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This study investigates how listeners cope with gradient forms of deletion of word-final /t/ when recognising words in a phonological context that makes /t/-deletion viable. A corpus study confirmed a high incidence of /t/-deletion in an /st#b/ context in Dutch. A discrimination study showed that differences between released /t/, unreleased /t/ and fully deleted /t/ in this specific /st#b/ context were salient. Two on-line experiments were carried out to investigate whether lexical activation might be affected by this form variation. Even though unreleased and released variants were processed equally fast by listeners, a detailed analysis of the unreleased condition provided evidence for gradient activation. Activating a target ending in /t/ is slowest for the most reduced variant because phonological context has to be taken into account. Importantly, activation for a target with /t/ in the absence of cues for /t/ is reduced if there is a surface-matching lexical competitor. [ABSTRACT FROM AUTHOR]

The ontogeny of rat Peyer's patches was studied with special reference to la-positive dendritic cells. The 16-day-old foetus contained large Ia-positive dendritic cells randomly distributed throughout the gut wall and mesentery. In cell suspensions prepared from the foetal gut, these cells showed the typical movement pattern of veiled cells, and they shared ultrastructural features with these and other antigen-presenting cells. The gut was found to be the first organ in which large numbers of these Ia-positive dendritic cells were found. At 16 days gestation, the Ia-positive dendritic cells were randomly distributed throughout the primitive gut wall, but at later stages accumulated in structures which were clearly recognizable as Peyer's patches from 20 days gestation onwards. T and B lymphocytes could be seen on the day of birth at the earliest, at first randomly distributed throughout the Peyer's patch, but afterwards concentrating in separate T- and B-cell regions. Two weeks after birth Peyer's patches consisted of densely populated B-cell nodules, mainly comprising surface 1gM (sIgM) positive cells, and internodular T-cell regions. la-positive dendritic cells were situated between the epithelial cells of the dome area, just underneath this epithelium in a loose reticular area and in the internodular 1-cell regions. These la-positive dendritic cells were acid phosphatase negative or only weakly positive. Some Ia-positive dendritic cells were also present in small intestinal villi at all ages studied. However, these cells started to express an increasing acid phosphatase activity in the 2 weeks following birth. Thus they resemble macrophages, while Peyer's patch dendritic cells show characteristics of antigen-presenting cells. [ABSTRACT FROM AUTHOR]

The intestinal immune response in rats following immunization with horseradish peroxidase (HRP) was studied morphologically. Various routes of immunization (intraperitoneal, intravenous, intraenteric and intra-Peyer's patch) were tested. Single injections did not evoke any specific antibody-containing (anti-HRP) cells in Peyer's patches (PP) and lamina propria of the small intestine. Only an intraperitoneal or intraenteric booster injection following intraperitoneal priming induced the formation of anti-HRP cells in PP and lamina propria. In the initial period of the immune response most of the anti-HRP cells were blast cells which were located mainly within the thymus-dependent interfollicular area of PP. Later on in the immune response more than 90% of the anti-HRP cells were located in the lamina propria of the villi and had the morphology of plasma cells. [ABSTRACT FROM AUTHOR]

The phenotypes and functions of various populations of non-lymphoid cells in the chicken spleen were investigated with monoclonal antibodies and after in vivo administration of antigens. Monoclonal antibody CVI-ChNL-68. l was used to detect red pulp macrophages, interdigitating cells, and monocytes, whereas CVI-ChNL-68.2 was used to detect ellipsoid-associated non-lymphoid cells (EANC). Two new monoclonal antibodies were developed: CVI-ChNL-74.2, which specifically recognized red pulp macrophages and a ring of macrophages surrounding the peri-ellipsoid lymphocyte sheath; and CVI-ChNL-74.3, which specifically recognized follicular dendritic cells (FDC) in germinal centres and small clusters of stromal cells in T-cell areas. After intravenous injection of lipopolysaccharide (LPS), the number of 68.1+ and 74.2+ macrophages decreased dramatically, whereas 68.2+ EANC and 74.3+ FDC were unaffected. After intravenous injection of heat-inactivated Brucella abortus, the numbers of both macrophages and EANC decreased. In contrast, a significant increase of 74.3+ cells was observed in the T-cell areas outside the germinal centres. As expected, intravenous injection of non-mitogenic antigens, such as keyhole limpet haemocyanin and Ficoll, and carrageenan did not affect the non-lymphoid cell populations. At least six subpopulations of non-lymphoid cells in the chicken spleen can now be discriminated with monoclonal antibodies. Our results show that mononuclear phagocytes are sensitive for mitogenic stimulators such as LPS and Brucella abortus. In contrast, stromal non-lymphoid cells are only sensitive to the particulate mitogen Brucella abortus. We conclude that the complex formed by ellipsoid cells, the pen-ellipsoid B-cell sheath, and the surrounding macrophages, is the functional equivalent of the mammalian marginal zone. [ABSTRACT FROM AUTHOR]

The ontogenetic development of macrophage subpopulations and Ia-positive non-lymphoid cells was studied in gut-associated tissue in fetal and neonatal Wistar rats. A two-step immunoperoxidase method was carried out on cryostat sections, a panel of monoclonal antibodies being applied and aimed specifically at rat macrophages (EDI, ED2 and ED3) and at Ia antigen (Ox4). The first EDI- positive macrophages appeared in the liver on Day 15 (gestational age), and they did not express Ia. In developing mesenteric lymph nodes and in the gut wall, macrophages were found for the first time on Day 17 and 18, respectively, of gestation. These early macrophages were also ED1-positive. Until birth, ED2 recognized few cells in the gut-associated tissue; on the day of birth this subpopulation showed a sudden and considerable increase. The distribution pattern of ED3-positive macrophages appeared to be the same in fetal and in adult rats; it was confined to lymph nodes and Peyer's patches. Ia-positive non-lymphoid cells appeared in the abdomen early in ontogeny. The first Ia-positive cells displayed dendritic features and were found on Day 15 of fetal life in the mesenchymal tissue between intestinal loops. A few days later, many Ia-positive ceils with a dendritic appearance were demonstrable in the gut wall and in developing mesenteric lymph nodes. Their number increased rapidly during the following days. Based on these results, the existence of two differentiation lines for dendritic cells and classical macrophages is discussed. The function of early Ia-positive cells in the abdomen is suggested as not being an antigen-presenting one. [ABSTRACT FROM AUTHOR]