Animal Molecular Breeding, 2024, Vol.14, No.6, 354-361 http://animalscipublisher.com/index.php/amb 358 during a CDV outbreak, suggesting a potential influence on TLR2 function and CDV resistance (Loots et al., 2018). In neotropical rodents, specific TLR4 haplotypes were associated with different levels of infection by nematodes and Hepacivirus, indicating that TLR4 diversity plays a role in pathogen resistance (Heni et al., 2020). Additionally, polymorphic residues in TLRgenes, such as I602S (TLR1) and D299G (TLR4), have been linked to differential immune responses in various species (Figure 2) (Mukherjee et al., 2019). Figure 2 Biochemistry of TLRs (Adopted from Mukherjee et al., 2019) Image caption: A, Structures and transmembrane domain morphologies of TLR and IL-1 receptor. The existence of LRR motif in the extracellular domain the unique feature of transmembrane TLRs, while the TIR domain is the feature that is homologous to IL-1 receptor. B, Recognition of molecular patterns from different infectious pathogens by TLRs. TLRs (TLR 1, 2, 4, 5, 6, 10) located on the plasma membrane of innate immune cells recognize distinct ligand from invading pathogens. TLR2 in its active form dimerizes either with TLR1 or TLR6 and respectively recognize triacyl- or diacyl-lipopeptide from bacteria. TLR5 senses flagellin protein of invading bacteria, whereas TLR4 binds with LPS moiety of gram-negative bacteria. Intracellular TLRs (TLR 7, 8, 9) generally recognizes patterns of the pathogens those entering in the cell. TLR3 and TLR7/8 respectively detect double (dsRNA) and single-stranded RNA (ssRNA) of viruses. TLR9 selectively recognizes double-stranded DNA of intracellular pathogens. CT, C terminus; Ig, immunoglobulin; IL-1, interleukin-1; LPS, lipopolysaccharide; LRR, leucine-rich repeats; NT, N terminus; TIR, Toll-interleukin-1 receptor domain; TLR, Toll-like receptor (Adopted from Mukherjee et al., 2019)
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