Development of the lymph nodes in the very young, and their evolution in the mature, nude rat.

We recently revised the concepts on the morphology of the lymph nodes of the young adult athymic nude rat. The present work studied the postnatal development of its nodal structures and their evolution with aging. The structural development of the deep cortex "units" was found to progress as usual. However, while the concentration of lymphocytes appeared to develop normally in the periphery of a unit, the center of the unit remained lymphocyte-depleted. Further, the peripheral cortex failed to develop over the middle part of a unit center. With aging, the peripheral cortex over the remainder of a unit center could atrophy and disappear completely. The present findings did not yield information as to whether thymic elements are necessary to trigger the development of a unit, but they revealed that its further development is determined by stimuli. It was concluded that, in the absence of T-cells, stimuli for cellular immune responses provoke the proliferation of the reticular or interdigitating cells of a unit center. On the other hand, an increase of these stimuli was concluded to cause the peripheral cortex to fail to develop over part of a unit center and, later, to atrophy over the remainder of the unit center. The mechanisms of the phenomena are discussed.

Ossification in nude mice. 1. Macroscopical study.

Ossification was studied in cleared fetuses, newborns, 1- and 6-week-old nu/nu and nu/+ mice of the B 10 LP background. The same ossification pattern was observed in nu/nu and nu/+ in the embryonal period as well as in newborn animals and mice aged 1 or 6 weeks. On the other hand, 6-week-old nu/nu mice exhibited a lower X-ray density of the skeleton and a lower thickness of the proximal tibial growth plate than 6-week-old nu/+ litter mates. The results indicate the influence of postnatal factors on the skeletal development of nu/nu mice.

Age-related decrease in transplantability of human tumours in nu/nu mice.

Experiments were designed to assess age-related changes in the transplantability of human tumours xenografted in congenitally athymic (nu/nu) mice. It has been found that the number of progressively growing human tumour xenografts decreased significantly with increasing age of BALB/c nu/nu recipients. These findings, taken together with a previously recognized increase in the frequency of endogenous interleukin 2 (IL-2)-producing cells with age of nu/nu mice, prompted us to investigate whether administration of exogenous IL-2 to young adult nu/nu mice could change the transplantability of human tumours in the mice. Peritumoral administration of exogenous interleukin 2 to 8-week-old nu/nu mice inhibited the growth of the human tumour xenografts. In vitro activation of nu/nu splenocytes with exogenous Il-2 resulted in the generation of killer cells which have been found to be cytolytic when allowed to react with human tumour targets in 51Cr cytotoxicity assay. In addition, it has been found that the percentage of IL-2-activated Thy 1.2+ and ASGM1+ cells substantially increased with increasing age of nu/nu spleen cell donors. These findings are compatible with the hypothesis that the observed age-related decrease in takes of human tumour xenografts might be determined by the increasing level of IL-2 production and subsequent maturation of IL-2-dependent effector cells.

The postnatal development of the ovary in the "nude" mouse.

The postnatal development of the ovary of the heterozygous nude (nu/+) mouse with the genetic background BALB/c is very similar--if not identical-- to that of other mouse strains. As other BALB/c mice, the nu/+ females become sexually mature during the 5th week post partum (p.p.). At this age the ovaries corpora lutea at various stages of differentiation. In the ovaries of newborn and 1 week-old homozygous (nu/nu) mice, the differentiation of oocytes into primary and secondary follicles is delayed. In the third postnatal week, the ovaries of homozygous females contain more atretic follicles than those of their heterozygous littermates. This increased degeneration of follicles may account for the greater mass of secondary interstitial tissue, which is observed in the ovaries of adult nu/nu females. In nine out of the 5 to 7 week-old nu/nu mice studied, the ovaries contained no-/or only very few corpora lutea. Thus in homozygous nude females, the onset of sexual maturity is delayed. This ovarial immaturity may persist throughout life. In other animals development may become normal. In addition to the impaired postnatal development of the ovary, unspecific inflammation of the uterine wall (endo- and/or myometritis) was detected in 47% of nu/nu animals older than five weeks. No direct correlation was, however, found between the delay of sexual maturation and the inflammatory changes in the uterus as many of the animals with an endo- or myometritis possessed mature ovaries. The low fertility of the female homozygous "nude" mouse seems, therefore, to be caused not only by an impaired differentiation of the ovary but also by inflammatory processes in the uterus.

Hairlessness does not influence growth retardation in nude mice. Computer image analysis study.

Ossification in 4-week-old nu/nu and nu/+ BALB/c and BFU mice was studied by X-ray analysis and by measurement of the thickness of the proximal tibial growth cartilage using CUE 4 Olympus computer image analysis. Not only altered architecture but also a significantly thinner proximal tibial growth plate was observed in athymic nu/nu as opposed to nu/+ and BFU mice. On the other hand, no significant differences were found between nu/+ and BFU littermates. Higher X-ray density of tail vertebrae was observed in nu/+ and BFU than in nu/nu mice. This comparison between athymic nu/nu and hairless euthymic BFU mice indicates that altered postnatal ossification in nude mice is not caused by hairlessness, but is due to other (immunological or endocrinological) differences.

[Extramedullary hematopoiesis in the liver of athymic mice during postnatal ontogeny and its modification by thymus transplantation o]. / Ekstramedulliarnoe krovetvorenie v pecheni bestimusnykh myshei v postnatal'nom ontogeneze i ego izmeneniia pri podsadke timusa.

Hemopoietic cells at different stages of differentiation were found in the liver imprints of adult thymus-less mutant mice BALB/c nu/nu, thus suggesting the presence of extramedullary hemopoiesis. During the postnatal development the intensity of leucopoiesis in the liver of mutant animals increased reliably and that of erythropoiesis suffered no marked changes. In the liver of adult BALB/c nu/nu mice, a high content of stem hemopoietic cells was found. The subcutaneous implantation of thymus to 2 weeks old BALB/c nu/nu mice resulted in the reliable decrease of leuco- and erythropoiesis in the liver. The neonatal thymectomy of the control mice BALB/c+/+ did not prevent the switching embryonic hemopoiesis in the liver off. A question of regulating influence of thymus on the process of switching hemopoiesis in the mouse liver off is discussed.

The development of the thymus in the nude mouse.

The developing thymus of nude mouse embryos (derived from homozygous, nu/nu x nu/nu, matings) has been examined from 13 days' gestation onwards for the presence of large basophilic stem cells or their lymphoid progeny. No trace of either stem cells or lymphocytes has been found at any stage, indicating that from the earliest stages of thymic development lymphopoiesis is defective. However, histological evidence alone is not sufficient to rule out the possibility that small numbers of lymphocytes may be present in the nude thymus. Recent evidence that nude mice born of heterozygous (nu/+) females possess some T lymphocytes and "T lineage" cells is discussed in relation to these findings. A series of morphological changes have been defined within the epithelial component of the developing nude thymus, further analysis of which may help to determine the nature of the thymic defect.

Husbandry of the "nude" mouse in conventional and germfree environments.

The "nude" mouse is a unique tool for immunologic studies. Its relatively short life span dictates the application of rigid environmental controls to increase longevity if the mouse is to assume the role of a practical experimental animal. In this paper we discussed the husbandry procedures employed to raise "nude" mice in our facilities under conventional, defined flora, and germfree conditions. Conventional and defined flora mice were raised on laminar flow stay-clean rocks, and germfree "nudes" were housed in self-contained germfree isolators. The major cause of morbidity and mortality among conventional and defined flora "nude" mice was fulminating hepatitis. We presented evidence that the etiologic agent of the disease was mouse hepatitis virus (MHV). Germfree "nude" mice were completely free from viral and bacterial diseases.

Cerebral aging: a quantitative study of gliosis in old nude mice.

Morphometric glial fibrillary acidic protein (GFAP) studies of the brains of 11 old (18-29 months) female, outbred athymic mice demonstrated astrocytic gliosis (increase in GFAP-positive astrocytes; GFAP-PA) in all mice with a consistent distribution pattern. Specific areas such as the central white matter, hippocampus, diencephalon, gray matter at the floor of the 4th ventricle, and posterior colliculi showed the change most conspicuously, revealing GFAP-PA both interstitially and perivascularly. There was no apparent demyelination in the affected white matter. In addition, there was an increase in GFAP-PA in the external limiting membrane surrounding the diencephalon and base of brain stem, but only to a minor degree over the cerebral hemispheres. The cerebral and cerebellar cortices and hypothalamus showed no significant increase. In contrast, all of the 2-month-old control animals showed only minor amounts of GFAP-PA, seen in the external limiting membrane and a trace in the cerebral white matter. The present data suggest that astroglial sclerotic change in various regions of the brain is an important morphological expression of cerebral aging. In view of the lack of other demonstrable histological changes (i.e., silver and amyloid stains were negative) or significant atrophy, the cause of the observed gliosis in BALB/c mice might represent a genuine aging change. As an incidental finding, aggregates of PAS-positive granules were noted in the Ammon's horn of most old animals, while none were seen in the young controls.

Hormonal basis of reproductive defects in athymic mice: reduced gonadotropins and testosterone in males.

We wished to determine if congenitally athymic nude male mice have the same reduction in circulating concentrations of gonadotropins and gonadal steroids observed in their female counterparts when compared to their normal heterozygous littermates. We therefore quantitated pituitary and circulating concentrations of gonadotropins and circulating levels of testosterone in 102 congenitally athymic mice and 101 of their heterozygous littermates ranging in age from 1 to 120 days. Although the developmental patterns observed for both circulating luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were similar to those previously observed in rats and mice, the athymic mice had significantly reduced concentrations of both pituitary and serum LH and FSH in comparison to the heterozygotes. In general, the reduced secretion of gonadotropins was most marked prior to sexual maturation but persisted in adult athymic males. Circulating concentrations of testosterone were also markedly reduced in the adult athymic males. Histologically, the number of Leydig cells appeared reduced in testes from 20-day-old athymic mice. However, no differences could be detected in testes from 40-day-old animals, and spermatogenesis appeared normal. Thus, unlike athymic females, athymic male mice appear to have normal reproductive capacity despite these hormonal abnormalities.