Activation-induced expression of murine CD83 on T cells and identificationof a specific CD83 ligand on murine B cells

Human CD83 is a cell surface protein expressed predominantly by dendritic c ells (DC) and lymphoid cells. So far, there exists no information on the fu nction and distribution of mCD83, Here we demonstrate that mCD83 is moderat ely expressed on resting T cells and DC, but strongly increases In its expr ession on T cells following activation with antigenic peptides or T cell re ceptor-specific mAb. When returning to the resting state, T cells down-regu late CD83 again. Ig fusion proteins which express the extracellular part of the mCD83 molecule (mCD83-Ig) specifically inhibit antigen-specific T cell proliferation and IL-2 secretion in spleen cell cultures from DO11.10 T ce ll receptor transgenic mice. Staining of spleen cells from BALB/c, XID and mu MT (B cell) knockout mice with mCD83-Ig proteins reveals the presence of a CD83 ligand predominantly expressed most likely by B220(+) cells since s pleen cells from mu MT knockout mice do not bind mCD83-Ig, CD83, besides it s established expression on human dendritic cells, thus, also represents a new marker molecule on activated T cells which with its specific ligand is involved in the regulation of T cell responses.