MCA2838 recognises a chicken orthologue of mamallian CD86, an intergral membrane protein, which is a member of the immunoglobulin superfamily. In mammals, CD86 is expressed by mature antigen-presenting cells, including activated B cells, activated T-cells, macrophages and dendritic cells. Mammalian CD86 functions as a costimulatory molecule of T cell through ligation of CD28 and CD152. This antibody recognises the molecule expressed on the surface of COS-7 cells transfected with the cDNA, accession number AM050135 in a mammalian expression vector. It detects a small population of chicken splenocytes stimulated with CD40 ligand.