrosine-p-azobenzenearsonate is unique in being a simple determinant that can be presented in the context of both I-A and I-E. I-E-restricted T cell clones derived from B10.A(5R) mice were found to fall into three groups: Type I clones recognized antigen only in the context of syngeneic apcs, Type II clones recognized antigen with the same highly specific major histocompatibility complex restriction but in addition proliferated in response to allogeneic stimuli; Type III clones were "degenerate" in their major histocompatibility complex-restricted recognition of antigen and proliferated when antigen-presenting cells bearing Eb beta Ek alpha (syngeneic), Ek beta Ek alpha, or Ed beta Ed alpha were used. These observations allow some conclusions to be drawn about sites on the I-E molecule that may be functionally significant in the presentation of this antigen. By using the B cell hybridoma LK35.2 as target cells, some of these T cell clones act as cytotoxic cells in the Class II-restricted manner predicted from the results of proliferative assays. Class II-restricted cytotoxicity can therefore be controlled by both I-A and I-E mouse Ir gene loci.

Failure to find holes in the T-cell repertoire

The ability of an animal to respond to a given antigenic peptide depends on its major histocompatibility complex (MHC) type. Some peptides are not immunogenic when combined with a particular form of the MHC-encoded molecule. This non-responsiveness is regulated by immune response (Ir) genes and is thought to arise by one of two distinct mechanisms. Either the MHC-encoded molecules physically fail to interact with the antigen, preventing the activation of T cells with appropriate receptors, or they limit the expressed repertoire of T cell clones so that no T cells are available to be activated by existing complexes of MHC-encoded molecules and antigen. Experimental evidence has been generated to support both mechanisms. However, the relative importance of each has not been clearly established. In this study we started with a peptide that was immunogenic in B10 mice; it was thus known to be able to interact with the MHC molecule, and T cells existed which could recognise the peptide-MHC complex. Based on previous experiments, we then changed only those parts of the peptide that we thought interacted with the T-cell receptor. All the new analogues created were still immunogenic, confirming that the amino-acid substitutions that we had made did not prevent productive interactions with the MHC-encoded molecule. No limitations ('holes') in the T-cell repertoire were found. The experiments demonstrate the vast potential of the T-cell population to recognize many different analogues, each in a unique way, and suggest that constraints on the diversity of the T-cell repertoire may not be a major explanation for Ir gene defects.