College of Agronomy, Liaocheng University, Liaocheng City, Shandong Province, P. R. China.
Dairy Cattle Research Center, Shandong Academy of Agricultural Science, Jinan City, Shandong Province, P. R. China.
PLoS One. 2022 Jun 30;17(6):e0268959. doi: 10.1371/journal.pone.0268959. eCollection 2022.
Complement component 3 (C3) is the key molecule of the three pathways of complement activation (alternative, classical, and lectin pathways), which are involved in phagocytosis, inflammation, and immunoregulation processes to destroy infectious microorganisms. In this study, three novel single-nucleotide polymorphisms (SNPs) (g.-1293C>G located in the 5'-flanking region, g.56T>C in exon I, and g.7017C>T in exon XII) of the C3 gene were detected using created restriction site polymerase chain reaction, restriction fragment length polymorphism, and DNA sequencing in 952 cattle from three Chinese breeds. The genotypes and haplotypes were analyzed to investigate the polymorphisms and their possible implications, with particular investigative focus on their associations with serum C3 level, complement hemolytic activity (CH50 and ACH50), and milk production traits. The g.56T>C SNP in exon I affected the serum ACH50 (P<0.01) and the milk somatic cell score (SCS) (P<0.05), and the g.7017C>T SNP in exon XII significantly affected the serum ACH50 values (P<0.01). Moreover, statistical analyses revealed that individuals with genotypic combination CCC/GCC showed significantly lower SCS and the lowest C3 concentration in serum compared with cows with CCC/GTT (P = 0.0007) and CTT/CTT (P = 0.0021); the individuals with CCC/CCT had significantly higher ACH50 values than those with CCC/CTC (P = 0.0008) and CTC/GTC (P = 0.001); cows with CCT/CTT had higher values of CH50 and 305-day milk yield (P>0.05). The C3 expression levels were significantly increased in lung and mammary tissues (P<0.05), while significantly decreased in heart, spleen, liver, and kidney tissues in mastitis cows compared with those in healthy animals (P<0.01), respectively. Bacterial counts of serum antibacterial activities were also completed to verify the effect of SNPs on resistance to mastitis pathogens. Genetically resistant cows (CCC/GCC) had serum with noticeably higher antibacterial activity against S. aureus and E. coli in vitro than the genetically susceptible CCC/GTT cows (P<0.05). Results from this study imply that the C3 gene plays a role in resistance to bacterial infection and that it can be used as a molecular marker for complement activity and traits related to milk production.
补体成分 3（C3）是补体激活三条途径（替代途径、经典途径和凝集素途径）的关键分子，参与吞噬作用、炎症和免疫调节过程，以破坏感染性微生物。在这项研究中，使用创建的限制性内切酶聚合酶链反应、限制性片段长度多态性和 DNA 测序在来自三个中国牛品种的 952 头牛中检测到 C3 基因的三个新的单核苷酸多态性（SNP）（位于 5'-侧翼区的 g.-1293C>G、外显子 I 中的 g.56T>C 和外显子 XII 中的 g.7017C>T）。分析基因型和单倍型，研究多态性及其可能的影响，特别关注它们与血清 C3 水平、补体溶血活性（CH50 和 ACH50）和产奶性状的关系。外显子 I 中的 g.56T>C SNP 影响血清 ACH50（P<0.01）和乳体细胞评分（SCS）（P<0.05），外显子 XII 中的 g.7017C>T SNP 显著影响血清 ACH50 值（P<0.01）。此外，统计分析表明，与 CCC/GTT 和 CTT/CTT 基因型个体相比，CCC/GCC 基因型个体的 SCS 和血清中 C3 浓度明显更低（P=0.0007）；CCC/CCT 基因型个体的 ACH50 值明显高于 CCC/CTC 和 CTC/GTC 基因型个体（P=0.0008）；CCT/CTT 基因型个体的 CH50 和 305 天产奶量较高（P>0.05）。与健康动物相比，乳腺炎牛肺和乳腺组织中的 C3 表达水平显著升高（P<0.05），而心脏、脾脏、肝脏和肾脏组织中的 C3 表达水平显著降低（P<0.01）。还完成了血清抗菌活性的细菌计数，以验证 SNP 对乳腺炎病原体抗性的影响。与遗传易感的 CCC/GTT 牛相比，具有遗传抗性的 CCC/GCC 牛（CCC/GCC）的血清对金黄色葡萄球菌和大肠杆菌的体外抗菌活性明显更高（P<0.05）。这项研究的结果表明，C3 基因在抵抗细菌感染方面发挥作用，可作为补体活性和与产奶性状相关的分子标记。
