The discovery of immunologic tolerance

The phenomenon of tolerance can be said to have begun with the seminal observations in 1945 by R. D. Owen that cattle dizygotic twins display red cell (chimerism--mosaicism as he called it--in adult life. Owen interpreted this extraordinary finding in terms of the much earlier discovery by F. R. Lillie that the placentae of cattle dizygotic twins undergo anastomosis early in fetal life, and he speculated that this would have permitted blood cells and their precursors to move from one twin to the other. Owen's discovery came out of the blue and it was ignored by immunologists until F. M. Burnet and F. Fenner highlighted it four years later in their influential monograph The Production of Antibodies, in which they predicted the existence of tolerance as a general phenomenon and developed their notion of "self-markers" to explain why the body does not react against self. Though it was Medawar's group that showed conclusively in 1953 that tolerance can be experimentally induced in fetal mice and in chick embryos, their entry into this field came from a totally different direction, an attempt to distinguish between mono- and dizygotic cattle twins by the exchange of skin grafts. This led to the seemingly paradoxic result that grafts exchanged between dizygotic twins were accepted (1951) and it was not until their cattle experiments had been virtually completed that they became aware of Owen's earlier discovery. Following the work of Billingham, Brent, and Medawar, and of Hasek, tolerance became incorporated into general immunologic theory and it helped to explain the fact that mammals do not normally suffer from injurious autoimmune manifestations. Ray Owen's discovery therefore has a secure place in the history of immunology.

The response of group-housed baboons to three enrichment toys

The behaviour of group-housed baboons was compared before and after the provision of durable cage toys. One adult male hamadryas baboon and 13 adult female olive baboons living in a large enclosure were observed after they were given seven nylon bones, seven Kong toys and seven Plaque Attackers. Observations were conducted four times per week on each subject over a 6-week period. Abnormal, cage-directed, inactive and self-directed behaviours all significantly decreased after the provision of the toys, while enrichment-directed activities significantly increased. Aggression did not differ between the no toy and toy conditions. Approximately 26% of the baboons were using the toys at any one time, and use of the Kong toys and the bones was higher than that of the Plaque Attackers. Individuals who used enrichment structures already present were also those who used the new toys the most.

The Influence of Siblings On Wild Infant Chimpanzee Social Interaction

Abstract

The presence or absence of older siblings influenced the social interactions of 17 wild infant chimpanzees between the ages of 6 and 24 months living at the Gombe National Park, Tanzania. The total amount of time spent in social interaction (contact, grooming and play) was similar for infants with and without siblings, as was the overall level of social interaction with the mother. However, subjects with siblings spent more time with their siblings, while subjects with no siblings interacted with other group members. These results indicate a possible set-point for infant chimpanzee social interaction. Developmental changes were also similar in both groups, but the infants with siblings had lower levels of interaction with the mother and higher levels of interaction with other group members during the age period of 12-18 months. The levels of social behaviors were not related to the sex of the infant.

Quantitative Studies on Tissue Transplantation Immunity. III. Actively Acquired Tolerance

'Actively acquired tolerance' introduces into immunology the concept of a specific inhibition of response. Tolerance of a tissue homograft comes about when an animal has been confronted in foetal life with cells taken from its future donor, or from some other member of the donor's inbred strain (section 3.1). It depends (a) upon an embryo's inability to respond to antigens by becoming immunized, and (b) upon its continued inability to do so in later life. Methods for inducing tolerance in mice (sections 3.2, 4.1, 9), rats and rabbits (section 3.4), and birds (sections 3.3, 5, 7) are described in full. In normal development, response to an antigenic stimulus by becoming tolerant gives way to response by becoming sensitized or immune. The transition from the one modality of response to the other occupies a 'null period' during which the exposure of animals to an antigenic stimulus has no appreciable effect. Most but not all mice and birds at birth or hatching have already entered this transitional period (sections 4.1, 5). Tolerance is antigenically specific. An animal injected in foetal life with cells from a donor A becomes completely tolerant of homografts transplanted in later life from a donor B if, and only if, B contains no antigens that are not also present in A. (In practice, this condition is most easily fulfilled when A and B are members of the same highly inbred strain.) The reaction of a tolerant animal against a homograft from an unrelated donor is not perceptibly impaired. Tolerance does not, however, discriminate between the tissues of a single individual; the inoculation of foetal or newborn mice with leucocytes or with the cells of a mammary carcinoma may confer tolerance of later homografts of skin (sections 4.2, 9). Tolerance of a homograft is neither caused by nor accompanied by an antigenic adaptation of the grafted cells. An animal that is tolerant of a homograft in one part of its body is tolerant in another; tolerance is systemic, and a tolerated graft does not build up a privileged position within its own lymphatic territory (section 4.3). Every degree of tolerance is possible, from that which allows a homograft to live only a few days beyond its normal median expectation of survival to that in which it is permanently accepted by and incorporated into its host. An inhibition of response which is partial may nevertheless be permanent, for the weakening of the 'secondary response' in partially tolerant animals is proportional to the weakening of the first (sections 3.2, 4.4). The stimulus which confers tolerance must be fully antigenic, i.e. must be one which would have caused an older animal to have become immune. Cells such as erythrocytes which have no power to elicit transplantation immunity are incapable of causing tolerance of tissue homografts; all treatments which abolish the power of cells to confer tolerance upon embryos will also abolish their power to make older animals immune (section 5). Immunological reactivity can be promptly and permanently restored to a tolerant animal by inoculating it with cells taken from the regional lymph nodes of actively immunized members of its inbred strain. It may also be restored, more slowly, by the inoculation of normal unimmunized lymph node cells. A tolerant mouse thus retains in full the power to give effect to an immunity of adoptive ('passive') origin; a tolerated homograft continues to be a source of antigenic stimuli, and its susceptibility to a reaction directed against it remains unchanged. Tolerance represents a central failure of the mechanism of the immunological reaction, and is not caused by an intercession at a peripheral level (section 6). The relationship between twinning, fertility, tolerance and red-cell chimerism is analyzed. Like dizygotic twin cattle, twin chicks that arise from double-yolked eggs are synchorial, are red-cell chimeras, and are tolerant of grafts of each other's skin. Tolerance and infertility are not causally connected. The tolerance produced in chicks by artificial synchorial parabiosis from the 10th day of embryonic life until hatching is accompanied by a true persistent red-cell chimerism. The disappearance of chimerism in partially tolerant chickens does not reveal a return to normal reactivity, for their secondary response to red cells reintroduced by cross-injection is profoundly impaired (section 7). Some measure of tolerance of skin heterografts may be achieved by the synchorial union of embryonic ducks and chicks (section 8). Tolerance may be produced by, and in respect of, tumour homografts, and by tumour homografts in respect of skin. A degree of immunity which does not suffice to hold in check the growth of a tumour may destroy a normal homograft completely; the growth of a tumour homograft is therefore a less exacting measure of tolerance than the survival time of a homograft of skin (section 9). A naturally acquired tolerance of maternal homografts is believed to occur, very rarely, in guineapigs, presumably by the accidental incorporation into a foetus of maternal cells. No such natural tolerance has been observed in mice or rabbits (section 10). Phenomena cognate with tolerance are considered. The partial inhibition of transplantation immunity which is caused by injecting adult animals with variously modified antigenic matter differs fundamentally from tolerance in mode of origin, for the substances which enhance the growth of homografts after administration to older animals have no power to confer tolerance upon embryos, and the substances which cause embryos to become tolerant merely cause adults to become immune (section 11.1). It is argued that the iso-antigens responsible for transplantation immunity should be sharply distinguished from those specialized end-products of differentiation which are iso-antigenic because they are potentially auto-antigenic, and which are potentially auto-antigenic because the antibody-forming system has no opportunity in normal development to become tolerant of their action (section 11.2). The phenomenon of tolerance is considered for its bearing upon the relationship between mammalian mother and foetus; upon the different stages of development at which immunity to different antigens may arise; upon the antigenic and genetic composition of the different tissues of a single individual; and upon the fate of iso-antigens in normal life (section 11.3).

The physiological and behavioral effects of radio music on singly housed baboons

The response of four singly caged baboons to radio music was measured using behavioral and physiological indices. Heart rate and blood pressure, measured through a tether system, as well as behavior, were recorded during a two-week period in which radio music was available in half of the samples. The behavior of the subjects, as well as their blood pressure, did not vary in relation to radio music. Heart rate was significantly lower when the radio was on.

Evaluation of the chimpanzee breeding program at the Southwest Foundation for Biomedical Research

The history of the chimpanzee (Pan troglodytes) breeding colony of the Southwest Foundation for Biomedical Research was evaluated over a 24-year period to determine age at conception, breeder rearing history, maternal competence, and infant rearing history. The records of 107 breeders and 268 live births were reviewed. Of the breeders with known rearing histories, 40 were wild-born (12 male and 28 female), 16 were reared by their mothers for at least 1 month (8 male and 8 female), and 13 were removed from their mothers immediately after birth (2 males and 11 females). The age of successful mating for males ranged from 7 to 32 years and for females from 7 to 41 years, although the upper limit indicates the age of the population and not reproductive senescence. The mother's rearing history was related to her maternal competence, defined as caring for an infant for at least 1 month. Of the wild-born females, 82% (18/22) were competent mothers. For females that had been reared in captivity with their mothers for 1 to 12 months, 71% (5/7) were competent. For females that had been removed from their mothers immediately and reared in a nursery by humans, only 14% (1/7) were competent. The rearing strategies have changed during the period under consideration. The number of infants reared by their mothers increased in the 1980s, while the number of infants removed from their mothers immediately for experimental reasons decreased and dropped to zero in the 1990s. Information on the history of the breeding colony has been used to make management decisions and to determine the expectations of the Southwest Foundation chimpanzee breeding program.

Self-recognition and abstraction abilities in the common chimpanzee studied with distorting mirrors

The reactions of chimpanzees to regular mirrors and the results of the standard Gallup mark test have been well documented. In addition to using the mark test to demonstrate self-recognition in a regular mirror, we exposed six female chimpanzees to mirrors that produced distorted or multiplied self-images. Their reactions to their self-images, in terms of mirror-guided self-referenced behaviors, indicated that correct assessment of the source of the mirror image was made by each subject in each of the mirrors. Recognition of a distorted self-image implies an ability for abstraction in the subjects in that the distortion must be rationalized before self-recognition occurs. The implications of these results in terms of illuminating the relative importance of feature and contingency of movement cues to self-recognition are discussed.

Long-term use of televisions, balls, and mirrors as enrichment for paired and singly caged chimpanzees

The evaluation of environmental enrichment techniques for nonhuman primates over long periods of time has had mixed results. Some studies report rapid habituation to new enrichment items, while others note continued use. We have investigated the use of three different enrichments that had been available to paired and singly caged chimpanzees for several years. Twenty subjects were observed during 200 hr of scan sampling while singly caged and while pair housed. Each subject had a variety of enrichments available and their use of a television, ball, and mirror were recorded. The chimpanzees had previous exposure to all of the items: televisions had been available for a mean of 22.75 months, balls had been available for 55.9 months, and mirrors had been available for 25.9 months. The results indicated that the chimpanzees continued to use the enrichments for small amounts of time (0.27%-1.53% of the observations) even after such prolonged exposure. Television and ball use were significantly higher than mirror use. Housing condition was not a significant factor in the analyses, contrary to expectations. We concluded that several simple enrichment items may be effective in offering variety and choices to the nonhuman primate and can be one element in a comprehensive environmental enhancement plan. © 1996 Wiley-Liss, Inc.

Feeding enrichment and body weight in captive chimpanzees

Although positive behavioral consequences have been attributed to feeding enrichment, physiological changes may also occur. In this study, the body weight records of a large chimpanzee colony were reviewed to determine if body weight was affected by the implementation of a daily enrichment program, including food items offered three to four times per week. Comparing the mean body weight by age groups indicated that the weight of female chimpanzees was significantly greater after feeding enrichment but that male body weight did not differ.

Social factors influencing performance of a foraging task for captive chimpanzees

The performance of captive chimpanzees (Pan troglodytes) during a simulated foraging activity was compared to that reported for the foraging behavior of wild chimpanzees. The ability to find hidden fruit in a large outdoor play area was measured for 34 subjects housed in ten separate groups. Sex differences were apparent, with females searching for and finding significantly more fruit than males did. Chimpanzees of high and medium dominance rank found more fruit than those of low rank. Neither age nor stage of the female sexual cycle exerted an influence. The subjects became more proficient at finding fruit during the second block of trials. The results reflect possible influences of captivity on chimpanzee social behavior.

Is epidermal cell proliferation in psoriatic skin grafts on nude mice driven by T-cell derived cytokines?

Plasminogen activity and DNA synthesis by epidermal cells have been reported to be doubled in psoriatic skin grafts compared with grafts of normal skin 6 weeks after transplantation to nude mice. In our study human lymphocytes disappeared from such grafts within 48 h whilst some DR-positive human dendritic cells were retained in the grafts for up to 4 weeks. However, the grafts were infiltrated by Thy 1.2+ mouse lymphocytes within 6 days and this infiltration persisted at a moderate level throughout the observation period. It consisted of perivascular aggregates, scattered dermal and papillary T cells, and some mouse T cells were also found in the epidermal compartment. Grafts of psoriatic and non-psoriatic control skin were infiltrated to a similar extent, suggesting a low-grade rejection response against the human xenografts. These findings raise the possibility that psoriatic keratinocytes are responding abnormally to inflammatory cytokines released by mouse lymphocytes reacting against the skin grafts.