The M9.D6 monoclonal antibody specifically reacts with mouse CD289 also known as toll-like receptor 9 (TLR9). CD289 is involved in the activation of innate immunity, in acquired immune responses, and autoimmune diseases. It is involved in the immune system's response to unmethylated CpG dinucleotide sequences such as those found in bacterial, viral, or synthetic DNA. CD289 assists in pathogen recognition and is expressed by subtypes of dendritic cells and B cells.