Genetic polymorphism of TLR4 gene and correlation with mastitis in cattle.

Toll-like receptor 4 (TLR4) recognizes pathogen ligands and mediates signaling to initiate innate and adaptive immune responses. In this experiment, a 316 bp and 382 bp fragments of TLR4 gene named T4CRBR1 and T4CRBR2, of Chinese Holstein, Sanhe cattle, and Chinese Simmental was amplified by polymerase chain reaction (PCR), respectively. The genetic polymorphisms in the three populations were detected by Single-Strand Conformational Polymorphism (SSCP) in the first locus and by digesting the fragments with restriction endonuclease Alu? in the second one. Results showed that both alleles (A and B) of two loci were found in all the three populations and the value of polymorphism information content (PIC) indicated that these were a moderate polymorphism. Statistical results of chi(2) test indicated that two polymorphism sites in the three populations fitted with Hardy-Weinberg equilibrium (P > 0.05). After sequencing, A-G single nucleotide polymorphism (SNP) was identified at nucleotide 4,525 in intron 1 of TLR4 gene and C-T SNP was identified at nucleotide 1,397 in exon 3 of TLR4 gene. Meanwhile, the effect of polymorphism of TLR4 gene on somatic cell score (SCS) was analyzed, the results indicated that the cattle with allele A in T4CRBR1 showed lower somatic cell score than that of allele B (P < 0.05). In short, the allele A might play an important role in mastitis resistance in bovine.