TLR9 and systemic lupus erythematosus: Excessive TLR receptor signalling is implicated in autoimmunity, with TLR2, TLR7 and TLR9 pursued as potential therapeutic targets in SLE.22 Abnormal excessive TLR signalling is thought to exacerbate unspecific immune cell activation.23 Interestingly, TLR7 expression was significantly upregulated in C2 and downregulated in C3 (Figure 4d).