0065-1281/02/104/1-077 $ 15.00/0 Lectin histochemistry of the rat lymph node: visualisation of stroma, blood vessels, sinuses, and macrophages. A contribution to the concept of an immune accessory role of sinus-lining endothelia* Jochen Düllmann 1, **, Els J. M. Van Damme 2 , Willy J. Peumans 2 , Maike Ziesenitz 1 , and Udo Schumacher 1 1 Institute for Anatomy, University Hospital Hamburg-Eppendorf, Hamburg, Germany, and 2 Laboratory for Phytopathology and Plant Protection, Catholic University Leuven, Belgium Received 22 January 2001 and in revised form 4 July 2001; accepted 23 August 2001 Summary The lectin Chelidonium majus agglutinin (CMA) was previously shown to visualise endothelia of all blood vessels and those lining sinuses of red pulp, stromal reticular meshwok (RM) and dendritic cells of lymphatic follicles in white pulp of the spleen in rats. The aim of the present study was the analysis of CMA and some other lectins in labelling RM, vascular structures and macrophages in lymph nodes of rats. It appeared that CMA stained the entire RM, dendritic cells, lining cells of sinuses and all types of blood vessels. Sinus-lining cells of lymph nodes were labelled with CMA and mannose-, GalNac-, and sialic acid-specific lectins. Moreover, lymph node macrophages were labelled above all by mannose specific lectins. The broad lectin-binding pattern of sinuses – not observed in rat spleen- and CMA-reactivity of both sinus-lining and dendritic cells corroborates the hypoth- esis that lymph node sinus-lining endothelia are precursors or a special type of immune accessory cells. Key words: lectin histochemistry – rat lymph node – reticular meshwork – sinus-lining cells – vasculature – laminin – macrophages Introduction Reticulum cells of lymphatic tissue consist of two dis- tinct populations: 1) the immune-accessory dendritic cells in B- and T-cell areas (Fossum, 1989; Tew et al., 1990) such as antigen-presenting follicular dendritic cells (FDCs) and their counterparts in T-cell areas, the interdigitating dendritic cells, and 2) special fibroblastic cells which form a tissue-specific extracellular matrix. In contrast to fibroblasts of connective tissue, these fibroblasts encapsulate fibres that they produce thus building up a lymphatic tissue-specific stromal reticular meshwork (RM) in which cells of the immune system reside. In addition, blood vessels and lymphatic sinuses of lymph nodes are suspended in this RM. On the basis of morphological and cytochemical criteria, lining cells of lymph node sinuses have formerly been considered as a littoral variant of fibroblastic reticulum cells. These cells have many cytoplasmic protrusions and projec- tions, some of them can also ensheath reticular fibres. *This contribution is dedicated to Prof. R. Gossrau on the occasion of his 61 st birthday **Correspondence to: Prof. Dr. J. Düllmann, Institute for Anatomy, University Hospital Hamburg-Eppendorf, Martinistr. 52, D20246 Hamburg, Germany; phone: +49-40-42803-3574; fax: +49-40-42803-5427; e-mail: duellmann@uke.uni-hamburg.de acta histochemica acta histochemica acta histochem. 104(1) 77–83 (2002) © Urban & Fischer Verlag http://www.urbanfischer.de/journals/actahist