Role of major histocompatibility complex gene products in delayed-type hypersensitivity

The Croonian Lecture, 1992. The key role of the thymus in the body's defence strategies

For centuries the thymus has remained a mysterious organ with largely unknown functions. The first demonstration of its crucial role in the development of the immune system was reported in 1961, when it was found that mice thymectomized at birth had poorly developed lymphoid tissues, impaired immune reactivities, and an inordinate susceptibility to develop infections. Although thymus lymphocytes were for a long time deemed immunoincompetent, it was shown in 1967 that they could respond to antigen by proliferating to give rise to a progeny of cells which did not secrete antibody (T cells), but which had a remarkable ability to induce bone marrow cells (B cells) to become antibody formers. This was the first unequivocal demonstration of a major division of labour among mammalian lymphocytes. Tremendous progress in our understanding of the function of the thymus and of the T cells derived from it followed. Distinct T cell subsets were characterized and shown to have an essential role in initiating and regulating a variety of immune responses. The ontogenetic events which occurred during their differentiation were mapped, and this allowed studies of the selection of the T cell repertoire. The major histocompatibility complex and associated peptides were shown to govern T cell selection and antigen activation, and the antigen-specific T cell receptor and the genes which code for it were characterized. Future studies should allow some insight into how to activate T cells more effectively for vaccination purposes, and how to switch them off to prevent autoimmune reactions and to induce tolerance to transplanted tissues.

Cytomegalovirus-specific cell-mediated immune responses in heart and heart-lung transplant recipients are not predictive for the occurrence of symptomatic CMV disease or tissue rejection

To study the predictive value of interferon-gamma (IFN-gamma) production in vitro for the occurrence of symptomatic CMV disease, 17 healthy adult volunteers were tested and 37 heart or heart-lung transplant recipients (CTRs) were studied at various time intervals after transplantation (Tx) for cell-mediated immune (CMI) responses to cytomegalovirus (CMV). At all intervals post Tx, in vitro IFN-gamma production in CTRs was significantly lower than in control subjects. The occurrence of CMV infection was associated with a trend toward inhibited CMI responses prior to the diagnosis, in comparison with CMI responses measured more than 4 weeks prior to or after the diagnosis of CMV infection. The occurrence of acute tissue rejection was associated with a trend toward enhanced CMV responses prior to the diagnosis, on the other hand. In the early post Tx period, the administration of antithymocyte globulin (ATG) or OKT3 monoclonal antibody and peak dosages of azathioprine were associated with significantly inhibited in vitro IFN-gamma production. Despite the demonstrated trends in vitro, IFN-gamma production does not appear to be uniformly predictive for the occurrence of symptomatic CMV disease or of acute tissue rejection in CTRs.

Synergistic effects of locally administered cytostatic drugs and a surfactant on the development of delayed-type hypersensitivity to keyhole limpet haemocyanin in mice

The immunomodulating effects of two locally administered cytostatic drugs, the active cyclophosphamide-derivative Z 7557 and the plant alkaloid VP-16, were compared with the effects of systemically administered cyclophosphamide and several established adjuvants: Freund's complete adjuvant, dextran sulphate, and dimethyl dioctadecyl ammonium bromide (DDA). All agents tested promoted the development of delayed-type hypersensitivity (DTH) to keyhole limpet haemocyanin (KLH) in mice. Locally administered cytostatic drugs were the most effective immunostimulatory compounds, whereas DDA was the least toxic agent tested. In order to increase the effectiveness and/ or reduce the toxicity of these agents we tested the efficacy of combinations of cytostatic drugs and DDA to enhance DTH. The results show that DDA and suboptimal amounts of locally administered cytostatic drugs act synergistically on DTH.

Immunohistological observations in rat kidney allografts after local steroid administration

In this report we investigated local regulatory mechanisms in graft rejection and their response to local immunosuppressive therapy. For this purpose local immunosuppression was induced in rat kidney allografts by intrarenal infusion of prednisolone. Intrarenal drug delivery resulted in high drug levels within the graft and low systemic drug levels. Systemic drug levels were by themselves not sufficiently immunosuppressive to induce graft survival, and local prednisolone levels within the graft proved to be responsible for prolongation of graft survival. During intrarenal drug delivery, systemic responsiveness to the renal allograft proved normal, since intrarenally treated grafts were infiltrated by MHC class II-positive host cells and, except for a somewhat lower percentage of macrophages, cellular infiltration in intrarenal treated grafts was comparable to untreated grafts. However, T cells and macrophages present in intrarenally treated grafts were not able to destroy the grafted tissue. Local immunosuppressive therapy resulted in inhibition of IL-2-R expression, absence of IFN-gamma, and prevention of MHC class II induction on grafted tissue. These observations strongly indicate the presence of local regulatory mechanisms in graft rejection. The experimental model described can be used for further analysis of these intragraft events. Moreover, the results demonstrate that local immunosuppressive therapy can contribute to effective inhibition of cellular immune response in graft rejection.

F1 mice make two species of antigen-specific, parental haplotype-restricted, T-helper factor whose restrictions correspond to the phenotype of the I-A determinants that they bear

Antigen-specific T-helper factor (ThF) bears I-A determinants and is I-A restricted in its action. This I-A restriction may be explained by ThF binding, and hence approximating antigen to its own I-A determinants, thereby facilitating recognition by the T cell (I-A presentation theory), or by a recognition site for I-A on the ThF which approximates the antigen to I-A+ antigen-presenting cells (I-A recognition theory). When ThF is produced in F1 mice there may be a dissociation between the I-A phenotype of the ThF and the I-A restriction of any recognition site for I-A. In practice, ThF is made by spleen cells from (CBA x B10)F1 [(H-2k x H-2d)F1] mice pretreated with cyclophosphamide (100 mg/kg) and immunized with picrylated parental spleen cells intravenously (3 x 10(7)). This procedure produces haplotype-restricted contact sensitivity (corresponding to the parental cells) but the unfractionated F1 ThF does not show haplotype-specific restriction in its action. In fact, the F1 mice produces two species of ThF, each bearing determinants of the I-A molecule of one parental haplotype (k or d). When the two species were separated with monoclonal anti-I-Ak and anti-I-Ad antibodies, the genetic restriction in their action corresponded to the phenotype of the I-A determinants that they carried. In a further experiment, F1 ThF was split into its constituent antigen-binding (Ag+) and antigen non-binding (Ag-) chains by reduction, and the two species of Ag- chains separated with monoclonal anti-I-A antibodies. After complementation with the Ag+ chain, the two species of Ag- chains showed genetic restriction in their action that corresponded to the phenotype of the I-A determinants that they carried. These findings support the I-A presentation hypothesis that antigen-specific ThF acts by approximating antigen to its own I-A determinants, and hence facilitates recognition by I-A-restricted T cells.

Prolonged survival of actively enhanced rat renal allografts despite accelerated cellular infiltration and rapid induction of both class I and class II MHC antigens

Administration of 1 ml of donor whole blood 7 d before renal transplantation produces long-term (greater than 100 d) graft survival in the DA (RT1a) into PVG (RT1c) rat strain combination. Using this model, the pattern and phenotype of infiltrating leukocytes were examined in rejecting and enhanced renal allografts, at days 1, 3, 5, and 7 after transplantation, by immunohistologic techniques. Paradoxically, enhanced grafts showed a more rapid and substantial leukocyte infiltrate, the phenotype of which was similar to that in rejecting grafts except for a reduced number of MRC OX-8+ cells and MRC OX-39+ cells. Graft infiltrating cells and splenocytes from transfused animals showed similar, although modest, levels of both nonspecific cytotoxicity and alloantigen-specific cytotoxicity. Immunohistologic analysis of MHC antigen distribution within the allograft revealed, unexpectedly, that enhanced grafts underwent an accelerated and extensive induction of both donor class I and class II MHC antigens. These findings were confirmed by allospecific quantitative absorption analysis, which showed severalfold increases in class I and class II MHC antigens by day 3 in enhanced grafts but not until day 5 in rejecting grafts. An additional observation was the more rapid disappearance of donor interstitial cells from enhanced grafts. These findings emphasize the overwhelming suppressive effect induced by an organ allograft after preoperative blood transfusion despite the associated induction of large numbers of potential effector cells and increased target antigen density within the graft.

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.

Tolerance to parenchymal self. Regulatory role of major histocompatibility complex-restricted, OX8+ suppressor T cells specific for autologous renal tubular antigen in experimental interstitial nephritis

BN rats develop interstitial nephritis after immunization with rabbit, but not rat renal tubular antigen. Using RT1n rat strains that differentially express tubular antigen, we investigated the unresponsiveness of BN rats to BN tubular antigen (BN-TBM) using delayed-type hypersensitivity (DTH) responses to BN-TBM as a measure of cell-mediated immunity. Our results indicate that rat strains expressing tubular antigen respond to immunization with BN-TBM with the clonal expansion of antigen-specific, cyclophosphamide-sensitive, OX8+, MHC-restricted suppressor T cells. Such suppression appears to be relevant to the maintenance of tolerance to parenchymal self, since chronic cyclophosphamide therapy abrogates suppression and results in significant interstitial nephritis.

Graft-vs.-host reactions: mechanisms and contemporary theories

A graft-vs.-host (GvH) reaction can be initiated by injection of immunocompetent lymphocytes into a histoincompatible host that is unable to reject these cells. The reaction is characterized by splenomegaly, hepatomegaly, lymph node atrophy, body weight loss, dermatitis, and diarrhea, often leading to mortality. The onset and severity of the GvH reaction are determined by differences in histocompatibility antigens between the donor and the acceptor, and by the number and nature of the transplanted allogeneic cells. Many different in vivo and in vitro systems have been devised for experimental studies of the GvH reaction. In several of these models, however, different parameters are measured. Furthermore, the conclusions drawn from these investigations sometimes contradict each other. This paper reviews the experimental data, and discusses the mechanisms underlying the GvH reaction.

Monocyte function in the acquired immune deficiency syndrome. Defective chemotaxis

The ineffective immune response in patients with the acquired immune deficiency syndrome (AIDS) contributes to severe and widespread infections and unrestricted growth by certain tumors. To determine whether monocyte dysfunction contributes to this immunosuppressed condition, we investigated monocyte chemotaxis in patients with AIDS. Using three different chemotactic stimuli, N-formylmethionylleucylphenylalanine, lymphocyte-derived chemotactic factor, and C5a des Arg, we studied the chemotactic responses of monocytes from seven homosexual men with AIDS, three homosexuals with lymphadenopathy and an abnormal immunological profile, seven healthy homosexual men, and 23 heterosexual control individuals. Monocytes from each of the AIDS patients with Kaposi's sarcoma and/or opportunistic infection exhibited a marked reduction in chemotaxis to all stimuli compared with the healthy control subjects. The reduced chemotactic responses were observed over a wide range of concentrations for each stimulus. Monocytes from AIDS patients who had clinically apparent opportunistic infection(s) exhibited a greater reduction in monocyte migration to all three stimuli than monocytes from the AIDS patient with only Kaposi's sarcoma. Monocytes from each of three homosexuals with lymphadenopathy and an abnormal immunological profile exhibited decreased chemotactic responses that were intermediate between those of the AIDS patients and the healthy heterosexual control subjects. In contrast to these findings, monocytes from each of seven healthy homosexuals exhibited normal chemotactic responses to the same stimuli. In addition, monocytes from AIDS patients exhibited reduced chemotaxis to soluble products of Giardia lamblia, one of several protozoan parasites prevalent in AIDS patients. Thus the immune abnormality in AIDS, previously thought to involve only the T-, B-, and natural killer lymphocytes, extends to the monocyte-macrophage. Defective monocyte migratory function may contribute to the depressed inflammatory response to certain organisms and to the apparent unrestricted growth of certain neoplasms in patients with AIDS.

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

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

Adoptive transfer of delayed type hypersensitivity reactions specific for Leishmania major antigens to normal mice using murine T cell populations and clones generated in vitro

Leishmania major specific murine T cell blasts and clones maintained in vitro were tested for their ability to adoptively transfer delayed type hypersensitivity (DTH) reactions to normal mice. These effector cells exhibited a Lyt 1+2- cell surface phenotype. They induced specific DTH reactions in syngeneic DBA/2 mice after local transfer in the footpad, (together with parasite antigens) or intravenous injection followed by challenge with parasite antigens in the footpad. The DTH reactions were specific for L. major antigens and required H-2 identity between the injected T cells (clones) and the adoptively transferred host. Using radioactively labelled T cell blasts for intravenous transfer, it was demonstrated that a large fraction of these functionally active cells localized in the spleen and footpad which had been challenged with parasite antigens.

Antiidiotypic immunity in interstitial nephritis. II. Rats developing anti-tubular basement membrane disease fail to make an antiidiotypic regulatory response: the modulatory role of an RT7.1+, OX8- suppressor T cell mechanism

Antiidiotypic immunity can successfully inhibit the development of antitubular basement membrane (alpha TBM) disease that produces interstitial nephritis. Rats normally immunized to produce disease, however, do not develop this regulatory and protective antiidiotypic effect. The failure to see such a regulatory response is functionally related to the influence of a nonspecific, RT7.1+, OX8-suppressor T cell that appears shortly after immunization. While this suppressor cell system can partially reduce the intensity of disease, it also limits the host's ability to specifically regulate the alpha TBM immune response and, hypothetically, leaves the disease process in an operationally active mode.

Induction of delayed type hypersensitivity against ultrasonicated Mycobacterium lepraemurium bacilli without simultaneous local reactivity against live bacilli or protective immunity

Delayed type hypersensitivity (DTH) was induced in C3H mice by subcutaneous immunization with Mycobacterium lepraemurium (MLM) antigens in Freund's complete (FCA) or Freund's incomplete (FIA) adjuvant. The total ultrasonicate (MLMSon-P) of MLM bacilli as well as the water soluble fraction (MLMSon-S) of this ultrasonicate was found effective. MLMSon-S was used as the test antigen. Specific DTH also developed after immunization with heat-killed MLM bacilli in FIA, but not with heat-killed bacilli in saline. Some mice were pre-treated with cyclophosphamide (CY) or splenectomized to augment the effect of immunization. In no instance was DTH to MLMSon-S accompanied by detectable local reactivity to live MLM bacilli measured as swelling of the infected footpad or by reduced multiplication or dissemination of the bacilli during the first 11 weeks after inoculation. As determined by testing in the infected footpad 8 weeks after inoculation, MLM infection did not induce DTH to MLMSon-S in non-immunized mice, and MLM infection was found to neither augment nor suppress established DTH to MLMSon-S. The experiments thus demonstrated a clear dissociation between DTH to MLMSon-S and local reactivity to live MLM bacilli, as well as between DTH to MLMSon-S and protective immunity to MLM infection.

Strain variation in the induction of tolerance by epicutaneous application of trinitrochlorobenzene

It has been postulated that a relationship exists between the density of epidermal Langerhans cells and the capacity of the epidermis to promote the induction of contact sensitization. This postulate was developed, in part, because (1) mouse tail epidermis contains fewer ATPase-positive (presumably Langerhans) cells than does abdominal epidermis, and (2) when tails of C57Bl/6 mice were painted with dinitrofluorobenzene (DNFB), the mice were less sensitive than those painted on the abdomen. In addition, tail-painted mice were shown to be tolerant to subsequent attempts at sensitization with DNFB. In this study we found that by painting the tails of mice with the hapten trinitrochlorobenzene (TNCB), sensitization was induced in certain mouse strains (BALB/c, A/J, and CBA--haplotypes H-2d, H-2a, H-2k, respectively), but tolerance resulted from painting the tails of other strains (C57Bl/6, C57Bl/10, and AB.Y--haplotype H-2b). The ability to become sensitive or tolerant is not related to Langerhans cell density as detected by ATPase staining. While the mechanism for this strain difference in the induction of tolerance is unknown, tolerance induced in C57Bl/6 mice is mediated in part by the generation of suppressor cells.

Polymorphism of genes involved in anti-tubular basement membrane disease in rats

Inbred strains of rats differ widely in their susceptibility to interstitial nephritis induced by rabbit renal tubular basement membrane (TBM) preparations. We now report that susceptibility is determined in part by an RT1-linked gene for effector cell responsiveness producing interstitial lesions. Furthermore, we also obtained evidence that the gene determining expression of the target TBM antigen is linked to the gene for albinism on the first linkage group. When non-susceptible rats lacking the TBM antigen but having the gene for cellular responsiveness were mated with non-susceptible rats which had the TBM antigen but lacked the gene for cellular responsiveness, the F1 hybrids were susceptible to the induction of interstitial nephritis. Although strains varied widely in the amount of anti-TBM antibody (alpha TBM-Ab) they produced, this variation does not appear to be controlled by RT1-linked genes, nor does the isotype or amount of antibody appear to be related to the susceptibility to infiltrating cellular lesions.

Biochemical characterization of a second family of human Ia molecules, HLA-DS, equivalent to murine I-A subregion molecules

In mice, two families of structurally distinct Ia molecules, one designated I-A and the other I-E, have been identified and characterized. The HLA-DR molecules represent one family of human Ia molecules equivalent to the murine I-E molecules on the basis of amino acid sequence homology. We describe the isolation and biochemical characterization of a second family of human Ia molecules, designated HLA-DS for second D-region locus, equivalent to the murine I-A molecules. The human HLA-DS molecules consist of two polypeptide chains, DS alpha (37,000 mol wt) and DS beta (29,000 mol wt), with 73% amino acid sequence identity to the murine I-A molecules. Furthermore, the HLA-DS molecules are closely linked genetically to HLA-DR molecules, a situation analogous to that observed in mice. The similarity in molecular weights of the DR and DS molecules might explain why others have failed to identify the latter in man.

Soluble factors in tolerance and contact sensitivity to 2,4-dinitrofluorobenzene in mice. IV. Characterization of migration inhibition factor-producing lymphocytes and genetic requirements for activation

The production of migration inhibition factor (MIF) in vitro by lymph node cells from mice with contact sensitivity to 2,4-dinitrofluorobenzene (DNFB) was investigated. MIF activity of cell-free culture supernatants was measured using a micro, indirect "hanging-drop" assay system. We found that DNFB-sensitized lymph node cells are stimulated to produce MIF by co-culture with DNP-labeled spleen cells or splenic adherent cells. The stimulation was quantitatively antigen-specific, as co-culture with TNP-spleen cells or TNP-splenic adherent cells induced only low levels of MIF activity. Pretreating the immune lymph node cells with different antisera plus complement, before addition of DNP-spleen cells, showed that MIF production is dependent on Ia- T cells. Additional experiments showed that in order for the T cells to be stimulated, homology at the I-A subregion of the major histocompatibility complex between the T cells and DNP-spleen cells is required. Collectively, these results correlate with our previous finding that transfer of contact sensitivity is mediated by Ia- T cells and indicate that both tests, i.e., transfer in vivo and MIF production in vitro, are measuring effector functions of the same T cell subset.

Non-H-2 restriction of expression of passively transferred delayed sensitivity

The results of this study of allogeneic restriction of passively transferred delayed sensitivity to Listeria antigens serve to illustrate the complexity of in vivo models. They show that the H-2 restriction observed when delayed-type hypersensitivity was transferred between H-2-congenic strains was no more severe than the restriction observed when delayed-type hypersensitivity was transferred between parental and F1 mice and between different strains sharing the same H-2 haplotype. It is obvious that genes, in addition to those of the H-2 locus, can be responsible for allogeneic restriction in vivo.

H-2-Restricted lethal graft-versus-host diseases

T cells from radiation chimeras in several strain combinations cause lethal GVHD in irradiated, bone-marrow-protected mice which share the D end of the H-2 complex with the T cells and also have foreign determinants. This phenomenon was not found with T cells from normal mice. I suggest that H-2-restricted GVD cells may be present in normal mice, but their effects may be masked by unrestricted GVH cells, which however, develop more slowly in the chimeras so that lethality due to restricted cells can be observed.

A one-receptor view of T-cell behaviour

The discovery of T cells and their behaviour has forced a re-evaluation of the immunological relationship between self and not-self. T cells seem to respond against foreign antigens only when the latter are in some form of association with self molecules encoded by the major histocompatibility complex. This has raised the question of whether T-cell recognition may depend on two separate receptors. I present here the case for a model of T-cell behaviour based on a single receptor.

Characterization of immunological depression in spontaneously hypertensive rats

Immunocompetent cell functions were evaluated in spontaneously hypertensive rats (SHR). Hematological studies revealed decreased absolute numbers of lymphocytes and increases number of polynucleic cells in the peripheral blood of SHR. The SHR had a reduced number of immature T lymphocytes in their thymuses in comparison with an original strain of Wistar rats, as detected by the rosette formation test with guinea pig erythrocytes. The antibody response to sheep red blood cells (SRBC) of the 3-month-old SHR was profoundly depressed and was about one-teeth that of the Wistar rats. Cell cooperation experiments suggest that the T lymphocytes of the SHR were selectively impaired in antibody responses to SRBC in cooperation with B lymphocytes. B lymphocytes from the bone marrow of the SHR were not affected and produced normal numbers of plaque-forming units. Cyclophosphamide treatment, which selectively depletes suppressor T lymphocytes, did not enhance the delayed-type hypersensitivity response to SRBC in SHR. This may rule out the possibility of the involvement of the suppressor mechanism in the T cell depression of the SHR.

Contact sensitivity to azobenzenearsonate and its inhibition after interaction of sensitized cells with antigen-conjugated cells

Painting mice on the skin with the diazonium salt of p-arsanilic acid elicited two types of T cell activity. One was restricted by the I region of the major histocompatibility complex and was responsible for the transfer of azobenzenearsonate (ABA) sensitivity to naive mice. The other was H-2K restricted and could be demonstrated by its ability to interact specifically with ABA-coupled cells in vitro and to inhibit nonspecifically the transfer of sensitivity by cells sensitized either to ABA or to another antigen. Free antigen, or antibody directed against the cross-reactive idiotype on the anti-ABA antibodies of A/J mice, could inhibit the H-2K-restricted suppressive activity induced in the ABA immune A/J cells.

Genetic restriction in the induction of contact sensitivity by footpad cell transfer

Cells taken from draining lymph nodes one day after application of oxazolone and picryl chloride induced contact sensitivity in syngeneic but not in allogeneic recipients. In contrast, the immunizing activity of cells taken four days after sensitization was not genetically restricted. The findings that '1-day' cells incubated with anti-hapten antibodies break down the genetic restriction, and that '4-day' cells lose their ability to induce contact sensitivity after complement treatment, suggest that two different mechanisms are involved in the induction of contact sensitivity.

Hapten-specific T cell responses to 4-hydroxy-3-nitrophenyl acetyl. VIII. Suppressor cell pathways in cutaneous sensitivity responses

In the current study, we examine the mechanism of suppression of cutaneous sensitivity (CS) responses to 4-hydroxy-3-nitrophenyl acetyl succinimide ester. Intravenous administration of haptenated syngeneic spleen cells induces a state of hapten-specific tolerance involving I-J bearing suppressor T cells that function at either the induction phase or the effector phase of the CS response. The effective phase suppressor cells (Tse) are genetically restricted by both Igh and H-2 region genes. However, a third cell population is also required in he immune lymphocyte population for immune suppression. This third cell population, termed Ts3, is an I-J+, cyclophosphamide-sensitive T cell, as shown by reconstitution experiments. Further, the Tse-Ts3 interaction is restricted by genes in he H-2 and Igh gene complexes. The results are discussed with respect to the pathway of cellular interactions leading to immuno suppression.

Genetic control of T helper cell function in the clawed toad Xenopus laevis

The genetic control of the collaboration between Xenopus T and B cells has been analyzed in vivo using cells from five strains of major histocompatibility complex-defined Xenopus. When carrier (fowl gamma-globulin)-primed T cells and hapten (dinitrophenylated keyhole limpet hemocyanin)-primed B cells differed by minor histocompatibility antigens or by only one haplotype of the major histocompatibility complex, the collaboration was efficient in the sense that large numbers of plaques, low-molecular weight antibodies and high-affinity IgM antibodies could be recorded in the cultures challenged with dinitrophenylated fowl gamma-globulin. However, when T and B cells differed at both alleles of the major histocompatibility complex, lower numbers of plaques were obtained, no low-molecular weight anti-hapten antibodies could be detected, and the IgM antibodies that were sometimes synthesized were of low affinity. This suggests that the major histocompatibility complex, or a gene linked with it, affects the collaboration between Xenopus T and B cells in a way perhaps similar to that described in mammals.

Immunoregulation

The immune system of higher vertebrates is a complex network of separate, interacting cell populations, each ontogenetically endowed with specific regulatory (inductive or suppressive) or effector functions. The products of at least two major gene clusters-the immunoglobulin structural genes and the genes of the major histocompatibility complex-are expressed as active and passive recognition structures on cells of the immune system and at least some of their secreted products. Macrophages play a critical role in the initiation of immune responses. Regulatory subsets of thymus-derived lymphocytes interact with macrophages and with each other in the control of immune effector cells. At every level of the immune response, cell interactions require that these regulatory cells recognize gene products of the major histocompatibility complex. Due to recent technical advances, rapid progress is being made in identifying subsets of human immunoregulatory cells; those identified to date show strong functional homology to previously well characterized murine cell subsets.

Positive selection of major histocompatibility complex-restricted suppressor T cells bearing the predominant idiotype in the immune response to lysozyme

The lysozyme system provides an excellent model for studying the role of multiple major histocompatibility complex (MHC) genes in the induction and regulation of Ir-gene controlled immune responses. Immunization of H-2b mice leads to concomitant activation of helper and suppressor activities by different epitopes on hen egg-white lysozyme (HEL) and thus phenotype unresponsiveness to native HEL. HEL-specific suppressor T cells in C57BL/10 nonresponder mice show MHC restriction, because their enrichment on antigen-pulsed macrophage monolayers requires syngeneic macrophages as well as HEL. The expression of the selected suppressor function requires interaction between the restricted suppressor precursor cell and an HEL-triggered, suppressor-inducer T cell. The MHC-restricted suppressor precursors bear the predominant idiotype found on anti-HEL antibodies, whereas MHC-restricted helpers do not.

Hapten-specific T cell responses to 4-hydroxy-3-nitrophenyl acetyl. VI. Evidence for different T cell receptors in cells that mediate H-21-restricted and H-2D-restricted cutaneous sensitivity responses

We have previously shown that cross-reactive sensitivity (CS) responses induced by 4-hydroxy-3-nitrophenyl acetyl-O-succinimide (NP-O-Su) and elicited by its 5-iodo analogue, 4-hydroxy-5-iodo-3-nitrophenyl acetyl-O-succinimide were observed in strains of mice possessing the Igh-1b allotype, but not in strains bearing allotypes Igh-1c or Igh-1j. These CS responses are mediated by T cells and can be transferred to naive recipients that are homologous at either the H-2K, H-2I, or H-2D regions of the major histocompatibility complex. We now extend our analysis of cross-reactive 4-hydroxy-3-nitrophenyl-acetyl (NP)-induced CS responses to inbred strains of mice expressing additional Igh-1 allotypes. In contrast to NP-induced delayed-type hypersensitivity responses, which only display 4-hydroxy-5-iodo-3-nitrophenyl acetyl (NIP) cross-reactivity in Igh-1b-bearing mice, cross-reactive CS responses can also be elicited in NP-primed mice carrying the Igh-1d, Igh-1e, or Igh-1f allotypes. Moreover, cross-reactive NP-induced CS responses could be transferred by NP-O-Su-primed lymph node cells from the AKR (Igh-1d) strain, into naive recipients homologous at the H-2D region, but only non-cross-reactive NP responses could be transferred into strains homologous at the H-2I region. Furthermore, the lack of cross-reactivity in the Igh-1j-bearing C3H strain was not the result of an inability of these mice to recognize NP in association with H-2K/D products, because NP-O-Su-primed cells from C3H donors transferred NP-specific CS responses into both H-2D and H02I homologous recipients. The results are discussed with respect to the nature of the T cell receptors that control NP responses.

Effects of blocking helper T cell induction in vivo with anti-Ia antibodies. Possible role of I-A/E hybrid molecules as restriction elements

To examine the role of Ia antigens in controlling T cell activation in vivo, unprimed (CBA X B6)F1 (H-2k X H-2b) T cells were positively selected to sheep erythrocytes (SRC) for 5 d in irradiated F1 mice in the presence of large doses of anti-Iak antibody. With selection in the presence of broad-spectrum anti-Iak antibody (A.TH anti-A.TL antiserum), the activated T cells were markedly reduced in their capacity to collaborate with either B10.BR (I-Ak I-Bk I-Jk I-Ek I-Ck) (kkkkk) or B10.A(4R) (kbbbb) B cells but gave good helper responses with B10 (bbbbb) and (B10 X B10.BR)F1 B cells. Because there was no evidence for suppression, these findings were taken to imply that the anti-Iak antibody bound to Ia determinants on radioresistant macrophagelike cells of F1 host origin and blocked the activation of the IGk-restricted subgroup of F1 T cells but did not affect activation of the Iab-restricted T cell subgroup. Analogous experiments in which F1 T cells were selected to SRC in F1 mice in the presence of monoclonal anti-I-Ak antibody gave different results. In this situation, the reduction in T cell help for Iak-bearing B cells applied to B10.A(4R) B cells but not to B10.BR B cells. With selection of F1 T cells in B10.A(4R) mice, by contrast, anti-I-Ak antibody blocked T cell help for both B10.A(4R) and B10.BR B cells. These data suggested that genes telomeric to the I-A subregion were involved in controlling T cell activation and T-B collaboration. Because no evidence could be found that I-B through I-C determinants per se could act as restrictions elements, the working hypothesis for the data is that Iak-restricted T cells consist of two subgroups of cells: one subgroup is restricted by I-A-encoded molecules, whereas the other is restricted by I-A/E hybrid molecules encoded by two separated genes situated in the I-A and I-E subregions, respectively. The notion that A/E hybrid molecules serve as restriction elements is in line with the findings of other workers that these molecules can act as alloantigens and control responses to certain antigens under double Ir gene control.

Nature of T lymphocyte recognition of macrophage-associated antigens. V. Contribution of individual peptide residues of human fibrinopeptide B to T lymphocyte responses

Guinea pig T lymphocyte responses to a decapeptide antigen (NH1-Asp5-Ans6-Glu7-Glu8-Gly9-Phe10-Phe11-Ser12-Ala13-Arg14-OH) of human fibrinopeptide B (hFPB) were examined using various synthetic peptide analogues containing single residue substitutions. Each analogue was examined for antigenicity as determined by an in vitro proliferative responses of hFPN-immune strain 2 guinae pig T cells. In addition, both strain 2 and strain 13 animals were immunized with each analogue and immunogenicity assessed by in vitro T cell-proliferative responses with the homologous immunizing analogue and the parent peptide. Replacement of arginine14 with lysine formed an immunogenic analogue which showed no antigenic cross-reactivity with the native peptide in strain 2 T cell responses. In addition, substitution of arginine14 with blocked lysine again produced a unique immunogenic analogue that showed little or no antigenic identity with the intact lysine analogue or the native peptide. In similar fashion, substitution of resideu phenylalanie10 with tyrosine or Phe(4-NO2) created unique immunogenic analogues with little or no antigenic identity to the native peptide with strain 2 T cells. By contrast, replacement of phenylalanine11 with either tyrosine or Phe(4-NO2) resulted in analogues with a total loss of immunogenicity and antigenicity in strain 2 T cell responses. An analogue in which glutamic acid7,8 were replaced with glutamine retained a small degree of antigenicity with hFPB-immune T cells, but T cells from strain 2 animals immunized with the Gln analogue responded only marginally to the Gln analogue while producing good proliferative responses with the native peptide. On the other hand, an analogue in which asparatic acid5 was replaced with asparagine retained most of the antigenic identity with hFPB for strain 2 T cell responses. None of thee analogues were immunogenic for strain 13 guinea pigs. These observations are discussed with respect to the contribution of each substituted residue to T cell respones, mechanism of Ir gene function, and a model for T cell recognition of small peptide antigens.

Surface receptors on lymphoreticular cells: sensory devices for host recognition of foreign antigens and neoplasia

Distinct types of cells in the lymphoreticular system regulate an individual's immunologic homeostasis and response to disease. By means of multiple receptors the cell membrane transfers signals between the environment and the cell. This article reviews the important surface antigens and receptors on normal and activated macrophages (e.g., receptors for the crystallizable fragment [Fc] of immunoglobulin), on lymphocytes derived from the bone marrow (e.g., immunoglobulins and immune-associated [Ia] antigens), on thymus-derived lymphocytes (e.g., Thy-1 antigens) and on "null' cells. Although many of these markers were originally defined in rodents and birds, analogous markers in humans have proved extremely useful in characterizing lymphoreticular cell populations in healthy and sick individuals. Established and postulated functions of the markers in host defence mechanisms are discussed.