J.A. Bascuas

Follicular dendritic cell activation in the Harderian gland of the chicken

The avian follicular dendritic cell changes that occur in the germinal center of the Harderian gland during the course of the immune response were studied by electron microscopy and the immunoperoxidase method was employed for the detection of S-100 protein. The chickens were injected twice with Salmonella O Antigen into the nictitating membrane at 9-day intervals. The follicular dendritic cells exhibited filiform processes at between 24 and 96 h after the second antigen administration. Filiform dendrites tended to convolute near the cell body. Therefore, it can be assumed that these processes make it more difficult for macrophages and B cells to make contact with the immune complexes retained by the follicular dendritic cells and, as a consequence, the period of antigen handling by these cells increases. Evidence is provided that the dendritic processes are closely associated with both lymphoblasts and lymphocytes. Furthermore, S-100 protein was found in the abovementioned cells exclusively and only in those cells where filiform dendrites were observed. These findings suggest that, during a secondary immune response, the follicular dendritic cell undergoes a functional activation which involves morphological changes and the phenotypic expression of the S-100 protein. This activation is hypothesized to be similar to that described for follicular dendritic cells in mammals after fixing immune complex.

Identification of avian dendritic cells in the spleen using a monoclonal antibody specific for chicken follicular dendritic cells.

In the chicken, circulating antigens enter the splenic white pulp via the Schweigger‐Seidel sheaths (ellipsoids), where they are bound by cells, the ellipsoid associated cells (EAC), which are located on the periphery of the ellipsoid. There is an increasing body of evidence that these antigen‐binding cells move through the PALS, to be finally located within the germinal centers, where these antigen‐transporting EAC function as follicular dendritic cells (FDC). The aim of the current study was to further study the relationship between the EAC, the FDC, and the antigen‐bearing EAC which migrate through the splenic white pulp.

Immunocytochemical and immunoelectron microscopy study of dendritic cells in the caecal tonsils of chickens infected with Eimeria tenella

In the present study S-100 protein containing cells in the caecal tonsil were investigated, both at light microscopic and at electron microscopic levels, after oral coccidia inoculation (Eimeria tenella). The birds were infected with a single (Day 0) or two (Days 0 and 21) infective doses of 500 oocysts. Immunoelectron reactivity for S-100 protein was demonstrated in infected chickens, but not in controls. It was found in follicular dendritic cells and interdigitating dendritic cells which were present in the germinal center and diffuse lymphoid tissue respectively, both of them being located in the deep lymphoid tissue near the muscular layer and around the deep glands. Outside the lymphoid tissue, immunoreactivity for S-100 protein was found in cells lying between the epithelial cells of the deep crypt epithelium. Positivity for S-100 protein was observed at 3, 12, 18, 24 and 48 h after the first inoculation as well as on Days 3, 5, 6, 7, 8, 25 and 30 of the experiment. Positive reaction for S-100 protein was detected both while schizont (the more immunogenic stage) development occurs and the number of sporozoites in the caeca lumen was higher, as well as when the production of oocysts reached a maximum. Complementary studies demonstrated that S-100 positive dendritic cells gave a negative reaction for esterase activity, whereas a subset of S-100 negative intraepithelial lymphocytes located between epithelial cells lining the deep glands exhibited esterase activity. These esterase positive cells are hypothesized to be involved in the regulation of local defences.

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.

Local immune response in the chicken Harderian gland to antigen given by different ocular routes.

The effectiveness of three ocular routes of antigen administration to produce a local immune response in the Harderian gland was studied. The routes were by eyedrop, injection into the ocular conjunctiva and injection into the nictitating membrane. The antigen was observed in the cytoplasm of macrophages located within the lymphoid tissue only after the injection into the nictitating membrane. The numbers of germinal centres and plaque forming cells found in the gland after injection into the nictitating membrane was higher than the numbers observed following the other two ocular applications. These findings indicate that the injection of the antigen into the nictitating membrane is the most effective ocular route for producing a local immune response in the Harderian gland.

Ultrastructural localization of a soluble antigen in the chicken Harderian gland

The relationship between plasma cells, macrophages, B and T cells, dendritic cells, and epithelium in the chicken Harderian gland have been studied by means of ultrastructural localization of the horseradish peroxidase following local immunization. After 5 d, peroxidase activity was found in vesicles located in macrophages and immature plasma cells. On day 7, peroxidase-antiperoxidase complexes were found in vesicles of the epithelial cells lining the secondary ducts and the acini, in the lumina of the ducts, and on the surface of lymphocytes located among these epithelial cells. Dendritic cells showing peroxidase activity on their surface were seen in the subepithelial lymphoid tissue and in the lymphoid follicles. On day 9, peroxidase activity was found as iccosomes on the surface of dendritic cells and lymphoblasts. These results indicate that immature plasma cells in the Harderian gland can take up antigen and may have a role in presenting it to T cells. Further, our results suggest that intraepithelial lymphocytes might be involved in antigen transportation from the epithelium to the subepithelial lymphoid tissue.