摘要:

AbstractNewborn rats and mice have rudimentary peripheral lymphoid tissues and are immunologically incompetent. The lymphoid system matures late in the third week after birth, shortly before weaning. The adrenal cortex also is relatively inactive neonatally and begins to secrete glucocorticoids in a mature fashion two weeks after birth. These experiments were designed to test the hypothesis that adrenal glucocorticoids induce maturation of the lymphoid system and immunological competence during the third postnatal week. Mice 10–12 days old were injected daily for 4–11 days with aminoglutethimide, an inhibitor of steroid biosynthesis. The adrenal glands and lymphoid tissues were prepared for histological examination 24 hours after the last injection and evaluated without knowledge of the treatment received. Aminoglutethimide caused adrenal dysplasia with a frequency proportional to dose. Effective doses also inhibited growth, and slightly larger doses were fatal. Therefore it was concluded that large doses of aminoglutethimide caused adrenal insufficiency, but the completeness of this insufficiency in surviving animals was not ascertained. Three phases in postnatal maturation of the lymphoid system were identified by examination of untreated littermate controls and reference to previous work. During the first week after birth, the thymus‐dependent lymphoid tissues grow by immigration of thymus‐derived cells that soon have the capacity for cell‐mediated immunity. During the second postnatal week, a new population of wandering lymphoid cells, presumptively derived from bone marrow, settles in lymphoid organs in response to antigenic stimulation, to form primary lymphoid nodules and a few plasma cells. Late in the third week after birth the machinery for humoral antibody synthesis matures with the appearance of germinal centers and numerous plasma cells, coincident with a great increase in production of immunoglobulin. This third phase of maturation was retarded in mice injected with near‐fatal doses of aminoglutethimide. Because these mice suffered neither involution of lymphoid tissue nor suppression of proliferation in thymus or thymus‐dependent lymphoid‐tissue, it was concluded that the effects of aminoglutethimide upon the development of germinal centers and plasma cells were selective and specific. Therefore these experiments support the hypothesis that glucocorticoid secretion plays a decisive role in maturation of immunological competence during the third week after birth in mice. This role appears to be the potentiation of cellular proliferation and differentiation of B cells in response to antigens, culminating in antibody synthesis. Maturation of adrenal glucocorticoid synthesis has also been implicated in the initiation of physiological involution of the thymus and cessation of intestinal absorption of antibodies during the third postnatal week i

ISSN:0002-9106    

DOI:10.1002/aja.1001370302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractCellular immunocompetence begins to develop in mice during the first week after birth, as indicated by skin allografting and graft‐versus‐host reactions, but delayed hypersensitivity has not yet been detected at this early age. The purpose of this study was to investigate the ontogeny of delayed hypersensitivity in suckling mice.Dinitrofluorobenzene (DNFB) is an antigenic hapten which, when applied to the skin, can elicit both delayed hypersensitivity and a humoral immune response. In adult mice the induction period of delayed hypersensitivity to DNFB is a blastogenic reaction (accumulation of lymphoblasts) in the diffuse, thymusdependent cortex of the lymph node draining the site of application. This blastogenic reaction reaches a peak three days after initial application of antigen and then subsides, to be followed by the development of germinal centers and numberous plasma cells — indicative of a humoral immune response — a week after initial sensitization.Suckling mice were sensitized by application of DNFB to the ears, and the auricular lymph nodes wer prepared for light and electron microscopy three and eight days after sensitization. The development of delayed hypersensitivity was assayed by applying DNFB to an ear, 5 to 12 days after initial sensitization, and measuring the increase in thickness of the ear 24 hours later.The results of these studies indicate that by two days of age, mice have the capacity to develop delayed hypersensitivity as shown by both a blastogenic reaction in the draining lymph node and a positive skin test. Mice sensitized at birth or on the next day did not respond in either way. Mice sensitized prior to two weeks of age did not develop the late phase of the response (the formation of germinal centers and plasma cells), which matured in parallel with the normal maturation of the machinery for antibody production during the third postnatal week.These observations strengthen the conclusion of previous investigations that the blastogenic response in the regional lymph node is the inductive phase of delayed hypersensitivity. Because the late phase of the response does not appear in mice sensitized before two weeks of age, these animals offer an unusual opportunity to study delayed hypersensitivity relatively uncomplicated by humoral antibody pro

ISSN:0002-9106    

DOI:10.1002/aja.1001370303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractMajor stages in the structural and functional evolution of the mammalian humero‐ulnar joint are described on the basis of paleontological and cineradiograhic evidence. In pelycosaurs (the earliest known fossil reptiles with mammalian affinities), the humerus projected laterad and more or less horizontally; locomotor movements were principally rotation about its proximodistal axis. Because the forearm moved in a plane perpendicular to this axis, the flexed elbow was subjected to substantial torque. The humero‐ulnar joint consisted of two pairs of facets that engaged upon humeral rotation and was principally a stabilizing rather than a flexion‐extension mechanism.Cynodonts (advanced mammal‐like reptiles ancestral to mammals) possessed an ulnar condyle rather than a trochlea. A condylar humero‐ulnar articulation, usually with a spiral configuration, was retained by early mammals and persists in slightly modified form among modern prototherians. The spiral joint allows the ulna to extend in a sagittal plane as the humerus rotates, adducts, and elevates.The primitive therian trochlea evolved by enlargement of the intercondylar groove separating the ulnar and radial condyles and by retention of part of the ulnar condyle mechanism. Cineradiography demonstrates the relationship of diverse types of mammalian humero‐ulnar joints to limb posture and excursion char

ISSN:0002-9106    

DOI:10.1002/aja.1001370304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe localization and morphologic characteristics of mouse primordial germ cells at stages of embryonal development preceding formation of the undifferentiated gonads have been studied by means of high resolution light microscopy and electron microscopy. At day 9 of intrauterine life, the germ cells are found in the wall of the hind‐gut, at days 10 and 11 in the dorsal mesentery, and at day 12 they are mostly in the genital ridges or adjacent areas. Our observations confirm the hypothesis that germ cells attain their definitive location by ameboid movements. On the basis of morphologic characteristics displayed during migration, germ cells appear to be highly undifferentiated elements; for their energy requirements, they may depend on close association with somatic cells and on availability of exogenous substances of metabolic importance. Upon arrival at the genital ridges, the cells lose their ameboid features and assume a structural organization which is much simpler than that of precedinng stages. This indicates that migration is followed by a period of relative quiescence; mitosis is now the only evident activity. Interphase cells may occasionally be connected by intercellular bridges; it would seem that the first mitotic divisions with incomplete cytokinesis, a feature known to characterize oogonia and spermatogonia in sexually differentiated gonads, occur shortly after arrival of the germ cells in the genital ridge

ISSN:0002-9106    

DOI:10.1002/aja.1001370305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe postnatal development of the respiratory system in the opossum has been traced, using 102 specimens divided into 11 groups according to snout‐rump length. At birth, the lung is markedly underdeveloped and is represented by a pumitive system of branching airways that end in a number of terminal chambers or sacs. The airways, constituting the conducting portion of the lung, are lined by columnar epithelium that is devoid of cilia and goblet cells. The terminal air chambers contain an extensive capillary bed and are surfaced by squamous epithelium interspersed with scattered cuboidal cells. By the 3 cm stage, bands of smooth muscle have differentiated in relation to the bronchial epithelium and scattered cilia are present in the epithelium of the trachea and bronchi. Air chambers immediately adjecent to established bronchi differentiate further and become incorporated into the bronchial tree and new air chambers develop at the most distal extent of the bronchial system up to the 15.5 cm stage. Numerous spaces lined by squamous epithelium, which represent the first appearance of the arbor alveolaris, appear within the cellular stroma of the lung of the 7 cm opossum. By the 20 cm (juvenile) stage, mature alveoli, containing many vacuolated cells, are present and a thick collagenous lamina has developed between the pleura and the lung parenchym

ISSN:0002-9106    

DOI:10.1002/aja.1001370306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001370301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY