Description: The KP1 antibody reacts with human CD68 which belongs to the sialomucin family and is closely related to the family of lysosomal-associated membrane proteins (lamps) and scavenger receptor. CD68 is predominantly an intracellular protein, found mainly in the late endosomal compartment but can be detected in smaller amounts on the surface of cells of mainly myeloid derived cells; monocytes and macrophages, dendritic cells (and in some langerhan cells), neutrophils, basophils mast cells, myeloid progenitor cells, and a subset of CD34+ hemopoietic bone marrow progenitor cells. The function has not been fully elucidated but based on it's homolgy and structure suggests a role in antigen processing or presentation and protection of the lysosomal membrane from hydrolytic enzymes. Reports have also seen expression in activated T cells, and about 40% of peripheral blood B-lymphocytes and 50% of all B-ALL. The KP1 antibody has also been reported to stain fibroblasts which may be due to a conserved epitope rather than fibroblasts expressing CD68.