The monoclonal antibody MR5D3 recognizes the Mannose Receptor (MR, also known as CD206), a member of the vertebrate C-type lectin family. MR is a pattern recognition receptor that is involved in both innate and adaptive immunity. The 175 kDa transmembrane protein consists of 5 domains: an amino-terminal cysteine-rich region, a fibronectin type II repeat, a series of eight tandem lectin-like carbohydrate recognition domains (responsible for the recognition of mannose and fucose), a transmembrane domain and an intracellular carboxy-terminal tail.The structure is shared by the family of multi lectin mannose receptors: the phospholipase A2-receptor, DEC 205 and the novel C-type lectin receptor (mannose receptor X). The MR recognises a wide range of gram positive and gram negative bacteria, yeasts, parasites and mycobacteria. Moreover, the MR has also been shown to bind and internalize tissue-type plasminogen activator.MR’s are present on monocytes and dendritic cells (DC) and are presumed to play a role in innate and adaptive immunity, the latter via processing by DC. The expression of MR as observed in immunohistology is present on tissue macrophages, dendritic cells, a subpopulation of endothelial cells, Kupffer cells and sperm cells. The expression of MR on monocytes increases during culture and can be enhanced by cytokines such as IL-4. Labelling of MR expressing monocytes/macrophages increases with prolonged incubation time probably due to internalization of the MR-antibody-complex. Detection of the MR with anti-MR monoclonal antibody MR5D3 can substitute staining for mannose containing probes as labeled mannosylated BSA, a technique which is more cumbersome and less specific.