TLR4 and infection: In response to pathogen infection, the Toll and IMD signaling pathways of D. melanogaster activate the p65-like transcription factor Dif and p105-like transcription factor Relish, respectively; The transcription factor then enters the nucleus and induces the expression of antimicrobial peptide (AMP) by binding to the κB binding site in the AMP gene promoter region (33, 36, 41) (Figure 1).