The antigenic stimulus in transplantation immunity

Establishment of immune suppression by cancer cells in the tumor microenvironment

With the clinical success of immune checkpoint inhibitors (ICIs), cancer immunotherapy has become an important pillar of cancer treatment in various types of cancer. However, more than half of patients fail to respond to ICIs, even in combination, uncovering a limited window of clinical responses. Therefore, it is essential to develop more effective cancer immunotherapies and to define biomarkers for stratifying responders and nonresponders by exploring the immunological landscape in the tumor microenvironment (TME). It has become clear that differences in immune responses in the TME determine the clinical efficacy of cancer immunotherapies. Additionally, gene alterations in cancer cells contribute to the development of the immunological landscape, particularly immune suppression in the TME. Therefore, integrated analyses of immunological and genomic assays are key for understanding diverse immune suppressive mechanisms in the TME. Developing novel strategies to control immune suppression in the TME from the perspective of immunology and the cancer genome is crucial for effective cancer immunotherapy (immune-genome precision medicine).

The impact of inflammatory stress on hypothalamic kisspeptin neurons: Mechanisms underlying inflammation-associated infertility in humans and domestic animals

Inflammatory diseases attenuate reproductive functions in humans and domestic animals. Lipopolysaccharide (LPS), an endotoxin released by bacteria, is known to disrupt female reproductive functions in various inflammatory diseases. LPS administration has been used to elucidate the impact of pathophysiological activation of the immune system on reproduction. Hypothalamic kisspeptin neurons are the master regulators of mammalian reproduction, mediating direct stimulation of hypothalamic gonadotropin-releasing hormone (GnRH) release and consequent release of gonadotropins, such as luteinizing hormone (LH) and follicle-stimulating hormone from the pituitary. The discovery of kisspeptin neurons in the mammalian hypothalamus has drastically advanced our understanding of how inflammatory stress causes reproductive dysfunction in both humans and domestic animals. Inflammation-induced ovarian dysfunction could be caused, at least partly, by aberrant GnRH and LH secretion, which is regulated by kisspeptin signaling. In this review, we focus on the effects of LPS on hypothalamic kisspeptin neurons to outline the impact of inflammatory stress on neuroendocrine regulation of mammalian reproductive systems. First, we summarize the attenuation of female reproduction by LPS during inflammation and the effects of LPS on ovarian and pituitary function. Second, we outline the inhibitory effects of LPS on pulsatile- and surge-mode GnRH/LH release. Third, we discuss the LPS-responsive hypothalamic-pituitary-adrenal axis and hypothalamic neural systems in terms of the cytokine-mediated pathway and the possible direct action of LPS via its hypothalamic receptors. This article describes the impact of LPS on hypothalamic kisspeptin neurons and the possible mechanisms underlying LPS-mediated disruption of LH pulses/surge via kisspeptin neurons.

ABO-incompatible heart transplantation in children-a systematic review of current practice

Pediatric heart transplantation has significantly improved in the survival of children with cardiomyopathy and/or complex congenital heart defects. With the increasing number of children needing transplantation, there is a growing demand for the organ, making it harder to cope with the increasing number of children on the waiting list. One of the advances that helped reduce the waiting list mortality significantly is the ability to transplant children from donors with ABO incompatibility. Modification of perfusion abilities and management of donor organ improves outcome in this select population, making ABO-incompatible transplantation an attractive option in the wider armamentarium available for pushing boundaries in these children without impacting on outcomes.

Medawar's Paradox and Immune Mechanisms of Fetomaternal Tolerance

Brazilian-born British biologist Dr. Peter Medawar played an integral role in developing the concepts of immunologic rejection and tolerance, which led to him receiving the Nobel Prize "for the discovery of acquired immunologic tolerance" and eventually made organ transplantation a reality. However, at the time of his early work in tolerance, a paradox to his theories was brought to his attention; how was pregnancy possible? Pregnancy resembles organ transplantation in that the fetus, possessing paternal antigens, is a semi-allogeneic graft that can survive without immunosuppression for 9 months. To answer this question, Medawar proposed three hypotheses of how a mother supports her fetus in utero, now known as "Medawar's Paradox." The mechanisms that govern fetomaternal tolerance are still incompletely understood but may provide critical insight into how to achieve immune tolerance in organ transplantation. Here, we review current understanding of the immune factors responsible for fetomaternal tolerance during pregnancy and discuss the potential implications for advances in transplantation science.

The Neonatal Window of Opportunity: Setting the Stage for Life-Long Host-Microbial Interaction and Immune Homeostasis

The existence of a neonatal window was first highlighted by epidemiological studies that revealed the particular importance of this early time in life for the susceptibility to immune-mediated diseases in humans. Recently, the first animal studies emerged that present examples of early-life exposure-triggered persisting immune events, allowing a detailed analysis of the factors that define this particular time period. The enteric microbiota and the innate and adaptive immune system represent prime candidates that impact on the pathogenesis of immune-mediated diseases and are known to reach a lasting homeostatic equilibrium following a dynamic priming period after birth. In this review, we outline the postnatal establishment of the microbiota and maturation of the innate and adaptive immune system and discuss examples of early-life exposure-triggered immune-mediated diseases that start to shed light on the critical importance of the early postnatal period for life-long immune homeostasis.

ABO-incompatible heart transplantation

PURPOSE OF REVIEW

ABO-incompatible (ABOi) heart transplantation (HTx) in young children has evolved from an experimental approach to a standard allocation option in many countries. Clinical and immunological research in ABOi transplantation has revealed insight into the immature immune system and its role in superior graft acceptance in childhood and antigen-specific tolerance.

RECENT FINDINGS

Multicenter experience has confirmed equal actuarial survival, freedom from rejection, and graft vasculopathy comparing ABOi with ABO-compatible HTx. Observations of reduced antibody production and B-cell immunity toward the donor blood group have been confirmed in long-term follow-up. Mechanisms contributing to tolerance in this setting involve the interplay between B-cells and the complement system and the development of B-cell memory. Better characterization of the ABH polysaccharide antigens has improved diagnostic methods and clinical assessment of blood group antibodies. Boundaries regarding age, immune maturity, and therapeutic interventions to extend the applicability of ABOi HTx have been explored and resulted in data that may be useful for HTx patients beyond infancy and ABOi transplantation of other organs. Tolerance of ABH antigens possibly extends to HLA response.

SUMMARY

The review provides insight into the clinical evolution of ABOi HTx and associated immunologic discoveries. Current experiences and boundaries are discussed together with recent and potential future developments for utilization in other patient and age groups.

The role of glycans in immune evasion: the human fetoembryonic defence system hypothesis revisited

Emerging data suggest that mechanisms to evade the human immune system may be shared by the conceptus, tumour cells, persistent pathogens and viruses. It is therefore timely to revisit the human fetoembryonic defense system (Hu-FEDS) hypothesis that was proposed in two papers in the 1990s. The initial paper suggested that glycoconjugates expressed in the human reproductive system inhibited immune responses directed against gametes and the developing human by employing their carbohydrate sequences as functional groups. These glycoconjugates were proposed to block specific binding interactions and interact with lectins linked to signal transduction pathways that modulated immune cell functions. The second article suggested that aggressive tumour cells and persistent pathogens (HIV, H. pylori, schistosomes) either mimicked or acquired the same carbohydrate functional groups employed in this system to evade immune responses. This subterfuge enabled these pathogens and tumour cells to couple their survival to the human reproductive imperative. The Hu-FEDS model has been repeatedly tested since its inception. Data relevant to this model have also been obtained in other studies. Herein, the Hu-FEDS hypothesis is revisited in the context of these more recent findings. Far more supportive evidence for this model now exists than when it was first proposed, and many of the original predictions have been validated. This type of subterfuge by pathogens and tumour cells likely applies to all sexually reproducing metazoans that must protect their gametes from immune responses. Intervention in these pathological states will likely remain problematic until this system of immune evasion is fully understood and appreciated.

The role of BCR isotype in B-cell development and activation

The development and function of B lymphocytes critically depend on the non-germline B-cell antigen receptor (BCR). In addition to the diverse antigen-recognition regions, whose coding sequences are generated by the somatic DNA rearrangement, the variety of the constant domains of the Heavy Chain (HC) portion contributes to the multiplicity of the BCR types. The functions of particular classes of the HC, particularly in the context of the membrane BCR, are not completely understood. The expression of the various classes of the HC correlates with the distinct stages of B-cell development, types of B-cell subsets, and their effector functions. In this chapter, we summarize and discuss the accumulated knowledge on the role of the μ, δ, and γ HC isotypes of the conventional and precursor BCR in B-cell differentiation, selection, and engagement with (auto)antigens.

A brief history of corneal transplantation: From ancient to modern

This review highlights many of the fundamental concepts and events in the development of corneal transplantation - from ancient times to modern. Tales of eye, limb, and even heart transplantation appear in ancient and medieval texts; however, in the scientific sense, the original concepts of corneal surgery date back to the Greek physician Galen (130-200 AD). Although proposals to provide improved corneal clarity by surgical interventions, including keratoprostheses, were better developed by the 17(th) and 18(th) centuries, true scientific and surgical experimentation in this field did not begin until the 19(th) century. Indeed, the success of contemporary corneal transplantation is largely the result of a culmination of pivotal ideas, experimentation, and perseverance by inspired individuals over the last 200 years. Franz Reisinger initiated experimental animal corneal transplantation in 1818, coining the term "keratoplasty". Subsequently, Wilhelmus Thorne created the term corneal transplant and 3 years later Samuel Bigger, 1837, reported successful corneal transplantation in a gazelle. The first recorded therapeutic corneal xenograft on a human was reported shortly thereafter in 1838-unsurprisingly this was unsuccessful. Further progress in corneal transplantation was significantly hindered by limited understanding of antiseptic principles, anesthesiology, surgical technique, and immunology. There ensued an extremely prolonged period of debate and experimentation upon the utility of animal compared to human tissue, and lamellar versus penetrating keratoplasty. Indeed, the first successful human corneal transplant was not performed by Eduard Zirm until 1905. Since that first successful corneal transplant, innumerable ophthalmologists have contributed to the development and refinement of corneal transplantation aided by the development of surgical microscopes, refined suture materials, the development of eye banks, and the introduction of corticosteroids. Recent developments, including the replacement of selected corneal layers rather than full-thickness keratoplasty, have the potential to improve or transform corneal transplant surgery in the future.

Review of the early diagnoses and assessment of rejection in vascularized composite allotransplantation

The emerging field of vascular composite allotransplantation (VCA) has become a clinical reality. Building upon cutting edge understandings of transplant surgery and immunology, complex grafts such as hands and faces can now be transplanted with success. Many of the challenges that have historically been limiting factors in transplantation, such as rejection and the morbidity of immunosuppression, remain challenges in VCA. Because of the accessibility of most VCA grafts, and the highly immunogenic nature of the skin in particular, VCA has become the focal point for cross-disciplinary approaches to developing novel approaches for some of the most challenging immunological problems in transplantation, particularly the early diagnoses and assessment of rejection. This paper provides a historically oriented introduction to the field of organ transplantation and the evolution of VCA.

THE ROLE OF HUMORAL ANTIBODIES IN REJECTION OF SKIN HOMOGRAFTS IN RABBITS : I. PASSIVE TRANSFER OF ISOIMMUNE SERUM TO CONDITIONED HOSTS

Gross and microscopic observations of skin homograft rejection carried out in cortisone-conditioned and non-conditioned rabbits seem to indicate that humoral antibodies play an important role in the phenomenon. Thus, local administration of isoimmune serum to animals bearing skin homografts resulted in a significantly earlier rejection of that particular test graft without modifying the course of a neighboring control-skin graft. This result appears to support the idea that homograft rejection is not only due to cellular antibodies but to a combination of both humoral and cellular immune responses, which should not be regarded as completely unrelated.

DEMONSTRATION OF MOUSE ISOANTIGENS AT THE CELLULAR LEVEL BY THE FLUORESCENT ANTIBODY TECHNIQUE

The fluorescent antibody technique has been applied for the demonstration of mouse isoantigens at the cellular level. Specific reactions were obtained by the indirect or "sandwich" technique with a variety of living normal and neoplastic cells. Isoantigens of the H-2 system and of other systems could be demonstrated as well and appeared to be localized at the cell membrane. As far as the H-2 system was concerned, the membrane localization could be confirmed on histological sections. Different types of non-specific staining reactions have been identified and described. Pinocytosis and cell injury led to such reactions that were morphologically distinguishable from the specific "ring" reaction and as far as pinocytosis is concerned, could be easily avoided by reducing the incubation time. In addition, a non-specific staining reaction morphologically indistinguishable from the specific "ring" reaction could be seen in a small proportion of bone marrow and lymph node cells but in no other cell type studied. The possible nature of this reaction is discussed.

Uterine MHC class I molecules and beta 2-microglobulin are regulated by progesterone and conceptus interferons during pig pregnancy

MHC class I molecules and beta(2)-microglobulin (beta(2)m) are membrane glycoproteins that present peptide Ags to TCRs, and bind to inhibitory and activating receptors on NK cells and other leukocytes. They are involved in the discrimination of self from non-self. Modification of these molecules in the placenta benefits pregnancy, but little is known about their genes in the uterus. We examined the classical class I swine leukocyte Ags (SLA) genes SLA-1, SLA-2, and SLA-3, the nonclassical SLA-6, SLA-7, and SLA-8 genes, and the beta(2)m gene in pig uterus during pregnancy. Uterine SLA and beta(2)m increased in luminal epithelium between days 5 and 9, then decreased between days 15 and 20. By day 15 of pregnancy, SLA and beta(2)m increased in stroma and remained detectable through day 40. To determine effects of estrogens, which are secreted by conceptuses to prevent corpus luteum regression, nonpregnant pigs were treated with estradiol benzoate, which did not affect the SLA or beta(2)m genes. In contrast, progesterone, which is secreted by corpora lutea, increased SLA and beta(2)m in luminal epithelium, whereas a progesterone receptor antagonist (ZK137,316) ablated this up-regulation. To determine effects of conceptus secretory proteins (CSP) containing IFN-delta and IFN-gamma, nonpregnant pigs were implanted with mini-osmotic pumps that delivered CSP to uterine horns. CSP increased SLA and beta(2)m in stroma. Cell-type specific regulation of SLA and beta(2)m genes by progesterone and IFNs suggests that placental secretions control expression of immune regulatory molecules on uterine cells to provide an immunologically favorable environment for survival of the fetal-placental semiallograft.

ES-cell derived hematopoietic cells induce transplantation tolerance

Background

Bone marrow cells induce stable mixed chimerism under appropriate conditioning of the host, mediating the induction of transplantation tolerance. However, their strong immunogenicity precludes routine use in clinical transplantation due to the need for harsh preconditioning and the requirement for toxic immunosuppression to prevent rejection and graft-versus-host disease. Alternatively, embryonic stem (ES) cells have emerged as a potential source of less immunogenic hematopoietic progenitor cells (HPCs). Up till now, however, it has been difficult to generate stable hematopoietic cells from ES cells.

Methodology/Principal Findings

Here, we derived CD45⁺ HPCs from HOXB4-transduced ES cells and showed that they poorly express MHC antigens. This property allowed their long-term engraftment in sublethally irradiated recipients across MHC barriers without the need for immunosuppressive agents. Although donor cells declined in peripheral blood over 2 months, low level chimerism was maintained in the bone marrow of these mice over 100 days. More importantly, chimeric animals were protected from rejection of donor-type cardiac allografts.

Conclusions

Our data show, for the first time, the efficacy of ES-derived CD45⁺ HPCs to engraft in allogenic recipients without the use of immunosuppressive agents, there by protecting cardiac allografts from rejection.

On the transplantation, regeneration and induction of bone: the path to bone morphogenetic proteins and other skeletal growth factors

The clinical and experimental transplantation of bone dates back to the seventeenth century and human allogeneic (homogeneic) bone has been successfully used as an alternative to autogenous bone since 1878, when Sir William Macewen reconstructed the right humerus of William Connell. This review describes how subsequent studies of bone transplantation led to the eventual discovery of a new family of secreted signalling molecules--the bone morphogenetic proteins (BMPs), and the realisation of the important role of polypeptide growth factors in mediating the growth, remodelling and regeneration of the skeleton. The development of suitable alternatives to both autogenous and allogeneic bone has been a goal of bone and biomaterials research for more than 30 years. The first requirement is a biocompatible, bioresorbable, osteoconductive framework supporting the ingrowth of host cells from the recipient bed. Many materials including collagen, calcium phosphate ceramics and synthetic polymers have been widely tested experimentally with varying success. The discovery of osteoinductive BMPs and their availability in recombinant human forms has given considerable impetus to the field. However, progress to date in engineering significant quantities of functional bone tissue in vivo has been disappointing; finding suitable carriers for BMPs has proven to be a greater challenge than expected. The dilemma for the clinician and the biotechnology industry, at present, is that, while recombinant human growth factors are readily available for clinical use, the lack of delivery systems that can adequately mimic both the physical properties and release kinetics of bone matrix remains a major handicap.

Studies on the transfer of lymph node cells. XI. Effect on the anti-Shigella agglutinin titers of recipient rabbits of the prior injection of leucocytes from the donor animals

The transfer to rabbits of homologous lymph node cells which have been incubated in vitro with Shigella-trypsin filtrate leads to the appearance of agglutinins to Shigella in the sera of the recipients. In the present study it has been found that the prior injection of the prospective recipients with blood leucocytes from the donor animals prevented the appearance of anti-Shigella agglutinins. The following observations have been made in this system: 1. The degree of the pre-injection effect was found to be a function of the number of leucocytes injected and of the interval between such pre-injection and the transfer of the antigen-incubated lymph node cells. 2. The pre-injection of leucocytes at appropriate intervals could also cause the failure of antibody to appear in sera of recipients of lymph node cells when these were obtained from donor rabbits injected with Shigella, 1, 2, or 3 days prior to cell transfer. 3. Agglutinins failed to appear in cell-transfer experiments after the pre-injection not only of blood leucocytes, but also of lymph node cells, peritoneal exudate cells, or thymus cells of rabbits. This effect was not brought about by pre-injection of erythrocytes of rabbits or leucocytes of chicken, cow, or horse. The pre-injection of leucocytes of human blood had an effect of partial suppression. 4. When the leucocytes for pre-injection were pooled from groups of rabbits, either the prospective donors of the lymph node cells or other rabbits, essentially complete suppression of agglutinin titers occurred regularly. When the leucocytes for pre-injection were obtained from an individual rabbit and the lymph node cells from another rabbit the suppression of the recipients' titers occurred sporadically. 5. When the recipient's own leucocytes were pre-injected the subsequent agglutinin titers were somewhat lower than those of the non-pre-injected controls. When the recipient's whole blood was re-injected as the source of leucocytes the subsequent agglutinin titers were as high as those of the non-pre-injected controls. 6. The pre-injection effect was not obtained if the leucocytes had been heated, frozen and thawed, suspended in distilled water, lyophilized, or treated with sodium iodoacetate. However, sonic oscillation or x-irradiation of the leucocytes had no effect on their capacity to bring about the pre-injection effect.

Quantitative assessment of angiogenesis and osteogenesis after transplantation of bone: comparison of isograft and allograft bone in mice

We performed a vital microscopic study in mice bearing dorsal skinfold chambers to characterize microvascular perfusion and leukocyte/endothelium interaction and their effects on elongation and mineralization of neonatal isograft and allograft bone. Isograft (C57/BL to C57/BL) and allograft bone (C57/ BL to BALB/C) revascularized simultaneously. However, vascular perfusion and density were lower in allograft bone than in isograft bone. Leukocyte/endothelium interaction was the same in isograft and allograft bones. Revascularization was not detected in allograft bone transplanted to presensitized recipients. Moreover, in preexisting vessels at the transplantation site, leukocyte/endothelium interaction was altered in allograft bone of presensitized recipients, despite a normal systemic leukocyte count. Femoral growth resulting from thickening of both epiphyses did not differ between experimental groups, however, mineralization occurred in isograft bone only. Isograft bone was histologically intact, allograft bone hypovital and allograft bone in presensitized recipients necrotic 12 days after implantation. Our findings suggest that graft incorporation or rejection is mediated by the microvasculature and that presensitizing of recipients accelerates rejection of allograft bone.

Quantitative studies on tissue transplantation immunity IV. Induction of tolerance in newborn mice and studies on the phenomenon of runt disease

A simple method for the induction of actively acquired tolerance of homologous tissues in newborn mice is described (§§2-1, 2-2 and 2-3). With some donor/recipient strain combinations a high proportion of mice injected intravenously with homologous tissue cells is rendered tolerant of skin grafts from animals of the donor strain (§§3-1, 3-4 and 3-5), provided that the cells are administered within 24 h of birth. As the age of the recipients increases, so the proportion of tolerant mice falls (§3-2); a ‘ eutral period’ in the life of the recipients lies between the latest age at which they can be rendered tolerant and the earliest age at which they can be rendered immune. The induction of tolerance is less effective when homologous cells are injected intraperitoneally into newborn mice, and (with our strains) wholly ineffective when they are injected subcutaneously (§3-3). Tolerance can be induced with spleen, bone marrow or thymus cells (§3-4), and abolished (‘adoptive immunization’) with sensitized spleen and thymus cells as well as with lymph node cells (§5-2). Further experiments on the specificity of tolerance are described (§5.1). In newborn rabbits, the intravenous inoculation of homologous spleen or thymus cells results in the induction of tolerance in only a small proportion of animals (§3-6). The injection of adult homologous lymphoid cells into newborn mice leads to the development of a syndrome described as runt disease because, in its extreme form, it is characterized by gross retardation in development (§3-5). Runt disease is marked by varying degrees of involution of the recipients’ lymph nodes, and by pathological changes in the spleen, liver and other organs (§3-7). In its acute form it is fatal, but when more mildly expressed it need not be a serious handicap (§3-5). Two possible causes of runt disease are considered and subjected to experimental test (§4). The theory that runt disease is infective in origin cannot be upheld (§4.1). O n the contrary, it is shown conclusively that runt disease is immunological in origin, and that it is the consequence of an immunological reaction of the homologous cells against the tissues of their hosts (§6-2). For (a) the injected homologous cells persist indefinitely in the tissues of their hosts (§3-8); (b) although the injection of Fxhybrid spleen cells into newborn mice of the parental strains is usually quite harm ­ less (§4-3), the injection of parental strain cells into hybrid recipients is followed by the typical syndrome of runt disease (§4-6); (c) mice can be protected from runt disease if they receive, together with the homologous cells,adult isologousspleen cells (§4-4); (d) the severity and frequency of runt disease are enhanced if sensitized homologous spleen cells are injected—i.e. cells from donors already sensitized by host strain tissues (§4-5); (e) acute runt disease can be avoided by the injection of adult tissue cells containing no, or only a very small proportion of, immunologically competent cells (§§4-2, 6-3); and (f) the severity and incidence of runt disease are largely determined by antigenic differences between donor and host strains (§6-2). Finally (g) it is already known that embryonic cells, though adept in producing tolerance, fail altogether to produce runt disease (§6-3). Tolerance of homologous tissues can occur in the complete absence of runt disease and cannot therefore depend upon the lymphoid hypoplasia that accompanies it (§6-3). O n the other hand, runt disease frequently depends upon the induction of tolerance by the injected cells, which are therefore able to persist and to react against the tissues of the host over a relatively long period of time. W ith certain donor/recipient strain combinations in which runt disease is particularly violent and rapid in onset, the induction of complete tolerance need not be necessary (§6-3), the young hosts succumbing to the disease before their own defence mechanism has m atured sufficiently to destroy the cells that cause it. W ith some donor/recipient strain combinations, the susceptibility to runt disease of hybrid mice injected with spleen cells from mice of the parental strains falls off with increasing age (§ 4-6), despite the fact that with this experimental design even adult recipients may be expected to be ‘ tolerant ’ of the injected cells. Similarly, the injection of adult mice made tolerant at birth with large doses of donor strain spleen cells does not bring about an increase in the severity of the disease (§4‘7). The production of runt disease in a severe form seems therefore to depend upon the hosts’ own lymphoid organs being relatively undeveloped when confronted with foreign lymphoid cells. It has been shown by Simonsen that the splenomegaly produced in chickens injectedin ovoor soon after hatching with homologous spleen or blood cells is due to a ‘ graft-against-host ’ reaction (§6*2), and the same interpretation has been put upon the ‘secondary disease’ which often occurs in irradiated mice protected against the effects of radiation by adult homologous spleen or bone marrow cells (§6-4). These two phenomena and runt disease are therefore considered to have a common etiology. The occurrence of runt disease is a sensitive indicator of the presence of immunologically competent cells in the inocula used to induce tolerance. The finding that blood leucocytes and thymus cells can cause runt disease when injected into newborn mice (§4-2) suggests that at least some of the cells among them are capable of immunological reactivity. Bone marrow cells, whilst bringing about some degree of lymphoid hypoplasia, do not cause acute runt disease, and they may therefore be used conveniently for the induction of tolerance with those donor/recipient strain combinations in which the injection of spleen cells is always lethal. Certain clinical implications are discussed (§6-5). It is suggested that the possibility of ‘graft-against-host’ reactions and the occurrence of immunologically competent cells in adult blood should be borne in mind in the interpretation of haemolytic disease and in devising treatments of any kind which depend upon the transplantation of lymphoid cells.

THE EXPRESSION OF HISTOCOMPATIBILITY ANTIGENS ON CELLULAR AND SUBCELLULAR MEMBRANES

The mouse isoantigens determined at the major histocompatibility locus known as H-2 have been found to be closely associated with the cellular surface membranes, with the membranes of the endoplasmic reticulum, and probably with those of the lysosomes as well. Mitochondrial membranes, on the other hand, show little or no H-2 antigen activity. Membrane material prepared from certain tissues, including brain and muscle, have no detectable H-2 antigenic activity. Evidence is presented which indicates that all of the H-2 antigens of the genome are expressed as a unit, supporting the hypothesis that the complex H-2 genetic locus consists of a single cistron. It is postulated that these histocompatibility antigens form some structural or functional unit in the membranes of cells.

The alloimmunogenicity of heated blood and lymphoid cells

Murine lymph node cells heated to 45 degrees C for 1 h or 56 degrees C for 15 min lost their ability to provoke a primary cytotoxic alloantibody response, though they were able to provoke a secondary response in animals primed with normal lymph node cells two months previously. The primary immunogenicity of whole blood and spleen cell preparations was destroyed by 56 degrees C but not by 45 degrees C treatment. Treatment of spleen cells with 45 degrees C heat, and ammonium chloride to remove red cells, destroyed their immunogenicity, whereas ammonium chloride treatment alone did not, suggesting that the red cells were the immunogenic component of heated spleen cells and, by implication, of blood. Further evidence for a difference in the immunogenicity of 45 degrees C heated blood and normal blood was provided by the finding that heated blood did not prime for a response to 45 degrees C lymph node cells given two months later. Preliminary investigations of the tolerogenicity of heated cells were unsuccessful, indicating, in view of the published data, that the precise protocol for tolerance induction is very critical.

Organ transplantation with special emphasis on Cyclosporin A

The history of organ transplantation and the development of immunosuppression therapy were discussed in detail, starting from Medawar's acquired immunological tolerance theory. The current status of transplantation of organs including the kidney, heart, liver and pancreas was reviewed. Current concepts of immunosuppression were discussed, with special emphasis on the use of Cyclosporin A.