Description: M9.D6 is generated against a peptide derived from the extracellular portion of mouse TLR9. Predominantly expressed as an intracellular protein, TLR9 is a ~115-120 kDa molecule which mediates response to unmethylated CpG dinucleotides in bacterial DNA. CpG DNA induces a strong T-helper-1-like inflammatory response and the proliferation of TLR9+ B cells. When stimulated with CpG DNA, TLR9-deficient (TLR9-/-) mice lacked splenocyte proliferation, inflammatory cytokine production from macrophages, and dendritic cell maturation, as compared with normal mice. To date, at least ten members of the Toll family have been identified. This family of type I transmembrane proteins is characterized by an extracellular domain with leucine-rich repeats and a cytoplasmic domain with homology to the type I IL-1 receptor. Members of the TLR family are involved in recognition and response to different microbial components including lipoproteins, peptidoglycans, and nucleic acids and play important roles in innate immunity and inflammation. TLR9 is not detected by flow cytometry using this antibody on RBC-lysed mouse splenocytes stained for intracellular TLR9. This may be due to limitations of antigen detection by flow cytometry. Further studies are needed to determine the relationship between mRNA expression and protein detection.