Determinant selection is a macrophage dependent immune response gene function

The role of islet antigen presenting cells and the presentation of insulin in the initiation of autoimmune diabetes in the NOD mouse

We have been examining antigen presentation and the antigen presenting cells (APCs) in the islets of Langerhans of the non-obese diabetic (NOD) mouse. The purpose is to identify the earliest events that initiate autoimmunity in this confined tissue. Islets normally have a population of macrophages that is distinct from those that inhabit the exocrine pancreas. Also found in NOD islets is a minor population of dendritic cells (DCs) that bear the CD103 integrin. We find close interactions between beta cells and the two APCs that result in the initiation of the autoimmunity. Even under non-inflammatory conditions, beta cells transfer insulin-containing vesicles to the APCs of the islet. This reaction requires live cells and intimate contact. The autoimmune process starts in islets with the entrance of CD4(+) T cells and an increase in the CD103(+) DCs. Mice deficient in the Batf3 transcription factor never develop diabetes due to the absence of the CD103/CD8α lineage of DCs. We hypothesize that the 12-20 peptide of the beta chain of insulin is responsible for activation of the initial CD4(+) T-cell response during diabetogenesis.

Variations in MHC Class II Antigen Processing and Presentation in Health and Disease

MHC class II (MHC-II) molecules are critical in the control of many immune responses. They are also involved in most autoimmune diseases and other pathologies. Here, we describe the biology of MHC-II and MHC-II variations that affect immune responses. We discuss the classic cell biology of MHC-II and various perturbations. Proteolysis is a major process in the biology of MHC-II, and we describe the various components forming and controlling this endosomal proteolytic machinery. This process ultimately determines the MHC-II-presented peptidome, including cryptic peptides, modified peptides, and other peptides that are relevant in autoimmune responses. MHC-II also variable in expression, glycosylation, and turnover. We illustrate that MHC-II is variable not only in amino acids (polymorphic) but also in its biology, with consequences for both health and disease.

Antigen processing and presentation to T cells

In this article Howard Grey and Robert Chesnut describe recent insights into the mechanism of antigen presentation and discuss the needfor antigen processing in the stimulation of T cells.

An integrated approach to epitope analysis II: A system for proteomic-scale prediction of immunological characteristics

Background

Improving our understanding of the immune response is fundamental to developing strategies to combat a wide range of diseases. We describe an integrated epitope analysis system which is based on principal component analysis of sequences of amino acids, using a multilayer perceptron neural net to conduct QSAR regression predictions for peptide binding affinities to 35 MHC-I and 14 MHC-II alleles.

Results

The approach described allows rapid processing of single proteins, entire proteomes or subsets thereof, as well as multiple strains of the same organism. It enables consideration of the interface of diversity of both microorganisms and of host immunogenetics. Patterns of binding affinity are linked to topological features, such as extracellular or intramembrane location, and integrated into a graphical display which facilitates conceptual understanding of the interplay of B-cell and T-cell mediated immunity.

Patterns which emerge from application of this approach include the correlations between peptides showing high affinity binding to MHC-I and to MHC-II, and also with predicted B-cell epitopes. These are characterized as coincident epitope groups (CEGs). Also evident are long range patterns across proteins which identify regions of high affinity binding for a permuted population of diverse and heterozygous HLA alleles, as well as subtle differences in reactions with MHCs of individual HLA alleles, which may be important in disease susceptibility, and in vaccine and clinical trial design. Comparisons are shown of predicted epitope mapping derived from application of the QSAR approach with experimentally derived epitope maps from a diverse multi-species dataset, from Staphylococcus aureus, and from vaccinia virus.

Conclusions

A desktop application with interactive graphic capability is shown to be a useful platform for development of prediction and visualization tools for epitope mapping at scales ranging from individual proteins to proteomes from multiple strains of an organism. The possible functional implications of the patterns of peptide epitopes observed are discussed, including their implications for B-cell and T-cell cooperation and cross presentation.

Perspective on antigen processing and presentation

The phenomenon of antigen processing and presentation and the concept that T cells recognize peptides resulting from the partial catabolism of proteins, are relatively new. These concepts were first recognized and developed at a time when lymphocyte immunity - the adaptive system - and cellular immunity, with its major component of activated macrophages, were not perceived as part of one integrated system. To me, it was the fundamental findings on the role of major histocompatibility (MHC) molecules that set the framework for understanding how phagocytes and the antigen presenting cell (APC) system interact with the adaptive cellular system, in a truly symbiotic relationship (1). In this chapter we make a historical review of the developments that, in my biased opinion, led to the understanding of antigen presentation as a central event. I emphasize my own work, placing it in my perspective of how I saw the field moving.

How the MHC selects Th1/Th2 immunity

While the effects of cytokines on T helper 1 (Th1)/Th2 differentiation are well documented, it is less clear why a dichotomy of effector cytokine production would initiate from antigen-specific lymphocytes. Nevertheless, in defined experimental systems, the interaction between T-cell receptor (TCR), peptide and major histocompatibility complex (MHC) can determine Th1/Th2 dominance. Here, Joseph Murray discusses how TCR affinity and ligand density might interface with innate forces in the selection of CD4+ T-cell functions.

Comparison of cytotoxic T lymphocyte responses induced by peptide or DNA immunization: implications on immunogenicity and immunodominance

To study the mechanisms that influence the immunogenicity and immunodominance of potential cytotoxic T lymphocyte (CTL) epitopes, we conducted a systematic analysis of the CTL response raised in HLA-A*0201/Kb (A2/Kb) transgenic mice against the viral antigen, hepatitis B virus polymerase (HBV pol). From a pool of 26 nonamer peptides containing the HLA-A*0201-binding motif, we selected A2-binding peptides, immunized A2/Kb animals, and tested the CTL raised against the peptide for recognition of HBV pol transfectants. Of nine immunogenic CTL epitopes, only four were recognized on HBV pol transfectants, whereas the other five were cryptic. Characterization of the peptide-specific CTL lines indicated that crypticity may result from either poor processing or low T cell receptor (TCR) avidity. To identify the immunodominant epitopes, we determined the CTL specificities induced in A2/Kb animals in response to priming with HBV pol cDNA. We obtained a response against three epitopes that were contained with the set of four epitopes recognized by peptide-specific CTL on HBV pol transfectants. Comparative analysis of cDNA priming and peptide priming revealed, therefore, the presence of a subdominant epitope. We conclude that for the HBV pol antigen, the repertoire of CTL specificities is shaped by major histocompatibility complex class I peptide binding capacity, antigen processing, and TCR availability.

Major histocompatibility complex regulation of T helper functions mapped to a peptide C terminus that controls ligand density

The functional status (Th1- versus Th2-like) of CD4 T cells primed against human collagen type IV (hCol IV) or a single 30mer peptide from the alpha 2 chain of this molecule is predicted by the major histocompatibility complex (MHC) class II (I-A) genotype of the responding mice. H-2s mice elicit Th1-like cell-mediated responses to these antigens, whereas Th2-like humoral responses are primed in H-2b,d,k mice. We now report that the ability of MHC to dictate T helper function in this system depends upon a single amino acid of the minimal alpha 2(IV) peptide. The C terminus of this minimal (12mer) peptide is -G-G-P-K, which is predicted to form a beta-turn. The present data demonstrate that the terminal lysine (K) stabilizes the immunogens full biological effects necessary for exclusive cell-mediated responses in H-2s mice. The lysine-truncated (11mer) peptide with otherwise identical sequence effectively primes T helper function in both H-2b and H-2s genotypes. Most importantly, our direct analysis of these peptides' presentation by live antigen-presenting cells (APC) reveals that the 12mer is bound at a log higher density on H-2s APC than on H-2b APC, and that the 11mer is presented at an equally low relative density on APC from both genotypes. In vitro analyses of 12mer/11mer cross-reactive Th clones demonstrate that I-As restricted clones require about 1-2 log lower doses of 12mer peptide than 11mer peptide to stimulate equivalent thymidine incorporation and cytokine release. By contrast, I-Ab-restricted (12mer/11mer cross-reactive) Th clones show no preference for the 12mer and require relatively high peptide doses similar to those required to stimulate the I-As clones with the 11mer peptide. Thus, the peptide dose requirements of Th clones reflect the high density of presentation associated with the 12mer: I-As ligand. Taken together, the results directly support the role of ligand density as an important control point in the functional decision of CD4 T cells.

Peptides determine the lifespan of MHC class II molecules in the antigen-presenting cell

Although many peptides are generated during the intracellular processing of protein antigens, only a few are selected for recognition by the immune system. The immunodominant epitope of hen egg white lysozyme (HEL) for H-2k mice is contained in a tryptic fragment of amino-acid residues 46-61 (refs 6, 7). The core of this T-cell epitope, from amino acids 52 to 61 (DYGILQINSR), contains those residues required for binding to the class II molecule I-Ak (ref. 7). Most of the naturally processed fragments recovered from I-Ak-bearing antigen-presenting cells (APCs) cultured with HEL contained this 52-61 core sequence, presented as a nested set of peptides with extensions at both the amino and carboxyl termini. We now compare the handling by APCs of peptides containing HEL 52-61 to establish whether there is an advantage for the APC in selecting extended peptides: different complexes between peptides and major histocompatibility complex (MHC) molecules varied greatly in the amount of time associated with the APC, and in their immunogenic strength. This difference in persistence is one of the factors contributing to the selection and immune recognition of peptide-MHC complexes by T cells.

A speculative view of immune recognition

The speculation that immunologically reactive haptens must be those attached to carriers' immunodominant epitopes suggests a clearer mechanism by which the mysterious hapten-carrier phenomena are generated. This review focuses on the molecular biological nature of immune recognition of hapten-protein antigens both by the T-cell and the B-cell. T and B lymphocytes specifically recognize one determinant of the same antigen molecule in two different ways and in different circumstances. The B-cell recognizes an antigen by the preliminary antigen receptors on the cell's surface, at the time it is still intact, interiorizes it and presents the processed antigenic peptide after an antigen processing procedure. In contrast, the T-cell recognizes a hidden antigenic determinant, together with portions of the MHC on the presenting cell. The immune memory is mainly directed to the hidden internal determinant of an antigen. Some aspects of the clonal selection theory of antibody formation are also discussed at the modern molecular level.

Identification of the naturally processed form of hen egg white lysozyme bound to the murine major histocompatibility complex class II molecule I-Ak

A murine B-cell lymphoma bearing the class II major histocompatibility complex molecule I-Ak was cultured with the protein antigen hen egg white lysozyme (HEL). The I-Ak molecules were purified, and their associated peptides were extracted for characterization. Five HEL peptides were identified. Four contained the 10 amino acid residues HEL 52-61 (DYGILQINSR) but were heterogeneous in length and flanking residues. This core sequence is known to confer a high binding affinity for I-Ak. One additional peptide contained the amino acid residues HEL 48-60. These data demonstrate that the HEL epitope containing residues 52-61 is the most abundant HEL epitope presented on the major histocompatibility complex of the antigen-presenting cells and consequently explains its immunodominance.

Cell-surface molecules in the regulation of immune responsiveness

This paper reviews current knowledge genetics, structure and function on three categories of cell-surface molecules that affect immune responsiveness. It is focused on human molecules, but some references to murine analogues are made. First, the Major Histocompatibility Complex (MHC) molecules are discussed from the point of view of the associative recognition of antigenic peptides. The multiplicity, polymorphism and heterozygosity of MHC genes is correlated with the fine structure and the function of the molecules encoded by these genes. Second, selected CD molecules that are involved in cell-cell interaction and transduction of signals are discussed and correlated with discrete subsets of T cells, finally, some cell-surface receptors, antigen-specific and interleukin-specific, are analyzes, the effect of various molecules on immune responsiveness is illustrated by the actual experimental data. A minimal or parsimonious of triggering an immune response in which the discussed molecules are involved is described as a starting point for further discussion.

Chemical and functional analysis of MHC class II-restricted T cell epitopes

Various aspects of antigen degradation and presentation are reviewed, in particular with respect to fragmentation of native vs. denatured proteins, different enzymatic machinery present in different cells and individuals, characterization of epitopes and their persistence on antigen-presenting cells as well as their capacity to interact with different MHC class II molecules. Finally, the structure of antigenic peptides is discussed.

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

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

T cells recognize both conformational and cryptic determinants on the insulin molecule

T lymphocytes from strain 2 guinea pigs were studied for recognition of isolated insulin A and B chains. Insulin-immune T cells require intact conformation of the interchain disulfide bond that forms the A chain loop but do not require the B chain. In addition, strain 2 T cells were unexpectedly found to recognize unique epitopes on isolated insulin B chain that are not generated by presentation of native insulin. These data show that the T cell repertoire of strain 2 guinea pig for insulin includes both conformational and cryptic determinants.

Immunological aspects of diabetes mellitus: prospects for pharmacological modification

It is now well known that insulin-dependent diabetes is a chronic progressive autoimmune disease. The prolonged prediabetic phase of progressive beta-cell dysfunction is associated with immunological abnormalities. A prediabetic period is suggested by the appearance of islet cell antibodies, anti-insulin antibodies, and anti-insulin receptor antibodies. The existence of activated T lymphocytes and abnormal T cell subsets are also other markers. There is still no concensus about the use of the immunosuppression superimposed upon conventional insulin therapy in early diagnosed IDDM and the follow-up of the relatives of IDDM patients who share the genetic predisposition and serological markers for the risk of future onset of IDDM. Treatment in the prodromal period cannot be justified because a link between the disease and early markers such as ICA has not been established with certainty (Diabetes Research Program NIH, 1983). Many immunopharmacological manipulations were reported to be effective in animal models. However, most of them are not readily applied to human subjects. Moreover, IDDM patients are now believed to be heterogeneous, with a complex genetic background. HLA-DR, and more recently DQ, are closely related to the genetic predisposition to IDDM but those genes are not themselves diabetogenic. The contribution of autoimmunity does not appear to be uniform, and in some cases, the contribution of virus is considered more important. There is a lack of a marker for the future onset of IDDM. ICA and ICSA were found after mumps infection, but the existence of those autoantibodies and even the co-existence of HLA-DR3 do not always indicate the future trend to insulin dependency. More precise markers will be disclosed through the biochemical analysis of the target antigens on pancreatic beta-cell for islet antibodies and effector T cells. Much safer and more effective immunopharmacological treatment will be developed through animal experimentation using rat and mouse models. The recent development and interest in this field will further facilitate the attainment of the goal for the complete prevention of IDDM.

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

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

Insulin autoantibody polymorphisms with greater discrimination for diabetes in humans

Insulin autoantibodies, like islet cell antibodies, are found not only in the sera of newly diagnosed Type 1 (insulin-dependent) diabetic patients and their relatives, but also in patients with other autoimmunities who do not develop diabetes. Insulin autoantibodies are oligo/monoclonal and frequently binding-site restricted. As determinant selection is genetically determined, we questioned whether certain polymorphisms of insulin autoantibodies, identified by their binding site on the insulin molecule, could better discriminate for Type 1 diabetes, which is also HLA determined. First, we raised monoclonal antibodies to human insulin by classic fusion methods in order to determine the range of antibody polymorphism, and identified five distinct types by their binding profiles to a panel of insulin variants, using an enzyme-linked immunosorbent assay. Two of these polymorphisms, type A and type B, were subsequently found in insulin autoantibody positive human sera using the same panel of insulin variants, and successfully distinguished diabetes-related from diabetes-unrelated individuals. Thus, the type B polymorphism was responsible for binding in 60% of 41 insulin autoantibody positive individuals with polyautoimmune disease but no personal or family history of diabetes (diabetes unrelated), but in only 2% of a group which comprised 17 newly-diagnosed insulin autoantibody positive Type 1 diabetic patients, 19 insulin autoantibody positive discordant twins of Type 1 diabetes and six insulin autoantibody positive healthy siblings of Type 1 diabetic patients (diabetes related) (p less than 0.01). Isolation of the type A polymorphism alone reduced the proportion of false negatives in the insulin autoantibody test for diabetes relatedness from 49% to 20% without diminishing its specificity.(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

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

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

The basis for the immunoregulatory role of macrophages and other accessory cells

Macrophages handle extracellular proteins and secrete diverse bioactive molecules and, therefore, influence the physiology of many tissues. They also have an important immunoregulatory role. The immune response to proteins involves the activation of the T helper subset of lymphocytes. The T helper cell is activated only when it interacts with the protein displayed on the surface of a macrophage or other accessory cell. This interaction involves restrictive proteins encoded in the major histocompatibility gene complex as well as growth-differentiating proteins.

HLA B37 determines an influenza A virus nucleoprotein epitope recognized by cytotoxic T lymphocytes

Human influenza A virus-specific, cytotoxic T cells have been shown previously to recognize the virus nucleoprotein on infected cells. CTL preparations from four HLA B37-positive donors were shown to recognize a synthetic peptide that corresponded to amino acids 335-349 of the nucleoprotein sequence. Influenza-specific CTL from 10 donors of other HLA types failed to recognize this epitope. CD8+ CTL lines were derived from lymphocytes of two HLA B37-positive donors and used to show that the peptide was represented on virus-infected cells and to determine the probable boundaries of the epitope.

Lymphocytes, polymorphonuclear leukocytes, macrophages and platelets in synovium involved by rheumatoid arthritis. A study with monoclonal antibodies

The inflammatory cell infiltrate involving synovial tissues from joints affected by rheumatoid arthritis (RA)++ has been contrasted with that present in synovium removed from joints involved by previous trauma (T) or osteoarthritis (OA). Cell deployment has been mapped by immunohistochemistry using monoclonal antibodies which recognise epitopes characterising T and B cells, polymorphonuclear leukocytes, mononuclear phagocytes and platelets. Mononuclear phagocytes were the most consistent feature of the rheumatoid inflammatory cell exudate and were present, particularly in the synovial layer, in all OA/T samples. The synovial cells lacked the C3b complement receptor, CR1, but expressed CR3, the receptor for C3bi. In rheumatoid synovium, interdigitating cells were difficult to identify but cells of dendritic morphology bore at least one macrophage epitope. T cells far out-numbered B cells and generally lacked the IL-2 receptor which is an indicator of T cell activation. Care is required in the estimation of the T helper/inducer (TH) T suppressor/cytotoxic (Ts) ratio. Polymorphonuclear leukocytes were demonstrated around vessels and near the synovial intimal cell layer suggesting rapid tissue transit. Extravascular platelets were sparse. Follicular dendritic cells were defined by their central location in lymphoid follicles and strong expression of CR1 receptors. HLA-DR expression was widespread except on endothelial cells.

Phospholipase treatment of accessory cells that have been exposed to antigen selectively inhibits antigen-specific Ia-restricted, but not allospecific, stimulation of T lymphocytes

The corecognition of antigen and class II major histocompatibility complex (MHC) molecules (Ia molecules) by the T-cell receptor is a cell surface event. Before antigen is recognized, it must be taken up, processed, and displayed on the surface of an Ia-bearing accessory cell (antigen-presenting cell, APC). The exact nature of antigen processing and the subsequent associations of antigen with the APC plasma membrane, Ia molecules, and/or the T-cell receptor are not well defined. To further analyze these events, we have characterized the processing and presentation of the soluble polypeptide antigen bovine insulin. We found that this antigen requires APC-dependent processing, as evidenced by the inability of metabolically inactivated APCs to present native antigen to antigen plus Ia-specific T-T hybridomas. The ability of the same APCs to present antigen after uptake and processing showed that this antigen subsequently becomes stably associated with the APC plasma membrane. To characterize the basis for this association, we analyzed its sensitivity to enzymatic digestion. APCs exposed to antigen, treated with phospholipase A2, and then immediately fixed lost the ability to stimulate bovine insulin plus I-Ad-specific hybridomas. In contrast, the ability of these same APCs to stimulate I-Ad allospecific hybridomas was unaffected. This effect of phospholipase is not mimicked by the broadly active protease Pronase, nor is there evidence for contaminating proteases in the phospholipase preparation. These results suggest that one consequence of antigen processing may be an antigen-lipid association that contributes to the anchoring of antigen to the APC membrane. The implications of this model are discussed.

Suppression of the delayed-type hypersensitivity response to hen egg white lysozyme (HEL) by HEL peptides in a genetically high-responder mouse strain: evidence for requirement of the loop structure for induction of suppressor T cells

The delayed-type hypersensitivity (DTH) response of C3H/HeN mice to hen egg white lysozyme (HEL) can be blocked by a single iv injection of a solution of HEL in buffered saline 7 days before sensitization of animals with HEL in complete Freund's adjuvant (CFA). The minimal structure of HEL required for the suppression was examined by determining the abilities of various HEL-derivative peptides to inhibit HEL-DTH. Treatment of normal mice with Ploop I X II, sequence 57-107 (Cys64-Cys80, Cys76-Cys94), or P17 (sequences 1-27 and 123-129 linked by Cys6-Cys127) 7 days before immunization with HEL resulted in marked suppression of the DTH response. This inhibition of DTH involved generation of suppressor T cells (Ts). The results suggested that two suppressor pathways are involved. These data, together with another recent finding (1) that an entirely different portion of HEL is a suppressor determinant (SD) in A/J mice, indicate that different epitopes act as SDs in different strains of mice. Of the loop region peptides tested, Plc (intact loop I joined to a linear peptide, residues 84-97) was found to be the minimum structure capable of suppressing the HEL-DTH response; loop I or II alone did not cause suppression. Activation of Ts cells by the loop peptide depended on its conformational structure; completely reduced and carboxymethylated Ploop I X II did not cause suppression.

Anti-Thy-1 response of H-2f/H-2r heterozygotes: an unusual case of genetic control

Anti-Thy-1 responsiveness of H-2r homozygous and H-2f/H-2r heterozygous mice was studied. Good responsiveness appeared to be independent of H-2 phenotype of responder but was influenced by the phenotype of the donor. These results were incompatible with the concept of Ir-Thy-1 genes controlling the response to cell-free Thy-1 in these mice. In contrast the results were indicative of the response to the cell-bound form of the Thy-1 antigen. It is proposed that good anti-Thy-1 response may reflect the presence of clones capable of recognizing the Thy-1 antigen in the context of or in association with incompatible class I H-2 molecules.

Recognition of human insulin in vitro by T cells from subjects treated with animal insulins

Structurally defined proteins and peptides have provided considerable information about the specificity and regulation of immune responses in inbred animals. Many diabetics require therapy with insulin; therefore, we used this defined protein as a model antigen to investigate immune responses in the outbred human population. In this report, we examine human T cell recognition of antigenic determinants on various insulins. A group of 25 subjects was selected from over 200 diabetics because of the magnitude of their in vitro responses. 13 of the 25 had significant T cell responses to human insulin despite treatment with only beef/pork insulin mixtures. This autoimmunity may be attributed to crossreactivity of lymphocytes highly reactive to "foreign" epitopes on therapeutic insulins. Alternatively, identical determinants shared by human and animal insulins may be recognized. By employing additional insulins not used therapeutically and isolated A and B chains, several potential mechanisms for lymphocyte autoreactivity to human insulin were demonstrated. Some epitopes are conformational and require recognition of an intact molecule, whereas other epitopes may arise from antigen processing at the cellular level. Studies using zinc-free insulins suggest that zinc-induced alterations of the molecular surface may result in some shared reactivities between animal and human insulin. Furthermore, T cell reactivity against "foreign" epitopes is more complex than anticipated from differences in amino acid sequence. The response patterns of many subjects indicate that the A-chain loop associates with the N-terminal B chain to form a complex determinant. This determinant is recognized more often than individual amino acids. We conclude that insulin therapy generates polyclonal T cell responses directed at multiple epitopes on the molecule. Many of these epitopes are not identified by amino acid exchanges and their presence on human insulin leads to apparent autoimmunity.

T helper cell recognition of idiotopes on lambda 2 light chains of M315 and T952: evidence for dependence on somatic mutations in the third hypervariable region

Previous work has indicated that BALB/c T helper cells (Th) recognize an idiotope expressed on a 88-114/117 fragment of V lambda 2 of BALB/c myeloma protein 315. In the present study the antigenic structure of this idiotope was further analyzed. Conventional carrier-specific Th elicited by immunization of BALB/c mice with free lambda 2(315) did not cross-react with the free lambda 2 chain of the BALB/c myeloma protein T952 which differs from lambda 2(315) in five amino acid positions (38, 94, 95, 96, 99). Similarly, Th primed with free lambda 2T952 did not respond to a boost with free lambda 2(315). Thus, BALB/c lambda 2(315)-specific Th recognize an idiotope that depends on some or all of the residues at positions 94, 95, 96 and 99. Furthermore, free lambda 2T952 contains an idiotope immunogenic to Th that depends on some or all of residues 38, 94, 95, 96 and 99. Th recognition of the free lambda 2T952 idiotope was quenched upon H + L chain assembly because Th elicited by free lambda 2T952 did not respond to a boost with the complete T952 myeloma protein. In contrast to the lack of Th cell cross-reactivity, some of the antisera from BALB/c mice immunized with free lambda 2T952 cross-reacted with free lambda 2(315), free lambda lJ558 and free lambda 3CBPC49 but not with free kappa W3129 or polyclonal L chains. The H chain of T952 (alpha, kappa 2) myeloma protein was abnormally short (Mr = 48 000) and T952 existed as a halfmere probably due to this H chain deletion. Furthermore, H and L chains were disulfide bonded to each other.

Cellular cytotoxicity to membrane-associated insulin in an autologous system

A method is described for the measurement of T-cell cytotoxicity to purified preparations of insulin, their high molecular weight fractions and C-peptide derivatives. The technique assesses cellular cytotoxicity to membrane associated insulin in an autologous system. Peripheral blood lymphocytes from 19 type 1 diabetic patients were stimulated in vitro for 6 days with the pharmaceutical preparation(s) used therapeutically. At the end of this period, they were set up in a 4-h cytotoxicity assay against 51Cr labelled PHA blast transformed lymphocytes in the presence of therapeutic insulin, monocomponent insulin, B-component or C-peptide. The results presented here demonstrate cytotoxicity to insulin B-component in diabetic patients who have received pork insulin for 2-6 years. The possible reasons for this finding are discussed.

Determinant-specific regulation of T helper cell responses to murine lambda light chains by both H-2 and non-H-2 genes

Previous work has revealed that the T helper cell (Th) responses to an antigenic determinant of V lambda 2(315) (called lambda 2.1) is regulated by both H-2 and non-H-2 genes. In the present study this was confirmed and extended to two other determinants, one shared between free lambda 2(315) and lambda 1(J558) (called lambda 2.2) and one unique for free lambda 1(J558) (called lambda 1.1). H-2 genes regulate the responses to the latter determinants, because BALB.B (H-2b) mice were low responders and BALB/c (H-2d) mice were high responders. Thus, the H-2d haplotype on BALB/c background was associated with high responder status. However, when the H-2d haplotype was examined on other genetic backgrounds than BALB/c, the animals could be classified as either intermediate or low responders, depending upon the non-H-2 background. This demonstrated that non-H-2 genes also influenced Th responses. Furthermore, C3H-H-2o, DBA/2 and B10.D2 mice (all H-2d) responded to only one (lambda 2.1) but not the other (lambda 2.2) of two determinants physically linked on the same polypeptide chain (lambda 2(315)). This indicated that the non-H-2 gene effect is capable of fine discrimination, i.e. the non-H-2 gene-mediated low responder phenotype may at least in part be due to failure of recognition of certain antigenic sites, like the H-2-linked Ir-gene defect. F1 hybrids responded to the same determinants as their parental strains; e.g., the BALB/c non-H-2 background exerted a dominant influence over the low responder background of C3H, B10 and DBA/2 strains.

Magnitude of response of histocompatibility-restricted T-cell clones is a function of the product of the concentrations of antigen and Ia molecules

The activation of specific T-cell clones by antigens is dependent upon the corecognition of restriction elements expressed on antigen-presenting cells (APC). For clones that respond by proliferation and lymphokine production, the restriction element is usually an Ia (I-region-associated) molecule. We show here that the magnitude of the proliferative response of such clones is a function of the product of antigen concentration and the number of Ia molecules expressed on APC. This conclusion was reached through the study of antigen concentration-response curves of T-cell clones specific for pigeon cytochrome c. These curves are characterized by a peak in thymidine incorporation, followed by a decrease in the magnitude of the response as antigen concentrations are increased. The decline in response at high concentrations was not the consequence of the emergence of suppressor cells in the APC population, as it was observed when cells of a cloned B-cell hybridoma line were used to present pigeon cytochrome c to these T-cell clones. The critical role of both antigen concentration and the number of Ia molecules on the APC in determining the magnitude of proliferation was demonstrated in several ways. (i) An inverse relationship was observed between the antigen concentration required for maximum proliferation and the number of APC present in culture. At high antigen concentrations, which caused responses less than maximum, reducing the number of APC actually increased the magnitude of the antigen-induced proliferation. (ii) Decreasing the number of relevant Ia molecules per APC (i.e., as in F1 hybrids) resulted in the requirement for an increased antigen concentration for maximal response and in enhanced proliferation at high antigen concentrations. (iii) In the presence of anti-Ia antibody, higher concentrations of antigen were required for maximal response; at high antigen concentrations, proliferation was enhanced in the presence of a monoclonal anti-Ia antibody directed against the Ia restriction element.

In vitro lymphocyte proliferation response to therapeutic insulin components. Evidence for genetic control by the human major histocompatibility complex

Genes in the major histocompatibility complex of mice and guinea pigs control immunologic responsiveness to insulins from other animal species. In order to determine if similar genetic control exists in man, we have examined lymphocyte proliferation responses to components of therapeutic insulins by employing lymphocytes from diabetic patients that receive insulin. Distinct groups of individuals demonstrated positive lymphocyte proliferative responses to beef insulin, beef and pork insulin, beef proinsulin, pork proinsulin, and protamine. Lymphocytes from the patient population were typed for the HLA-A, B, C, and DR antigens. An increased frequency of certain HLA antigens was found in those individuals that responded to the following therapeutic insulin components: beef, HLA-DR4; beef and pork, HLA-DR3; beef proinsulin, HLA-BW4, CW2, CW5, DR2, and DR5; protamine, HLA-CW3, CW5, and DR7. The results demonstrate that the human immune system recognized the structural differences between human and beef and/or pork insulin. These differences are two amino acids in the A chain, alpha loop, of beef insulin and the single terminal amino acid, alanine, which is common to pork and beef insulins. Positive responses to both beef proinsulin and pork proinsulin demonstrated the capability of restricted recognition of more complex proteins represented by the C-peptide in these insulin preparations. Lymphocyte proliferative responses to protamine were also restricted, which suggests a genetic control to this antigen. The association of these responses with HLA alloantigens strongly suggests that genes within the human major histocompatibility complex control recognition and lymphocyte response to therapeutic insulin components.

Different repertoires of mouse T cells for bovine insulin presented by syngeneic and allogeneic cells

Splenic T cells were primed, after removal of alloreactive cells, to beef insulin on allogeneic antigen-presenting cells (APC). The fine specificity of in vitro secondary response was tested in combinations H-2b (responder) T cell-H-2k (nonresponder) APC, and vice versa, using separated chains of beef and pork insulin. The response in both combinations exhibited identical specificity patterns demonstrating that both responder and nonresponder APC could present the same array of insulin epitopes to allogeneic T cells. The determinants presented to allogeneic T cells include the A-chain loop epitope and the B-chain determinant(s) that were found to be immunogenic for H-2b and H-2d T cells, respectively, in the context of syngeneic major histocompatibility complex (HC) molecules. In addition, minor determinants were detected in the A chain outside the loop that are not immunogenic in syngeneic T cell-APC combinations. Inhibition of T cell proliferation with monoclonal antibodies has shown that class II MHC molecules of the nonresponder (Ak alpha Ak beta, Ek alpha Ek beta) as well as those of the responder APC (Ab alpha Ab beta) are equally capable of presenting virtually all insulin epitopes recognizable by T cells. The data, therefore, demonstrate that the selective recognition of different insulin epitopes observed in syngeneic or semisyngeneic T cell-APC combinations does not result from determinant selection at the level of APC.

Hapten-reactive inducer T cells. I. Definition of two classes of hapten-specific inducer cells

Hapten-reactive inducer T cell clones can be divided into two groups based on their activation specificity. The first and largest group is conjugate specific. These clones are activated only by hapten coupled to the same carrier protein used for in vitro selection. The second group, which is quite rare, is hapten specific. Clones of this type are activated by hapten coupled to all foreign and autologus proteins tested. Both types of clones corecognize soluble antigen in association with products of the I-A locus. The hapten-specific cells were used to analyze the molecular basis of I-A vs. I-E gene control. The physiologic significance of hapten- and carrier-specific inducer T cells in the response to foreign antigens and autoantigens is discussed.

Recognition of lambda 1 and lambda 2 murine light chains by carrier-specific isologous T helper cells; effect of L-H chain assembly

Previous studies from this laboratory have revealed an antigenic site located on the variable domain of the lambda 2 light chain of BALB/c myeloma protein 315 (the V lambda 2(315) site). This site is recognized by conventional carrier-specific T helper cells (Th) of BALB/c mice and is expressed on both the free and assembled V lambda 2(315) domain. The present work defines two new antigenic sites associated with murine lambda chains. The first site was associated with free lambda 1-chain of myeloma protein J558. It was recognized by splenic Th from animals that had been primed with free lambda 1J558 in complete Freund's adjuvant; when transferred to irradiated animals the primed Th responded to a boost with (4-hydroxy-5-iodo-3-nitro-phenyl)acetate (NIP)-free lambda 1J558 in saline, but did not respond to NIP-complete J558 or NIP-free lambda 2(315). Priming with complete J558 failed to elicit Th that responded to NIP-free lambda 1J558. This determinant was therefore only expressed on the free (as opposed to the assembled) form of lambda 1J558, and it was not shared with free lambda 2(315). The second antigenic site was shared between free lambda 1J558 and free lambda 2(315). It was defined by free lambda 2(315)-primed Th which responded to a boost with NIP-free lambda 1J558. Since priming with free lambda 1J558 did not elicit Th that recognized NIP-free lambda 2(315), the cross-reaction was undirectional. The free lambda 2(315)-primed Th failed to respond to the complete J558, and M315-primed Th failed to respond to NIP-free lambda 1J558, indicating that the second (cross-reactive) antigenic site, like the first, was only expressed on free lambda chains. Completely reduced and alkylated (unfolded) free lambda 1J558 and free lambda 2(315) chains elicited Th that recognized native (folded) free chains. Thus, free lambda 1J558 bears two antigenic determinants recognized by Th, one private and a second shared with free lambda 2(315). Lambda 2(315) also bears two determinants, a cross-reactive one on free lambda 2(315) shared with free lambda 1J558, and a private one located on the V lambda 2(315) domain of the complete M315. The discussion is focused on possible explanations for the quenching of the two new lambda chain determinants upon light-heavy chain assembly and why, by contrast, the private V lambda 2(315) site is maintained in the complete M315.

Antigen-presenting cells from nonresponder strain 2 guinea pigs are fully competent to present bovine insulin B chain to responder strain 13 T cells. Evidence against a determinant selection model and in favor of a clonal deletion model of immune response gene function

To test directly the determinant selection hypothesis of immune response gene function, we primed strain 13 T lymphocytes in vitro with allogeneic bovine insulin pulsed strain 2 macrophages. Strain 2 macrophages were found to be fully competent to present bovine insulin B chain to strain 13 T cells despite the fact that strain 2 guinea pigs are normally totally unresponsive to this antigen. These results are incompatible with a strict interpretation of the determinant selection hypothesis, which would have predicted that strain 2 macrophages would have been restricted to the presentation of A chain loop determinants. In addition, a comparison of the reactivity profiles of self-Ia- and allo-Ia-restricted strain 13 T cells to a series of synthetic B chain peptide fragments revealed that the allo-Ia-restricted populations could be activated by autologous guinea pig insulin. Taken together, these observations strongly suggest that the clonal deletion of self-reactive cells is likely to be I region restricted and that nonresponsiveness to any protein antigen may result from a restriction in the T cell repertoire that is generated during ontogeny by a clonal deletion mechanism of tolerance to self.

Analysis of cells of the mononuclear phagocyte series in experimental mycobacterial granulomas by monoclonal antibodies

Two distinct types of granulomas were produced in the draining lymph nodes by immunizing guinea pigs with Mycobacterium bovis BCG or Mycobacterium leprae, as reported earlier (Narayanan et al., J. Pathol. 134:253-265, 1981). In the BCG-induced granuloma there is successful containment, killing, and degradation of the organisms with the presence of epithelioid cells and fibrosis. M. leprae, on the other hand, induces a granuloma where there is an absence of organization of the cells, failure to completely degrade the organisms, absence of epithelioid cells, and minimal fibrosis. By using a macrophage-specific monoclonal antibody and an anti-Ia monoclonal antibody and applying the immunoperoxidase, immunofluorescence, and fluorescence-activated cell sorter analysis techniques, the epithelioid cells of the BCG granuloma were found to have macrophage-specific antigen, but not detectable amounts of Ia antigen. This suggests that these cells have a close relationship to other cells of the mononuclear phagocyte series with which they share a common antigen. The absence of Ia antigen, on the other hand, suggests that epithelioid cells may not be involved in antigen presentation or other accessory cell functions where the presence of Ia antigen is crucial. The macrophages in the M. leprae-induced granuloma expressed both macrophage-specific and Ia antigens.

Molecular events in the processing of avidin by antigen-presenting cells (APC). II. Identical processing by APC of H-2 high- and low-responder mouse strains

The differences between the immune response (Ir) phenotypes of H-2 gene-controlled high- and low-responder mice have been attributed to events occurring at the interaction between antigen-presenting cells (APC) and lymphocytes. To investigate this interaction we undertook a study of molecular events in the processing of avidin, a molecule whose uniquely strong affinity for binding to biotin renders it traceable at very low concentrations, and a molecule to which the T-lymphocyte immune response is controlled by Ir genes. In this paper we describe the generation of processed avidin by APC and characterize it biochemically and immunologically. We found that APC of H-2 genetically high- and low-responder mice were indistinguishable in their capacity to generate immunogenic processed avidin (PA). Immunogenic PA differed from native avidin in size and carbohydrate moieties, but preserved its capacity to bind biotin, and was 1000-fold more efficient than NA as an immunogen for primed T lymphocytes. Primed T lymphocytes appeared to recognize PA that was conformationally intact. Highly immunogenic PA was not H-2 restricted. Thus, differences in the Ir phenotype of the response to avidin could not be attributed to determinant selection by APC.

Mechanism responsible for the induction of I-J restriction on TS3 suppressor cells

The mechanisms responsible for the induction of I-J restrictions on third-order suppressor T cells (TS3) were analyzed. The I-J phenotype of the antigen-coupled cells used for priming restricted the specificity of the TS3 population. Thus, TS3 cells were only generated after priming with antigen-coupled I-J homologous cells. Identity at the I-JM (and I-E) subregions was sufficient for TS3 induction. Furthermore, priming of H-2 heterozygous mice with antigen-coupled parental cells generated TS3 that were restricted to the parental haplotype used for priming. The splenic cell population responsible for antigen presentation and induction of TS3 cells was fractionated. The cells involved in antigen presentation were found in the splenic adherent population and were absent in the fraction containing splenic nonadherent T and B cells. The subsequent activation and interaction of TS3 cells is also restricted by genes in the H-2 complex. The results are discussed in terms of a general mechanism responsible for the induction of restrictions in T helper and TS3 cells.

The use of unideterminant fragments of ferredoxin in the genetic mapping of determinant specificity of the immune response

The ferredoxin (Fd) molecule is a small non-mammalian immunogenic protein containing 55 amino acid residues with only two major antigenic determinants located with the NH2-terminal heptapeptide and the COOH-terminal pentapeptide. Selective enzyme cleavages of Fd with either trypsin or carboxypeptidase A result in the inactivation of the antigenic determinants by the removal of a tripeptide at the NH2-terminal and two amino acid residues at the COOH-terminal, effectively leaving 52 and 53 amino acid fragments respectively, each containing a single antigenic determinant. Fd digested with both enzymes yielded a 50 amino acid peptide with both determinants inactivated. Purity of these digests was assessed using monoclonal antibodies in standard and antigen-blocking ELISAs. The doubly digested peptide had virtually no reactivity with anti-Fd sera, reconfirming that the central cysteine-rich region is serologically silent. It was found that the sum of the reactivities of the N- and C-determinant-bearing peptides as equal to that of the native Fd and that the ratio of the reactivities could be used to assess determinant selectivity in the response to Fd in congenic recombinant strains of mice. This method was used in mapping the determinant selectivity in the antibody response to the MHC of mice to the left of the I-B subregion. Use of the B10.HTT strain indicated that separate genes mapping to the same subregion code for the magnitude of the antibody response and the determinant selectivity of the response.