Development Of Self-tolerance Research Articles

Analysis of the Development of B-Cell Precursors in Day Three Incubated Chicken Embryos

Background: In mammals, birds, and amphibians, the B lineage of lymphoid cells first arise during embryogenesis and are distinguished by their capacity to produce immunoglobulin. For the purpose of researching the development of the B-cell repertoire and the development of self-tolerance, these early B-cell precursors are of utmost importance. The genetic and/or microenvironmental variables that control the beginning of immunoglobulin synthesis in embryonic haemopoietic cells are, however, poorly understood. Purpose: The ontogeny of B-cell precursors in chicken embryos from day three of incubation was examined in this work. Research methods: The terms "ontogeny, B-cell, precursors, chicken embryos, incubation" were used in a thorough literature search in the PubMed, NCBI, and Google Scholar databases. After all articles were picked based on the inclusion and exclusion criteria, 38 papers that satisfied the criteria for inclusion were collected. Result: The study's findings show that clglarge basophilic hemopoietic stem cells and cIg+ small lymphoid B-cell precursors are two types of migrant cells that appear to enter the embryonic bursa of Fabricius. Hence, B lymphopoiesis does not only take place in the bursa of Fabricius in the avian embryo. Although the yolk sac and the hemopoietic tissues around the dorsal aorta are strong candidates, the identity of the extra-bursal location remains unknown. Conclusion: Hence, general haemopoietic organs may serve as the initial site of B lymphopoiesis in both birds and mammals. Only later in the course of avian development do the bursal follicles become accessible and take over.

Inhibitors of the PD-1/PD-L1 Pathway Can Mobilize the Immune System: An Innovative Potential Therapy for Cancer and Chronic Infections.

Title: Compounds Useful as Immunomodulators Patent Application Number: WO 2015/034820 Al Publication date: 12 March 2015 Priority Application: US 61/873,398 Priority date: 4 September 2013 Inventors: Chupak, L. S.; Zheng, X. Assignee Company: Bristol-Myers Squibb Company; Route 206 and Province Line Road, Princeton, NJ 08543, USA Disease Area: Cancer and infectious diseases such as hepatitis C Biological Target: PD-1/PD-L1 pathway Summary: The invention in this patent application relates to compounds represented generally by formula (I), which possess activities as inhibitors of the PD-1/PD-L1 interactions and therefore may potentially be useful in the treatment of cancer as well as infectious diseases such as hepatitis C. T-cells or lymphocytes are white blood cells that are essential for the immune system. They are capable of searching for and destroying infected and/or cancerous cells. Programmed death protein 1 (PD-1), also known as cluster of differentiation 279 (CD279), is a cell surface receptor on the T cells. The binding of PD-1 with either one of its two known ligands, programmed death-ligands 1 and 2 (PD-Ll or PD-L2), has been shown to suppress T cell receptor activating signals. The PD-l/PD-L1 pathway down regulates the immune responses during resolution of an infection or a tumor, or during the development of self-tolerance. Studies have shown that blocking the PD-1/PD-Ll interactions using antibodies to the PD-Ll protein restores and augments T cell activation in many systems. A recent study has shown that therapy with a monoclonal antibody to PD-Ll benefited patients with advanced cancer. Blocking the PD-1/PD-Ll pathway by monoclonal antibodies enhanced the immune response and resulted in tumor rejection or control of infection in preclinical animal models. It can also restore in vitro antigen-specific functionality to T cells fromHIV,HCV, or HBV patients. Other reports show that blocking the PD-1/PD-L1 interaction enhances T cell activity in chronic infection systems andmay augment therapeutic immune response to a number of histologically distinct tumors. It also enhances the responses to vaccination, including therapeutic vaccination in chronic infections. The term “T cell exhaustion” describes the conditions of the T cells resulting from chronic antigen stimulation that occurs during chronic infections and tumor disease. These cells are characterized by elevated levels of PD-1 and dysfunctional activities toward chronic antigen. Targeting PD-L1 protein to inhibit the PD-1/PD-L1 pathway has been shown to restore antigen-specific T cell immune functions in vitro and in vivo, including enhanced responses to vaccination in the setting of tumor or chronic infection. The inhibition of the interaction of PD-Ll with PD-1 is thus a viable and promising therapeutic target for the treatment of cancer and/or chronic infections. The invention in this patent application presents compounds with activities as inhibitors of the PD-1/PD-Ll protein/protein interactions. These compounds may potentially be useful therapy to enhance immunity in patients with cancer or chronic infections.

Autoimmune Polyglandular Syndromes: Interplay Between the Immune and the Endocrine Systems Leading to a Diverse Set of Clinical Diseases and New Insights into Immune Regulation

During the last 50 years, three major classes of autoimmune polyglandular syndromes (APSs) have been defined, and their characteristics and heritability have been delineated. Simultaneously, studies of the immunologic bases of these syndromes provided fundamental information in understanding immune regulation. Genetic analyses of patients and their families with APS type 1 (autoimmune polyendocrinopathy candidiasis, ectodermal dystrophy) identified the autoimmune regulator (AIRE) gene, which drives the expression of peripheral tissue-specific antigens in thymic cells and is critical in the development of self-tolerance. Mutations in this gene cause APS type 1. In contrast, studies in APS type 2 have been instrumental in understanding the role of human leukocyte antigen type II and related molecules in the pathogenesis of polygenetic autoimmune diseases such as type 1A diabetes. Immune dysfunction polyendocrinopathy, enteropathy, X-linked syndrome, which is caused by mutations in the forkhead box P3 gene, has been a model for studying regulatory T cell biology. The APSs epitomize the synergies that the merger of clinical and basic science can achieve. This is the environment that George Eisenbarth was able to create at the Barbara Davis Center for Diabetes.

Negative Selection Assay Based on Stimulation of T Cell Receptor Transgenic Thymocytes with Peptide-MHC Tetramers

Thymocyte negative selection is a requirement for the development of self tolerance. Although it is possible to assay the induction of cell death in thymocytes in vitro using antibody cross-linking, this stimulus is much stronger than the normal range of T cell receptor ligands that could be encountered during normal development. Signaling in thymocytes is finely balanced between positive and negative selection stimuli, where a negative selecting ligand can be only marginally higher affinity than a positive selecting ligand. We have therefore developed an assay for the induction of negative selection that can distinguish such cases, and that is amenable to high-throughput analysis. The assay is based on the induction of activated caspase 3 in thymocytes expressing a defined T cell receptor, after stimulation with MHC-peptide tetramers in vitro for 24 hours or less.

Crosstalk between Nitric Oxide and T helper cells

Crosstalk between Nitric Oxide and T helper cells

Means to an end: apoptosis and other cell death mechanisms

One million cells in our bodies die every secondthey commit suicide by a mechanism known as apoptosis. Apoptosis is essential for survival of the body as a whole and has critical roles in various developmental processes and the immune system. In Means To An End, Douglas Green provides a clear and comprehensive view of apoptosis and other cell death mechanisms. Taking a bottom-up approach, he starts with the enzymes that perform the execution process (a family of proteases termed caspases) and examines their cellular targets and the ways in which they are activated. He then looks at the molecular machinery that links signals that cause cell death to caspases, emphasizing the importance of the BCL-2 family of proteins and the role of cytochrome c released from mitochondria. The final stage of the process, phagocytic removal of dead or dying cells, is also covered. Green outlines the roles of apoptosis and death mechanisms such as necrosis in embryogenesis, neuronal selection, and the development of self-tolerance in the immune system. In addition, he explains how cell death defends the body against cancer and traces the evolutionary origins of the apoptosis machinery back over a billion years. The book is thus of great use to all biologists interested in how cells function in the context of multicellular organisms and will appeal to everyone from undergraduates encountering the topic for the first time to researchers actively working in the field.

Thymus microenvironment in human primary immunodeficiency diseases

Severe combined immunodeficiencies represent a heterogeneous group of genetic disorders affecting genes of both early and late steps in lymphocytes development, a process tightly controlled by thymic epithelial cells. Detailed analysis of thymic morphology aids to the assessment of the severity of the immune disorder and may be critical to the understanding of the role of the genetic defects in the pathophysiology of these diseases. In this review, we highlight recent advancements in the characterization of the thymic microenvironment in primary immunodeficiencies. Crosstalk between thymocytes and thymic epithelial cells is essential to preserve thymic architecture and function, and therefore to promote T-cell maturation and development of self-tolerance. Early severe defects in T-cell development result in profound abnormalities of thymic epithelial cells differentiation with loss of AIRE expression and severe reduction of thymic dendritic and T-regulatory cells. Differently, later defects in T-cell development that are permissive for normal thymocytes development allow cortico-medullary differentiation with partially preserved AIRE expression and dendritic/T-regulatory cells distribution. Hypomorphic mutations in the same genes partially permissive to T-cell development may result in a more complex phenotype with immunodysreactivity and peculiar thymic alterations. Although the molecular and genetic bases of primary immunodeficiencies directly aid to both diagnosis and management of the patients, the detailed analysis of thymic morphology critically contributes to unveil the pathophysiology of these diseases.

Mounting Evidence for Vitamin D as an Environmental Factor Affecting Autoimmune Disease Prevalence

Low vitamin D status has been implicated in the etiology of autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, insulin-dependent diabetes mellitus, and inflammatory bowel disease. The optimal level of vitamin D intake required to support optimal immune function is not known but is likely to be at least that required for healthy bones. Experimentally, vitamin D deficiency results in the increased incidence of autoimmune disease. Mechanistically, the data point to a role for vitamin D in the development of self-tolerance. The vitamin D hormone (1,25-dihydroxy vitamin D(3)) regulates T helper cell (Th1) and dendritic cell function while inducing regulatory T-cell function. The net result is a decrease in the Th1-driven autoimmune response and decreased severity of symptoms. This review discusses the accumulating evidence pointing to a link between vitamin D and autoimmunity. Increased vitamin D intakes might decrease the incidence and severity of autoimmune diseases and the rate of bone fracture.

Normal thymic architecture and negative selection are associated with Aire expression, the gene defective in the autoimmune-polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED).

T cell development is tightly controlled by thymic stromal cells. Alterations in stromal architecture affect T cell maturation and the development of self-tolerance. The monogenic autoimmune syndrome APECED (autoimmune-polyendocrinopathy-candidiasis-ectodermal dystrophy) is characterized by the loss of self-tolerance to multiple organs. Although mutations in the autoimmune regulator (AIRE) gene are responsible for this disease, the function of AIRE is not known. Here we report on the spatial and temporal pattern of murine Aire expression during thymic ontogeny and T cell selection. Early during development, thymic Aire transcription is critically dependent on RelB and occurs in epithelial cells in response to lymphocyte-mediated signals. In adult tissue, Aire expression is confined to the medulla and the corticomedullary junction, where it is modulated by thymocytes undergoing negative selection. Aire may determine thymic stromal organization and with it the induction of self-tolerance.

Cellular basis of long-term organ transplant acceptance: Pivotal role of intrathymic clonal deletion and thymic dependence of bone marrow microchimerism-associated tolerance

Long-term acceptance of MHC-incompatible organ allografts without chronic immunosuppressive therapy has been achieved in experimental animals. There are also reports, mainly in liver transplant, of patients who after complete withdrawal of immunosuppressants still have a functioning graft. It has been proposed that organ transplant implies a migratory flux of donor “passenger” leukocytes out of the graft into the recipient tissues or organs, serving to establish a persistent condition of “microchimerism,” and being a tolerogenic precursor of chimeric cells. Although there is evidence that the same migratory mechanisms apply to all organ grafts, migration of passenger leukocytes is less in organs other than the liver, such as the kidney and heart. To enhance the acceptance of organs less tolerogenic than the liver, perioperative infusion of donor bone marrow has been attempted to increase the migration of donor leukocytes of bone marrow origin. It has been suggested that such peripheral donor microchimerism is not only associated with long-term acceptance of the organ graft but that it plays an active role in induction and maintenance of unresponsiveness. However, the intimate mechanisms(s) responsible for prolonged organ survival in this setting remains speculative. Experimental evidence that the thymus plays the major role in the development of self-tolerance and is also critical in the induction of acquired tolerance to exogenous antigens has focussed the attention on the intrathymic events that lead to donor-specific unresponsiveness to allograft. Data are available showing that after direct intrathymic injection of donor cells, clonal deletion of maturing host thymocytes occurs and is the major mechanism in the induction of donor-specific tolerance. The central role of the thymus in transplant tolerance is also supported by more recent findings that in mixed allogeneic bone marrow chimeras in mice with a nonmyeloablative conditioning regimen, migration of donor bone marrow-derived dendritic cells to the thymus serves to negatively select newly developing host T cells. Therefore, the peripheral T-cell component would be devoid of alloreactive population. Thus, lifelong intrathymic clonal deletion is the only significant mechanism involved in the maintenance of donor-specific T- cell tolerance that would allow the subsequent vascularized organ from the same donor to survive indefinitely. (Am J Kidney Dis 1998 Feb;31(2):197-212)

Acquired transplant tolerance.

Increasing the acceptance rate of organs is the central goal of transplantation research. Long-term survival of vascularized organs without chronic immunosuppressive therapy has been achieved in experimental animals. In humans, the possibility of achieving immunological tolerance and a drug-free state has been reported occasionally in patients who after withdrawal of immunosuppressants because of major toxicity still carry a functioning graft. It has been proposed that organ transplant implies a migratory flux of donor 'passenger' leukocytes out of the graft into the recipient tissue or organs, to establish a persistent condition of 'microchimerism'. Although there is evidence that the same migratory mechanisms apply to all organ grafts, migration of 'passenger' leukocytes is less in kidney and heart than in liver. To enhance the acceptance of organs less tolerogenic than liver, perioperative infusion of donor bone marrow has been attempted to increase the donor 'passenger' leukocyte load. It has been suggested that the established microchimerism is not only associated with long-term acceptance of the graft, but it also plays an active role in induction and maintenance of donor-specific unresponsiveness. However, the intimate mechanism(s) responsible for prolonged graft survival in this setting remain speculative. Experimental evidence is also available that the thymus plays a major role in the development of self-tolerance and is critical in the induction of acquired tolerance to exogenous antigens. It has been reported that after intrathymic injection of donor cells clonal deletion of maturing thymocytes occurs and is the major mechanism in the induction of donor-specific tolerance, since peripheral T-cell component would be devoid of alloreactive population. Studies are warranted in the near future to explore whether the thymus technique can be employed to prolong survival or induce tolerance to allograft in humans. An interesting novel strategy for transplant tolerance is also the oral administration of alloantigens, which has been recently applied to the cardiac transplant model in rat. All these approaches will have a major impact in the near future on transplant medicine, opening new perspectives to obtain indefinite graft survival.

The failure of a combination of thyroid and thymus allografts to prevent the development of autoimmunity in thyroidectomized foetal lambs.

Previous experiments have shown that surgical removal of the thyroid gland from the foetal lamb one third of the way through gestation prevents the development of self tolerance towards thyroid-specific determinants. As a result, self thyroid tissue reintroduced into the foetal lamb after maturation of the immune system is not recognized as self and is subject to autoimmune thyroiditis. Furthermore, the transplantation of a thyroid allograft into a foetal lamb immediately after extirpation of its own gland has been shown not to direct the development of self tolerance to thyroid determinants. In the present experiment, foetal lambs were submitted to removal of the entire thyroid gland and the majority of the thymus gland, at 51-54 days of gestation followed by the immediate implantation of thyroid and thymic allografts. The additional implantation of thymus tissue did not affect the previously observed incapacity of a thyroid allograft to facilitate induction of organ-specific tolerance by the thyroid allograft. It was inferred that any T lymphocytes generated within the thymus graft and tolerant of thyroid-specific determinants had not had the capacity to suppress the activity of autoreactive cells generated in the host's thymus.

Arsenite induced sensitization and self-tolerance of Reuber H35 hepatoma cells.

Our data show that a short incubation with arsenite (30-300 microM) induces a biphasic change in cellular sensitivity towards a second exposure to arsenite. A transient sensitization was followed by the development of self-tolerance. Sensitization was measured using the step-down protocol; i.e., application of a high dose of arsenite pretreatment (100 or 300 microM) followed immediately by incubation in a low dose of arsenite (1-30 microM), with extensive rinsing in between. Whereas no effect of 1 and 3 microM on cellular survival is observed without pretreatment, a large decrease in cell survival can be established when these low doses of arsenite are applied immediately after a 1 hr pretreatment with 100 or 300 microM arsenite. According to the step-down protocol, a high dose of toxic compounds is applied and is followed by prolonged incubation in a lower concentration of the initial toxic compound. This might be a more accurate model for studying the effects of toxic insults on cells and organisms in the manner in which they occur in their natural environment. The level of tolerance was determined by a 1 hr test treatment with 300 microM arsenite applied at different times after pretreatment. Using this fractionated treatment protocol, it was established that tolerance increases with the increasing time intervals between the sodium arsenite treatments, during the 6 hr studied. These observations suggest that sensitization gradually decreases, whereas tolerance develops. Furthermore, our data indicate that the condition of pretreatment determines the extent to which the early sensitivity increases, as well as the development of tolerance later on. A relatively high arsenite concentration leads to more sensitized cells, which are transformed into more tolerant cells in comparison with the effect of a lower arsenite concentration.

Linkage of Faulty Major Histocompatibility Complex Class I to Autoimmune Diabetes

Pancreatic islet cells are the targets of an autoimmune response in type I diabetes. In the nonobese diabetic (NOD) mouse model of autoimmune diabetes, expression of major histocompatibility complex (MHC) class I proteins was inversely correlated with diabetes; in this mouse a mutation in the MHC class II-linked gene for the putative MHC class I peptide transporter was also present. Mice deficient in MHC class I expression because they do not produce beta 2-microglobulin also developed late onset autoimmune diabetes. In cells from humans with type I diabetes expression of MHC class I was decreased; subsets of prediabetics categorized as most likely to become hyperglycemic also had low MHC class I. T cell responses to self antigens are faulty in diabetics. In sets of genetically identical twins that are discordant for diabetes, the defect appeared to reside with the antigen presenting cell. Thus, a lack of surface MHC class I protein is associated with autoimmune diabetes; the concomitant defect in antigen presentation may impair the development of self tolerance, which could result in autoimmune disease.

Self-reactive T cells in murine lupus: Analysis of genetic contributions and development of self-tolerance

Our understanding of the immune mechanisms that lead to systemic lupus erythematosus has been greatly advanced by the availability of murine models which display both serological and clinical features of the human disease. Studies have demonstrated that CD4 + T cells are required for the full expression of disease in these mice. (NZB × NZF)F 1 mice exhibit a lupus-like disease (elevated levels of IgG antinuclear antibodies and a fatal glomerulonephritis) that is not characteristic of either parent. At least three gene loci have been identified in NZW mice that could potentially contribute to a T cell-dependent autoimmune disease, including the T cell receptor α- and β-chain gene complexes and the major histocompatibility complex (MHC). The NZW T cell receptor β-chain complex appeared to be particularly unusual in that the Cβ1, Dβ2, and Jβ2 gene segments have been deleted. However, an analysis of (NZB × NZW)F 1 × NZB backcross mice revealed no association of disease expression with the presence of this allele. There was also no correlation of disease incidence with the presence of the NZW T cell receptor α-chain allele. In contrast, nearly 90% of the backcross mice with the NZW MHC expressed severe autoimmune disease compared with 12% of the mice that did not carry this haplotype. Additional studies strongly suggested that the gene(s) within the NZW MHC is the only dominant NZW genetic contribution to F 1 disease. We also determined if self-reactive T cells are able to escape thymic tolerance in autoimmune New Zealand and MRL lpr lpr mice. In nonautoimmune mice expressing I-E, T cells utilizing Vβ17a and Vβ11 encoded domains have been shown to be clonally eliminated in the thymus. Similarly, Vβ8.1 + and Vβ6 + T cells are tolerized in nonautoimmune mice expressing Mls-1 a. These T cell subsets were quantitated in the lymph nodes and spleens of (NZB × NZW)F 1, (NZB × SWR)F 1, and MRL- lpr lpr mice before and after the development of lupus-like disease. The results indicate that peripheral T cells in these mice, including the massive CD4 −, CD8 − T cell population in lpr mice, have been modified by normal mechanisms of tolerance such that potential self-reactive Vβ specificities have been eliminated in the thymus.

Interception of the development of self tolerance in fetal lambs

Investigation of the nature of immunological self tolerance has usually relied upon experimental protocols in which the tolerant state is interrupted in mature animals with the production of autoimmune disease. While such research has improved the understanding of those processes operative in overt autoimmunity, it has not been informative in relation to events associated with the establishment of self tolerance. Any description of this state which is to be based on observation will necessitate the use of experimental systems that permit observation of animals during the development of self tolerance. The present experiment entailed intervention approximately one third of the way through the gestation period of fetal lambs. An earlier experiment had established that 54-day fetal lambs would accept allografts of adult skin. This indicated that the capacity to discriminate between self and non-self had not been acquired at that age. Fetuses at this stage of gestation were submitted to either partial or total removal of the thyroid gland. The excised tissue was then implanted in nude mice for periods of 5 to 9 weeks. It was subsequently replaced subcutaneously, either in the original donor or in another fetus at a comparable stage of gestation. At postmortem examination, several weeks later, self implants in lambs from which the thyroid gland had been completely removed displayed autoimmune thyroiditis of varying degrees of severity. However, self implants in partially thyroidectomized animals were uniformly free from autoimmune manifestations. This implied that these reactions had not been directed against contaminating murine tissues in the implants replaced in completely thyroidectomized lambs. All allogeneic implants were subject to vey heavy lymphocytic infiltration, usually with accompanying necrosis consistent with allograft rejection. This was taken as an indication that hypothyroid fetal lambs had become immunocompetent by the time of thyroid reimplantation. Spontaneous immunological reactivity against reimplanted self thyroid tissue by thyroidectomized lambs was interpreted as a failure to acquire the capacity for self recognition as a result of antigen deprivation.

Expression in transgenic mice of class I histocompatibility antigens controlled by the metallothionein promoter.

To study the effects of increased expression of major histocompatibility complex class I molecules on the development of self-tolerance, transgenic mice were produced that expressed the H-2Kb gene under the control of the metallothionein promoter. Administration of zinc enhanced transgene expression in liver, kidney and exocrine pancreas. No evidence suggestive of an autoimmune response was found in transgene-expressing tissues in mice otherwise allogeneic to H-2Kb. Despite this lack of responsiveness in vivo, T cells could be stimulated in vitro to lyse H-2Kb-bearing target cells. No infiltration was detected in transgenic mice after irradiation and reconstitution with bone marrow cells. When spleen cells were used for reconstitution, however, dense lymphocytic infiltration was seen, particularly in the portal tracts of the liver, and this was accompanied by piecemeal necrosis and apoptosis of periportal hepatocytes. This aggressive response progressively diminished with time, and by 12 weeks after reconstitution many of the portal tracts were free of infiltration while the others showed no accompanying necrosis. The picture at this stage was similar to that seen in chronic persistent hepatitis. These results suggest that, in addition to negative selection in the thymus, peripheral mechanisms not involving clonal deletion or permanent clonal anergy can prevent immune responses to self molecules.

Development of self-tolerance in normal mice. Appearance of suppressor cells that maintain adult self-tolerance follows the neonatal autoantibody response.

T cell populations from BALB/c mice at different ages were analyzed to determine when in development Ts cells specific for the anti-mouse RBC (MRBC) autoantibody response become activated. Previous studies have shown that adult CD8+ T cells actively suppress this autoimmune response and adult spleen cells depleted of CD8+ cells can generate an anti-MRBC response in culture with MRBC. The present results demonstrate that T cells from mice less than 1 wk of age do not suppress the in vitro anti-MRBC response of adult spleen cell populations depleted of CD8+ Ts cells. By 2 wk of age Ts cells are detectable in this anti-self response and reach adult levels by 3 wk of age. Non-specific "natural suppressor" cells normally present in neonatal spleen cell populations are unable to suppress this autoantibody response, although they are active in suppressing anti-SRBC responses in the same cultures. Before the appearance of Ts cells active in the anti-MRBC response, neonatal spleen cell populations can generate anti-MRBC antibody-forming cells, both spontaneously in vivo and in vitro. The in vitro anti-MRBC response of neonatal spleen cells was shown to be Ag driven and Ag specific. The ability of unfractionated spleen cells to generate this response in vitro declines with age and is relatively low by 3 wk. This decline in responsiveness occurs simultaneously with the appearance of suppression specific for the anti-MRBC response, suggesting that the two events may be causally related.

Induction of self-tolerance and enhanced stress protein synthesis in L-132 cells by cadmium chloride and by hyperthermia

The effect of heat shock or cadmium treatment on protein synthesis and cell survival in L-132 cells has been examined. After cadmium treatment, the synthesis of a polypeptide of Mr 68000 (P68) was greatly enhanced over that of untreated cells. Besides P68 the synthesis of another polypeptide of Mr 89000 (P89) was also enhanced in heat-shocked cells. Both heat shock and cadmium treatment induced self-tolerance. The kinetics of the synthesis of induced polypeptides correlated well with the development of self-tolerance. The patterns of peptide maps obtained after partial proteolytic digestion from P68 induced in cadmium-treated ana heat-shocked cells were virtually identical. However, neither heat-shocked cells did not confer cadmium tolerance nor did cadmium-treated cells induce thermotolerance.