Toll-related receptor (PubMed:10973475). Probably specific to larval innate immunity (PubMed:22022271). Involved in the tracheal immune response of larvae to Gram-negative and perhaps Gram-positive bacteria; upon infection it negatively regulates the immune deficiency (Imd) signaling cascade specifically in the respiratory epithelium to prevent the overexpression of antimicrobial peptides (AMP) (PubMed:22022271). Involved in the NF-kappa-B-dependent apoptosis of unfit cells during cell competition (PubMed:25477468). Involved in neuron-specific glycosylation (PubMed:12588858, PubMed:17264077). Positively controls the neuromuscular junction (NMJ) growth in presynaptic motorneurons, probably via the JNK pathway (PubMed:24662564). During development of the peripheral nervous system, may function in the NF-kappa-B (rel) regulatory cascade to repress expression of the neuron-specific genes sc and ase in non-neuronal cells (PubMed:18000549). Promotes heterophilic cell adhesion with 18w in vitro (PubMed:25363762). May have a minor role in leg development (PubMed:21158756). May be involved in determining the proximal cell fate in the wing, possibly by negatively regulating the Dpp signaling pathway.(PubMed:17078066). May also be involved in the Dpp signaling pathway in the eye (PubMed:17078066). Possibly functions with 18w and Toll-6 during convergent extension, to help direct proper planar cell polarity, cell intercalation and axis elongation (PubMed:25363762). May interact (via the extracellular domain) with 18w (via the extracellular domain). In larvae, localizes to the apical cell membrane in trachea epithelial cells. At the cellular blastoderm stage, expressed in 8 segmentally repeated stripes, and 14 stripes at germ band extension (at protein level) (PubMed:12617819). Expressed in the neurogenic region during the blastoderm and germ band extension stages (at protein level) (PubMed:12617819). Expressed zygotically (PubMed:12617819). Expressed throughout development, with two peaks of expression at mid-embryogenesis (6-12 hours old embryos) and in early larvae stages (PubMed:10973475). First detected in the cellular blastoderm as two distinct anterior and posterior bands (PubMed:12588858). By germband retraction (late stage 12), segmentally repeated stripes span the width of the germband (PubMed:25363762, PubMed:12588858). In embryos (stages 12-15), detected in ectodermal cells that surround differentiating neurons of the ventral nerve cord and peripheral nervous system (PubMed:12588858). In third instar larvae, expressed at high levels in the tracheal epithelium, and at relatively lower levels in the gut and fat body (PubMed:22022271). In the wing imaginal disks, expressed in the proximal region around the wing pouch and noctum, and in the hinge regions (PubMed:17078066, PubMed:21158756). Also expressed in the anterior compartment of the leg imaginal disks (PubMed:21158756). In larvae, detected in the blood cells, lymph glands and fat body (PubMed:12617819). In third instar larvae to the pre-pupae stage, high levels of expression across the lateral noctum except where dorsocentral and scutellar bristles form (PubMed:18000549). In late stage third instar larvae, expressed throughout the lateral noctum epithelium, except for the SOPs (anterior postalar, supraalar and sensilla trichoidea) in which expression decreases as SOPs develop (PubMed:18000549). By Gram-negative bacteria, in the respiratory epithelium (PubMed:22022271). Up-regulated during vesicular stomatitis virus (VSV) infection (PubMed:22464169). Viable (PubMed:18000549, PubMed:22022271). The legs of some adults have the correct number of segments but are bent between the tibia and tarsus, causing the leg to twist in the wrong direction (PubMed:21158756). Formation of ectopic bristles on the heminota (PubMed:18000549). Slight decrease in the branch length of NMJ3 and a reduced number of boutons at NMJ3 and NMJ4 (PubMed:24662564). In larvae, tracheal cell morphology is normal and basal expression levels of the AMP gene Drs are unaffected (PubMed:22022271). However after infection with Gram-negative bacteria, the respiratory epithelium displays an over-active immune response with a greater increase in expression of AMPs (Drs, Dro and AttC) compared to wild-type larvae (PubMed:22022271). In adults, no effect on the immune response to septic injury using a mixture of Gram-positive and Gram-negative bacteria; adults are able induce expression of antibacterial peptide genes (Drs, AttA, DptA and Mtk) and mount a proper innate immune response (PubMed:21158756). No visible effect on the development of the embryo central nervous system (PubMed:21158756). Belongs to the Toll-like receptor family. In some plant proteins and in human SARM1, the TIR domain has NAD(+) hydrolase (NADase) activity (By similarity). However, despite the presence of the catalytic Asp residue, the isolated TIR domain of human TLR4 lacks NADase activity (By similarity). Based on this, it is unlikely that Toll-like receptors have NADase activity.