The role of H-2 linked genes in helper T-cell function. IV. Importance of T-cell genotype and host environment in I-region and Ir gene expression

The somatically generated portion of T cell receptor CDR3α contributes to the MHC allele specificity of the T cell receptor

Mature T cells bearing αβ T cell receptors react with foreign antigens bound to alleles of major histocompatibility complex proteins (MHC) that they were exposed to during their development in the thymus, a phenomenon known as positive selection. The structural basis for positive selection has long been debated. Here, using mice expressing one of two different T cell receptor β chains and various MHC alleles, we show that positive selection-induced MHC bias of T cell receptors is affected both by the germline encoded elements of the T cell receptor α and β chain and, surprisingly, dramatically affected by the non germ line encoded portions of CDR3 of the T cell receptor α chain. Thus, in addition to determining specificity for antigen, the non germline encoded elements of T cell receptors may help the proteins cope with the extremely polymorphic nature of major histocompatibility complex products within the species.

A signal integration model of thymic selection and natural regulatory T cell commitment

The extent of TCR self-reactivity is the basis for selection of a functional and self-tolerant T cell repertoire and is quantified by repeated engagement of TCRs with a diverse pool of self-peptides complexed with self-MHC molecules. The strength of a TCR signal depends on the binding properties of a TCR to the peptide and the MHC, but it is not clear how the specificity to both components drives fate decisions. In this study, we propose a TCR signal-integration model of thymic selection that describes how thymocytes decide among distinct fates, not only based on a single TCR-ligand interaction, but taking into account the TCR stimulation history. These fates are separated based on sustained accumulated signals for positive selection and transient peak signals for negative selection. This spans up the cells into a two-dimensional space where they are either neglected, positively selected, negatively selected, or selected as natural regulatory T cells (nTregs). We show that the dynamics of the integrated signal can serve as a successful basis for extracting specificity of thymocytes to MHC and detecting the existence of cognate self-peptide-MHC. It allows to select a self-MHC-biased and self-peptide-tolerant T cell repertoire. Furthermore, nTregs in the model are enriched with MHC-specific TCRs. This allows nTregs to be more sensitive to activation and more cross-reactive than conventional T cells. This study provides a mechanistic model showing that time integration of TCR-mediated signals, as opposed to single-cell interaction events, is needed to gain a full view on the properties emerging from thymic selection.

T lymphocytes responding to Mls-locus antigens are Lyt-1+, 2- and I-A restricted

We have investigated primary and secondary responses of mouse splenic T cells to strong mixed lymphocyte stimulating antigens controlled by the Mls locus using MHC-identical mixtures of cells. Our studies show that strong primary Mls-locus specific responses involve recognition of self I-A antigens, since BUdR and light suicide or F1 into parent radiation bone-marrow chimeras both demonstrate a preference of unprimed F1 T cells to respond to Mls-locus antigens associated with one parent's MHC antigens. Furthermore, conventional anti-I-A antisera and monoclonal anti-I-A antibody both inhibit Mls-locus responses in an MHC-specific manner. Finally, as is typical of T cells responding to I-A antigens or to nominal antigens associated with self I-A, Mls-locus responses are mediated by Lyt-1+, 2 cells. One striking finding in these studies was the very high frequency of cells capable of responding to Mls-locus antigens, the highest being 1/300 splenic T cells. This plus evidence for recruitment during primary Mls-locus responses may account for reports of a lack of I-A restriction in secondary anti-Mls locus responses to strong Mls-locus antigens, a finding with which we concur. The possibility that these secondary responses between noncongenic strains of mice may be directed at other genetic loci is also discussed. These experiments leave open the question of the biological role of the Mls-locus and of the very large number of T cells reactive to it.

Thymic selection revisited: how essential is it?

Intrathymic T cell development represents one of the best studied paradigms of mammalian development. Lymphoid committed precursors enter the thymus and the Notch1 receptor plays an essential role in committing them to the T cell lineages. The pre-T cell receptor (TCR), as an autonomous cell signaling receptor, commits cells to the alphabeta lineage while its rival, the gammadeltaTCR, is involved in generating the gammadelta lineage of T cells. Positive and negative selection of immature alphabetaTCR-expressing cells are essential mechanisms for generating mature T cells, committing them to the CD4 and CD8 lineages and avoiding autoimmunity. Additional lineages of alphabetaT cells, such as the natural killer T cell lineage and the CD25+ regulatory T cell lineage, are formed when the alphabetaTCR encounters specific ligands in suitable microenvironments. Thus, positive selection and receptor-instructed lineage commitment represent a hallmark of the thymus. Ectopically expressed organ-specific antigens contribute to thymic self-nonself discrimination, which represents an essential feature for the evolutionary fitness of mammalian species.

The growth of the very large CD8+ T cell clones in older mice is controlled by cytokines

Older humans and mice frequently contain very large clones of CD8(+) T cells. In mice these cells are phenotypically very similar to memory CD8(+) T cells. Like memory CD8(+) T cells, most members of the clones are in continuous slow division, apparently independently of Ag stimulation. Proliferation of the CD8(+) clonal T cells is inhibited in mice treated with Ab to the IL-2R beta-chain that blocks signaling by either IL-2 or IL-15. However, inhibition of IL-2 increases the numbers of dividing clonal cells. Therefore, like normal memory CD8(+) T cells, expansion of the clones is driven by IL-15 and inhibited by IL-2 and is probably limited by the amounts of IL-15 and IL-2 present in the host. Control by these two cytokines may account for the fact that, although the clones can be very large, they do not overwhelm or kill their hosts. Nevertheless the clonal cells compete successfully with normal memory CD8(+) T cells for growth. Perhaps the clonal cells use IL-15 more effectively or are more resistant to the inhibitory effects of IL-2. Thus they might affect the immune response of their hosts by competing for factors that stimulate and inhibit normal CD8(+) memory T cells.

Antiviral Cytotoxic Activity Across a Species Barrier in Mixed Xenogeneic Chimeras: Functional Restriction to Host MHC

Reconstitution of lethally irradiated mice with a mixture of mouse and rat bone marrow cells (mouse + rat→mouse) results in mixed xenogeneic chimerism and donor-specific tolerance. The current study demonstrates that mouse and rat T lymphocytes that have developed in xenogeneic chimeras are restricted to Ag presentation by mouse, but not rat, APC. Restriction to host Ags results in functional immunocompetence with generation of antiviral cytotoxic activity in vivo, within and across species barriers. These data demonstrate for the first time that the host thymus is sufficient to support development and positive selection of functional cross-species T lymphocytes. The superior immunocompetence, as compared with fully xenogeneic (rat→mouse) chimeras, may prove to be of significant benefit in the clinical application of xenotransplantation to solid organ transplantation and immune reconstitution for AIDS.

An Abd transgene prevents diabetes in nonobese diabetic mice by inducing regulatory T cells

Susceptibility to the human autoimmune disease insulin-dependent diabetes mellitus is strongly associated with particular haplotypes of the major histocompatibility complex (MHC). Similarly, in a spontaneous animal model of this disease, the nonobese diabetic (NOD) mouse, the genes of the MHC play an important role in the development of diabetes. We have produced transgenic NOD mice that express the class II MHC molecule I-Ad in addition to the endogenous I-Ag7 molecules in order to study the role of these molecules in the disease process. Although the inflammatory lesions within the islets of Langerhans in the pancreas appear similar in transgenic and nontransgenic animals, transgenic mice develop diabetes with greatly diminished frequency compared to their nontransgenic littermates (10% of transgenic females by 30 weeks of age compared to 45% of nontransgenic females). Furthermore, adoptive transfer experiments show that T cells present in the transgenic mice are able to interfere with the diabetogenic process caused by T cells from nontransgenic mice. Thus, the mechanism by which I-Ad molecules protect mice from diabetes includes selecting in the thymus and/or inducing in the periphery T cells capable of inhibiting diabetes development.

Signal for T-cell differentiation to a CD4 cell lineage is delivered by CD4 transmembrane region and/or cytoplasmic tail

Mature T cells express either CD4 or CD8 on their surface. Most helper T cells express CD4, which binds to class II major histocompatibility complex (MHC) proteins, and most cytotoxic T cells express CD8, which binds to class I MHC proteins. In the thymus, mature CD4+CD8- and CD4-CD8+ T cells expressing alpha beta T-cell antigen receptors (TCR) develop from immature thymocytes through CD4+CD8+ alpha beta TCR+ intermediates. Experiments using mice transgenic for alpha beta TCR suggest that the specificity of the TCR determines the CD4/CD8 phenotype of mature T cells. These results, however, do not indicate how a T cell differentiates into the CD4 or CD8 lineage. Here we show that the CD4 transmembrane region and/or cytoplasmic tail mediates the delivery of a specific signal that directs differentiation of T cells to a CD4 lineage. We generated transgenic mice expressing a hybrid molecule composed of the CD8 alpha extracellular domains linked to the CD4 transmembrane region and cytoplasmic tail. We predicted that this hybrid molecule would bind to class I MHC proteins through the extracellular domains but deliver the intracellular signals characteristic of CD4. By crossing our transgenic mice with mice expressing a transgenic alpha beta TCR specific for a particular antigen plus class I MHC protein, we were able to express the hybrid molecule in developing thymocytes expressing the class I MHC-restricted TCR. Our results show that the signal transduced by the hybrid molecule results in the differentiation of immature thymocytes expressing a class I-restricted TCR into mature T cells expressing CD4.

Epithelial expression of major histocompatibility complex (MHC) antigens in normal rat salivary and lacrimal glands

The presence and distribution of MHC class I and class II antigens within these glands of Wistar and Lewis rats was studied using monoclonal antibodies and an indirect immunoperoxidase technique. In rats of both strains and sexes, MHC class 1 antigens were expressed by ductal epithelium in addition to vascular endothelium and other connective tissue elements. Except for a small proportion of secretory cells within lacrimal glands, acini were uniformly negative for class I antigen. MHC class II immune response-associated (Ia) antigens were expressed by stromal dendritic cells in all glands. Glandular expression of Ia was limited to submandibular glands of the two strains. In Lewis rats, staining was detected in some striated and collecting ducts, whereas positive glandular reactivity in Wistar rats was predominantly within the granular-cell tubules. Quantitative histomorphometric studies of Wistar submandibular glands, taken from 2.5-60-week-old male and female animals, demonstrated a close relationship between the extent of glandular Ia reactivity and postnatal granular-cell tubule development. These results indicate that whilst constitutive expression of Ia is a feature of rat submandibular epithelium, the glandular components involved are strain dependent.

Ia restriction specificity of KLH-specific T cells from allogeneic bone marrow chimeras is influenced by histocompatibility at the H-2 and minor histocompatibility loci

Ia restriction specificity involved in T cell proliferative responses to keyhole limpet hemocyanin (KLH) has been analyzed using a variety of allogeneic bone marrow chimeras. The chimeric mice were prepared by reconstituting irradiated AKR, SJL, B10.BR and B10.A(4R) mice with bone marrow cells from B10 mice. When such chimeric mice had first been primed with KLH in complete Freund's adjuvant (CFA), T cells from H-2 incompatible fully allogeneic chimeras showed significantly higher responses to KLH in the presence of antigen-presenting cells (APC) of donor strain (B10) than APC of recipient strain. However, in H-2 subregion compatible chimeras, [B10----B10.A(4R)], which were matched at the H-2D locus and at minor histocompatible loci, the T cells could mount vigorous responses to KLH with antigen-presenting cells (APC) of either donor or recipient type. The same results were obtained as well with chimeras that had been thymectomized after full reconstitution of lymphoid tissues by donor-derived cells. A considerable proportion of KLH-specific T cell hybridomas established from [B10----B10.A(4R)] chimeras exhibited both I-Ab and I-Ak restriction specificities. The present findings indicate that the bias to donor Ia type of antigen specific T cells is determined by donor-derived APC present in the extrathymic environment but that cross-reactivity to the recipient Ia is influenced to some degree by histocompatibility between donor and recipient mice, even though the histocompatible H-2D locus and minor histocompatibility loci seem not to be directly involved in the I-A restricted responses studied herein.

Sequential analysis of the thymocyte differentiation in fully allogeneic bone marrow chimera in mice. II. Further characterization of the CD4+ or CD8+ single positive thymocytes

Differentiation of CD4+8- and CD4-8+ single-positive (SP) thymocytes in fully allogeneic bone marrow chimeras were investigated using multicolor cytometric analysis. The proportion of CD3+ cells in CD4+ SP population derived from donor mice considerably increased between day 12 and 14 after bone marrow transplantation (BMT), and gradually increased thereafter. The proportion of V beta 8+ cells in the CD3+CD4+ population remained constant (around 20%) at each period, suggesting that alpha and beta chains were used as TCR. The proportion of J11d+ cells in the CD4+ SP thymocytes transiently increased from day 12 to 14 and decreased thereafter, even though almost half of CD4+ SP cells were still dull J11d+ at day 35 after BMT. When CD8+ SP populations were analyzed, the proportion of CD3+ cells was very small until day 18. Thereafter, the proportion considerably increased and reached a maximum (83.2%) at day 21. The proportion of V beta 8+ cells in the CD3+ CD8+ SP population fell within range between 20 and 30%. However, before day 18, most of the V beta 8+ cells were dull positive, while after day 21 the majority were bright V beta 8+. Further, CD8+ SP cells at day 12, 14 and 18 were largely bright J11d+. After day 21, however, the proportion of bright J11d+ cells rapidly decreased. Similar results were obtained when the sequence of appearance of CD4+ and CD8+ SP cells was compared among bright CD3+, bright V beta 8+ or J11d- mature populations. The CD4+ SP cells regularly appeared earlier than CD8+ SP cells in the mature populations. These findings indicate that a considerable heterogeneity exists within both CD4+ and CD8+ SP populations and that the differentiation process for CD4+ SP cells precedes that for CD8+ SP cells.

Sequential analysis of the thymocyte differentiation in fully allogeneic bone marrow chimera in mice. I. Relationship between functions and surface characteristics of thymocytes

Differentiation of thymocytes according to surface phenotype, functional status and cell size was investigated using fully allogeneic bone marrow chimeras. Most of the donor-derived thymocytes obtained from chimeras 9 days after hematopoietic reconstitution were CD4-8- and IL2R+. At day 14, CD4+8+ cells became prominent in the thymus. Eighty-six per cent of thymocytes were CD4+8+ and 9% were CD4-8- at this stage. After day 21, the proportion of CD4+8- or CD4-8+ single positive cells transiently increased and then declined to normal level at day 42. Further, the mean size of CD4+ or CD8+ single positive cells in chimeric thymuses at day 21 after reconstitution was markedly larger than that at day 35. When proliferative responses to various stimuli (PMA + rIL2, anti-CD3 mAb (2C11) and anti-V beta 8 mAb (F23.1] were evaluated, significant responses were generated by thymocytes for the first time at around day 28 and the responses reached their peaks at day 35. These findings demonstrated that the process of thymocyte differentiation in the fully allogeneic chimeras was similar to ontogenic development as observed in fetal mice. However, the tempo at which the differentiation of surface phenotypes and development of functions proceeded was quite different from that seen in normal mice. The relationship among surface phenotypes, cell size and functions of developing thymocytes of bone marrow chimeras is discussed.

Transplantable polyoma virus-induced epitheliomas harbor immature T lymphocytes

Some salivary epitheliomas induced in C3H/Bittner (C3H/Bi) mice by neonatal injection of the fifth in vitro passage of parotid tumor agent isolate of mouse polyoma virus are infiltrated with T lymphocytes having an immature phenotype. Serially transplantable tumor lines have been obtained from primary salivary epitheliomas, and some of these secondary tumors are also infiltrated with variable proportions of immature T cells. A subline has been selected which, in syngeneic hosts, becomes richly infiltrated by immature lymphocytes, as defined by bearing both CD4 and CD8 surface markers. While some sublines produced this infiltrate, others did not. There is no relationship between the extent or nature of the T-cell infiltrate and the passage number (generation) of the tumors or the residence period of the transplanted tumors in the host. The results strongly suggest that subsets of salivary epitheliomas resemble the thymic microenvironment sufficiently that T-lymphocyte maturation, at least in part, proceeds readily.

Involvement of I-A-restricted B-B cell interaction in the polyclonal B cell differentiation induced by lipopolysaccharide

The present study has examined a functional role of Ia molecules expressed on murine B cells in polyclonal B cell differentiation induced by lipopolysaccharide (LPS). Reverse, IgM PFC responses of unprimed B cells induced by LPS in the apparent absence of T cells and adherent accessory cells were markedly inhibited in a haplotype-specific manner by Fab monomer fragment of anti-class II (Ia) but not anti-class I MHC monoclonal antibody (mAb). However, the degree of inhibition of LPS responses of H-2-heterozygous F1 B cells expressing both parental I-A products by either one of anti-I-A mAb was at best half that of the parental B cells. Interestingly, when (B10 x B10.-BR)F1 (H-2b/k) B cells were fractionated into adherent and nonadherent populations by their ability to bind to parental B10 B cell monolayers, LPS responses of F1 B cells adherent to and nonadherent to the B10 B cell monolayers were selectively inhibited by anti-I-Ab and anti-I-Ak mAb, respectively. These results suggest that LPS-responsive F1 B cells comprise at least two separate populations with restriction specificity for only one of the parental I-A products expressed on B cells. In addition, it was demonstrated that the I-A-restriction specificity of LPS-responsive B cells is "plastic" and determined by H-2-genotype of bone marrow cells present during B cell ontogeny but not by that of radiation-resistant host elements. Namely, the LPS responses of B10-derived B cells from (B10 + B10.BR) (H-2b x H - 2k)F1 radiation bone marrow chimeras but not from B10 (H-2b x H-2k)F1 chimeras became sensitive to the inhibition of anti-I-Ak mAb in the presence of mitomycin C-treated I-Ak-positive B cells, supporting a notion of receptor-Ia molecules interactions rather than like-like interactions. Thus, the present results provide evidence indicating that B-B cell interaction via recognition of self-I-A products is a crucial event in the polyclonal B cell differentiation induced by LPS.

Disparate functions of I-A and I-E molecules on B cells as evidenced by the inhibition with anti-I-A and anti-I-E antibodies of polyclonal B cell activation

Polyclonal differentiation of unprimed B cells into IgM-producing cells induced by lipopolysaccharide (LPS) or T cell-derived lymphokine B151-TRF2 has been shown to contain a process of I-A-restricted B-B cell interaction, so that the B cell responses are inhibited by monoclonal antibodies (mAb) specific for I-A molecules. On the other hand, the B cell responses are also inhibited by anti-I-E mAb, although I-E molecules are not involved in such B-B cell interaction. In this study, we examined the mechanism underlying the anti-I-E-mediated inhibition of the B cell responses. The B cell responses induced by LPS or B151-TRF2 were inhibited by either anti-I-A or anti-I-E mAb added on day 0 over a 5-day culture period, whereas when added on day 3 the responses were inhibited only by anti-I-E mAb and not by anti-I-A mAb. To gain insight into the mechanism underlying the anti-I-E-mediated inhibition, we prepared monovalent Fab and divalent F(ab')2 fragments of anti-I-A and anti-I-E mAb and examined their effects on the B cell responses. We found that the B cell responses were inhibited by the F(ab')2 but not Fab fragment of anti-I-E mAb, whereas the Fab fragment of anti-I-A mAb still gave effective inhibition. The F(ab')2 but not Fab fragment of anti-I-E mAb induced increases in cyclic AMP (cAMP) levels in B cells, whereas the undigested anti-I-A mAb did not induce such increases. Furthermore, adenylate cyclase inhibitors, which inhibit cellular cAMP accumulation, circumvented the B cell responses inhibited by anti-I-E but not anti-I-A mAb. Thus, these results indicate that the anti-I-E-mediated inhibition of the B cell responses requires increases in intracellular cAMP levels induced by cross-linking of I-E molecules. In contrast, anti-I-A mAb inhibits the B cell responses without cross-linking of I-A molecules and cAMP accumulation. These results reinforce a unique function of I-A molecules as restriction elements in the Ia-restricted B-B cell interaction.

A nondeletional mechanism of thymic self tolerance

T cells become tolerant of self antigens during their development in the thymus. Clonal deletion of thymocytes bearing self-reactive T cell receptors is a major mechanism for generating tolerance and occurs readily for antigens expressed by bone marrow-derived cells. Tolerance to antigens expressed on the radioresistant thymic stromal elements is demonstrated here to occur via a nondeletional mechanism. For minor lymphocyte stimulatory (Mls-1a) and major histocompatibility complex (MHC) antigens, this alternate form of tolerance induction results in clonal anergy.

Positive selection of the T cell repertoire: where and when does it occur?

The T cell repertoire is shaped by both positive and negative influences. T lymphocytes that express the V beta 6 variable region are positively selected in the thymus by cells expressing major histocompatibility complex (MHC) class II E molecules. To identify these cells, we have quantitated V beta 6+ T lymphocytes in a set of transgenic mice showing variant patterns of E expression in the thymus. We demonstrate that class II molecules must be expressed on epithelial cells of the cortex for positive selection to occur. Using a direct assay of unmanipulated thymocytes, we show that positive selection is manifest only as a rather late event in thymocyte differentiation, after the maturation of cortical double-positives into single-positives.

Donor and recipient specific tolerance in cells from semi-allogeneic, H-2 subregion compatible or fully allogeneic bone marrow chimeras attributable to clonal deletion

Specificities of tolerance induced in allogeneic bone marrow (BM) chimeras which had been established by injecting allogeneic BM cells pretreated with anti-Thy-1 mAb alone (without complement (C)) were analyzed using Simonsen's splenomegaly assay. Lymphocytes from fully allogeneic, semi-allogeneic and H-2 subregion compatible BM chimeras were specifically unresponsive to donor and recipient antigens (Ag). However, cells from H-2 subregion compatible chimeras initiated as vigorously a GVHR in F1 recipient mice, which were disparate at H-2K and I-A regions, as did spleen cells of donor mice, which were incompatible at the entire H-2 and minor histocompatibility regions of the recipients. The donor cells from such chimeras that initiated these considerable GVHR were either CD4+ or CD8+ T cells. Furthermore, synergistic effects by the CD4+ and CD8+ T lymphocytes were also observed. We found no evidence for a suppressive mechanism(s) in maintenance of the specific tolerance in allogeneic chimeras. Further, when lymphoid cells from these chimeras were adoptively transferred to irradiated mice of the donor strain and maintained for 5 days in the absence of recipient Ag (tolerogen), the adoptively transferred cells were shown to retain their unresponsiveness to the recipient Ag. These results reveal that T lymphocytes from allogeneic BM chimeras prepared by our method had been specifically induced to a tolerant state to both donor and recipient Ag and that the major mechanism of induction and maintenance of long-lasting tolerance is attributable to clonal deletion of both CD4+ and CD8+ T cell subsets rather than to the development of a population of suppressor cells of any sort.

Influence of the major histocompatibility complex on positive thymic selection of V beta 17a+ T cells

A monoclonal antibody was used to show directly positive thymic selection of the T cell repertoire in mouse strains expressing the 17a beta-chain variable domain (V beta 17a) of the T cell receptor. In the absence of the potent tolerizing class II major histocompatibility complex (MHC) molecule, I-E, peripheral expression of V beta 17a+ T cell receptors varied with the MHC haplotype of the mouse strain. In the most extreme case, H-2q mice expressed high peripheral levels of CD4+ V beta 17a+ T cells (14 to 19 percent), whereas H-2b mice expressed low levels (3 to 4 percent). Analysis of (b x q)F1 mice and chimeric mice showed that these differences were determined by positive thymic selection and implicated the thymic epithelium as the controlling cell type.

The thymus selects the useful, neglects the useless and destroys the harmful

Although efficient at reacting to foreign antigen in the context of MHC, mature T cells do not normally react to self antigens presented by self MHC. In this review, Harald von Boehmer and colleagues describe the investigation of self MHC restriction and self-tolerance using TCR transgenic mice expressing a receptor for the male-specific minor histocompatibility antigen, H-Y, in the context of class I H-2Db MHC antigens, on many of their T cells. CD4-8+ T cells expressing the transgenic receptor were positively selected by the restricting H-2Db MHC antigens in female transgenic mice. In the male TCR transgenic mice, CD4+8+ thymocytes were deleted, and transgene-expressing T cells with high surface-density of CD8 were-absent from the periphery. The remaining T cells could not be activated by male H-Y stimulator cells, as they lacked or expressed only low levels of CD8 molecules.

Characterization of variant and parental-cross-protective immunity to immunogenic variants of a murine fibrosarcoma using the local adoptive transfer assay

The purpose of this study was to characterize the lymphocyte populations responsible for rejection of immunogenic (Imm+) tumor variants, and the cross-protective immunity engendered by Imm+ variants against the weakly immunogenic parental tumor. Immunogenic clones of the weakly immunogenic methylcholanthrene-induced fibrosarcoma MCA-F have been generated using 1-methyl-3-nitro-1-nitrosoguanidine, 5-aza-2'-deoxycytidine, or ultraviolet radiation (UV-B; 280-320 nm). These clones grow progressively in immunosuppressed adult-thymectomized irradiated mice, but are rejected by immunocompetent syngeneic hosts. The parental MCA-F tumor grows progressively in both groups. Mice that have rejected a challenge of 1 x 10(5) Imm+ cells show an anamnestic immune response against both the Imm+ clone and the parental MCA-F tumor. Using the local adoptive transfer assay and depletion of T-cell subsets with antibody plus complement, we show that immunity induced by the Imm+ variants against the parent MCA-F was mediated by the Thy1.2+, L3T4a+ population without an apparent contribution by Lyt2.1+ cells. Although antivariant immunity was also dependent upon Thy1.2+ cells, depletion of either the L3T4a+ or the Lyt2.1+ cells failed to abolish immunity against the variant. A role for Lyt2.1+ T lymphocytes in antivariant immunity, but not antiparent immunity, was supported by the results of cytotoxic T lymphocyte (CTL) assays. Following immunization with high numbers (1 x 10(5) to 5 x 10(5) of viable Imm+ cells, antivariant, but not antiparent CTL activity was detected in mixed lymphocyte tumor cell cultures. Immunization with lower numbers (3 x 10(4] of viable Imm+ or with high numbers of mitomycin-C-treated Imm+ engenders only antivariant immunity without parental cross-protection. Under these conditions lymphocytes mediating immunity against the variant in the local adoptive transfer assay were exclusively of the Thy1.2+, L3T4a+ phenotype, with no contribution from the Lyt2.1+ cells. Identical results were obtained for Imm+ clones of MCA-F induced by methylnitronitrosoguanidine, 5-azadeoxycytidine, and UV-B, suggesting that the nature of the antitumor immunity engendered by Imm+ is not significantly affected by the agent used. Furthermore, these results demonstrate that the cross-reactivity and cellular effectors of antitumor immunity in this system are influenced by the immunizing dose of Imm+ cells: the predominant effectors of both antivariant and parental-cross-reactive immunity were of the CD4+ T cell subclass, with a CD8+ cytotoxic population contributing to antivariant immunity only after high-dose immunization.

The T-cell repertoire is heavily influenced by tolerance to polymorphic self-antigens

T cells with V beta 3+ alpha beta receptors are deleted by self-tolerance in mice with particular major histocompatibility complex/self-antigen combinations. This also occurs for other V beta elements. Polymorphism in the major histocompatibility complex and/or the self-antigens that cause massive deletion of T cells using particular V beta elements may be maintained by the need to balance the advantage of a diverse T-cell repertoire against the potential involvement of those elements in autoimmune disease.

Positive selection of antigen-specific T cells in thymus by restricting MHC molecules

Thymus-derived lymphocytes (T cells) recognize antigen in the context of class I or class II molecules encoded by the major histocompatibility complex (MHC) by virtue of the heterodimeric alpha beta T-cell receptor (TCR). CD4 and CD8 molecules expressed on the surface of T cells bind to nonpolymorphic portions of class II and class I MHC molecules and assist the TCR in binding and possibly in signalling. The analysis of T-cell development in TCR transgenic mice has shown that the CD4/CD8 phenotype of T cells is determined by the interaction of the alpha beta TCR expressed on immature CD4+8+ thymocytes with polymorphic domains of thymic MHC molecules in the absence of nominal antigen. Here we provide direct evidence that positive selection of antigen-specific, class I MHC-restricted CD4-8+ T cells in the thymus requires the specific interaction of the alpha beta TCR with the restricting class I MHC molecule.

Thymic major histocompatibility complex antigens and the alpha beta T-cell receptor determine the CD4/CD8 phenotype of T cells

T-cell receptors and T-cell subsets were analysed in T-cell receptor transgenic mice expressing alpha and beta T-cell receptor genes isolated from a male-specific, H-2Db-restricted CD4-8+ T-cell clone. The results indicate that the specific interaction of the T-cell receptor on immature thymocytes with thymic major histocompatibility complex antigens determines the differentiation of CD4+8+ thymocytes into either CD4+8- or CD4-8+ mature T cells.

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 effect of thymus environment on T cell development and tolerance

During development in the thymus, T cells are deleted if their receptors are able to recognize self major histocompatibility complex (MHC) proteins. We show that such clonal deletion can occur because of interaction between receptors on T cells and MHC expressed on bone marrow-derived cells. In addition, development in the thymus picks out T cells to mature if their receptors will be restricted for antigen recognition in association with self MHC alleles expressed on thymus epithelial cells. This process is usually thought to involve positive selection of T cells bearing receptors with high and low affinity for MHC on thymus epithelium, and subsequent deletion of high affinity cells by interaction with bone marrow-derived cells. Our data do not fit such a model, but rather suggest that MHC molecules on thymus epithelium and bone marrow-derived cells may not be seen identically by T cell receptors.

An adjunct trait of HEL/I-Ab-specific T helper cell is sensitivity to antigen-specific immunosuppression

The present study tests whether the specific inhibition of helper T (Th) cell (and T hybridomas) by suppressor T (Ts) cells is a phenotypic trait of Th cells correlating with their acquired specificity for antigen/major histocompatibility complex or a genotypic trait not related to selection of the T cell repertoire for antigen. To do this we took advantage of the fact that H-2d parental strains of mice commonly restrict recognition of chicken egg-white lysozyme to the L3 peptide (a.a. 105-129) and H-2b parental mice to the L2 peptide (a.a. 13-105). F1 hybrids of these strains display two subsets of lysozyme-reactive T cells, one for each parental phenotype. Using (B10 X B10.D2)F1 mice reconstituted with B10.D2 bone marrow, we were able to develop genetic H-2d T cell clones that could express an atypical specificity, that is L2/I-Ab. Clones of this type, like genetic H-2b, are also sensitive to the inhibiting effects of HEL-activated Ts cells. To overcome some of the drawbacks of using heterogeneous populations of T, B and accessory cells in our assays, we constructed T hybridomas from HEL-immune, chimeric lymph node T cell blasts which respond to a unique antigen/major histocompatibility complex with production of the lymphokine interleukin 2. Our results indicate that all HEL/I-Ab-specific T cells (helper and hybridomas) are inhibited by suppression regardless of the T cell's haplotype at the H-2 locus: H-2b (B10), H-2d (D2) or H-2b,d (BDF1). Furthermore, there is a strict correlation between the antigen and I-A specificity: I-Ab-restricted T cells recognize non-L3 determinants even though some are derived from H-2d mice.

The relationship between epithelial Ia expression and the inflammatory cell infiltrate during experimental oral carcinogenesis

The development of oral epithelial expression of Ia antigens and its relationship to the presence of IL-2r+ (CD25+) cells was investigated in rats treated with the water soluble carcinogen 4-nitroquinoline-N-oxide (4NQO). Acetone fixed frozen sections of the palate and tongue were stained using an indirect immunoperoxidase technique and monoclonal antibodies to rat Ia (I-A & I-E) and IL-2 receptor. After 4 weeks 4NQO treatment all rats expressed oral epithelial Ia but thereafter (2-9 months) expression was present in only 20-40% of animals. Epithelial expression of Ia by histologically normal, dysplastic and neoplastic epithelium was always associated with the presence of an underlying inflammatory cell infiltrate containing CD25+ cells. Overall there were significantly more CD25+ cells in tissue specimens containing Ia+ epithelium compared with Ia- epithelium. Furthermore, during the first 4 weeks of carcinogen treatment, a significant positive correlation was found between the CD25+ cell density and occurrence of focal epithelial Ia expression. These results, together with analysis of the T cell, NK cell, macrophage and B cell content of the infiltrates induced by 4NQO, suggest that the CD25+ cells represent activated T cells. Thus, our results in this experimental model are consistent with the idea that epithelial expression of Ia is the result of production of IFN-gamma by locally activated T cells.

Structural considerations of T-cell cognizance of antigen

Work summarized herein describes two congenic strains of mice, C57BL/10 and B10.BR, which differ at the I-A region of the MHC where C57BL/10 and B10.BR are I-Ab and I-Ak respectively. Using various antigens to stimulate, in vitro, primed T lymphocytes, studies on the responsiveness of these two strains to immunization with TMVP and with its tryptic peptide number 8 representing residues 93-112 of the protein are described. These studies revealed that in the C57BL/10 strain TMVP and peptide 8 exhibit cross reactivity on the T-cell level, whereas in the B10.BR strain these two antigens do not exhibit such cross reactivity. Further studies revealed that the cross reactivity is mapped to the I-A region of the MHC with cross reactivity between TMVP and peptide 8 exhibited in mice with I-Ab (referred to as cross reactive-CR) but not with I-Ak (referred to as non cross reactive-NCR). Cell depletion and reconstitution experiments revealed that cross reactivity (or the lack thereof) could be attributed to antigen presenting cells (APC). A profound difference between the strains was also expressed on the level at which their immune T-cells reacted in vitro to stimulation by various derivatives of peptide 8. The studies suggest that the strains differ in their responsiveness to the various orientations in which the T-cell epitope(s) are presented. Assuming that TMVP, but not peptide 8, is altered during processing by APC and assuming that antigen processing by APC of CR and NCR is similar, the difference which the strains exhibit in recognizing different orientations of the epitope may account for the difference in the cross reactivity between TMVP and peptide 8 exhibited by these strains. Further investigations revealed that the strains also differ in their response to pre-immunization with TMVP prior to immunization with peptide 8. Whereas preimmunization of the C57BL/10 (CR) mice with TMVP did not affect subsequent response to immunization with peptide 8, preimmunization of B10.BR (NCR) mice with TMVP suppressed the response to subsequent immunization with peptide 8. It is suggested that the presentation of the T-cell epitope(s) in the correct orientation by the appropriate Ia is crucial for the activation of T helper cells but that such presentation does not play a decisive role in the activation of T suppressor cells.

Experimental strategies for the study of cellular immunity in renal disease

This overview has examined some of the current experimental options available for the study of cellular immunity in the immunopathogenesis of renal disease. T cell immunity, where it has been examined, seems to have a particularly pivotal role in orchestrating and regulating functional patterns of renal injury. The use of the research methods presented here for the study of cell-mediated interactional events in kidney disease, however, has lagged behind similar efforts in other organ systems. We hope, therefore, this report will serve to stimulate and strengthen further interest in the cell biology of the nephritogenic immune response.

Regulation of T15 idiotype dominance. III. Phosphocholine-specific B-cell activation in vivo requires major histocompatibility complex-restricted T-cell help

We have examined the requirement for major histocompatibility complex (MHC)-restricted T-cell help in the secondary in vivo antibody response to phosphocholine (PC). The memory response to PC has been demonstrated previously to be comprised of T15-dominant IgM and IgG3 plaque-forming cells (PFC) derived primarily from the Lyb-5+ B-cell subset, and IgG1 and IgG2 PFC, few of which bear the T15 idiotype and are predominantly derived from the Lyb-5- B-cell subset. Using carrier-primed (A X B)F1 T cells which have matured in a parentA chimeric environment so that "self" recognition is of the MHC determinants of parentA but not parentB, we have found that parentA PC-primed B cells, but not parentB PC-primed B cells, are activated. Even in the presence of an ongoing parentA anti-PC response, parentB PC-primed B cells were not activated, indicating that the restriction was between the helper T cell and the B cell, not between T-helper and accessory cells. MHC-restricted T-cell help was required by B cells producing T15+ and T15- IgM, IgG3, IgG1, and IgG2 responses.

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.

Identity of cells that imprint H-2-restricted T-cell specificity in the thymus

The thymus has two important roles in controlling the specificity of T lymphocytes. First, T cells differentiating in the thymus are rendered tolerant of 'self' antigens, particularly antigens encoded by the major histocompatibility complex, the H-2 complex in mice. Second, the thymus imbues T cells with the property of H-2-restricted recognition of antigen, that is, the capacity of T cells to react with foreign antigens presented in association with self H-2 gene products. Until recently it has generally been assumed that self-tolerance and H-2-restricted specificity both reflect early T-cell contact with self H-2 determinants expressed on thymic epithelial cells. Recent evidence suggests, however, that intrathymic cells of the macrophage/dendritic cell (Mphi/DC) lineage also have a role in shaping T-cell specificity. In particular, it has been found that the tolerance to graft-type H-2 determinants which normally ensues when T cells differentiate in an H-2-different thymus fails to occur when the thymus is pretreated with deoxyguanosine (dGuo), a procedure that selectively destroys Mphi/DC but spares epithelial cells. In contrast to these findings on tolerance induction, evidence is presented here that dGuo-treated thymus grafts do imprint T cells with H--2-restricted specificity for antigen. It appears, therefore, that induction of tolerance and H--2 restriction are controlled by different cells in the thymus.

Ia-positive macrophages bind and internalize viable lymphocytes in murine thymus

Macrophages have been shown to be present in thymus throughout its development. In the present study monoclonal and polyclonal antimacrophage reagents were used to identify, quantitate, and determine the distribution of thymic macrophages. Those studies demonstrated that significant numbers of macrophages were evenly distributed throughout the cortex and medulla, and that macrophages account for most, if not all, Ia positivity in murine thymus. Suspensions of thymic cells prepared by enzyme digestion contained 2-4% macrophage antigen-positive cells, over 95% of which were I-Ak positive in double-labeling studies. Removal of lymphocytes and macrophages left only epithelial cells and those failed to label for Ia. Subsequent to mild enzymatic digestion, up to 80% of the thymic macrophages were in the form of lymphocyte/macrophage rosettes. Morphologic evaluation of the thymocyte rosettes revealed that some of the macrophages contained internalized lymphocytes. The proportion of macrophages with internalized lymphocytes generally was less than 10%, but during the first 4 weeks of life values often approached 30%. Nurse cells, which were shown through double labeling to express both Ia and macrophage-associated antigen, were included in the population of rosetted cells which had internalized lymphocytes. The results demonstrated that there is a high level of interaction between lymphocytes and Ia-positive macrophages in the thymus which is greatest during the immediate postnatal period.

Bone marrow-derived thymic antigen-presenting cells determine self-recognition of Ia-restricted T lymphocytes

We previously have demonstrated that in radiation-induced bone marrow chimeras, T-cell self-Ia restriction specificity appeared to correlate with the phenotype of the bone marrow-derived antigen-presenting (or dendritic) cell in the thymus during T-cell development. However, these correlations were necessarily indirect because of the difficulty in assaying thymic function directly by adult thymus transplant, which has in the past been uniformly unsuccessful. We now report success in obtaining functional T cells from nude mice grafted with adult thymuses reduced in size by treatment of the thymus donor with anti-thymocyte globulin and cortisone. When (B10 Scn X B10.D2)F1 nude mice (I-Ab,d) are given parental B10.D2 (I-Ad) thymus grafts subcutaneously, their T cells are restricted to antigen recognition in association with I-Ad gene products but not I-Ab gene products. Furthermore, thymuses from (B10 X B10.D2)F1 (I-Ab,d)----B10 (I-Ab) chimeras transplanted 6 months or longer after radiation (a time at which antigen-presenting cell function is of donor bone marrow phenotype) into (B10 X B10.D2)F1 nude mice generate T cells restricted to antigen recognition in association with both I-Ad and I-Ab gene products. Thymuses from totally allogeneic bone marrow chimeras appear to generate T cells of bone marrow donor and thymic host restriction specificity. Thus, when thymus donors are radiation-induced bone marrow chimeras, the T-cell I-region restriction of the nude mice recipients is determined at least in part by the phenotype of the bone marrow-derived thymic antigen presenting cells or dendritic cells in the chimeric thymus.

Analyses of H-2 restriction specificity of helper T cells in fully allogeneic bone marrow chimera in mice

Using irradiation bone marrow chimeras to analyze restriction specificity of helper T cells, we found that recipient H-2 type dictated the H-2 type which the T cells recognize as self (adaptive differentiation). T cells from (H-2b----H-2k) chimeras cooperate with non-T cells bearing Iak to generate a vigorous PFC response to sheep erythrocytes (SRBC) in vitro, but not with genetically identical H-2b cells. However, when T cells from the chimeras and H-2b non-T cells were adoptively transferred into irradiated (donor X recipient) F1 mice with SRBC, marked responses were seen in recipient spleens where radio-resistant F1 macrophages might exist and act as antigen presenting cells (APC). From these in vitro and in vivo observations, we considered that in the primary antibody response to a T dependent antigen such as SRBC, only T cell-macrophage (APC) matching is required. In contrast, when T cells from H-2 incompatible chimeras which had been primed with SRBC in vivo were analyzed in vitro, these cells cooperated also with H-2b non-T cells. These findings indicate that there may be two separate stages of T cell differentiation during which the self restriction specificity is acquired: one appears to be responsive to intrathymic influences and is not associated with antigenic stimuli, and the other shows signs of being responsive to post-thymic stimuli and of involving antigenic presentation. Moreover, the latter appears to utilize the influence of donor type macrophages.

Enhanced alveolar macrophage-mediated antigen-induced T-lymphocyte proliferation in sarcoidosis

Expansion of T-lymphocyte numbers is a characteristic feature of the alveolitis of pulmonary sarcoidosis. One mechanism that may influence the numbers of T-lymphocytes in the lung is the process of antigen presentation in which alveolar macrophages, in the presence of antigen, induce T-lymphocytes to replicate. To evaluate this process in sarcoidosis, alveolar macrophages were obtained by bronchoalveolar lavage, pulsed with tetanus toxoid, and co-cultured with purified autologous T cells. Strikingly, antigen-pulsed alveolar macrophages from sarcoid patients induced more than a twofold increase in autologous T-lymphocyte proliferation compared with the response seen using cells from normal or patients with idiopathic pulmonary fibrosis (P less than 0.001), all comparisons). In contrast, when monocytes were used as the antigen presenting cell, no significant differences were observed in T cell proliferation induced by antigen among the three groups. The enhanced T-lymphocyte proliferation induced by sarcoid alveolar macrophages was not dependent on the compartment from which the T cells were derived, and was independent of the specific antigen used. One possible explanation for augmented antigen presentation seen in sarcoid is that an increased percentage of sarcoid alveolar macrophages express HLA-DR or HLA-DS surface antigens. However, most normal and sarcoid alveolar macrophages express HLA-DR and HLA-DS surface antigens, and the percentage of macrophages expressing these antigens was not significantly different in the two groups. Thus, while the mechanisms of the enhanced antigen presentation in the sarcoid lung are unknown, the process of antigen-driven, alveolar macrophage-modulated lung T cell proliferation may explain, at least in part, the expansion of lung T-lymphocyte numbers that characterizes this disease.

Cell surface antigen expression on thymocytes: development and phenotypic differentiation of intrathymic subsets

Our current working model incorporates features from both the previously accepted models of intrathymic differentiation and attempts to fit some of the more recent data regarding functional differentiation, as well as the fact that our understanding of the non-lymphoid components is only marginal at best. 1. There is indeed a high level of cell death in the cortex (in the Ly1,2,3+/L3T4+ subpopulation). However, a small proportion of cells, perhaps the blasts with the same phenotype, escape the selective environment of the cortex and migrate into the medulla. Much of the cellular division in the thymus is either inappropriate or non-productive (discussed above). This is further supported by the recent indication that several cDNA clones derived from a thymocyte library have defective reading frames resulting in incomplete genetic coding for the beta chain of the T cell receptor molecule (Hedrick et al. 1984). 2. The "cortical" versus "medullary" phenotypes fail to distinguish immature versus mature (functional) subsets. The dLy1 cells, which are among the most immature thymocytes, as discussed above, are at least partially cortisone resistant and enriched in the PNA/NAg cells (Fowlkes et al., manuscript in preparation). Furthermore, low Thy-1 cells, a type of cell usually expected to be a mature, medullary thymocyte, are seen at the cortical, subcapsular sites as well as in the medulla (van Ewijk et al. 1981). 3. The dLy1 intrathymic progenitor cells appear to be radioresistant but capable of sustaining only limited self-renewal in irradiated thymi (Basch et al. 1978, Sharrow et al. 1983). The dLy1 cells have already been depleted from the intrathymic population when the peak of the first wave of cellular regeneration is detected in irradiation chimeras (Sharrow et al. 1983). 4. Thymocytes with the dLy1 phenotype are proliferative, subcapsular (outer cortical) cells that represent a thymocyte progenitor pool which can be demonstrated to differentiate into Ly1,2+;L3T4+ cells in vitro (Ceredig et al. 1983c, Fowlkes et al. 1984). In addition, the finding that the dLy1 cells can be seen as a high proportion of cells early in graft repopulation supports the concept that adult thymocyte differentiation follows the same pattern seen in fetal ontogeny. Thus an earlier suggestion that the fetal dLy1 cells would give rise directly to cells with a mature bLy1 phenotype (Mathieson et al. 1981) may be less likely. However, we may have been examining only one of two intrathymic progenitor subsets by the isolation of the dLy1 cells.(ABSTRACT TRUNCATED AT 400 WORDS)