Distribution of bursal secretory dendritic cells in the chicken.

BACKGROUND: The bursa of Fabricius provided the microenvironment for B-cell differentiation. Continuous contact between lymphoid cells and antigen in the bursa further suggested that antigenic material has an important influence on the maintenance and development of B cells in the bursa. In addition, a dendritic cell, the bursal secretory dendritic cell (BSDC), has been identified in the medulla. The hypothesis that, in the bursal follicles, the contact between the lymphoid cells and the antigen may be mediated by dendritic cells prompted us to identify a bursal dendritic cell that becomes activated after contact with the antigen. METHODS: A polyclonal antiserum to S-100 protein was used to identify bursal dendritic cells because S-100 protein, a calcium-binding protein, has been shown to be a marker for the identification of chicken dendritic cells following recent contact with antigen. RESULTS: At every age investigated, S-100-positive cells showed a location and shape identical to those described for BSDCs. Positive cells were found within and under the follicle-associated epithelial cells (FAE), indicating that these cells were strategically placed where they would encounter the antigen. In addition, positive cells were found arranged along the corticomedullary junction, which is a regenerative zone for the BSDC. After 10 weeks of age, the number of positive cells dramatically decreased, suggesting that the endocytic activity of the FAE may become impaired as the bursa regresses. CONCLUSIONS: The polyclonal antiserum to S-100 protein identified the BSDCs in the bursal follicles. Positive cells may be BSDCs that have undergone a functional activation after contact with the antigen. These cells may have a role as antigen-presenting cells in the bursal follicles. Hence, these cells may be involved in the events that lead to B-cell differentiation.

Immunoglobulin classes synthesised by the chicken Harderian gland after local immunisation.

The immunoglobulin (Ig) levels in tears and sera were compared after antigen administration (salmonella O antigen) by eyedrop and injection into the nictitating membrane, to determine the Ig classes synthesised by the plasma cells in the chicken Harderian gland. Samples of tears and sera were collected from immunised and control birds between 24 hours and 24 days after the antigen or sterile saline was administered. Samples were assayed for IgA, IgG and IgM concentrations using radial immunodiffusion. It is suggested that most of the IgG found in tears after local immunisation has an extraglandular origin.

Immunocytochemical detection of dendritic cell by S-100 protein in the chicken.

Positivity for S-100 protein in paraffin embedded chicken lymphoid tissue was found by using a polyclonal antibody against whole bovine S-100 protein. The S-100 protein-containing cells were observed in the locations which have been reported to contain avian dendritic cells such as the medulla of the bursal follicles, and the germinal centers and T-dependent areas in the spleen, Peyer's patches, caecal tonsil and Harderian gland. Positive cells were also found in the location where ellipsoid associated cell have been described, and between epithelial cells covering the Peyer's patches and the caecal tonsil, as well as between the cells lining the ducts within the Harderian gland. Macrophages were devoid of immunostaining. Our results confirm the location described elsewhere for chicken dendritic cells and indicate that S-100 protein can be considered as a cell marker for the identification of the chicken dendritic cell. Intraepithelial positive cells may be interdigitating dendritic cells in an unusual location (their function being the transport of the antigen from the epithelium to the diffuse lymphoid tissue), or cytotoxic T-lymphocytes which, in mammals, are immunoreactive for S-100 protein.

Myofibroblasts and myoepithelial cells in the chicken harderian gland.

An electron microscopic study of the myoepithelial cells in the chicken Harderian gland provides evidence that these cells can be transformed into myofibroblasts. After the application of a Brucella ovis suspension in sterile saline onto the eyeball, every 5 minutes for half an hour, myoepithelial cells gradually develop over a 90-minute period the characteristic features of myofibroblasts: bundles of intracytoplasmic microfilament; abundant rough endoplasmic reticulum; prominent Golgi complex; and surface membrane differentiations, that provide attachment to neighbouring epithelial cells. No typical desmosomes are observed. Besides, the intercellular space between epithelial cells and myofibroblasts increases and the basement membrane adjacent to myofibroblasts disappears. Hypoxia is hypothesized to be involved in the transformation of myoepithelial cells into myofibroblasts.