CD101 is a disulfide-linked homodimeric type 1 glycoprotein. The peptide is comprised of 7 extracellular V-type IgSF domains. CD101 is highly expressed on monocytes, granulocytes, mucosal T cells, and on activated peripheral blood T cells. Expression is weak on resting T and B and NK cells, absent from platelets and weak or absent from most hematopoietic cell lines. CD101 is thought to play a co-stimulatory role in TCR/CD3-mediated T cell activation. Monoclonal antibodies against CD101 inhibit allogeneic T cell responses. Studies suggest that CD101 plays a major role in the activation of T cells by skin dendritic cells.