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An ovary from a syngenic newborn donor was grafted into each ear of 9 ovariectomized and 3 intact adult female DA strain rats. Cycling resumed in ovariectomized animals after an average interval of 24 days. The average duration of the resumed cycles was 6 days. The histology and ultrastructure of grafted ovaries are compared with those of normal ones. Thecal cells became luteinized in grafted ovaries. The ultrastructure of interstitial tissue cells from grafted ovaries reflects increased specialization for steroidogenesis.

Over the past decade has come general recognition that, directly or indirectly, immunology intrudes into nearly every aspect of mammalian reproduction. Charles Darwin's notion that the profligacy of women led to reduced fertility gained plausibility with the subsequent discovery of the auto- and alloantigenicity of spermatozoa and of testicular material. From this observation arose the reasonable expectation that immunological control of fertility may be feasible. Discovery of the importance of natural transfer of immunity from mother to offspring, the ontogeny of the immune response and recognition that pregnancy is an almost consistently successful violation of the "laws of transplantation" are only a few highlights or components of the burgeoning, multifaceted field we have come to recognize as the immunology of reproduction. An overview of this subject will be presented with regard to its evolutionary origins, its accomplishments, its current trends and some of its potentialities. The immunology of reproduction has not developed in isolation; in recent years it has benefited enormously from developments in other fields, and in its turn it has exerted its own impact on other disciplines, especially on transplantation. The present preoccupation of many immunologists with immunoregulation stems largely from independent discoveries in the realm of reproductive immunobiology: the etiology of Rh disease and its prophylaxis, and the principle of immunological tolerance, from investigations on the peculiarities of dizygotic twins in cattle.

One of the most intriguing shortcomings of modern immunology, especially transplantation immunology, is its failure to provide a satisfactory final explanation for the consistent non-rejection of immunogenetically alien conceptuses in utero, even in specifically preimmunized females. Certainly, there is no shortage of hypotheses. Over the past few years various observations have utterly refuted the simplistic notion that the much-mated but nulliparous or gravid females are immunologically unaware of the presence and activities of allogeneic cells transiently or chronically within their reproductive tracts. This evidence has engendered the belief that some kind(s) of active response(s) on the part of the female, following early recognitive events, plays an important, if not essential, role, in conjunction with adaptive hypoantigenicity of the trophoblast, not only in conferring selective benefits upon the conceptus from the time of implantation, but also in affording it protection from the possible hazards of a cellular immunity. Evidence is emerging that during mating, implantation, placentation, and gestation (1) various fetal and histocompabibility antigens are presented to the mother in a unique manner; (2) she does respond to these; and (3) her responses aid in the establishment and maintenance of a harmonious state of immunological coexistence with her fetus. There are reasonable grounds for believing that a complete understanding of the immunobiology of the maternal-fetal relationship may facilitate significant advances in both transplantation and tumour immunology.

As a mucosal organ, the uterus is unique in being subject to exposure to three types of antigen: chronically to micro-organisms, episodically to sperm bearing both auto- and alloantigens as well as soluble antigens in seminal plasma, and to conceptuses--nature's allografts--expressing transplantation antigens. That the uterus is effective in handling pathogens is evidenced by the rarity of infections. Local macrophages, immunocytes, and a secretory immune system, most evident in the cervix, probably underlie this attribute. Mammals' reproductive success hints that the uterus is immunologically discriminating toward the nonharmful but biologically important antigens of classes 2 and 3. Why sperm are not normally destroyed immunologically in the female prior to fertilization and why conceptuses are not rejected are central unresolved questions in reproductive immunology. Undoubtedly, important immunoregulatory principles are operating in this remarkable organ and its decidua. Better to understand antigenic exposure in the rat uterus, we have reinvestigated its lymphatic drainage using labeled cell injection and microanatomical procedures. Despite abundant lymphatics in the myometrium, cells placed in the uterine lumen did not readily gain access to the lymphatic system. There was a paucity of lymphatics in the endometrium, but Ia-positive dendritic cells were abundant. Soluble antigen exposure via the uterus failed to evoke a primary antibody response yet did prime the host for a secondary response. This restriction of systemic antigen presentation from the uterus, in conjunction with both cellular and noncellular immunoregulatory principles acting locally, may be important to ensure maternal hyporesponsiveness to paternal alloantigens.

The fate of solid tissue allografts--skin or parathyroid glands--implanted in the interstitial tissue of the testis was investigated using inbred rats. The results affirm that the testis is an immunologically privileged site despite its efficient lymphatic drainage. Skin allografts survived at least several days longer than orthotopic grafts of similar size, whether major histocompatibility complex (MHC)-compatible or MHC-incompatible, and failed to induce an alloantibody response in most recipients or to prime for secondary antibody responses on rechallenge. Further assessment employed parathyroid grafts that allowed appraisal of their function and its duration, by monitoring serum calcium levels. Most intratesticular MHC-incompatible parathyroids survived for at least twice as long as control grafts in nonprivileged sites, with a median survival time (MST) of 41 days--and one-third of the grafts functioned at 100 days. MHC-compatible grafts fared even better (MST of 60 days), some surviving more than 400 days. Most F1 hybrid grafts survived virtually indefinitely. Splenectomy 5-23 days prior to implantation had a beneficial rather than a detrimental effect on the privilege afforded intratesticular parathyroid allografts. Allograft rejection was accompanied by antibody production in only one-half the animals. Grafts that had undergone functional rejection at the time of recovery usually had an intense mononuclear cell infiltrate, and long-term surviving grafts displayed varying degrees of cellular infiltration among cords of healthy, functional chief cells. Accepted parathyroids were destroyed by active immunization of the host but were unaffected by passively administered alloantibodies. The possible mechanisms controlling graft rejection in this unique privileged site are discussed.

The 6th decade of this century was particularly important for transplantation immunology. The universality of allograft rejection by normal hosts had won general acceptance and, experimentally, several means of abrogating host reactivity to allografts were discovered. These included sub-lethal whole body irradiation, administration of certain corticosteroid hormones and inoculation of very young animals with living cellular inocula from the future graft donor--i.e., classic, neonatal tolerance. The latter was particularly important since it indicated the feasibility of a specific, permanent solution to the clinical allograft problem. Radiation and drug-induced tolerance in adult subjects came along and chemical immunosuppressants, which led to successful clinical use of azathioprine. The important rediscovery of ALS pointed towards the development and clinical application of monoclonal antibodies many years later. With the development of immunogenetics and transplantation biology came recognition that the conceptus is a highly successful allograft, raising the question of how it is able to withstand rejection by its immunocompetent mother for the duration of pregnancy. Hopefully, knowledge of the principle(s) involved when they are finally elucidated will be applicable to clinical allograft recipients. Although functional hypoantigenicity of the syncytial trophoblast probably plays a major role in protecting the allogeneic conceptus, a strong case now exists that local, cell-based, immunosuppressive and immunoprotective activity within the placenta and decidua, mediated by suppressor and other cells, is important.

A polyoma virus-induced CB strain hamster tumour has been defined with regard to its immunogenetic specificity (§ 3.1) and evaluated as a convenient source of cells from which a crude but biologically active, strain-specific 9transplantation antigen’ can easily be pre­pared. This antigen is resistant to repeated freezing and thawing, lyophilization and sub­sequent storage at 5°C (§ 3.3). Although the extracted antigen elicited ‘ direct hypersensitivity ’ reactions when inoculated intracutaneously into MHA strain hamsters specifically presensitized against CB tissue antigens by means of skin homografts or lymphoid cellular inocula, it was incapable of inciting transplantation immunity in normal MHA hosts. However, when emulsified in complete Freund’s adjuvant and injected into the footpads of MHA recipients, the material was immunogenic as evidenced by ( a ) their accelerated rejection of subsequent test tumour or skin homografts, ( b ) their prompt rejection of skin homografts hitherto sustained in a privileged site, and ( c ) their capacity to give direct reactions when challenged intracutaneously with cells or antigen extract from CB strain donors (§ 3.4). Exposure of normal MHA lymphoid cells to CB antigen in vitro altered their behaviour in such a way as to suggest a prompt transformation to an ‘immune’ or specifically activated status—such cells, after careful washing, were capable of inciting ‘immune lymphocyte transfer’ reactions in the skins of MHA and (MHA x CB) F 1 hosts. However, various findings leave open the possibility that the sensitization actually took place in the skin of the host animal into which the cells were transferred after their exposure to the antigen in vitro (§ 3.7). Chronic treatment, over a 90-day period, of adult MHA hamsters with CB antigenic material administered intracutaneously and intraperitoneally, without adjuvant, induced a high degree of tolerance in respect of subsequent homografts of CB skin (§ 3.8).

In mice,H-Y, a histocompatibility locus on theY-chromosome, is responsible for the rejection of male skin isografts by females of many isogenic strains. As a histocompatibility locusH-Yis unique and important experimentally because of its apparent lack of alleles and its absence in females (§1). Using mice of theC57BL/6 strain, where theMSTof male to female grafts is 25 ± 2.5 days, a comparison has been made of the various means by which adult females can be rendered unresponsive of theYantigen (as revealed by inability to reject male skin isografts). The extent to which these various tolerance-inducing procedures result in the establishment of detectable levels of cell chimerism, and the susceptibility of these tolerant states to abrogation by transfer of isologous lymphoid cells have also been investigated. A high proportion of adultC57 females were rendered tolerant of theYantigen following: (a) Intravenous or intraperitoneal inoculation of very high dosages (at least 500 million) of isologous male spleen cells. The former route was the more effective, and repeated exposures to the antigenic stimulus were more effective than single ones (§4.1). (b) The receipt of orthotopic skin grafts from infantC57 males (§4.2). (c) Multiparity byC57 males (§4.3). (d) About 3 weeks’ parabiotic union with isologous males, or isologous females which were themselves to lerant of theYfactor as a consequence of neonatal inoculation with isologous or even homologous (Astrain) male cells (§4.4). Parabiosis with females rendered tolerant through multiparity was ineffective. Furthermore, parabiosis of specifically sensitized females with isologous males did not affect their immunological status. Indeed, some of the male partners succumbed to 'parabiosis intoxication'. A sensitive test for chimerism was developed, capable of revealing the presence of as few as 12500Y-antigen-containing cells in a standard test population of 20 million spleen cells (§6.1). On the basis of this test (§6.2), females rendered tolerant by inoculation of isologous male cells at birth, or in adult life, were chimeric as were females neonatally inoculated with (CBA×C57)F1spleen cells. Chimerism was infrequent in females rendered tolerant by neonatal injection of homologous marrow cells. It was consistently demonstrable in females rendered tolerant by parabiosis with isologous males but not in females which had been made tolerant by parabiosis with females rendered unresponsive by neonatal injection with homologous (AU) marrow cells, or in females rendered tolerant by multiparity. These findings indicate that apparently similar states of tolerance of theYfactor can be induced in adult hosts by two widely disparate antigen dosage ranges (§7.2), achieved by different regimens of administration or exposure. The lower effective dosage ranges do not result in the establishment of detectable levels of cell chimerism. Attempts to induce tolerance of theYantigen by means of single or multiple, spaced intravenous or intraperitoneal injections of very low dosages (ranging from 7 × 103to 2 × 106) of isologous male splenic cells were only marginally successful (§4.5). The results of studies on the abolition of tolerance of theYfactor by transfer of isologous lymphoid cells from specifically sensitized females (§5; §7.5) indicated that a necessary condition for abrogation of tolerance was a demonstrable level of chimerism. Putatively non-chimeric or very low level chimeric tolerant females were unaffected by the intraperitoneal transfer of even three donor equivalents of immune cells. However, such animals could easily be made susceptible to adoptive immunization either by giving them a second isograft of male skin, or by increasing the number ofY-antigen-containing cells in their bodies by injecting them with 20 to 30 million isologous male spleen cells, at about the time of transfer of immune lymphoid cells. These findings suggest that when lymphoid cells are transferred from a sensitized to a tolerant, or probably even to a normal host, further antigenic stimulation is necessary to make them immunologically effective (§7.5). Possibly the transferred cell population does not include enough ‘ready-made’ cells of the type that can immediately circulate in the blood stream and infiltrate and mount an effective immunologic attack upon a well established ‘target’ graft. The phenomenon of ‘split-tolerance’ is discussed in relation to some new observations bearing upon it (§7.4), which suggest that the phenomenon may apply to homologous as well as toF1hybrid cellular inocula.

Publisher Summary This chapter discusses different aspects of transplantation immunity and presents complete review of the lymphocyte and its role in different types of immunological reactions in experimental animals and in in vitro systems. The lymphoid tissues of a normal mammal constitute about 1% of its body weight and the predominant cellular component is the “small” lymphocyte. Lymphocytes serve as trephocytes and stem cells and even regulators of tissue growth and size. On the basis of their morphology and size, lymphocytes are subdivided into “large,” “medium,” and “small” varieties. The majority of the lymphocytes present within the lymphoid tissues as well as in the blood and lymph are of the “small” variety. The large and medium lymphocyte categories represent a much more heterogeneous population of cells, some of which possess a strongly basophilic cytoplasm. Electron microscope studies of the ultrastructure of these cells reveals two types, both distinguishable from small lymphocytes on the basis of their cytoplasmic organelles and their more abundant cytoplasm. Among the characteristics of small lymphocytes, their ubiquity, mobility, and longevity are desirable attributes of any cell type the role of which is to participate in the recognition, effector, and memory aspects of immunological phenomena. The recirculating small lymphocytes, rather than the sessile lymphoid cell population, play an important role in the primary response of rats to skin homografts.