Monoclonal antibody 5C6 FAT recognizes a membrane glycoprotein on human monocytes and macrophages which is expressed in intermediate and late inflammatory stages. CD163 is a scavenger receptor for the haemoglobin-haptoglobin complex, and is upregulated by glucocorticoids and IL-10. The extracellular portion of the receptor is regularly shed and can be found in the circulation (see also our product S-1015, sCD163 ELISA). An important function of CD163 seems to be in the adhesion of monocytes to activated endothelial cells. CD163-positive cells include skin histiocytes, Kupffer cells, spleen macrophages of the red pulp, and some thymus macrophages. The antigen is also found abundantly in human term placenta, and regularly in acute and chronic inflammatory lesions. The red R-Phycoerythrin label is particularly useful to avoid the greenish autofluorescence of some cells in their resting state.