Tlr9 Knockout mouse models

Recognition of microbial DNA runs through Tlr9, the mouse ortholog of human TLR9, whose endosomal receptor binds unmethylated CpG-containing single-stranded DNA at a site on the concave ectodomain surface while a second pocket engages a free 5 prime xCx dinucleotide, cooperativity that explains why activation is sequence and end dependent and why UNC93B1 trafficking plus cathepsin-mediated cleavage are prerequisites for signaling to MyD88, IRAK4, and IRF7. Species divergence is practical rather than theoretical, since mouse TLR9 prefers GACGTT-containing motifs whereas human TLR9 favors GTCGTT, so CpG oligonucleotide adjuvants and antagonists are not interchangeable and ectodomain humanization is warranted for translational pharmacology. Nulls are viable and, importantly, show worsened lupus in several autoimmune backgrounds despite reduced anti-DNA responses, revealing a regulatory function that complicates simple loss of function logic. Because Tlr7 shares the UNC93B1 and IRF7 axis, plan compound alleles around interferon output, autoantibody specificity, or adjuvant potency.

Whole body loss of Tlr9 gives the clearest readout when the question is whether the gene is required at all. Follow up tissue work can still move to a conditional allele if lethality or compensation appears.