Anat Embryol (2003) 207:85–94 DOI 10.1007/s00429-003-0331-8 ORIGINAL ARTICLE Julia Jörns · Ulrich Mangold · Ulrich Neumann · Els J. M. Van Damme · Willy J. Peumans · Uwe Pfüller · Udo Schumacher Lectin histochemistry of the lymphoid organs of the chicken Accepted: 11 April 2003 / Published online: 11 June 2003  Springer-Verlag 2003 Abstract Cellular interactions within the immune system are in part mediated via the carbohydrate-rich coat of the cell membrane, the glycocalyx, of which the terminal carbohydrate residues are of particular functional impor- tance. Thus, these carbohydrate residues from thymus, bursa of Fabricius, spleen and bone marrow of 2- and 30- day-old chickens were investigated by lectin histochem- istry. In the thymus, mannose as well as N-acetyl- glucosamine (glcNAc)-specific lectins labelled macro- phages, epithelial reticulum cells and lymphocytes within the cortex. In the bursa of Fabricius, the brush border of the lining epithelium, the macrophages and the endothe- lium were labelled by mannose-specific lectins. The follicle-associated epithelium was labelled by a broad spectrum of lectins. Epithelial cells that separated the cortex from the medulla and large mononuclear cells in the cortex were only being labelled by N-acetyl-galacto- samine (galNAc)-specific and glcNAc-specific lectins, respectively. In the spleen, lymphocytes of the peri- ellipsoid lymphocyte sheaths and macrophages of the red pulp were labelled by lectins of nearly all sugar speci- ficities. In general, glycotopes of these organs were more intensively labelled in the 2-day-old chicken than in the 30-day-old chicken, indicating changes in glycotope expression during post-hatching development. Thus, cells of the avian immune system are as rich and diverse in their lectin binding sites as their mammalian counterparts, indicating that similar carbohydrate lectin interactions between cells and matrices take place in birds as well. Keywords Carbohydrates · Lymphocytes · M cells · Follicle-associated epithelium · Peri-ellipsoid lymphocyte sheaths Introduction All vertebrate cells are covered by a carbohydrate-rich coat, the glycocalyx, which plays an important functional role in cell-to-cell and cell-to-matrix interactions. The terminal carbohydrate residues of this glycocalyx have been partially characterised by the use of lectins, proteins or glycoproteins of non-immunological origin, which specifically bind to defined carbohydrate residues. If labelled, they can be used to detect carbohydrate residues in tissue sections. The analysis of the terminal carbohydrate residues of the glycocalyx of immune cells is of interest because cell- to-cell and cell-to-matrix interactions, which play an important functional role in various processes of the immune response, are mediated at least in part by these carbohydrate residues (Hounsell 2000). For example, immunologically competent cells within the bloodstream have to interact with endothelia when they migrate through them in order to reach lymphatic organs or other regions where they fight invading pathogens. This process is called homing of the lymphocytes and it is in part mediated by these terminal sugar residues (Lowe 1994). Until now, studies concerning the binding of lectins to cells of the immune system have been mainly performed in mammals, including humans (Lu et al. 2002), and only occasionally have been performed using avian species. For example, thymic lymphocytes of 10-day-old chick embryos were shown to react with the lectins PHA and Con A (Sällström and Alm 1973), while another study demonstrated the reactivity of lymphocytes isolated from J. Jörns ( ) ) · U. Mangold · U. Schumacher Institute for Anatomy II, Experimental Morphology, University Hospital Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany e-mail: joerns@uke.uni-hamburg.de Tel.: +49-40-428032586, Fax: +49-40-428035427 U. Neumann Clinic for Poultry, School of Veterinary Medicine Hannover, 30559 Hannover, Germany E. J. M. Van Damme · W. J. Peumans Laboratory for Phytopathology and Plant Protection, Catholic University, Leuven, Belgium U. Pfüller Department of Phytochemistry, University of Witten/Herdecke, 58448 Witten, Germany