The rat anti-mouse CD8a monoclonal antibody YTS 105.18 (rat IgG2b kappa) reacts with the mouse CD8a protein (T-cell surface glycoprotein CD8 alpha chain) encoded by the mouse CD8A gene that encodes the CD8a chain of the dimeric CD8 protein. The mouse CD8 protein is primarily responsible for cell-mediated immune defense and T-cell development. CD8A has been widely reported as a potential prognosis and diagnostic marker for several diseases, such as inflammatory disorders and tumors. YTS 105.18 is a rat IgG2b anti-CD8a monoclonal antibody that does not deplete CD8+ T-cells in vivo and is widely used for the blockade of CD8+ T-cell activity in mice. Inoculation of mice with YTS 105.18 induces tolerance to zenograft transplantation and reduces insulin-dependent diabetes mellitus (IDDM) in NOD mice. Some suppliers and researchers state that YTS 105.18 is a rat IgG2a monoclonal antibody. Its sequence of the heavy chain indicates that it is a rat IgG2b antibody. Our recombinant YTS 105.18 antibodies have a part (variable regions) or complete amino acid sequences of the rat anti-mouse CD8a monoclonal antibody (hybridoma clone name or number: YTS 105.18).